The global burden of foodborne disease is staggering and persistent. Pathogens such as E. coli, Salmonella typhi, Staphylococcus aureus, Listeria, Shigella, Campylobacter, and Vibrio have been implicated in outbreaks across the globe, lurking in uncooked and undercooked poultry, pork, beef, fish, eggs, dairy products, fresh vegetables, fruits, and even dried goods like cereals, spices, and chocolates. Risk factors ranging from inadequate personal hygiene among food handlers to exposure of foods to insects in cooking environments continue to drive the prevalence of these illnesses. Conventional laboratory detection methods, while accurate, often demand expensive equipment, trained personnel, and days of waiting, a timeline that can allow contaminated products to reach consumers before anyone realizes there is a problem. The researchers behind the new work argue that rapid detection strategies deployed at the point of consumption are an essential complement to existing surveillance systems.

The core of the innovation lies in how the nanoparticles themselves are made. Rather than relying on chemical or physical synthesis routes that can be costly and environmentally taxing, the team harnessed Bacillus subtilis, a bacterium with demonstrated iron-reducing potential identified in the group’s earlier experiments. To produce iron oxide nanoparticles, the researchers inoculated sterile nutrient broth with the isolate, incubated it at 37 degrees Celsius for 48 hours, and mixed the recovered culture supernatant with a cocktail of iron salts. Over 120 hours of static incubation at room temperature, the microbial machinery reduced the metal precursors into nanoparticles. For gold, the team dispersed wet B. subtilis biomass directly into a chloroauric acid solution and agitated it in the dark for 72 hours, letting cellular enzymes, likely including NADH-dependent reductase and nitrate reductase, drive the bio-reduction.

Characterization confirmed that both particle types had formed as intended. Ultraviolet-visible spectroscopy showed the iron oxide nanoparticles absorbing at 261 nanometers, squarely within the expected 250 to 350 nanometer range for Fe3O4, while the gold nanoparticles displayed the characteristic surface plasmon resonance peak at 548 nanometers. Scanning electron microscopy revealed mean particle sizes of 72 nanometers for the iron oxide particles and 118 nanometers for the gold, with FTIR analysis detecting functional groups such as alcohol hydroxyl stretches, amine bends, and carbon-carbon skeletal vibrations that point to the microbial metabolites capping the particles. X-ray diffraction patterns matched the standard reference files for both magnetite and metallic gold, and energy dispersive X-ray spectroscopy confirmed the elemental signatures, with iron accounting for 49.32 percent of the iron oxide particles and gold 33.31 percent of the gold nanoparticles.

Assembling the two particle types into a single functional nanocomposite required careful chemistry. The iron oxide nanoparticles were first capped with ethylenediaminetetraacetic acid, or EDTA, a ligand that prevents aggregation and stabilizes the notoriously difficult-to-manage magnetic particles. The gold nanoparticles were separately coated with one of two polymers: polyethyleneimine, known as PEI, or polyethylene glycol 6000, known as PEG. Both polymers are rich in amine groups that carry positive charges, while the EDTA-capped iron oxide surfaces are negatively charged. When the two suspensions were combined and gently heated, electrostatic attraction drove the particles to self-assemble into iron oxide-gold nanocomposites. EDX analysis revealed a meaningful difference between the two versions: the PEI-linked composites contained 75.56 percent elemental gold but only 7.40 percent iron, while the PEG-linked versions held 61.40 percent gold and 20.00 percent iron, suggesting the polymer choice shapes how the components integrate.

With the nanocomposites in hand, the researchers turned them into biosensors by functionalizing them with three different chromogens, compounds that change color under specific biochemical conditions. The candidates were 2-nitrophenyl-alpha-D-glucopyranoside, or 2-NPGP; urea; and 2,3,5-triphenyl tetrazolium chloride, or TTC, a well-known redox indicator. Each chromogen was attached independently to both the PEI-linked and PEG-linked nanocomposites, creating a panel of candidate sensors that were then tested against three enteric bacteria isolated from livestock: the Gram-negative Salmonella typhi and Escherichia coli, and the Gram-positive Staphylococcus aureus. Bacterial cultures were standardized to concentrations spanning from 10 to 100 million colony-forming units per milliliter, and the mixtures were monitored visually and by spectrophotometry at 540 nanometers.

