Bangladesh Cattle Farm Study Finds Multidrug Resistance and Colistin Resistance Gene

Four of 17 Pseudomonas isolates resisted colistin

Researchers examining cattle farms in Bangladesh found four Pseudomonas aeruginosa isolates resistant to colistin, an antibiotic reserved for difficult infections, in a study covering 158 samples collected between October 2023 and June 2024. The team also detected mcr-1, a gene associated with colistin resistance, despite a national ban on the drug in food animals and animal feed described by the study authors.

The findings, published on 25 March 2025, bring together evidence from cattle, soil and agricultural water in Dhaka and Barisal. Among 24 Enterococcus faecalis isolates, 66.66% were classified as multidrug resistant. The corresponding figure among 17 P. aeruginosa isolates was 23.52%, equivalent to about 16 and four isolates respectively.

The 2025 cattle farm study, published in Discover Bacteria by a team including Abu Bakkar Siddique and Md Hafizur Rahman, points to a practical problem for livestock health: bacteria found around farms can carry resistance to several medicines at once, narrowing the choices available when infections need treatment.

Antimicrobial resistance means that a medicine becomes less effective against a microorganism. The bacteria, rather than the animal or person receiving treatment, develop or acquire the ability to withstand the drug. Monitoring resistance in both animals and their surroundings helps identify where difficult bacteria and resistance genes are present.

What the researchers sampled

The team collected feces, rectal swabs, wound swabs, soil and water from cattle farms, mainly in Dhaka, with fewer samples from Barisal. This approach examined bacteria in animals alongside bacteria in the farm environment.

Samples were collected using sterile techniques, kept cool and transported within six hours. Laboratory work took place at the AMR Reference Laboratory in Savar, Dhaka. Researchers grew bacteria on selective culture media and used biochemical identification, including the VITEK 2 system, before testing their responses to antibiotics.

E. faecalis was recovered from 24 of the 158 samples, or 15.18%. P. aeruginosa was recovered from 17 samples, or 10.75%. An isolate is a bacterial culture separated from a sample so that researchers can identify it and test it.

The main dates place the findings in context:

• 2022: An earlier Bangladesh study documented resistant enterococci in food animals and fresh retail meat.
• October 2023 to June 2024: Researchers collected and examined the 158 samples for the cattle farm investigation.
• 25 March 2025: The cattle farm study was published in Discover Bacteria.

Why these two bacteria matter

P. aeruginosa is an opportunistic pathogen, meaning it can cause disease when conditions allow, particularly in animals or people with weakened defenses. It can cause respiratory and urinary infections and form biofilms, communities of bacteria attached to surfaces within a protective layer that can make infections harder to clear.

E. faecalis commonly lives in the digestive tract. Under some conditions it can cause infections, including mastitis, an infection of the udder, and endocarditis, an infection involving the inner lining of the heart. It can also carry resistance genes that are relevant to the wider bacterial population.

The two organisms therefore give researchers different views of farm health. One is an adaptable environmental bacterium capable of causing disease; the other is a familiar intestinal organism that can become harmful and serve as a reservoir for resistance.

Farm workers, veterinarians, animals and the surrounding environment can come into contact through wounds, feces, water and contaminated surfaces. The study authors identify direct contact and the food chain as possible routes by which resistant bacteria associated with livestock could reach people.

Enterococcus showed the greater multidrug burden

E. faecalis isolates were tested against 13 antibiotics. The researchers classified isolates resistant to more than three antibiotic classes as multidrug resistant. Under that definition, roughly two thirds of the 24 isolates met the threshold.

Cefuroxime had the highest reported resistance rate, at 70.83%, followed by penicillin at 66.67%. None of the isolates was classified as susceptible to penicillin. Resistance and intermediate responses are separate laboratory categories, which explains how the resistance percentage could be below 100% while susceptibility was zero.

Tigecycline had the highest reported susceptibility among the antibiotics tested against E. faecalis, at 70.83%, while 12.50% of isolates were resistant. Nitrofurantoin and linezolid each had a susceptibility rate of 58.33%. Ciprofloxacin susceptibility was much lower, at 12.50%.

Some drug and species combinations require particular caution in interpretation. Enterococci have natural resistance to cephalosporins, the antibiotic family that includes cefuroxime and cefoxitin. Their response to those drugs belongs alongside an understanding of the organism's biology when assessing treatment choices and the burden of acquired resistance.

Pseudomonas retained susceptibility to several drugs

All 17 P. aeruginosa isolates were susceptible to meropenem in the laboratory tests. Gentamicin and imipenem each showed 94.12% susceptibility, equivalent to 16 of the 17 isolates. Amikacin and cefepime each showed 88.24% susceptibility, or 15 isolates.

No isolates were classified as resistant to amikacin or cefepime, although some had intermediate responses. Piperacillin produced an intermediate response in 58.82% of isolates, showing why a simple division between susceptible and resistant would miss part of the findings.

Tigecycline had the highest reported resistance rate in this group, at 35.29%. P. aeruginosa generally has poor susceptibility to tigecycline, so this result also needs to be understood in the context of the bacterium's natural defenses.

