The research, published in New Microbes and New Infections, analyzed the medical records of 218 pediatric patients aged zero to eighteen years who received intravenous colistin for at least 72 hours for confirmed multidrug-resistant Gram-negative bacterial infections between 2010 and 2024. Seventy-four children received colistin as monotherapy, while 144 received colistin-based combination therapy with at least one additional antibiotic active against Gram-negative bacteria. The investigators, led by Ajaree Rayanakorn, Peninnah Oberdorfer, and Wasan Katip, set out to answer a question that has divided infectious disease specialists for years: does adding a second drug to colistin actually save lives in children, or does it merely add cost, complexity, and potential side effects?

The stakes are considerable. Multidrug-resistant Gram-negative bacteria, including Acinetobacter baumannii, Pseudomonas aeruginosa, Klebsiella pneumoniae, and carbapenem-resistant Enterobacteriaceae, are among the most feared pathogens in modern hospitals. Reported mortality rates from these infections range from 26 to 80 percent, and a meta-analysis cited by the authors found that patients with these infections face a 1.78-fold higher risk of death compared with those infected by other organisms. The burden falls especially heavily on the World Health Organization’s South-East Asia region. In Thailand alone, approximately 19,000 additional deaths each year are attributed to multidrug-resistant bacteria, and more than 80 percent of those deaths involve Gram-negative organisms. The World Health Organization has designated the development of new treatments for these pathogens as a global research priority, but new drugs remain scarce, leaving older agents like colistin as last-resort options.

Colistin, also known as polymyxin E, works through a mechanism that differs from most modern antibiotics. The molecule carries both hydrophilic and lipophilic properties, allowing it to attack the lipopolysaccharide component of Gram-negative bacterial membranes. By disrupting the membrane structure, colistin exerts a direct bactericidal effect, and pediatric studies have reported clinical cure rates of up to 89 percent in multidrug-resistant Gram-negative infections. However, its clinical efficacy as a single agent remains controversial, and in vitro experiments have repeatedly shown that colistin can act synergistically with carbapenems, cephalosporins, sulbactam-containing regimens, fluoroquinolones, and fosfomycin. Those laboratory findings drove widespread adoption of combination therapy in clinical practice, even though rigorous clinical evidence, particularly in children, has been largely absent.

To untangle the effects of treatment from the effects of illness severity, the Thai team employed a sophisticated statistical technique known as inverse probability of treatment weighting. This is critical because, in everyday practice, sicker children tend to receive combination therapy. In the unadjusted data, the combination group indeed appeared more severely ill: their median Pediatric Index of Mortality 3 score was higher, septic shock was more common, ventilator-associated pneumonia occurred more frequently, and roughly half were receiving vasoactive drugs compared with about a third of the monotherapy group. Propensity scores were estimated through multivariable logistic regression incorporating variables including sex, age, pediatric Glasgow Coma Scale, pediatric Sequential Organ Failure Assessment score, PIM3 score, septic shock, intensive care unit status, vasoactive drug use, baseline serum creatinine, ventilator-associated pneumonia, and bacteremia. After weighting, all standardized mean differences fell below the 0.1 threshold, indicating that the two groups had become statistically comparable across these measured prognostic factors.

The results were striking in what they did and did not show. After the weighting adjustment, colistin-based combination therapy was not associated with any significant difference in the primary outcome of 30-day mortality compared with monotherapy, with an adjusted odds ratio of 2.50 and a wide confidence interval spanning 0.69 to 9.15. Nor did the combination improve mortality at the end of treatment, clinical response, or the rate of nephrotoxicity, the most feared side effect of colistin, which was defined using consensus criteria based on serum creatinine increases or the RIFLE kidney injury classification. Across all of these clinical endpoints, the two strategies performed essentially the same.

There was, however, one clear exception. Children receiving combination therapy were significantly more likely to achieve microbiological response, meaning that follow-up cultures from the originally infected site no longer grew the multidrug-resistant organism. After adjustment, the odds of microbiological clearance were 3.62 times higher in the combination group, a result that reached statistical significance with a p-value of 0.037. The authors suggest this enhanced bacterial eradication may reflect genuine synergistic activity between colistin and carbapenems, particularly against Acinetobacter baumannii, which dominated the cohort, accounting for more than 82 percent of isolates in both treatment groups. The most frequently used combination regimen was colistin with meropenem, given to nearly 63 percent of the combination group.

The disconnect between better bacterial clearance and no survival benefit is a recurring puzzle in antimicrobial research, and the authors offer several plausible explanations. Outcomes in critically ill children are shaped by host immune response, organ dysfunction, baseline disease severity, and comorbidities, any of which may blunt the clinical impact of eradicating bacteria. Colistin also penetrates lung tissue poorly, which matters in a cohort where roughly 70 percent of infections were pulmonary. Microbiological clearance may simply arrive too late in the course of critical illness to alter its trajectory. The findings align with a systematic review and meta-analysis by Wang and colleagues, which likewise found no mortality or clinical response differences between colistin monotherapy and combination therapy but demonstrated improved microbiological eradication with combination regimens. On the safety front, the absence of excess nephrotoxicity in the combination group is reassuring and supports the view that colistin-associated kidney injury is primarily dose-dependent and driven by patient-specific risk factors rather than synergistic toxicity between colistin and its partners.