The results separated the candidates sharply. The 2-NPGP-functionalized nanocomposites linked by PEI produced a gradual color change from colorless to pale only with Staphylococcus aureus, reaching a detection limit of 10,000 CFU per milliliter, a sensitivity the researchers attribute to the catalytic action of beta-D-galactosidase produced by that organism. The urea-functionalized versions, whether linked by PEI or PEG, showed no color change with any of the three pathogens, a result that surprised the team given earlier reports of urea-based detection. The key difference, they suggest, is that previous studies incorporated the enzyme urease directly into their detection systems, whereas this setup relied on enzymes naturally secreted by the bacteria, which may not have been sufficient to drive the reaction. The PEG-linked 2-NPGP composites likewise failed to respond to any pathogen.

The standout performer was the TTC-functionalized nanocomposite linked by PEI. Within two hours of exposure, Salmonella typhi triggered a progression from colorless to light pink and ultimately to an intense red by the 24-hour mark. Escherichia coli produced a light pink color at six hours, indicating a slower enzymatic reaction, while Staphylococcus aureus produced no visible change at all. The detection limit for this configuration was 100 million CFU per milliliter. Critically, control experiments using TTC alone without the nanocomposite showed no color change, demonstrating that the PEI-linked iron oxide-gold structure significantly enhances the chromogenic properties of TTC. The researchers propose a mechanism centered on dehydrogenase enzymes in viable bacterial cells: hydrogen ions released from the pathogens, complemented by hydrogen ions from PEI, interact with the synthetic ion receptor of TTC and induce the color change. Differences in how Salmonella and E. coli regulate homologous genes governing lipopolysaccharide modifications and proton release may explain why the E. coli response lagged behind.

Why did PEI succeed where PEG failed? The researchers point to PEI’s low molecular weight, which generates high cationic charge density, making it more compatible and specific with TTC, itself a cationic salt. As a positively charged compound, TTC can initiate electrostatic interactions with the anionic plasma membranes of viable Salmonella and E. coli cells, and the PEI scaffold appears to facilitate that encounter. PEG-linked composites, by contrast, showed no response to any pathogen, possibly because of an absence of available hydrogen ions or repelling interactions from unidentified ions associated with the polymer. The selectivity is itself an asset: a sensor that ignores Staphylococcus aureus while flagging the two Gram-negative enteric pathogens could, with further development, help distinguish between different contamination scenarios in food testing.

The team is candid about the work’s limitations. Real-time tests on actual food samples were not conducted, and the detection limit of the TTC sensor, while functional, is higher than some competing approaches. Translating the platform from standardized laboratory cultures to the messy matrix of real food will require further validation and optimization. Still, the study establishes a foundation for what the authors describe as a simple, selective, sensitive, and cost-effective bio-receptor for timely detection of foodborne pathogens, particularly Salmonella typhi. Compared with chemical and physical nanoparticle synthesis methods used in most biomedical sensing research, the eco-friendly microbial route offers a sustainability advantage, and the visual readout, requiring no complex setup, positions the technology for point-of-care or even consumer-facing applications. If subsequent studies confirm its performance on real food matrices, bacteria-grown nanocomposites that blush red in the presence of typhoid-causing contamination could become a practical first-line indicator for improving food safety and public health.

Subject of Research: Biosynthesized iron oxide-gold nanocomposite biosensors for colorimetric detection of enteric foodborne bacterial pathogens

Article Title: Colorimetric-based detection of enteric bacterial pathogens using chromogens-functionalized iron oxide-gold nanocomposites biosynthesized by Bacillus subtilis

Article References: Daramola, O. B., Torimiro, N., & George, R. C. (2025). Colorimetric-based detection of enteric bacterial pathogens using chromogens-functionalized iron oxide-gold nanocomposites biosynthesized by Bacillus subtilis. Discover Biotechnology, 2(1), Article 1. https://doi.org/10.1007/s44340-025-00008-z

Image Credits: AI Generated

DOI: 10.1007/s44340-025-00008-z

Keywords: colorimetric detection, foodborne pathogens, iron oxide-gold nanocomposites, Bacillus subtilis, biosynthesis, Salmonella typhi, Escherichia coli, triphenyl tetrazolium chloride, polyethyleneimine, nanoparticles, food safety, biosensors

