Abraham, R. J. | Search bioRxiv

bioRxiv2026

The frequency of resistant Escherichia coli isolation from seagulls is positively related to human population density

Antimicrobial resistance (AMR) is a major global public health threat. Wild birds, including seagulls, are increasingly recognised as potential reservoirs and disseminators of resistant bacteria linked to human activity. The objective of the study was to assess the association between human population density and the occurrence of Escherichia coli resistant to critically important antimicrobials in Australian seagulls. Faecal samples were collected from seagull populations in coastal regions across Australia representing differing human population densities. Resistant E. coli isolates were identified and characterised using multilocus sequence typing and plasmid incompatibility group analysis to determine relatedness to human associated lineages. The frequency of resistant E. coli isolation increased with human population density. The predominant sequence types ST10, ST131 and ST354 comprised 24.5% of isolates and belong to globally distributed human associated lineages linked to extraintestinal pathogenic E. coli. Many isolates carried IncF and IncI plasmids, which are key vectors of blaCTX-M extended spectrum beta lactamase genes and plasmid mediated quinolone resistance determinants commonly reported in human clinical strains. IMPORTANCEThese findings support the contention that seagulls primarily acquire resistant bacteria through contact with anthropogenic activities. Once acquired, these bacteria may be disseminated to other seagulls, birds and animals, including being transmitted to humans.

microbiology↗

bioRxiv2022

Antimicrobial Resistance, Genomic, and Public Health Insights into Enterococcus spp. from Australian Cattle

Enterococci are opportunistic, potentially life-threatening pathogens of humans that are difficult to manage due to antimicrobial resistance. Historically, enterococci entering the food-chain through livestock have been viewed as a likely source of antimicrobial resistance in humans. Australian human-derived clinical enterococci have a propensity to be resistant to multiple classes of antimicrobials including vancomycin. Recent Australian studies involving pigs and chicken have virtually excluded these species as reservoirs of infection for resistant enterococci in humans. However, the Australian bovine population has not been similarly assessed. This study investigates the antimicrobial resistance profiles of enterococci from Australian cattle and the phylogenetic relationship between E. faecium isolated from cattle and human sepsis cases. Minimum inhibitory concentration assays were performed for E. faecium (n=343), E. faecalis (n=92), and E. hirae (n=284) against a panel of 15 antimicrobials. The majority of isolates were sensitive to all tested antimicrobials. Erythromycin resistance was most prevalent for E. faecium isolates (18.7%), daptomycin for E. faecalis (12.1%) and tetracycline for E. hirae (13.3%). Phenotypically, 1 E. faecalis was resistant to vancomycin and 9 were resistant to linezolid (E. faecium n=4, E. faecalis n=2, E. hirae n=3) but this was not confirmed with any know genotype. A subset of 67 E. faecium isolates selected for comparative phylogenetic analysis revealed that bovine isolates clustered with other livestock-derived and van-negative human isolates. In conclusion, there is a low prevalence of antimicrobial resistance amongst enterococci from Australian cattle which are unlikely to be precursor strains to vancomycin-resistant strains currently circulating in Australian hospitals. ImportanceEnterococci resistant to critically important antimicrobials such as vancomycin and linezolid are difficult to manage in health care settings. Historically, there has been the belief that livestock can act as a reservoir of resistance for human infections. Previous studies in poultry and pork have demonstrated that isolates derived from these livestock are unlikely to be precursor strains for currently circulating vancomycin resistant-Enterococci causing infection in humans. To date, there has been no study looking at the genetic similarity of bovine derived Enterococci and the relationship to human pathogenic strains. In this study we performed phenotypic and genotypic characterization of bovine derived Enterococci along with comparative phylogenetic analysis with other livestock derived and human sepsis derived E. faecium isolates. We found that while non-vancomycin resistant strain sharing occurs between hosts, cattle are unlikely to be precursor strains for vancomycin resistant human E. faecium infections.

microbiology↗