The headline numbers are stark. Among 94,790 E. faecium isolates reported across 349 studies, 18,679 were vancomycin-resistant, yielding a pooled global prevalence of 25 percent (95% CI: 21–29 percent) for VREfm. Among 144,481 E. faecalis isolates from 339 studies, 2,960 were resistant, giving a pooled prevalence of 5 percent (95% CI: 3–6 percent) for VREfs. Because Egger’s regression test indicated significant publication bias in both datasets, the researchers applied the trim-and-fill method, which adjusted the estimates upward to 33 percent for VREfm and 8 percent for VREfs. In other words, roughly one in three E. faecium isolates worldwide may now carry vancomycin resistance once the bias in published literature is accounted for.

Temporal trends are equally alarming. The pooled prevalence of VREfs rose from 1 percent before 2000 to 12 percent during 2021–2025 (p = 0.0026), while VREfm climbed from 11 percent before 2000 to 29 percent in the same recent period (p = 0.0095). This is not a trend confined to a single region or population. Previous meta-analyses in Asia, India, and Iran have documented similar increases, and the new global analysis confirms that the rise in vancomycin resistance is a worldwide phenomenon driven by continued antimicrobial selective pressure and the persistence of healthcare-adapted resistant lineages.

Geographic patterns reveal a divided world. For VREfs, Africa had the highest continental prevalence at 13 percent (95% CI: 4–26 percent), while Oceania recorded essentially zero. For VREfm, South America topped the list at 57 percent (95% CI: 26–86 percent), whereas Africa showed the lowest at 5 percent (95% CI: 1–12 percent). Country-level analysis highlighted Greece (50 percent) and Slovakia (44 percent) as hotspots for VREfs, and Ireland (100 percent, based on 39 isolates) and Argentina (74 percent, based on 46 isolates) for VREfm. The authors caution that several of these country estimates rest on small sample sizes and high heterogeneity, so they should be interpreted as signals rather than definitive rates. Conversely, near-zero pooled prevalences with zero heterogeneity were observed for VREfm in Uganda, Tunisia, and Norway, and for VREfs in South Korea and Saudi Arabia, indicating highly consistent studies with very low or absent resistance in those settings.

The source of isolates matters enormously. For VREfs, non-clinical isolates showed a higher pooled prevalence (8 percent; 95% CI: 3–13 percent) than clinical isolates (4 percent; 95% CI: 3–6 percent), a statistically significant difference (p = 0.0267). Environmental water (26 percent) and animal stool (40 percent) emerged as particularly important reservoirs, suggesting that these non-clinical sources play a critical role in the circulation and spread of resistant clones. For VREfm, rectal swabs (76 percent; 95% CI: 38–99 percent) and hospital environmental samples (74 percent; 95% CI: 33–99 percent) had the highest prevalence, reflecting the capacity of E. faecium to colonize the gastrointestinal tract and persist on inanimate surfaces for days to months. This parallel between colonized patients and contaminated surfaces sustains VRE transmission within healthcare settings.

Infection setting analysis reinforced the hospital-centric nature of the problem. VREfm prevalence was significantly higher in hospital-acquired infections (29 percent; 95% CI: 21–38 percent) than in community-acquired infections (1 percent; 95% CI: 0–7 percent), a difference the authors attribute to antibiotic selective pressure, prolonged hospitalization, ICU stays, and extensive use of invasive medical devices. For VREfs, the difference between hospital-acquired (5 percent) and community-acquired (3 percent) infections was not statistically significant, though ICUs still showed the highest ward-level prevalence at 8 percent. Hematology wards, interestingly, showed the highest VREfm prevalence at 49 percent, likely reflecting the vulnerability of immunocompromised patients to enterococcal bacteremia.