The scale of the findings is striking. At their peak, annual prevalence estimates reached 347 cases per 100,000 population in primary care settings in 2017 and 314 per 100,000 in hospitals in 2016, figures that consistently exceed the threshold of more than 100 cases per 100,000 person-years used to define high-burden settings. Even after years of gradual decline, the most recent estimates from 2023 stood at 143 per 100,000 in primary care and 167 per 100,000 in hospitals, still well above that benchmark. Hospital admissions accounted for 47.62 percent of all typhoid-related visits, and cumulative deaths over the nine-year period included 11,991 recorded in hospitals, corresponding to an average annual hospital mortality rate of 0.57 per 100,000 population.

Methodologically, the study is a serial cross-sectional analysis built on an unweighted sample of 2,499,681 unique individual records, which, after applying BPJS Kesehatan’s stratified sampling weights, represents a national population of approximately 290 million people. Cases were identified using physician-assigned ICD-10 codes, primarily A01.0 for typhoid fever, recorded as either primary or secondary diagnoses. To avoid inflating prevalence with repeat consultations for the same illness, the researchers applied an episode-based filtering approach: encounters occurring within 30 days of a preceding record for the same individual were treated as part of a single clinical episode, a boundary chosen because typhoid’s incubation period typically ranges from 6 to 30 days and relapses most commonly occur two to three weeks after treatment ends. Only the final record within each episode was retained for analysis.

The choice of data source matters because diagnosing typhoid fever in endemic settings is notoriously difficult. The Widal agglutination test, long used in low-resource settings, has poor sensitivity and specificity because of high background seroprevalence, and rapid diagnostic tests offer only modest improvements. Blood culture remains the reference standard, but its sensitivity drops after prior antibiotic use, and laboratory capacity and cost constraints mean microbiological confirmation is rarely performed in routine Indonesian practice. In primary care, where reimbursement is capitation-based, laboratory confirmation is not routinely required at all; in hospitals, supporting investigations such as Tubex, Typhidot, or Widal testing are generally undertaken for reimbursement claims, though these do not replace culture confirmation. The study’s estimates therefore describe the burden of physician-coded typhoid requiring healthcare utilisation rather than microbiologically confirmed disease, a distinction the authors acknowledge carefully.

Demographically, the burden fell unevenly. Adults aged 19 to 64 accounted for roughly half of all typhoid-related visits, yet the highest prevalence was observed among children under five years of age in both primary care and hospital settings. Adjusted analyses using Poisson regression with robust variance estimation revealed that children aged 0 to 5 years had a modestly higher likelihood of hospitalisation compared with working-age adults, with an adjusted prevalence ratio of 1.02, while adolescents aged 6 to 18 showed a ratio of 1.03. The most pronounced elevation appeared among people aged 65 and older, whose adjusted prevalence ratio of 1.07 was the highest of any age group, despite this group having the lowest overall prevalence of typhoid-related visits. The authors suggest this may reflect comorbidities, frailty, and a lower clinical threshold for admitting older patients rather than greater disease severity per se.

Socioeconomic vulnerability emerged as another powerful determinant. Individuals enrolled in the subsidised insurance scheme, which serves low-income households, had a 7 percent higher likelihood of hospitalisation than those in the formal sector, with an adjusted prevalence ratio of 1.07. Members of Class III, the most affordable tier of care with the simplest inpatient facilities, contributed the largest share of visits across all settings. These patterns, the researchers argue, reflect underlying socioeconomic disadvantage and potential barriers to timely access to care, meaning that by the time subsidised patients reach hospital, their illness may be more advanced. The intersection of age-related vulnerability and social disadvantage, they conclude, shapes severe disease trajectories in ways that targeted interventions must address.

Geographically, the study uncovered pronounced subnational clustering that national-level statistics had long obscured. Primary care prevalence was highest in Central Java province at a mean annual 302 per 100,000, followed by Bengkulu at 289, while hospital prevalence peaked in Aceh at 496 per 100,000, followed by Gorontalo and North Sumatra. When provinces were aggregated into the INA-CBGs regional classification, the highest annual prevalence reached 2,367 visits per 100,000 population in region 1, covering Java, Indonesia’s most populous island, for primary care, and 2,213 per 100,000 in region 3, covering Sulawesi and parts of Sumatra and Kalimantan, for hospitals. Urban areas consistently showed higher prevalence than rural ones across both care settings throughout the study period.