The study’s limitations deserve careful attention. As a retrospective, single-center analysis at a 1,400-bed tertiary teaching hospital, its findings may not generalize to institutions with different resistance patterns and prescribing habits. The cohort, while among the largest pediatric studies in this field, remained modest in size, and the wide confidence intervals around key estimates, particularly the 30-day mortality odds ratio, reflect that imprecision. The inclusion of all multidrug-resistant Gram-negative infections, rather than only carbapenem-resistant organisms, complicates extrapolation to the subgroup where combination therapy is most often recommended. Residual confounding from unmeasured variables, including the timing of antibiotic initiation and dosing appropriateness, cannot be excluded, and the predominance of Acinetobacter baumannii may limit applicability to other pathogens. The authors themselves characterize the results as hypothesis-generating rather than definitive.

Even with those caveats, the study carries practical weight for clinicians confronting these infections in children. The message is not that combination therapy is useless, but that its benefits may be narrower than assumed: it may help clear bacteria without adding kidney risk, yet it does not appear to reduce mortality. The authors conclude that the decision to use combination therapy should be individualized, potentially reserved for situations where rapid bacterial clearance is most critical, such as bloodstream infections or ventilator-associated pneumonia caused by Acinetobacter baumannii. For many other children with multidrug-resistant Gram-negative infections, colistin alone may deliver comparable clinical outcomes. Confirming that conclusion will require the kind of study that has long been missing in this vulnerable population: large, multicenter, prospective trials, ideally randomized, designed specifically to define optimal treatment strategies for pediatric patients facing some of the most dangerous bacteria in modern medicine.

Subject of Research: Colistin monotherapy versus combination therapy for pediatric multidrug-resistant Gram-negative infections

Article Title: Efficacy and safety of colistin monotherapy versus colistin-based combination therapy in pediatric patients with multidrug-resistant gram-negative infections: A propensity score analysis

Article References: Rayanakorn, A., Oberdorfer, P., & Katip, W. (2026). Efficacy and safety of colistin monotherapy versus colistin-based combination therapy in pediatric patients with multidrug-resistant gram-negative infections: A propensity score analysis. New Microbes and New Infections, 74, Article 101857. https://doi.org/10.1016/j.nmni.2026.101857

Image Credits: AI Generated

DOI: 10.1016/j.nmni.2026.101857

Keywords: colistin, multidrug-resistant Gram-negative bacteria, pediatric infections, combination therapy, Acinetobacter baumannii, meropenem, nephrotoxicity, propensity score analysis, antimicrobial resistance, Thailand, hospital-acquired pneumonia, microbiological response

Carbapenem-resistant Gram-negative bacteria, often abbreviated CR-GNB, represent one of the most feared threats in contemporary medicine. Carbapenems belong to the beta-lactam family of antibiotics, chemically related to penicillin, and they work by blocking the enzymes bacteria use to build their cell walls. Their broad activity and stability against many beta-lactamase enzymes have long made them the drugs of last resort for serious infections caused by organisms such as Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Escherichia coli. When bacteria acquire or evolve mechanisms to defeat these drugs, typically by producing carbapenemases or by remodeling the porous outer membrane and efflux pumps characteristic of Gram-negative cells, clinicians are left with a dwindling arsenal of older, more toxic agents such as colistin, often with limited evidence to guide dosing. The World Health Organization has repeatedly flagged carbapenem-resistant Gram-negatives as a critical priority for new antibiotic development, and the burden falls disproportionately on low- and middle-income countries where surveillance and infection control resources can be stretched thin.

Jordan has been something of a data gap in this global picture. While regional neighbors and high-income countries have produced extensive resistance surveillance, detailed predictors of carbapenem resistance among Jordanian ICU patients have been scarce. The new study, led by Mohammad Gharaibeh of the Jordanian Ministry of Health and Tamer Osman of the US Naval Medical Research Unit EURAFCENT, set out to close that gap by mining the country’s national surveillance system. The team included every patient with a laboratory-confirmed Gram-negative infection across the participating public hospital ICUs over the six-year window. Laboratory identification and antimicrobial susceptibility testing followed the Clinical and Laboratory Standards Institute’s M100 standards, the widely used benchmark for interpreting minimum inhibitory concentrations, and the researchers applied multivariate logistic regression to disentangle which clinical factors independently predicted resistance rather than merely correlating with it.

The headline number is stark: 451 of the 1,180 isolates, or 38 percent, were carbapenem-resistant. The microbiology behind that figure is not uniform, however. Acinetobacter baumannii and Klebsiella species emerged as the predominant resistant pathogens, a pattern consistent with global trends, since both organisms are notorious for acquiring plasmid-borne carbapenemase genes and for surviving on dry hospital surfaces and medical equipment. Escherichia coli, by contrast, remained mainly carbapenem-susceptible in this dataset, offering a small measure of reassurance that resistance in Jordan is concentrated in the organisms most adept at hospital survival rather than uniformly distributed across the Gram-negative spectrum. That distinction matters for clinicians, because it suggests that empiric treatment decisions for suspected ICU infections should weigh the likely organism as much as the local resistance prevalence.

