Hampson, D. J. | bioRxiv Science

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↗

bioRxiv2021

Proximity to human settlement is directly related to carriage of critically important antimicrobial-resistant Escherichia coli and Klebsiella pneumoniae in Silver Gulls

Human population and activities play an important role in dissemination of antimicrobial resistant bacteria. This study investigated the relationship between carriage rates of critically important antimicrobial-resistant (CIA-R) Escherichia coli and Klebsiella pneumoniae by Silver Gulls and their proximity to human populations. Faecal swabs (n=229) were collected from Silver Gulls across 10 southern coastline locations in Western Australia (WA). The sampling locations included main town centres and remote areas. Fluoroquinolone and extended-spectrum cephalosporin-resistant E. coli and K. pneumoniae were isolated and tested for antimicrobial sensitivity. Genome sequencing was performed to validate phenotypic resistance profiles and determine the molecular characteristics of strains. CIA-R E. coli and K. pneumoniae were detected in 69 (30.1%) and 20 (8.73%) of the faecal swabs respectively. Two large urban locations tested positive for CIA-R E. coli (frequency ranging from 34.3%-84.3%), and/or for CIA-R K. pneumoniae (frequency ranging from 12.5%-50.0%). A small number of CIA-R E. coli (3/31, 9.7%) were identified at a small tourist town, but no CIA-R bacteria were recovered from gulls at remote sites. Commonly detected E. coli sequence types (STs) included ST131 (12.5%) and ST1193 (10.0%), and five K. pneumoniae STs were found. Resistance genes including blaCTX-M-3, blaCTX-M-15 and blaCTX-M-27 were identified in both bacterial species. High-level colonisation of CIA-R E. coli and K. pneumoniae in Silver Gulls in and around urban areas compared to remote locations substantiates that anthropogenic activities are strongly associated with acquisition of resistant bacteria by gulls. ImportanceHumans play an important role in dissemination of antimicrobial resistant bacteria. This study investigated the relationship between carriage rates of resistant bacterial pathogens (Escherichia coli and Klebsiella pneumoniae) among Silver Gulls and their proximity to human populations. The frequency of resistant E. coli carriage was high (ranging from 34.3 - 84.3%) in the samples collected from areas with high human population density while resistant K. pneumoniae frequencies at these sites varied from 0 to 50%. However, resistant E. coli and K. pneumoniae were not recovered from any of the remote sites that did not have a permanent human population. This study, conducted across a large stretch of the southwestern Australian coastline, indicated that seagulls act as vectors in carrying and disseminating antimicrobial resistant bacteria, including clinically significant strains. High-level colonisation of resistant E. coli and K. pneumoniae in Silver Gulls in and around urban areas compared to remote locations substantiates that human activities are strongly associated with acquisition of resistant bacteria by Silver gulls.

microbiology↗