The concentration of cases in densely populated Java is particularly revealing because it runs counter to a simple sanitation narrative. Several provinces in Java exhibited both relatively high percentages of households with access to improved sanitation and high typhoid prevalence, while provinces outside Java with better sanitation access generally showed lower prevalence. Previous research has documented widespread use of shallow, contaminated groundwater as a household drinking water source and poor sanitation management in dense and informal urban settlements on Java, and parts of Sumatra and Sulawesi where cases clustered also show WASH infrastructure access below the national figure. The eastern provinces of Papua and Papua Barat recorded the lowest prevalence, at 24 and 10 per 100,000 respectively in primary care, but the authors caution this likely reflects lower healthcare utilisation and under-ascertainment rather than genuinely low transmission.

The temporal trends carry their own lessons. A marked decline in cases occurred during 2020 and 2021, coinciding with the COVID-19 pandemic, likely reflecting the reallocation of 20 to 40 percent of general ward beds to COVID-19 care, reduced healthcare-seeking, and non-pharmaceutical interventions such as social distancing and improved hand hygiene that may have limited faecal-oral transmission. When cases rebounded in 2022, the increase was more pronounced among inpatients than outpatients, which the authors attribute to the restoration of routine inpatient services rather than a true rise in disease severity. Earlier fluctuations during 2016 and 2017 may relate to the rapid expansion of insurance membership, evolving referral policies, and maturation of coding practices during the early phase of the scheme’s implementation.

The implications extend well beyond Indonesian borders. The Global Burden of Disease 2023 study estimates that Indonesia has the highest typhoid incidence, 99 per 100,000, and mortality rate, 1.29 per 100,000, in Southeast Asia, yet those figures rely substantially on modelled extrapolation in a country lacking nationwide culture-confirmed surveillance. The new claims-based estimates, which exceed even the GBD figures, arrive as neighbouring countries move forward with typhoid conjugate vaccine introduction: Nepal and Pakistan have incorporated the vaccine into routine immunisation, and Bangladesh introduced it in 2025, following the World Health Organization’s 2018 recommendation of a single dose for children from six months of age. Indonesia, however, continues to face financing constraints and competing priorities, with policymakers citing a lack of robust contemporary epidemiological data. The authors also point to complementary environmental surveillance showing Salmonella Typhi in 13 percent of 406 wastewater samples collected from treatment plants, manholes, rivers, and public spaces, evidence of persistent community transmission. Combined with rising multidrug and extensively drug-resistant strains documented across endemic settings, and imported cases linked to travel from Indonesia reported abroad, the converging evidence strengthens the case for introducing the vaccine alongside targeted water and sanitation improvements, prioritising high-burden regions and vulnerable populations, and building serosurveillance and wastewater monitoring into the country’s surveillance architecture.

Subject of Research: Population-based epidemiology of typhoid fever in Indonesia using national health insurance claims data

Article Title: Burden of typhoid fever in primary and hospital care in Indonesia: a serial cross-sectional study using national health insurance (BPJS Kesehatan) data, 2015–2023

Article References: Oktaria, V., Ramadhani, A. D., Maula, A. W., Murni, I. K., Watts, E., Baehaqi, I. S., Dinari, R., Wiryawan, D. A., Daniel, D., Donato, C. M., & Bines, J. E. (2026). Burden of typhoid fever in primary and hospital care in Indonesia: a serial cross-sectional study using national health insurance (BPJS Kesehatan) data, 2015–2023. The Lancet Regional Health – Western Pacific, 75, Article 101994. https://doi.org/10.1016/j.lanwpc.2026.101994

Image Credits: AI Generated

DOI: 10.1016/j.lanwpc.2026.101994

Keywords: typhoid fever, Indonesia, Salmonella Typhi, BPJS Kesehatan, epidemiology, hospitalisation, typhoid conjugate vaccine, water sanitation and hygiene, antimicrobial resistance, health insurance claims, subnational disparities, wastewater surveillance