When the researchers adjusted for confounding factors, four independent predictors of carbapenem resistance stood out. Infections acquired inside the ICU, rather than present on admission, carried roughly two and a half times the odds of being carbapenem-resistant, with an odds ratio of 2.44. Pneumonia more than doubled the odds as well, at an odds ratio of 2.77, a finding that aligns with the well-documented role of ventilator-associated pneumonia as a reservoir for resistant organisms in the airways of intubated patients. The use of invasive devices, including central lines, urinary catheters and endotracheal tubes, raised the odds 3.37-fold, reflecting how these devices breach the body’s natural barriers and provide surfaces for biofilm formation, where bacteria embedded in a protective extracellular matrix can exchange resistance genes and evade both antibiotics and immune defenses. Most striking of all, admission to a high-risk ICU unit tripled the odds of resistance, with an odds ratio of 3.33, underscoring that the ecology of individual units, shaped by their case mix, antibiotic pressure and staffing, can be as decisive as any single patient characteristic.

Each of these risk factors tells a mechanistic story. ICU-acquired infection implies prolonged exposure to the hospital environment, where resistant strains circulate on hands, equipment and surfaces, and where selective pressure from broad-spectrum antibiotic use favors organisms that have already learned to resist carbapenems. Pneumonia in ventilated patients combines device exposure with a compromised lower respiratory tract, where secretions colonized by resistant Gram-negatives can seed frank infection. Invasive devices act as literal bridges from the contaminated environment into normally sterile body sites, and their duration of use is one of the most consistently modifiable factors in hospital epidemiology. The high-risk unit finding suggests that resistance is not randomly distributed but clusters where the most vulnerable patients, the heaviest device use and the most intensive antibiotic prescribing converge, creating conditions in which resistant strains can amplify and spread from patient to patient.

The mortality data give these risk factors their weight. Nearly 70 percent of patients with carbapenem-resistant infections died, compared with 42 percent of those with susceptible infections, and after statistical adjustment the resistant group faced a 3.15-fold increased risk of death, with a confidence interval running from 2.392 to 4.145. Part of that excess mortality reflects the biology of resistance itself: when first-line and second-line antibiotics fail, definitive therapy is delayed, allowing infection to progress, and the salvage regimens that remain, such as colistin-based combinations, are less effective and more nephrotoxic than the carbapenems they replace. Part of it also reflects the fact that patients who develop resistant infections tend, by the very risk factors identified here, to be sicker and more device-dependent to begin with. Either way, the numbers reinforce a message that infectious disease specialists have been repeating for years: preventing resistance is inseparable from preventing death in critical care.

The authors argue that their findings point toward concrete, actionable interventions. Strict hand hygiene remains the single most cost-effective barrier against transmission, particularly for organisms like A. baumannii that persist in the environment. Antimicrobial stewardship programs, which audit and constrain the use of broad-spectrum antibiotics, reduce the selective pressure that allows resistant strains to outcompete susceptible ones. And the proper management of invasive devices, including daily review of whether each catheter and line is still needed, prompt removal when it is not, and aseptic insertion and maintenance technique, directly targets the strongest modifiable predictor identified in the study. Because the analysis drew on a national surveillance network spanning 13 public hospitals, the results are less vulnerable to the single-center biases that plague much of the resistance literature, although the retrospective design still means that only associations, not proven causal chains, can be established.

For the region and beyond, the study carries a warning and a template. The warning is that in Jordanian public hospital ICUs, as in many settings across the Middle East and other low- and middle-income regions, carbapenem resistance has reached a prevalence at which empiric therapy decisions, infection control investment and surveillance infrastructure can no longer be treated as optional. The template is the surveillance system itself: a coordinated national network, standardized laboratory methods aligned with CLSI benchmarks, and shared analysis between the Ministry of Health and international research partners, funded in this case through the Armed Forces Health Surveillance Division’s Global Emerging Infections Surveillance program. As resistance genes continue to move across borders with patients, food and the environment, the Jordanian experience suggests that knowing exactly who is at risk, the device-bearing, the ventilated, the long-staying, the patients in the highest-pressure units, is the first step toward keeping the last-line antibiotics working for the patients who need them most.

