Implications of foraging and interspecies interactions on carriage of Escherichia coli resistant to critically important antimicrobials in birds.

Globally, gulls have been associated with carriage of high levels Escherichia coli resistant to critically important antimicrobial (CIA), a major concern as these antimicrobials are the sole or only one alternative amongst few available to treat severe life-threatening infections in humans. Previous study of Australian Silver Gulls demonstrated high levels of resistance to CIAs particularly fluoroquinolone and extended spectrum cephalosporin among E. coli (carriage 24% and 22% respectively). This study was aimed to identify and characterise strains from four distinct bird species inhabiting a common coastal environment, determine the frequency of carriage of CIA-resistant E. coli, and examine if these resistant clones and their resistance-encoding mobile genetic elements could be transmitted between species. CIA-resistant E. coli was detected in Silver Gulls (53%), Little Penguins (11%) and feral pigeons (10%), but not in Bridled Terns. In total, 37 different sequence types were identified including clinically significant human-associated lineages such as ST131, ST95, ST648, ST69, ST540, ST93, ST450 and ST10. Five main mobile genetic elements associated with blaCTX-M-positive E. coli isolated from three bird species were detected. Examination of clonal lineages and mobile genetic elements (MGEs) provided indirect evidence of transfer of resistance between bird species. The carriage of CIA-resistant E. coli by gulls and pigeons sharing proximity with humans, and in some instance food-producing animals increases the likelihood of further bi-directional dissemination. IMPORTANCE It has been shown that 20% of Australian Silver Gulls carry drug resistant Escherichia coli of anthropogenic origin associated with severe diseases such as sepsis and urinary tract infections in humans. To further characterise the dynamics of drug resistant E. coli in wildlife populations, we investigated the carriage of critically important antimicrobial (CIA) drug resistant E. coli in four bird species in a common environment. Our results indicate that gulls, pigeons and penguins carried drug resistant E. coli, and analysis of mobile genetic elements associated with resistance genes indicated interspecies resistance transfer. Terns, a bird species that forage on natural food sources at sea and distant from human, did not test positive for drug resistant E. coli. This study demonstrates carriage of CIA-resistant bacteria in multiple bird species inhabiting areas commonly inhabited by humans, and provides further evidence for a leap-frog effect of resistance between wildlife, facilitated by feeding habits.