Typhoid fever remains one of the world’s most consequential waterborne diseases. Salmonella enterica serovar Typhi, a Gram-negative bacterium restricted to humans, causes a systemic febrile illness accompanied by diarrhoea and abdominal cramps, and without prompt antibiotic treatment it can lead to severe complications and death. Global estimates attribute more than ten million illnesses and roughly one hundred thousand deaths each year to the disease, with the overwhelming burden falling on low- and middle-income countries where sanitation infrastructure is inadequate and contaminated water sustains transmission. South Africa is considered a low-endemicity setting, yet outbreaks continue to occur, particularly among vulnerable communities in informal settlements and densely populated areas with limited access to safe water. One of the country’s largest documented outbreaks, in Delmas in 1993, produced more than a thousand cases and was traced epidemiologically to the municipal water supply, although the bacterium was never actually isolated from the water itself.

That persistent gap between epidemiological suspicion and environmental proof is precisely what the new study set out to address. South Africa’s national surveillance system, run through the Group for Enteric, Respiratory and Meningeal Disease Surveillance in South Africa at the National Institute for Communicable Diseases, relies heavily on clinical case detection supported by whole-genome sequencing. Five confirmed typhoid outbreaks have been detected in the past five years, including one between January and October 2025 that produced 147 laboratory-confirmed cases across eight provinces. Yet no definitive source has ever been identified for any of these outbreak-associated cases. Because S. Typhi is shed in the faeces of infected individuals, wastewater networks and urban rivers can act as sensitive indicators of community-level transmission, an approach already demonstrated in Blantyre, Malawi, and Vellore, India, where environmental monitoring detected pathogen circulation independently of fluctuations in clinical reporting. Comparable data from South Africa had been essentially absent.

The isolates at the centre of the study came from the Jukskei River, a major waterway running through Johannesburg in Gauteng Province. As part of a broader twelve-month surveillance study, researchers sampled water monthly at five sites along the river during 2023, collecting sixty samples in total. Four S. Typhi isolates were recovered, a recovery rate of 6.7 percent, and all four came from March 2023 at two sites roughly 3.35 kilometres apart: one within a business district and the other inside a recreational park. The DNA was extracted, sequenced on an Illumina platform at approximately one-hundred-fold coverage, and analysed through a bioinformatics pipeline incorporating quality control, species confirmation, assembly, annotation, serovar prediction, multilocus sequence typing, and screening for antimicrobial resistance determinants, plasmids, virulence factors, and Salmonella pathogenicity islands.

The genomic results revealed a picture of unexpected diversity. Genome sizes ranged from 4.67 to 4.73 megabase pairs, all with the characteristic 52.2 percent GC content of Salmonella enterica. Multilocus sequence typing assigned two isolates to sequence type 1 and two to sequence type 2, both of which are among the most commonly reported S. Typhi types worldwide. Critically, the two ST1 isolates belonged to genotype 4.3.1, better known as the H58 lineage, with one further resolved as the East African I sublineage. H58 emerged in Asia before spreading through repeated intercontinental introductions into Africa, where sustained intra-continental transmission established it across countries including Tanzania, Kenya, Malawi, Zambia, Zimbabwe, and South Africa. It is the lineage most strongly associated with multidrug resistance, and it has driven three major enteric fever outbreaks in South Africa between 2020 and 2021. Until now, however, no whole-genome-confirmed H58 isolate had ever been reported from an environmental source such as a river anywhere in the country.

The resistance profiles of the two H58 isolates were alarming. Both carried a suite of genes conferring resistance to aminoglycosides, beta-lactams, phenicols, sulfonamides, and trimethoprim: aph(6)-Id, aph(3″)-Ib, blaTEM-1, catA1, sul1, sul2, and dfrA7. One isolate additionally carried a point mutation in the gyrA gene, S83F, within the quinolone resistance-determining region, a change classically associated with reduced fluoroquinolone susceptibility. Mobile genetic element analysis identified an IncQ1 plasmid replicon co-located on the same contig as several resistance genes, alongside the insertion sequence IS26, which is widely recognised as a key driver of genomic plasticity and has been implicated in the majority of antimicrobial resistance gene transfer events among plasmids. IncQ1 plasmids are highly mobilisable with a broad host range, and surface waters are considered hotspots for plasmid-mediated horizontal gene transfer, raising the possibility that the river itself could serve as an arena for resistance dissemination, although the authors caution that complete plasmid reconstruction and conjugation experiments were not performed.