Subject of Research: Risk factors for carbapenem-resistant Gram-negative bacterial infections in intensive care units in Jordan

Article Title: Risk factors associated with carbapenem-resistant Gram-negative bacterial infections in intensive care units in Jordan

Article References: Gharaibeh, M., Sayyouh, O., El-Shokry, M., Nasrat, S., Ramadan, M., Khraisat, W., Alamer, L., Natour, A., Aljbour, M., Abushawer, Z., Abdallah, N., Migdadi, N., Harb, S., Awad, E., Bataienh, E., Battah, S., Ikermawi, R., Said, M., Alhawarat, M., & Osman, T. (2026). Risk factors associated with carbapenem-resistant Gram-negative bacterial infections in intensive care units in Jordan. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-13526-w

Image Credits: AI Generated

DOI: 10.1186/s12879-026-13526-w

Keywords: carbapenem resistance, Gram-negative bacteria, intensive care units, antimicrobial resistance, hospital-acquired infections, Acinetobacter baumannii, Klebsiella, pneumonia, invasive devices, infection control, Jordan, surveillance

The threat the researchers set out to address is well documented. The World Health Organization’s 2024 Bacterial Priority Pathogens List places carbapenem-resistant Gram-negative bacteria, including Acinetobacter baumannii and members of the Enterobacteriaceae family, among the most critical targets for new treatment strategies. In Brazilian hospitals, surveillance by the national health regulatory agency ANVISA has catalogued a grim roster of resistant organisms, from carbapenem-resistant Pseudomonas aeruginosa to cephalosporin-resistant Klebsiella pneumoniae. Because resistance genes circulate freely among humans, animals, and the environment, the field increasingly favors a One Health approach, and the new study embraced that perspective by testing bacteria isolated from both human hospital patients and veterinary clinical cases.

Chemically, the extract proved remarkably rich. Using high-performance liquid chromatography coupled with high-resolution tandem mass spectrometry, the team tentatively annotated 41 distinct metabolites. Eleven peaks belonged to the flavonoid family, largely in glycosylated forms, including derivatives of quercetin, kaempferol, and myricetin, along with catechin, epicatechin, epigallocatechin gallate, procyanidin B2, tiliroside, and prodelphinidin B3. Several of these flavonoid dimers and glycosides had never before been reported in the genus Mouriri. The analysis also revealed ellagic acid derivatives and, for the first time in this genus, pentacyclic triterpenes, with fragmentation patterns consistent with asiatic acid and terminolic or myrianthic acid. These compound classes are well known in the natural products literature for antimicrobial and antibiofilm properties, providing a plausible chemical basis for the biological effects that followed.

On its own, the extract showed meaningful but moderate antibacterial activity. Against a reference strain of Staphylococcus aureus, the minimum inhibitory concentration fell below 78.1 micrograms per milliliter, a level the authors classify as strong. Clinical isolates of S. aureus and S. pseudintermedius required 156.25 micrograms per milliliter, while the notoriously hardy Gram-negative pathogens Acinetobacter baumannii and Klebsiella pneumoniae yielded MIC values of 312.5 and 625 micrograms per milliliter, respectively. The reduced susceptibility of these Gram-negative organisms is unsurprising: their outer membranes, studded with lipopolysaccharides and restrictive porin proteins, form a formidable barrier that excludes many antimicrobial compounds, including most unmodified plant extracts.

The real headline came from the combination experiments. When the extract was paired with conventional antibiotics using the checkerboard microdilution method, synergistic interactions emerged against several of the most resistant strains. Combining the extract with ampicillin produced a fractional inhibitory concentration index of 0.09 against a beta-lactamase-producing Escherichia coli strain, 0.5 against clinical S. aureus, and 0.19 against K. pneumoniae when paired with ciprofloxacin. In practical terms, the presence of the extract cut the required antibiotic dose fourfold against S. aureus and K. pneumoniae and an impressive sixteenfold against E. coli. Additive effects extended this modulatory reach to S. pseudintermedius, a Shiga toxin-producing E. coli of veterinary origin, a multidrug-resistant Staphylococcus species, and A. baumannii. Notably, the K. pneumoniae isolate in the study was resistant to seventeen different antibiotics, including last-resort drugs such as colistin, meropenem, and ertapenem, yet the extract combination partially restored ciprofloxacin susceptibility.

Beyond killing planktonic bacteria, the extract attacked one of the most stubborn forms of resistance: the biofilm. Biofilms are sessile microbial communities encased in a self-produced extracellular matrix that shields cells from antibiotics and immune attack, and they are implicated in more than 65 percent of human infections, from endocarditis to catheter-associated disease. At 500 micrograms per milliliter, the extract inhibited biofilm formation by 73.3 percent in S. aureus and 68 percent in E. coli, and inhibition against the Gram-positive strain remained near 70 percent even at half that concentration. Atomic force microscopy provided striking visual confirmation: untreated S. aureus formed dense, well-organized biofilms of spherical cells roughly 780 nanometers in diameter, whereas extract-treated surfaces showed fragmented, disrupted architecture with markedly reduced matrix deposition.

One curious observation deserves attention. At the highest concentration tested, 1000 micrograms per milliliter, the extract actually stimulated biofilm formation in both strains, a paradoxical reversal reminiscent of the so-called Eagle effect described previously in bacterial and fungal biofilms, where higher antimicrobial concentrations sometimes exert weaker effects than lower ones. The authors caution that the mechanism behind this response remains unknown and will require further study, but the finding underscores a practical lesson for natural product development: dose optimization matters, and more is not always better.