Laboratory methods also shape reported resistance rates. Studies combining biochemical tests with multiplex PCR or PCR reported the highest prevalence estimates for both species, suggesting that combined phenotypic and molecular approaches improve diagnostic accuracy. For antimicrobial susceptibility testing, disc diffusion combined with E-test methods yielded the highest VREfs prevalence (21 percent), while the E-test alone reported the highest VREfm prevalence (64 percent). Interpretive guidelines influenced results as well: CLSI criteria produced the highest VREfs estimate (5 percent), while EUCAST criteria produced the highest VREfm estimate (36 percent). These differences in breakpoints and susceptibility categorization mean that reported vancomycin resistance rates may depend as much on the laboratory method as on the biology of the pathogen itself.

The clinical implications are serious. E. faecium is classified as one of the ESKAPE pathogens because of its ability to acquire multidrug resistance determinants and persist in healthcare settings, and it accounts for approximately 77 percent of vancomycin-resistant enterococcal bacteremia cases, with E. faecalis contributing 9 percent. Rising VRE prevalence reduces the effectiveness of glycopeptide therapy and increases reliance on last-resort agents such as linezolid, daptomycin, and tigecycline. Comparative clinical data for these alternatives remain limited, and therapy choice is influenced by resistance patterns, infection site, and patient factors, making accurate surveillance of resistance trends essential for guiding empiric treatment.

The authors argue that their integrated approach, combining clinical and environmental isolates within a single analytical framework, overcomes limitations of previous reviews that focused mainly on clinical sources. Environmental enterococci may serve as reservoirs of vancomycin resistance determinants and contribute to the transmission of resistance genes to hospital-associated populations, a dynamic that clinical-only surveillance systematically underestimates. The findings support One Health surveillance strategies that integrate clinical, environmental, and animal sampling to improve infection prevention, antimicrobial stewardship, and public health responses to VRE dissemination.

Despite substantial heterogeneity across studies and uneven geographic representation, the analysis provides a robust foundation for targeted interventions. The authors call for standardized antimicrobial susceptibility testing methods and interpretive criteria, incorporation of whole-genome sequencing to characterize resistance determinants and distinguish clonal transmission from gene dissemination, and future multicenter prospective studies spanning the One Health continuum. Frameworks such as the WHO Global Antimicrobial Resistance and Use Surveillance System (GLASS) can improve data consistency and quality, particularly in regions with limited surveillance capacity. As vancomycin resistance continues its upward trajectory, the message from this global synthesis is clear: the battle against resistant enterococci cannot be won in hospital wards alone, because the environment is an active partner in the spread of resistance.

Subject of Research: Global prevalence and temporal trends of vancomycin-resistant Enterococcus faecium and Enterococcus faecalis from clinical and environmental sources

Article Title: Global Prevalence of Vancomycin‐Resistant Enterococcus faecium and Enterococcus faecalis Isolated From Clinical and Environmental Sources: A Systematic Review and Meta‐Analysis

Article References: Narimisa, N., Navidifar, T., Hameed, T. T., Mohammadzadeh, R., Abdoli, F., Ghamari, M., Nourollahi, D., Ansari, F., Ansari, A., & Bostanghadiri, N. (2026). Global Prevalence of Vancomycin‐Resistant Enterococcus faecium and Enterococcus faecalis Isolated From Clinical and Environmental Sources: A Systematic Review and Meta‐Analysis. MicrobiologyOpen, 15(5), Article e70434. https://doi.org/10.1002/mbo3.70434

Image Credits: AI Generated

DOI: 10.1002/mbo3.70434

Keywords: antimicrobial resistance, vancomycin-resistant enterococci, VRE, Enterococcus faecium, Enterococcus faecalis, systematic review, meta-analysis, One Health, hospital-acquired infections, public health, Global, Prevalence

The study’s central finding is that silver ions outperformed every other metal tested by a wide margin. At a concentration of just 0.3125 millimolar, silver produced inhibition zones of up to 19.00 plus or minus 1.15 millimeters against the target organisms, and its minimum inhibitory concentration—the lowest concentration that stops visible bacterial growth—was a remarkably low 0.078 millimolar. Gold ions came in second with a minimum inhibitory concentration of 2.5 millimolar, while zinc and copper showed only moderate activity and required substantially higher concentrations. Aluminium was the weakest performer of the five, showing the least antibacterial effect across all the tested strains. This ranking matters because it gives food safety engineers a hierarchy of candidates when designing metal-based sanitizing strategies or antimicrobial surface coatings.