Perhaps the most novel molecular finding was the detection of qacEΔ1, a gene associated with reduced susceptibility to quaternary ammonium compounds, a class of disinfectants widely used in food processing facilities. The gene had previously been reported in clinical multidrug-resistant S. Typhi isolates from paediatric patients, but never before in S. Typhi recovered from an urban river. In both H58 isolates, qacEΔ1 was co-localised on the same contig with sul1 and dfrA7, a pattern consistent with the well-documented tendency of disinfectant resistance and antibiotic resistance determinants to travel together on mobile elements such as integrons. No plasmids or insertion sequences were identified on those particular contigs, however, and phenotypic susceptibility to quaternary ammonium compounds was not tested, so the practical implications of the gene’s presence remain an open question for future investigation.

The virulence repertoire of the isolates was equally complete. All four carried genes for adhesion, iron acquisition, and toxin production, including sinH, iroB, iroC, and cdtB, along with the full complement of Salmonella pathogenicity islands from SPI-1 through SPI-10 in the ST1 isolates, while the ST2 isolates lacked only SPI-4. Mercury resistance genes were consistently present in all four genomes. Pairwise SNP comparisons showed the four river isolates were genetically distinct from one another, differing by between 50 and 382 SNPs, which suggests they originated from separate transmission sources rather than a single contamination event, despite being recovered in the same month from sites less than three and a half kilometres apart.

The epidemiological significance emerged when the team expanded the analysis to 128 S. Typhi genomes from South Africa collected in 2023, combining the four river isolates with 124 clinical isolates from the EnteroBase database and applying a core genome MLST hierarchical clustering scheme. The analysis identified twelve clusters of at least three isolates differing by five or fewer alleles, and four of those clusters each contained one of the Jukskei River isolates alongside two or more clinical isolates. The largest cluster comprised four clinical isolates and one environmental isolate differing by no more than two alleles. The clinical isolates in these clusters were collected between February and April 2023, overlapping precisely with the March recovery of the river isolates. Because national surveillance recorded no outbreaks during that period, with 2023 case numbers at baseline levels, the clustering points to small, localised transmission events rather than widespread dissemination, likely sustained by chronic sewage contamination of the river and exposure among communities along its banks.

Genomic relatedness alone cannot resolve the direction of transmission, whether bacteria moved from contaminated water into people or from infected individuals into the river, and the authors are careful not to overstate the claim. But the study delivers the first genomic evidence that a polluted South African urban waterway harbours the same high-risk, multidrug-resistant H58 genotypes circulating in human populations, and it argues persuasively for extending the country’s already advanced genomic surveillance framework to include routine environmental monitoring of high-risk rivers. Within a One Health approach, such integrated monitoring could reveal contamination sources earlier, sharpen outbreak investigations that have historically ended without a confirmed source, and support more timely public health interventions before resistant typhoid strains find new pathways from water to community.

Subject of Research: Genomic surveillance of multidrug-resistant H58 Salmonella Typhi in an urban South African river and its phylogenetic links to clinical typhoid cases

Article Title: Genomic Detection of Multidrug‐Resistant H58 ST1 Salmonella Typhi in a South African Urban Waterway Reveals Epidemiological Links With Clinical Isolates

Article References: Duze, S. T., Marimani, M., & Patel, M. (2026). Genomic Detection of Multidrug‐Resistant H58 ST1 Salmonella Typhi in a South African Urban Waterway Reveals Epidemiological Links With Clinical Isolates. MicrobiologyOpen, 15(5), Article e70408. https://doi.org/10.1002/mbo3.70408

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DOI: 10.1002/mbo3.70408

Keywords: Salmonella Typhi, typhoid fever, H58 lineage, whole-genome sequencing, antimicrobial resistance, environmental surveillance, Jukskei River, Johannesburg, wastewater, IncQ1 plasmid, qacEΔ1, One Health