Safety data provided an essential green light. In an acute oral toxicity assay following OECD guideline principles, mice received a single 2000 milligram per kilogram dose of the extract and were monitored for fourteen days. Body weight gain, relative organ weights, gross necropsy findings, and histopathology of the spleen, heart, liver, kidneys, lungs, and stomach all remained within normal limits in both sexes. Hematological parameters were largely unchanged, with the exception of a modest but significant rise in white blood cell counts in males, which the authors interpret as possible immunomodulatory activity rather than pathology. Serum biochemistry showed no signs of liver injury, though bilirubin levels dropped significantly in both sexes, a change the researchers link to the antioxidant properties previously described for Mouriri extracts.

The study’s One Health dimension amplifies its significance. Several of the most resistant organisms tested, including veterinary isolates of S. pseudintermedius resistant to eight antibiotics and E. coli strains resistant to up to eight drugs, came from animal clinical sources, reminding readers that resistant bacteria travel readily between animals and people through direct contact, food chains, and the environment. The authors also point to broader ecological and socioeconomic stakes: M. elliptica is native to the fire- and drought-adapted Cerrado, propagates readily under cultivation, and produces edible, antioxidant-rich fruits, meaning that a single species could simultaneously supply antimicrobial leads, nutrition, and income for local communities, strengthening the case for conserving a biome under severe threat.

Caveats remain, and the researchers are candid about them. The checkerboard assay, while a widely used screening tool with documented agreement with time-kill kinetics in prior literature, is not the gold standard for confirming synergy, and the precise molecular mechanisms by which the extract sensitizes bacteria, whether through efflux pump inhibition, membrane permeabilization, or interference with beta-lactamase enzymes, have not yet been demonstrated directly. Sub-chronic and chronic toxicity studies are also needed before any therapeutic development. Still, the convergence of chemical novelty, synergistic potency against WHO priority pathogens, demonstrable antibiofilm action, and a clean acute safety profile marks Mouriri elliptica as a promising candidate in the global search for antibiotic adjuvants, and a vivid reminder that solutions to the resistance crisis may be growing quietly in the world’s threatened savannas.

Subject of Research: Antibiotic-adjuvant and antibiofilm activity of Mouriri elliptica leaf extract against multidrug-resistant Gram-negative clinical bacteria

Article Title: Adjuvant Antibacterial Effects of Mouriri Elliptica Against Clinical Multidrug Resistant Gram‐Negative Bacterial Strains

Article References: Freire, T. V., Marques, A. C. D. F., Gonçalves, V. D. S., Moslaves, I. S. B., Toffoli‐Kadri, M. C., Silva, A. F. C. D., Giz, M. J., Figueiredo, P. D. O., Micheletti, A. C., & Yoshida, N. C. (2026). Adjuvant Antibacterial Effects of Mouriri Elliptica Against Clinical Multidrug Resistant Gram‐Negative Bacterial Strains. MicrobiologyOpen, 15(5), Article e70392. https://doi.org/10.1002/mbo3.70392

Image Credits: AI Generated

DOI: 10.1002/mbo3.70392

Keywords: antimicrobial resistance, Mouriri elliptica, Brazilian Cerrado, antibiotic adjuvants, multidrug-resistant bacteria, biofilm, flavonoids, triterpenes, Klebsiella pneumoniae, Acinetobacter baumannii, One Health, natural products

The urgency behind the research reflects a grim epidemiological reality. Antimicrobial resistance is escalating worldwide as antibiotics are overused in medicine and agriculture, and the pipeline for genuinely new drugs has thinned to a trickle. The ESKAPE pathogens, a group that includes Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species, have become emblematic of the crisis because they evade nearly every class of conventional antibiotic through efflux pumps, destructive enzymes such as beta-lactamases, target modifications, and the horizontal acquisition of resistance genes. Pseudomonas aeruginosa, for instance, deploys an array of secreted toxins delivered through type II and III secretion systems, while Acinetobacter baumannii survives desiccation, forms stubborn biofilms on hospital surfaces, and has become notorious for carbapenem resistance. Staphylococcus aureus rounds out the trio with immune-evasive proteins, pore-forming toxins, and the now-ubiquitous methicillin-resistant lineage known as MRSA.

Nanoparticles offer a fundamentally different attack strategy. Because of their tiny size and enormous surface-area-to-volume ratio, metal nanoparticles can interact with bacterial cells in ways that conventional drugs cannot. Silver and gold nanoparticles are thought to disrupt bacterial membranes, generate reactive oxygen species that damage cellular machinery, interfere with vital metabolic processes, and even potentiate existing antibiotics. Crucially, these mechanisms operate in concert and are less likely to trigger the classical resistance pathways that neutralize small-molecule drugs. Nanoparticles can also penetrate biofilms, the dense microbial communities that shield chronic infections from both antibiotics and immune cells. The catch has always been synthesis: traditional chemical and physical production methods can be expensive, energy-intensive, and environmentally unfriendly, and the resulting particles may carry toxic residues.

