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One in Three Bacterial Isolates from Eastern Cattle Egrets Was Multidrug Resistant

Eastern cattle egret in breeding plumage perched on a branch in Mumbai, India
Research · Disease, parasites & microbiology

A study of urban eastern cattle egrets (Ardea coromanda) in Udaipur, Rajasthan, found multidrug resistance in one third of the coliform bacterial isolates recovered from their droppings. The study was published on 30 March 2026 in Environmental Monitoring and Assessment. The paper used the traditional, broadly defined name Bubulcus ibis; the Indian population studied here is treated as eastern cattle egret.

Researchers collected 45 fresh faecal samples from city-dwelling cattle egrets between July 2022 and June 2023, with 15 samples collected in each of the monsoon, winter and summer seasons. Laboratory analyses produced 60 bacterial isolates belonging to six genera: Escherichia, Enterobacter, Klebsiella, Proteus, Salmonella and Shigella.

E. coli accounted for two-thirds of the isolates

Escherichia coli was by far the most common species, accounting for 66.7% of the isolates. The researchers also detected Enterobacter chuandaensis and Escherichia fergusonii, which they report as new bacterial records for cattle egrets.

Overall coliform abundance showed no clear seasonal difference, but the composition of the bacterial community did. The kinds of coliform bacteria recovered from the birds therefore changed through the year even though the overall bacterial load remained broadly similar among seasons.

One-third of the isolates were multidrug resistant

The isolates were tested against 15 antibiotics. Resistance was recorded in all isolates tested against linezolid and rifampicin, while 46% were resistant to erythromycin. Gentamicin remained effective against the isolates. Overall, 33.3% of the bacterial isolates were classified as multidrug resistant, with E. coli showing the highest level of resistance.

The authors place the findings in a One Health context, which treats human, animal and environmental health as interconnected. Eastern cattle egrets frequently use urban environments, livestock areas and other habitats where wildlife, domestic animals and people overlap. The authors argue that such birds may carry resistant bacteria between different parts of the environment and call for broader genomic surveillance to clarify how antimicrobial-resistance genes circulate among wildlife, livestock, people and their shared surroundings.

Sources and image credit

  1. Kumari, A., Singh, N. A., & Koli, V. K. (2026). Seasonal dynamics of coliform diversity and antibiotic resistance in city-dwelling Cattle Egrets (Bubulcus ibis) in Udaipur, India: Implications for One Health. Environmental Monitoring and Assessment, 198(4), 382. https://doi.org/10.1007/s10661-026-15257-6Primary peer-reviewed study published 30 March 2026. Forty-five faecal samples collected across monsoon, winter and summer in Udaipur yielded 60 coliform isolates; Escherichia coli comprised 66.7%, and 33.3% of isolates were multidrug resistant.

Image: Gannu03 / Wikimedia Commons — wild eastern cattle egret in breeding plumage photographed in Mumbai, India, 15 April 2024; representative Indian species image, not one of the Udaipur study birds; cropped to 16:9 · CC BY-SA 4.0 · Source

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