Fulvic acid belongs to a family of organic materials known as humic substances, the dark, chemically complex residues left behind when microorganisms decompose plant and animal matter. Humic substances are conventionally divided into three fractions according to their solubility: humic acid, which dissolves in alkaline solutions but precipitates when the pH drops below 2; humin, which is insoluble under all conditions; and fulvic acid, the fraction that remains soluble across the entire pH range. This solubility gives fulvic acid unusual versatility, and its molecular architecture is studded with reactive functional groups, including carboxyl, phenolic, quinone, carbonyl, hydroxyl, and amine moieties, many of which have documented biological activity. The exact structure of fulvic acid remains incompletely understood, but capillary electrophoresis and mass spectrometry studies suggest it should be viewed not as a single high-molecular-weight compound but as an assembly of smaller molecules that associate in solution.

The research team collected cow dung from cattle farms in village Chanesar Chachar, Taluka Pano Aqil, District Sukkur, dried it for five to six days at room temperature, and ground it into a fine powder. Extraction followed the protocol of the International Humic Substances Society: the powdered manure was mixed with 80 milliliters of 5 percent sodium hydroxide solution, shaken for four hours, and left to stand for twelve hours. After dilution with deionized water and centrifugation at 3000 revolutions per minute, hydrochloric acid was added to bring the pH down to between 1 and 2, precipitating the humic acid fraction and leaving fulvic acid in the supernatant, which was then collected and dried for analysis. The method is deliberately simple, relying on cheap reagents and standard laboratory equipment, which is precisely what makes the approach attractive for resource-limited settings.

One of the study’s most technically interesting observations concerns extraction efficiency. When 25 grams of dung powder were processed per liter of 0.5 N sodium hydroxide, the yield was 2.5 grams, or 10 percent of the starting mass. Doubling the raw material to 50 grams produced 4 grams, an 8 percent yield, and 100 grams yielded just 6 grams, or 6 percent. The percentage yield therefore falls as the solid loading rises, an inverse relationship the authors attribute to reduced solvent accessibility and less efficient mass transfer at higher concentrations, possibly compounded by saturation effects in the alkaline solubilization process. For anyone hoping to scale up production, the lesson is counterintuitive but clear: less material per batch extracts more efficiently, a trade-off between throughput and yield that will need optimization before any industrial process could be contemplated.

Characterization of the extracted material relied on three complementary analytical techniques. Ultraviolet-visible spectroscopy showed a maximum absorption at 316 nanometers, closely matching a commercial fulvic acid standard from Aldrich, indicating similar chromophoric structures arising from pi-to-pi-star transitions in aromatic and conjugated systems. Fourier transform infrared spectroscopy then mapped the functional group chemistry: a broad band between 3400 and 2900 reciprocal centimeters corresponding to O-H and N-H stretching, a sharp peak near 2929 from aliphatic C-H stretching of methyl and methylene groups, bands between 1598 and 1507 assigned to aromatic carbon-carbon stretching and quinone and conjugated carbonyl contributions, a peak at 1420 reflecting carboxylate asymmetric stretching and phenolic C-O stretching, and a strong absorption at 1034 from C-O stretching of alcohols and polysaccharide structures. The spectrum of the extracted material closely paralleled that of the standard, confirming successful isolation of humic-type functional groups.

X-ray diffraction completed the structural picture. The diffraction pattern displayed a broad background hump between 15 and 35 degrees two-theta, the signature of a largely amorphous material, superimposed with several sharp crystalline peaks. The most intense peak appeared at approximately 44.71 degrees with a d-spacing of 2.0276 angstroms, and a second prominent peak at 31.74 degrees with a d-spacing of 2.8195 angstroms. The combination of diffuse scattering and discrete reflections indicates a semi-crystalline structure in which small crystalline domains are embedded in a dominant amorphous matrix, with minimal impurities, consistent with the successful isolation of a heterogeneous natural organic mixture rather than a single crystalline compound.