That is where green synthesis enters the picture. Rather than using synthetic reducing and stabilizing agents, green synthesis harnesses plant phytochemicals such as flavonoids, alkaloids, phenols, and terpenoids to simultaneously reduce metal salts into nanoparticles and cap their surfaces, all in a single step. The Nonea lutea plant, a member of the Boraginaceae family with a long history in traditional medicine, proved an ideal candidate. Its aerial parts, collected in Mazandaran province in northern Iran and verified by botanists at the Sari School of Pharmacy, were dried, ground, and extracted with methanol before being combined with silver nitrate under optimized conditions of pH, temperature, and reaction time.

The resulting silver nanoparticles were extensively characterized before any biological testing. Ultraviolet-visible spectroscopy revealed a characteristic surface plasmon resonance band at roughly 425 nanometers, confirming the conversion of silver ions to metallic silver, a change that was visible to the naked eye as the reaction mixture shifted from pale yellow to dark brown. Electron microscopy showed predominantly spherical particles: field-emission scanning electron microscopy placed diameters between 22 and 37 nanometers, while transmission electron microscopy yielded an average size of about 13.5 nanometers. Notably, the images revealed a thin organic coating around each particle, the fingerprint of plant-derived biomolecules acting as capping agents. X-ray diffraction confirmed a cubic crystalline structure with an average crystallite size near 26.9 nanometers, energy-dispersive X-ray spectroscopy detected elemental silver along with carbon and oxygen from adsorbed biomolecules, and a zeta potential of minus 32.9 millivolts indicated strong electrostatic repulsion and good colloidal stability.

With the particles characterized, the team turned to the clinical battlefield. They collected 100 isolates each of P. aeruginosa, A. baumannii, and S. aureus from patients at five hospitals affiliated with Mazandaran University of Medical Sciences, spanning burn units, intensive care, surgery, and emergency wards. From these, 15 multidrug-resistant isolates of each species were selected for nanoparticle testing based on strict criteria: resistance to at least three antibiotic classes, carriage of major resistance and virulence genes, and diverse clinical origins. Molecular screening by polymerase chain reaction revealed an alarming genetic landscape. Every one of the 15 Pseudomonas isolates carried the exoU, exoA, bla CTX-M, bla TEM, and bla OXA-2 genes. All Acinetobacter isolates harbored the biofilm genes bap and csuE, and every Staphylococcus isolate carried the icaA biofilm gene, with most also bearing the methicillin resistance determinant mecA.

When the green-synthesized silver nanoparticles met these formidable organisms in broth microdilution assays, the results were remarkable. Minimum inhibitory concentrations ranged from 0.19 to 1.56 micrograms per milliliter against Pseudomonas aeruginosa, 0.19 to 0.78 against Acinetobacter baumannii, and just 0.19 to 0.39 against Staphylococcus aureus. Minimum bactericidal concentrations tracked closely behind, suggesting the particles do not merely stall growth but actively kill the bacteria. The statistics confirmed what the raw numbers implied: the green silver nanoparticles significantly outperformed the green gold nanoparticles, the chemically synthesized silver nanoparticles, and the chemically synthesized gold nanoparticles for every species tested, with p-values below 0.001 across comparisons. Activity was slightly weaker against Pseudomonas than against Staphylococcus, a difference the authors attribute to the thick peptidoglycan armor of Gram-positive cell walls potentially slowing nanoparticle penetration, though the precise mechanism remains to be verified experimentally.

The comparative failures proved as instructive as the successes. Green-synthesized gold nanoparticles from the same plant extract required concentrations of 100 to 200 micrograms per milliliter to inhibit growth, and chemically synthesized silver and gold nanoparticles of both types showed essentially no useful activity, with minimum inhibitory and bactericidal concentrations exceeding 500 micrograms per milliliter. The stark gap between chemically produced and plant-derived silver particles points to a tantalizing conclusion: the phytochemical coating itself may be central to antimicrobial performance. Nonea lutea is rich in flavonoids, alkaloids, saponins, tannins, and phenolic compounds with documented biological activity, and the researchers suggest these bioactive surface molecules may act synergistically with the metallic core. The superior intrinsic antimicrobial nature of silver ions compared with gold likely contributes as well.

The findings compare favorably with earlier green synthesis studies. Silver nanoparticles made from Feijoa sellowiana, for example, achieved similar inhibitory concentrations against standard laboratory strains, but the Nonea lutea particles matched that potency against genuine multidrug-resistant clinical isolates and delivered lower bactericidal values in the same experimental setting. The proximity of inhibitory and bactericidal concentrations hints at a bactericidal mode of action, consistent with proposed mechanisms of membrane disruption and reactive oxygen species generation described across the wider literature, though the authors are careful to note that these mechanisms remain hypotheses requiring direct confirmation through techniques such as electron microscopy, membrane permeability assays, and time-kill experiments. Encouragingly, no significant correlation was found between specific resistance gene carriage and nanoparticle susceptibility, suggesting the silver particles may sidestep the genetic determinants that defeat conventional antibiotics.

