High prevalence of multi-drug-resistant bacteria in faecal samples from UK passerine birds

Wild birds are a near ubiquitous sight in gardens, offering pleasure to many people through supplementary feeding, song, or other interactions. However, they are also potential carriers of many bacteria, including Campylobacter spp., Salmonella spp., Enterococcus spp., and E. coli; some of these may be resistant to commonly used drugs. This study collected faecal samples from multiple species of UK passerine birds, isolating bacterial pathogens to assess carriage and drug resistances associated with those bacteria. 75% of birds were carrying at least one bacterial species which was multi drug resistant (MDR; resistant to three or more classes of antimicrobial), with 11.6% of birds carrying Salmonella spp., 18.9% carrying Campylobacter spp., 78% carrying Enterococcus spp., and all carrying E. coli strains. Many of these strains were shown to be MDR with 70%, 88%, 32% and 59% respectively. Intercontinental migration was shown to be a risk factor for carriage of many of the pathogens, as was an associated with human habitation. Age was also a risk factor with younger birds twice as likely to carry Campylobacter spp. than adults, and house sparrows (Passer domesticus) and blackbirds (Turdus merula) being particularly high-level carriers compared to other species. The high-level carriage and shedding of MDR E. coli and other zoonotic pathogens within the faecal samples of multiple species of passerine birds offers a timely reminder of the risks which these bacteria, and their drug resistance profiles may pose to human and animal health in the UK and worldwide. It also shows a level of high environmental contamination, which birds may continue to contribute towards, until our use of antimicrobials, and level of drug-resistant bacteria is decreased. Developing mechanisms for reducing levels of carriage of MDR bacteria in wild bird populations through, for example, increased hygiene around bird feeding practices, may be key in reducing environmental contamination.