MRSA found in one in ten Bangladeshi buffaloes

A survey of buffaloes in northeastern and southeastern Bangladesh has found molecular evidence of methicillin-resistant Staphylococcus aureus in the noses of 43 of 400 animals examined, indicating that the bacterium is circulating in livestock that have received comparatively little research attention. The cross-sectional study, conducted from April 2023 to September 2024, provides a baseline estimate of MRSA carriage among buffalo and raises questions about antimicrobial use, animal health and possible transmission to people. Overall, 78 animals, or 19.5%, carried S. aureus that was confirmed by polymerase chain reaction targeting the species-specific nuc gene. Among them, 43 carried mecA-positive strains, equivalent to 10.5% of all buffaloes sampled and 55.1% of the S. aureus-positive animals. The results make the buffalo nasal tract a potentially important reservoir for resistant bacteria, even though most of the animals did not show obvious signs of illness.

Researchers collected random nasal swabs from animals of different ages, sexes and health conditions in selected upazilas in the Sylhet and Noakhali districts. Each swab was placed immediately into buffered peptone water and transported in an icebox at approximately 4°C. The sample-size calculation indicated that at least 382 animals were needed to estimate MRSA prevalence with an absolute precision of 5%, and the investigators collected 400. Following enrichment, organisms were cultured on mannitol salt agar and then subjected to biochemical identification, including catalase and coagulase tests. DNA was extracted from presumptive S. aureus isolates, and PCR was used to detect nuc and the methicillin-resistance determinant mecA. Confirmed positive and no-template controls were included in the assays.

The molecular screening also examined resistance genes associated with antibiotic classes commonly used in veterinary and human medicine, along with virulence determinants linked to toxins, tissue damage, adhesion and biofilm formation. The targets included aac(3)-IV, associated with gentamicin resistance; tetA, linked to tetracycline resistance; strA, associated with streptomycin resistance; and sul1, which confers resistance to sulfonamides and is often associated with mobile genetic elements. Virulence testing covered the alpha-hemolysin gene hla, the enterotoxin A gene sea, the biofilm-associated adhesion gene icaA and the fibronectin-binding protein gene fnbA. Phenotypic susceptibility testing was conducted separately by disk diffusion on Mueller–Hinton agar against 13 antibiotics from eight classes, following Clinical and Laboratory Standards Institute criteria, with S. aureus ATCC 25923 used for quality control.

MRSA prevalence varied among the seven locations reported in the results, ranging from 5.36% in Zakiganj to 14.55% in Swarna Dweep, although the differences between locations were not statistically significant. The age pattern was also uneven: carriage was detected in 6.25% of calves younger than one year, 14.13% of buffaloes aged one to three years and 8.65% of animals older than three years. The study did not find a statistically significant age association. A clearer difference was observed by sex, with 14.83% prevalence among males and 6.88% among females, a difference that reached statistical significance at p = 0.01. The cross-sectional design cannot establish why these patterns occurred, but differences in housing, movement, animal contact, antimicrobial exposure or other management conditions could plausibly influence colonization.

The strongest association was with respiratory illness. MRSA was detected in 25.21% of buffaloes with respiratory symptoms, compared with 4.27% of clinically healthy animals, a highly significant difference at p less than 0.001. This pattern does not establish whether MRSA caused the observed illness, contributed to it or was acquired more readily by animals already vulnerable to respiratory disease. Nevertheless, it suggests that resistant S. aureus is not confined to overtly diseased animals. The detection in healthy buffalo is particularly relevant because asymptomatic carriers can maintain the organism and transmit it through direct contact, respiratory droplets and contaminated objects. The researchers therefore regard the nasal tract as an important ecological niche in which the pathogen may persist and spread unnoticed.

Phenotypic testing showed that the 43 MRSA isolates were frequently resistant to antibiotics used in routine animal care. Resistance was highest for cefoxitin, detected in 97.7% of isolates, followed by ceftriaxone at 86.0%, tetracycline at 65.12% and ampicillin at 58.14%. Amoxicillin-clavulanic acid resistance reached 55.81%. Gentamicin resistance was found in 48.84% of isolates and resistance to trimethoprim-sulfamethoxazole in 41.86%. In contrast, most isolates remained susceptible to levofloxacin, which showed 86.05% susceptibility, and ciprofloxacin, at 81.40%. Susceptibility was also high for amikacin and azithromycin. These findings indicate that the isolates were not uniformly resistant to every antimicrobial and that laboratory-guided treatment might be possible, but the authors caution that fluoroquinolone resistance can emerge rapidly in S. aureus.