The road from laboratory dish to clinic is long, and the authors are measured in their claims. This was an in vitro proof-of-concept study; biofilm disruption, synergy with existing antibiotics, pharmacokinetics, toxicity, and in vivo efficacy all remain untested. Nonetheless, the study makes a compelling case that sustainable, plant-mediated nanotechnology can produce particles capable of confronting the worst pathogens hospitals have to offer. As antibiotic discovery falters and resistance genes spread through mobile genetic elements, the idea that a desert wildflower’s chemistry, combined with nothing more exotic than silver and careful engineering, could help fill the therapeutic void is a reminder that some answers to modern medicine’s hardest problems may be growing quietly in the hills of northern Iran.

Subject of Research: Green synthesis of plant-mediated silver and gold nanoparticles and their antibacterial activity against multidrug-resistant clinical pathogens

Article Title: Antibacterial efficacy of Nonea lutea-mediated silver and gold nanoparticles against multidrug-resistant clinical pathogens harboring virulence and resistance genes

Article References: Jasim, H. H., Gholami, M., Ahanjan, M., Ebrahimzadeh, M. A., & Goli, H. R. (2026). Antibacterial efficacy of Nonea lutea-mediated silver and gold nanoparticles against multidrug-resistant clinical pathogens harboring virulence and resistance genes. International Microbiology. https://doi.org/10.1007/s10123-026-00898-x

Image Credits: AI Generated

DOI: 10.1007/s10123-026-00898-x

Keywords: antimicrobial resistance, silver nanoparticles, green synthesis, Nonea lutea, Pseudomonas aeruginosa, Acinetobacter baumannii, Staphylococcus aureus, MDR pathogens, nanomedicine, virulence genes, MIC, plant extract

The significance of targeting biofilms cannot be overstated. Biofilms are structured communities of bacteria encased in a self-produced matrix of polysaccharides, proteins, and extracellular DNA. Within this matrix, bacteria adopt gene expression profiles that differ dramatically from their free-floating, planktonic counterparts, altering their morphology, surface properties, and susceptibility to antibiotics. Cells buried in a biofilm are shielded by enzymatic degradation of antimicrobials, active efflux pumps, and reduced permeability, which is why biofilm-associated infections on catheters, ventilators, and implants so often defy standard treatment regimens. Among the virulence factors that govern this process in A. baumannii, the biofilm-associated protein known as Bap, encoded by the bap gene, plays a critical role in adhesion to bronchial cells, structural integrity of the biofilm, and the development of water channels that distribute nutrients through the community. Disrupting bap has been shown to reduce biofilm thickness, volume, and interbacterial adhesion, making it an attractive molecular target.

In the new study, published in MicrobiologyOpen, the team collected 100 clinical isolates of A. baumannii from patients at a burn hospital affiliated with Mazandaran University of Medical Sciences. The isolates came from wounds, urine, and blood samples of 50 male and 50 female patients ranging in age from six months to 88 years, distributed across adult burn, intensive care, surgical, and pediatric burn units. Wound samples accounted for the majority of isolates at 73 percent, followed by urine at 15 percent and blood at 12 percent. Identification was confirmed through conventional microbiological and biochemical methods as well as polymerase chain reaction targeting the blaOXA-51 beta-lactamase gene, a molecular signature of the species. The researchers then used a microtiter plate crystal violet staining assay to classify each isolate as a weak, moderate, or strong biofilm producer.

The nanoparticles themselves were produced through green synthesis, an approach in which plant extracts serve as both reducing and capping agents. Phytochemicals such as flavonoids, terpenoids, and polysaccharides donate electrons to reduce silver ions into metallic silver nanoparticles while simultaneously stabilizing their surfaces. This method is cost-effective, environmentally sustainable, and avoids the toxic solvents associated with conventional chemical synthesis. Nepeta pogonosperma, a member of the Lamiaceae family identified in 1984, has a long history in traditional medicine across Iran and neighboring regions, where it has been used to treat conditions ranging from pneumonia and influenza to stomach disorders and asthma. Astrodaucus persicus, a member of the Apiaceae family native to Asia, has traditionally been consumed as a food additive in Iran and Turkey, and plants in this family exhibit antibacterial, hepatoprotective, antitumor, and apoptosis-inducing activities.

When the researchers measured the minimum inhibitory and minimum bactericidal concentrations of the two nanoparticle formulations, the results were striking. MIC and MBC values against the 100 clinical isolates ranged from 0.1 to 40 micrograms per milliliter, but for more than 94 percent of isolates these values fell between 0.1 and 3 micrograms per milliliter. For AgNP@Ap, the Astrodaucus persicus formulation, 80 of the isolates were inhibited at concentrations of 0.1 to 0.5 micrograms per milliliter, while the Nepeta formulation inhibited 52 isolates at that same low range. A significant correlation emerged between biofilm formation intensity and susceptibility: over 90 percent of strong and moderate biofilm producers exhibited MIC and MBC values between 0.1 and 3 micrograms per milliliter, suggesting that the most dangerous biofilm-forming strains were also the most vulnerable to the nanoparticles.