What makes the work particularly timely is the mechanism behind the metal ions’ lethality. The researchers used propidium iodide uptake assays, a standard technique in which a fluorescent dye that cannot cross intact cell membranes floods into bacteria whose membranes have been compromised. The strong propidium iodide signal observed after metal ion exposure indicated that these ions damage the bacterial membrane and disrupt overall cell integrity. This is consistent with decades of literature on silver and copper toxicity, in which cations bind to thiol groups in proteins, interfere with the peptidoglycan and outer membrane layers, and collapse the electrochemical gradients bacteria depend on to import nutrients and expel toxins. Because metal ions attack multiple cellular targets simultaneously, the classic single-gene resistance mechanisms that defeat antibiotics are far less effective against them.

Perhaps the most striking mechanistic result involved reactive oxygen species. When the team measured intracellular oxidative stress, silver induced by far the highest generation of reactive oxygen species, with fluorescence intensity readings rising from roughly 93,855 to 165,407 across the experimental conditions—values substantially higher than those triggered by the other metals. Reactive oxygen species are chemically aggressive molecules that oxidize DNA, proteins, and lipids, and their accumulation inside bacterial cells is a hallmark of metal-mediated killing. This oxidative burst suggests that silver’s superiority is not simply a matter of membrane damage but of a broader, multi-pronged assault that overwhelms the bacteria’s antioxidant defenses, pushing cells into an irreversible death spiral.

Biofilms were the second front of the investigation, and they are arguably the more important one for the dairy industry. Biofilms are structured communities of bacteria encased in a self-produced matrix of extracellular polymeric substances that anchor them to surfaces and shield them from disinfectants, desiccation, and immune attack. On stainless steel pipelines, tanks, and valves, biofilms act as persistent sources of contamination that can survive clean-in-place procedures and repeatedly seed finished products. The researchers quantified biofilm eradication using microtiter plate assays and found that silver again led the field, achieving a fifty percent biofilm eradication concentration of just 0.156 millimolar. Gold and copper followed as the next most effective agents, while zinc and aluminium lagged behind.

To test performance under realistic conditions, the team grew biofilms of the multidrug-resistant pathogens directly on stainless steel surfaces of the kind used in dairy equipment, then treated them with the metal ions and examined the results with confocal laser scanning microscopy and scanning electron microscopy. These imaging techniques allowed the researchers to visualize both the remaining biomass and the structural integrity of the biofilm matrix. The verdict was clear: silver reduced biofilm biomass by more than sixty percent, while gold achieved reductions of over forty percent. Electron micrographs revealed damaged cells and disrupted architecture in the treated biofilms, confirming that the metal ions penetrate the protective matrix and kill the embedded cells rather than merely detaching them from the surface.

One of the study’s most practically valuable contributions is its systematic exploration of metal combinations. Using the checkerboard assay method, in which two or more agents are tested across a grid of paired concentrations, the researchers calculated fractional inhibitory concentration indices for every pairing. An index of 0.5 or below indicates synergy, meaning the combination is more effective than the sum of its parts, while values up to 1.0 indicate an additive interaction. The copper-gold, zinc-copper, and zinc-silver pairs all showed synergistic or additive interactions, with indices ranging from 0.5 to 0.75. Even more intriguing was the ternary combination of copper, zinc, and silver, which produced a notable additive interaction with an index of 0.512. Combination therapy is attractive for practical applications because pairing metals allows each to be used at lower concentrations, reducing cost, potential toxicity, and the environmental burden of metal residues while maintaining or improving killing power.

The implications for the dairy sector are significant. Antimicrobial resistance is escalating globally, and food processing environments are recognized as important nodes in the dissemination of resistant strains. Heat-resistant, multidrug-resistant E. coli isolates have been documented in dairy products, and biofilms on equipment surfaces are a known mechanism by which such strains persist through cleaning cycles. Metal ion-based approaches offer several advantages over conventional chemical sanitizers: they do not select for resistance in the same way antibiotics do, they remain active over extended periods when incorporated into surfaces, and they can be combined with existing hygiene protocols. The Karnal team’s comparative data now provides a rational basis for choosing which metals, and which combinations, deserve further development as coatings or sanitizing formulations for food contact surfaces.