Of the 43 MRSA isolates, 38, or 88.4%, met the study’s definition of multidrug resistance by being resistant to at least three antimicrobial classes. Their multiple antibiotic resistance indices ranged from 0.23 to 0.54. A value above 0.2 has been interpreted as compatible with isolates originating in high-risk settings where antimicrobial use may be frequent or poorly controlled. The MDR isolates displayed numerous resistance combinations, with some resistant to seven tested drugs across five or more classes. Molecular screening found aac(3)-IV in 15.38% of all S. aureus isolates, sul1 in 10.25%, tetA in 8.97% and strA in 5.12%. Some multidrug-resistant isolates carried several of these genes together, supporting the phenotypic findings and showing that resistance determinants can circulate together within the buffalo population.

Virulence genes were less common than resistance genes but were present in a substantial minority of the 78 S. aureus isolates. The enterotoxin A gene sea occurred most frequently, in 17.94% of isolates, followed by hla in 11.53% and icaA in 6.41%. No isolate carried fnbA. The presence of sea raises a food-safety concern because the toxin can cause food poisoning, while hla encodes a pore-forming cytotoxin that can contribute to tissue damage. The icaA determinant participates in biofilm production, which may assist persistent colonization on mucosal surfaces and surfaces within the environment. Detection of these genes does not by itself demonstrate that the corresponding toxins or biological functions were expressed, but it identifies subsets of isolates with potential clinical or epidemiological importance.

The study has several limitations that constrain its conclusions. The sample was relatively small for detailed subgroup and risk-factor analysis, no odds ratios or multivariable models were reported, and the cross-sectional design cannot show how carriage changes over time or identify direct transmission pathways. The investigators also did not collect information on antimicrobial use, perform minimum inhibitory concentration testing, screen for the alternative resistance determinant mecC or apply advanced molecular typing such as multilocus sequence typing and SCCmec analysis. Sampling was restricted to nasal swabs, so colonization at other sites may have been missed. These constraints mean that the reported prevalence should not automatically be generalized to all buffalo populations in Bangladesh or interpreted as a direct measurement of zoonotic transmission.

Even with those limitations, the results support stronger surveillance of livestock-associated antimicrobial resistance in Bangladesh. The combination of substantial MRSA carriage, multidrug resistance, elevated resistance indices and the presence of virulence determinants points to a need for routine monitoring, improved herd biosecurity, veterinary oversight and more disciplined antimicrobial use. Nasal screening could complement milk testing in dairy buffalo, while longitudinal studies could establish whether carriage persists, how animals acquire the organism and whether interventions reduce transmission. The findings also support a One Health approach: livestock, veterinary practice, food systems and human health are linked by the movement of resistant organisms and resistance genes. By treating buffalo as a potential reservoir rather than a neglected host, farmers, veterinarians and public-health teams can design control measures before multidrug-resistant strains become more entrenched.

Subject of Research: Prevalence, antimicrobial resistance and virulence determinants of MRSA in Bangladeshi buffaloes

Article Title: Molecular Prevalence and Antimicrobial Resistance Patterns of Methicillin‐Resistant Staphylococcus aureus in Buffaloes from Bangladesh

Article References: Ghosh, P. K., Ali, M., Hossain, H., Tuha, M. M.-E.-A., Roy, M., Ahmed, T., Rahman, A., Chowdhury, M. S. R., Rahman, M. M., Uddin, M. B., Rahman, M. M., & Hossain, M. M. (2026). Molecular Prevalence and Antimicrobial Resistance Patterns of Methicillin‐Resistant Staphylococcus aureus in Buffaloes from Bangladesh. Veterinary Medicine and Science, 12(6), Article e71295. https://doi.org/10.1002/vms3.71295

Image Credits: AI Generated

DOI: 10.1002/vms3.71295

Keywords: MRSA, buffalo, Bangladesh, nasal carriage, antimicrobial resistance, Staphylococcus aureus, livestock surveillance, virulence genes, One Health, Molecular, Prevalence, Antimicrobial