At sub-inhibitory concentrations of 1 microgram per milliliter for AgNP@Ap and 1.171 micrograms per milliliter for AgNP@Np, both formulations interfered with biofilm development in the 20 strongest producers. For AgNP@Ap, 40 percent of isolates showed 41 to 60 percent inhibition of new biofilm formation and 10 percent showed inhibition exceeding 80 percent. AgNP@Np performed comparably, with 30 percent of isolates showing 41 to 60 percent inhibition and 10 percent showing greater than 80 percent inhibition. Crucially, the nanoparticles did not merely prevent new biofilms from forming; they also dismantled established ones. When pre-formed biofilms were treated, 45 percent of isolates exposed to AgNP@Ap showed 41 to 60 percent disruption, and 50 percent of those exposed to AgNP@Np fell into the same category, with some isolates experiencing up to 80 percent or greater biomass loss.

The molecular analysis revealed why these effects matter. Among the 100 isolates, 93 exhibited elevated bap gene expression, with fold-changes spanning from 2-fold to as high as 20-fold relative to the reference strain. Every isolate showing more than a 5-fold increase was a strong biofilm producer, and statistical testing confirmed that strong biofilm formers expressed bap at significantly higher levels than weaker producers. When the strong producers were treated with sub-MIC concentrations of the nanoparticles, bap expression dropped significantly compared with untreated controls at both 24 and 48 hours, with the reduction becoming more pronounced at the longer exposure. Quantitative real-time PCR with the 16S rRNA gene as an internal control, analyzed using the comparative 2^-ΔΔCt method, documented these changes precisely. Notably, isolates with higher baseline bap expression tended to have lower MIC and MBC values, indicating greater susceptibility to the nanoparticles.

The authors emphasize that these green-synthesized particles are not simply bits of metallic silver. Prior characterization showed that AgNP@Np particles are spherical, with an average crystallite size of 31.68 nanometers, a hydrodynamic diameter of 233 nanometers, and a zeta potential of −35.1 millivolts indicating good colloidal stability. Fourier-transform infrared spectroscopy confirmed that polyphenols, carbohydrates, and amides from the plant extract form an organic corona around the silver core. These capping molecules are not inert; many phytochemicals possess intrinsic antibacterial, anti-adhesion, and quorum-sensing inhibitory activities. The anti-biofilm efficacy observed is therefore likely the product of synergy between the silver core, which disrupts bacterial membranes, generates reactive oxygen species, and interferes with transcriptional machinery, and the bioactive plant-derived surface layer, which may modulate the sustained release of bactericidal silver ions. Differences in the phytochemical profiles of the two plants—polyphenols and flavonoids in Nepeta versus monoterpenes and benzodioxole compounds in Astrodaucus—likely explain the subtle variations in performance between the two formulations.

The findings arrive at a moment when the clinical urgency of A. baumannii infections has never been greater, particularly for burn patients and intensive care populations, where biofilm-mediated persistence drives mortality. Because silver nanoparticles target multiple biological pathways simultaneously, the likelihood of resistance developing is reduced compared with single-target antibiotics, and prior studies have documented similar effects, including reductions in bap expression with chemically synthesized silver nanoparticles at higher concentrations. The consistency of the present results, achieved at lower concentrations in multidrug-resistant clinical isolates rather than laboratory strains, strengthens the case for clinical relevance. The authors caution, however, that translating these nanoparticles into practice requires further work: precise mechanisms of action, long-term safety profiles, potential side effects, and integration into medical devices and treatment protocols all remain to be established. Still, the study offers compelling evidence that an eco-friendly, low-cost synthesis route rooted in traditional medicinal plants can disarm one of the hospital’s deadliest pathogens at the level of its own genes.

Subject of Research: Plant-based silver nanoparticles as anti-biofilm agents against Acinetobacter baumannii

Article Title: Effect of Green‐Synthesized Silver Nanoparticles From Nepeta pogonosperma and Astrodaucus persicus on the Reduction of Bap Gene Expression in Strong Biofilm‐Producing Acinetobacter baumannii Clinical Isolates

Article References: Kakavan, M., Gholami, M., Ahanjan, M., Ebrahimzadeh, M. A., Hossein Nataj, A., Mousavi, T., & Goli, H. R. (2026). Effect of Green‐Synthesized Silver Nanoparticles From Nepeta pogonosperma and Astrodaucus persicus on the Reduction of Bap Gene Expression in Strong Biofilm‐Producing Acinetobacter baumannii Clinical Isolates. MicrobiologyOpen, 15(5), Article e70391. https://doi.org/10.1002/mbo3.70391

Image Credits: AI Generated

DOI: 10.1002/mbo3.70391

Keywords: Acinetobacter baumannii, silver nanoparticles, green synthesis, biofilm, bap gene, antimicrobial resistance, Nepeta pogonosperma, Astrodaucus persicus, qRT-PCR, nosocomial infections, nanomedicine, ESKAPE pathogens