At the same time, the researchers and the broader field are careful to note the challenges that remain before metal ion treatments can be deployed at scale. Metal concentrations that are lethal to bacteria must be balanced against considerations of mammalian cell toxicity, corrosion of equipment, and regulatory limits on metal residues in food. Prior work has shown that there are concentration windows in which antibacterial cations achieve maximal efficacy with minimal cytotoxicity, and identifying those windows for each metal pair and surface type will be essential. Environmental release of silver and copper from processing facilities also raises ecological questions, since these ions are toxic to aquatic microorganisms at low concentrations. The study, funded by the Indian Council of Medical Research and supported by the Indian Council of Agricultural Research, was conducted entirely in vitro, so field trials on operating dairy lines will be the necessary next step.

Nevertheless, the study delivers a clear and actionable message: not all metals are equal, and rational combination is the path forward. Silver stands out as the single most potent ion against ESBL-producing E. coli, MRSA, and VRE, both as free-floating planktonic cells and as surface-attached biofilms, and its oxidative stress mechanism helps explain why. Gold, copper, and zinc each have roles to play, particularly in synergistic combinations that lower the required doses of each component. As the food industry confronts the twin pressures of antimicrobial resistance and consumer demand for chemical-free sanitation, metal ion science is moving from the laboratory bench toward the milking parlor, and this comparative evaluation provides the quantitative groundwork for that transition.

Subject of Research: Antibacterial and anti-biofilm efficacy of metal ions against multidrug-resistant pathogens on dairy equipment surfaces

Article Title: Comparative antibacterial, synergistic, and anti-biofilm efficacy of metal ions against multidrug-resistant pathogens on dairy equipment surfaces

Article References: Adrija, R., Garg, M., Parachalil, K., Sahu, M., Vij, S., Pradhan, D., Mallappa, R. H., & Vishweswaraiah, R. H. (2026). Comparative antibacterial, synergistic, and anti-biofilm efficacy of metal ions against multidrug-resistant pathogens on dairy equipment surfaces. 3 Biotech, 16(11), Article 454. https://doi.org/10.1007/s13205-026-05084-4

Image Credits: AI Generated

DOI: 10.1007/s13205-026-05084-4

Keywords: antimicrobial resistance, metal ions, silver ions, biofilms, dairy equipment, MRSA, ESBL E. coli, VRE, stainless steel, synergistic combinations, reactive oxygen species, food safety

Enterococci are gram-positive bacteria that normally colonize the intestinal tracts of humans and animals, where they usually live as harmless commensals. Yet two species in particular, Enterococcus faecalis and Enterococcus faecium, are among the most important causes of opportunistic and healthcare-associated infections. Enterococcus faecium is notorious for its capacity to acquire resistance to penicillins and, increasingly, to glycopeptides such as vancomycin, an antibiotic class introduced in 1955 that kills bacteria by binding to peptidoglycan precursors and blocking cell wall synthesis. Vancomycin-resistant enterococci were first described more than two decades after the drug’s introduction, and among resistant E. faecium isolates the vanB genotype has become the most prevalent in several European countries. VanB-type resistance is known for phenotypic variability, meaning that laboratory phenotype does not always reliably reflect the underlying resistance genes, a property that has now proven consequential in a dramatic way.

The public health stakes are considerable. The World Health Organization’s 2024 Bacterial Priority Pathogens List classifies vancomycin-resistant E. faecium as a high-priority pathogen, and according to the European Centre for Disease Prevention and Control the mean vancomycin resistance rate among European E. faecium isolates stands at roughly 20 percent. Austria had long reported comparatively low figures, with the national action program on antibiotic resistance documenting a resistance rate of just 3 percent among invasive isolates in 2023. That picture changed abruptly. After years without any invasive vancomycin-resistant E. faecium infections, the diagnostic laboratory serving Graz and the wider region observed the resistance rate among E. faecium-positive blood cultures climb to 6 percent in 2024 and then to 20 percent in the first half of 2025. By June 2025, thirty-one resistant isolates had been collected, and virtually all could be attributed to a single previously unreported lineage, ST117/CT7799.