For veterinarians, the practical value of these measurements is to help guide further testing and careful prescribing. Choosing a medicine still depends on the organism causing the infection, the infection site, the animal's condition and veterinary rules governing its use.

Colistin results bring a ban into focus

Colistin received a separate assessment using the minimum inhibitory concentration, or MIC. This measures the lowest concentration of an antibiotic that stops visible bacterial growth. Researchers tested different concentrations using an agar dilution method.

Four P. aeruginosa isolates, or 23.53%, were classified as resistant at concentrations of at least four micrograms per milliliter. Three, or 17.65%, were classified as intermediate at two micrograms per milliliter. The remaining 10 were classified as susceptible: five at one microgram per milliliter and five at 0.5 micrograms per milliliter or lower.

The authors reported no colistin resistance among E. faecalis isolates. Enterococci are naturally resistant to polymyxins, the antibiotic group containing colistin, so clinical interpretation requires species specific testing standards and knowledge of that natural resistance.

The authors state that Bangladesh has banned colistin use in food animals and animal feed. Finding resistance and an associated gene makes surveillance relevant to both animal health and the protection of an antibiotic used for difficult human infections. How the detected resistance arose and reached these farms remains unresolved.

Gene screening adds detail and a numerical discrepancy

Researchers used polymerase chain reaction, or PCR, to search for nine selected resistance genes. PCR looks for particular stretches of genetic material, allowing a laboratory to check whether a targeted gene is present.

Among E. faecalis isolates, blaCTX-M was detected in 41.66%, blaOXA-48 in 25%, VIM-1 in 12.5% and blaNDM-1 in 8.3%. With 24 isolates tested, those percentages correspond to approximately 10, six, three and two isolates respectively. These genes are associated with mechanisms that can undermine members of the beta lactam antibiotic family.

The researchers also detected mcr-1 in P. aeruginosa. The paper's results section gives its prevalence as 21.05%, while the abstract gives 23.52%. The paper identifies 17 P. aeruginosa isolates; the differing percentages leave the exact prevalence of the gene unclear.

Resistance genes can move between bacteria on mobile pieces of DNA, including plasmids. The authors called for genomic sequencing, which examines bacterial genetic material in much greater detail, to investigate how resistance genes are distributed and move among livestock, farm environments and veterinary settings.

The study also reported statistical associations between antibiotic response patterns: ciprofloxacin with imipenem, and meropenem with levofloxacin, in P. aeruginosa; chloramphenicol with ciprofloxacin, and cefoxitin with cefuroxime, in E. faecalis. The authors proposed further molecular work to investigate the mechanisms behind those associations.

Earlier Bangladesh research found resistance in meat too

A 2022 enterococci study examined 352 samples from food animals and fresh retail meat in Bangladesh. It recovered Enterococcus species from 201 samples, or 57%. Prevalence was 62% in farm samples and 41% in retail meat samples, a difference of 21 percentage points.

E. faecalis accounted for 52% of isolates in that investigation. Across the enterococci tested, resistance was reported to tetracycline in 74%, erythromycin in 65% and ciprofloxacin in 34%.

The earlier researchers identified 51 enterococci that were not susceptible to vancomycin. Of those, 47 were multidrug resistant and 20 were resistant to linezolid, another medicine used against difficult infections. That amounts to about 92% and 39% of the 51 isolates respectively.

Vancomycin resistance genes vanA, vanB and vanC2/C3 were detected, alongside genes associated with bacterial traits involved in infection, including gelE, asa1 and cpd. The newer cattle farm study found no vanB among its E. faecalis isolates. The investigations covered different sample groups: the earlier work included retail meat and multiple Enterococcus species, while the newer work focused on two bacterial species from cattle farms and their surroundings.

What wider surveillance needs to answer

The cattle farm study offers a snapshot from selected farms over a defined sampling period. Most sampling was in Dhaka, with fewer specimens from Barisal, and the gene screen covered nine targets. The authors called for broader surveillance and genomic sequencing to investigate resistance across connected animal and environmental settings.

Repeated sampling across more farms would help show whether the same resistance patterns persist, expand or change. Sequencing could provide a more detailed picture of the detected genes and the bacteria carrying them. Collecting information on antibiotic use alongside laboratory results would also help connect prescribing practices with resistance patterns.

For Bangladesh's livestock sector, the immediate issue is concrete: some bacteria recovered from cattle farms resisted several antibiotic classes, while four P. aeruginosa isolates resisted colistin under the study's testing criteria. Better monitoring, infection prevention and veterinary oversight are central to the response proposed by the researchers.

Key Points

• Researchers examined 158 cattle farm and environmental samples collected in Dhaka and Barisal between October 2023 and June 2024.
• Multidrug resistance was reported in 66.66% of 24 E. faecalis isolates and 23.52% of 17 P. aeruginosa isolates.
• Four P. aeruginosa isolates were classified as colistin resistant; three had intermediate responses.
• The colistin resistance gene mcr-1 was detected, although its reported prevalence differs between the paper's abstract and results.
• All 17 P. aeruginosa isolates were susceptible to meropenem in laboratory testing.
• Earlier Bangladesh research also found multidrug resistant enterococci in food animals and retail meat.
• The authors called for wider surveillance and genomic sequencing to investigate the movement of resistance genes.