Wild birds do not carry antibiotic-resistant Salmonella

A research team led by Pennsylvania State University has recently investigated the types of Salmonella enterica – a pathogen that sickens millions of people each year – circulating among wild bird populations. While domestic birds are known to carry antibiotic-resistant Salmonella strains, the scientists discovered that, fortunately, the strains of bacteria found in wild birds did not usually harbor antimicrobial resistant genes.

Scientists have long worried that wild birds carrying antimicrobial-resistant Salmonella may pose a high risk to public health because they could spread the resistant bacteria across vast areas in short periods of time. In order to clarify whether this was indeed the case, the scientists fully sequenced 375 Salmonella enterica strains from wild birds collected in 41 U.S. states from 1978 to 2019. 

 “To find what antibiotics a particular Salmonella strain is resistant to, we don’t have to run the traditional lab-based tests anymore – where you grow it on some type of media, expose it to antibiotics, and it either grows or it doesn’t,” explained study senior author Edward Dudley, a professor of Food Science at Penn State. “Now, we can sequence the entire genome, and by identifying certain gene markers, we can predict – with almost perfect precision – what antibiotics the organism will be resistant to.”

The genetic analyses revealed that the most dominant Salmonella enterica strain found in wild bird populations was Typhimurium, accounting for 68 percent of the bird isolates. However, less than two percent of these isolates were identified to be resistant to antibiotics or heavy metals. Interestingly, all the multi-resistant strains were isolated from raptors or water birds, while none were found in songbirds.

“While we’ve known for a while that wild birds can carry Salmonella, the strains they carry appear to be of lesser concern to human health. The assumption was that these Salmonella – like the bacteria we can isolate from domesticated farm animals – would carry large numbers of antimicrobial-resistance genes. We found the opposite to be true,” Professor Dudley concluded.

The study is published in the journal Environmental Microbiology.

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By Andrei Ionescu, Earth.com Staff Writer