The outbreak’s first signal appeared in February 2024, when automated VITEK2 susceptibility testing flagged vancomycin resistance in a clinical E. faecium isolate even though disk diffusion, gradient testing, and broth microdilution all failed to confirm it under routine conditions. When the laboratory reorganized its workflow to route all enterococcal isolates through automated testing and systematically re-examined results, five further isolates with the same distinctive phenotype emerged within months. All came from specimens obtained for genuine infection diagnostics rather than screening, and every case was confirmed as vanB-type resistance by molecular PCR. Retrospective review of raw instrument data found no evidence of this phenotype in the laboratory’s records before 2024, strongly suggesting a genuinely new arrival. Early cases clustered around invasive procedures performed at a single hospital, and a second transmission chain later surfaced among urology patients who had undergone double-J catheterization in an operating room shared with surgeons. Notably, environmental surface sampling by the hospital infection control team failed to locate the organism, and nearly all affected patients had either been hospitalized for at least four days or had recent inpatient care history with the same provider.

To characterize the outbreak, the team subjected twenty non-duplicate isolates to whole genome sequencing using both Illumina short-read and Oxford Nanopore long-read platforms, achieving highly concordant results between technologies. Core genome multilocus sequence typing based on 1,423 loci revealed a strikingly homogeneous cluster: even isolates sampled sixteen months apart differed by no more than six alleles, far below the cluster threshold of three alleles used for assignment once the clonal relationship was established. The nearest local control strain, isolated at the same site during the same period, differed by 159 alleles, and the closest reference strain from the Robert Koch Institute collection differed by 142 alleles. Searches of the cross-national surveillance platform MiGenomeSurv showed the next closest relative still 76 alleles away, confirming that CT7799 represents an entirely novel lineage. The clone was provisionally named VREfmstyr, after Styria, the Austrian federal state where it was first isolated.

Genomic analysis also illuminated the genetic architecture of resistance. All outbreak isolates carried a complete copy of the transposon Tn1549, the mobile element responsible for vanB-mediated vancomycin resistance, inserted into the chromosome. Long-read assemblies proved essential: short-read assemblies fragmented the transposon across three contigs, obscuring its structure, whereas long reads revealed three matching blocks separated by two intervening regions of 1,494 and 1,417 base pairs containing insertion sequence elements, including an ISL3-like transposase of the ISEfa11 family and an IS3-like ISEnfa3-family transposase alongside a helix-turn-helix domain protein. An additional IS91 transposase was found inserted in a YodL domain protein upstream of the vanB gene cluster. All seven vancomycin resistance genes, vanB, vanY-B, vanW-B, vanH-B, vanX-B, vanR-B, and vanS-B, were identical across every outbreak isolate, underscoring the clone’s remarkable genetic stability despite months of circulation. Based on the classification scheme of the Norwegian VRE study group, the vanB cassette appears to be a hybrid between variants typically associated with different sequence types, hinting at a recombination event in the strain’s recent history.

The true significance of the study, however, lies in its systematic evaluation of diagnostic methods, and the results are sobering. Broth microdilution, the reference standard for antimicrobial susceptibility testing, correctly identified only 16 of 31 isolates, or 52 percent, as vancomycin resistant when read after the standard 24 hours of incubation, even though all control strains behaved as expected. Extending incubation to 48 hours eventually pushed minimum inhibitory concentrations above the susceptibility breakpoint for all isolates, but the growth around concentrations of 2 milligrams per liter and above was so sparse that even trained personnel could easily overlook it. Gradient testing from two different manufacturers failed to detect resistance in every single case at 24 hours, and disk diffusion was equally deceptive: all isolates produced inhibition zone diameters clearly wider than the 12-millimeter resistance threshold, and the zone edges lacked the fuzzy appearance that typically signals vancomycin resistance. Only VITEK2 automated testing, which correctly flagged all 31 isolates under routine settings, proved reliable, a finding that diverges from earlier studies reporting only 81 percent sensitivity for low-MIC resistant strains and possibly reflecting improvements in newer test cards and software.