The antimicrobial testing followed classical microbiological methodology. Reference strains of E. coli (ATCC 25922), P. aeruginosa (ATCC 27853), and Salmonella Typhi (ATCC 14028) were cultured on Mueller-Hinton agar, and inocula were standardized to the 0.5 McFarland turbidity standard. Fulvic acid was dissolved in dimethyl sulfoxide, with the solvent held at or below 1 percent by volume and a solvent-only control included to rule out false positives. In the agar well diffusion assay, the dose-response relationship was unambiguous. At 0.1 grams per 5 milliliters, no inhibition zones appeared against any of the three organisms. At 0.2 grams per 5 milliliters, zones of 11, 10, and 9 millimeters emerged for E. coli, P. aeruginosa, and S. Typhi respectively. Raising the concentration to 0.4 grams per 5 milliliters expanded the zones to 12, 11, and 11 millimeters, and at 0.8 grams per 5 milliliters the zones reached 14, 15, and 12 millimeters. The maximum concentration tested, 1.6 grams per 5 milliliters, produced the largest zones: 16 millimeters against E. coli, 15 against P. aeruginosa, and 14 against S. Typhi.

Quantitative susceptibility testing sharpened the hierarchy. Using a two-fold dilution series from 1000 down to 31.25 micrograms per milliliter, the team determined minimum inhibitory concentrations ranging from 250 to 1000 micrograms per milliliter and minimum bactericidal concentrations from 500 to 2000 micrograms per milliliter. E. coli proved the most susceptible, inhibited at 250 micrograms per milliliter, followed by P. aeruginosa at 500, while Salmonella Typhi required a full 1000 micrograms per milliliter. The authors connect this graded susceptibility to differences in cell envelope architecture: P. aeruginosa deploys a famously impermeable outer membrane and active efflux pumps, while E. coli and S. Typhi present different membrane compositions and permeability characteristics. Mechanistically, the antimicrobial action is attributed to fulvic acid’s phenolic, carboxylic, and quinone functional groups, which may disrupt microbial membranes, chelate essential metal ions, and generate redox-mediated oxidative stress, mechanisms well documented for structurally related phytophenolic compounds.

The authors are careful to frame these results as preliminary, and the caveats deserve emphasis. The activity was demonstrated only against planktonic, free-floating bacteria in vitro, using agar diffusion and broth dilution assays. No mechanistic studies of bacterial interaction pathways, no cytotoxicity profiling on mammalian cell lines, no stability or bioavailability assessments, and no tests against clinically resistant strains or biofilm models were performed. The dataset, as the researchers themselves state, is insufficient to support direct application in biomedical, agricultural, or environmental systems, and any translational implications must be considered tentative. What the study does establish is a proof of concept: cow dung is a viable, low-cost raw material for fulvic acid extraction, the isolated product carries the structural fingerprints of authentic fulvic acid, and it exerts measurable, concentration-dependent antibacterial activity against three major Gram-negative pathogens.

Even within those limits, the work lands at a compelling moment. Humic substances are already used in agriculture as soil conditioners and fertilizers, added to animal feed to improve growth and immunity, and investigated as anti-inflammatory, antitumor, and wound-healing agents. If subsequent research confirms that fulvic acid’s antimicrobial effects survive purification, formulation, and contact with living systems, a substance that farmers currently discard, or that poses a disposal and sanitation burden in much of the developing world, could be converted into a feedstock for natural antimicrobials. The road from a petri dish in Khairpur to a clinic or a feed additive is long, and the required in vivo studies, toxicity evaluations, and resistance testing will take years. But the underlying idea, that the answer to drug-resistant bacteria might be composting at the edge of the village, is exactly the kind of cross-disciplinary leap that the antimicrobial resistance crisis demands, and this study offers the first careful, spectroscopically verified evidence that the leap is worth taking.

Subject of Research: Antimicrobial activity of fulvic acid extracted from cow dung against Gram-negative bacteria

Article Title: Antimicrobial activity of fulvic acid extracted from bovine dung against selected gram-negative pathogens: a preliminary in vitro assessment

Article References: Chachar, Z. A., Dharejo, S. A., & Pirzada, T. (2026). Antimicrobial activity of fulvic acid extracted from bovine dung against selected gram-negative pathogens: a preliminary in vitro assessment. Discover Chemistry, 3(1), Article 548. https://doi.org/10.1007/s44371-026-00935-8

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00935-8

Keywords: fulvic acid, cow dung, antimicrobial resistance, Gram-negative bacteria, Escherichia coli, Pseudomonas aeruginosa, Salmonella Typhi, humic substances, FTIR spectroscopy, X-ray diffraction, minimum inhibitory concentration, natural antimicrobials