Screening carried a similar message of failure. When seven representative isolates were plated on kanamycin-vancomycin agar and four commercially available chromogenic VRE screening media, three of the four commercial agars yielded no growth at all after 24 hours, and the sole medium showing some activity was only weakly positive for four isolates and negative for the remaining three. Prolonging incubation to 48 and even 72 hours improved results only marginally and inconsistently across manufacturers, while the outbreak strain failed entirely to grow on kanamycin-vancomycin agar. These findings matter because VRE often constitutes only a small fraction of the intestinal enterococcal population, making selective screening media indispensable for controlling transmission, and because prior research has already shown that sensitivity drops sharply for strains with vancomycin minimum inhibitory concentrations below 16 milligrams per liter. Only CHROMagar VRE proved dependable after standard incubation, and even that required confirming results under the study’s specific conditions.

Intriguingly, when a representative isolate was exposed to vancomycin on a gradient strip for more than 100 hours, single colonies eventually grew within the inhibition zone, and after two passages the derivative consistently displayed a minimum inhibitory concentration of at least 32 milligrams per liter. Sequencing revealed that this resistant derivative carried a single nucleotide substitution in the vanS-B gene, the sensor kinase that regulates the vancomycin resistance operon, causing an amino acid change from serine to arginine at position 243. This observation suggests that the outbreak clone’s occult phenotype stems from a regulatory mutation or arrangement that dampens resistance expression, and that vancomycin pressure can select for compensatory variants restoring full resistance. The authors caution, however, that whether the insertion elements or the specific allele differences in vanR-B, vanY-B, and vanW-B are causally responsible for the difficult-to-detect phenotype remains an open question demanding further investigation.

The implications reach well beyond Styria. Because many diagnostic laboratories worldwide rely on 24-hour disk diffusion zone readings to determine vancomycin susceptibility, a strain with this phenotype could spread through hospitals without triggering any alarm, quietly colonizing patients and contaminating environments while appearing fully susceptible on paper. The research team recommends that laboratories verify the adequacy of their screening media and incubation times, and adapt their susceptibility testing protocols by prolonging incubation, adding molecular vanB PCR testing, or employing automated VITEK2 analysis. Given the clone’s demonstrated epidemic potential, its absence from all prior surveillance databases, and the growing proportion of invasive infections it now accounts for in the region, surveillance studies will be essential to determine whether ST117/CT7799 remains a local phenomenon or whether laboratories across Europe and beyond must urgently reassess whether their diagnostic procedures can catch a superbug designed, by evolutionary accident, to stay invisible.

Subject of Research: Emergence and diagnostic challenges of a novel vancomycin-resistant Enterococcus faecium clone (ST117/CT7799) in Austria

Article Title: Emergence of a Novel, Phenotypically Difficult‐to‐Detect Vancomycin‐Resistant Enterococcus faecium Clone (ST117/CT7799)

Article References: Forstner, P., Uitz, C., Dabernig‐Heinz, J., Wagner, G. E., Bender, J., Fischer, M., Siebenhofer, D., Werner, G., Busche, T., Klages, L. J., Rückert‐Reed, C., Steinmetz, I., & Dichtl, K. (2026). Emergence of a Novel, Phenotypically Difficult‐to‐Detect Vancomycin‐Resistant Enterococcus faecium Clone (ST117/CT7799). MicrobiologyOpen, 15(5), Article e70393. https://doi.org/10.1002/mbo3.70393

Image Credits: AI Generated

DOI: 10.1002/mbo3.70393

Keywords: vancomycin-resistant Enterococcus faecium, VRE, ST117/CT7799, hospital outbreak, antimicrobial resistance, vanB operon, Tn1549 transposon, whole genome sequencing, diagnostics, Austria, infection control, cgMLST