Gulls as Sources of Environmental Contamination by Colistin-resistant Bacteria

Alan B. Franklin,Nicole L. Barrett,Jonas Bonnedahl,Andrew M. Ramey,Susan A. Shriner,Jeffrey C. Chandler,Loredana M. McCurdy,Christina A. Ahlstrom,Kevin T. Bentler

doi:10.1038/s41598-020-61318-2

Abstract

In 2015, the mcr-1 gene was discovered in Escherichia coli in domestic swine in China that conferred resistance to colistin, an antibiotic of last resort used in treating multi-drug resistant bacterial infections in humans. Since then, mcr-1 was found in other human and animal populations, including wild gulls. Because gulls could disseminate the mcr-1 gene, we conducted an experiment to assess whether gulls are readily colonized with mcr-1 positive E. coli, their shedding patterns, transmission among conspecifics, and environmental deposition. Shedding of mcr-1 E. coli by small gull flocks followed a lognormal curve and gulls shed one strain >101 log10 CFU/g in their feces for 16.4 days, which persisted in the environment for 29.3 days. Because gulls are mobile and can shed antimicrobial-resistant bacteria for extended periods, gulls may facilitate transmission of mcr-1 positive E. coli to humans and livestock through fecal contamination of water, public areas and agricultural operations.

Highlights

In 2015, a new antimicrobial resistant gene was discovered in Escherichia coli in domestic swine in China[1]
Www.nature.com/scientificreports duration of shedding and of fecal contamination into the environment? We were interested in the question: If gulls are readily colonized with mcr-1 positive E. coli, do they exhibit shedding patterns suggestive of maintenance or bridge hosts16? To address these questions, we conducted an experiment where we inoculated ring-billed gulls (Larus delawarensis), a ubiquitous and wide-ranging species in North America[17], with two strains of mcr-1 positive E. coli
We collected a total of 296 samples to assess bacterial colonization, shedding, transmission, and detection relative to the experimental inoculation of two groups of ring-billed gulls, each inoculated with a different strain of mcr-1 positive E. coli and housed in separate rooms with contact controls

Summary

Introduction

In 2015, a new antimicrobial resistant gene was discovered in Escherichia coli in domestic swine in China[1]. We conducted an experiment where we inoculated ring-billed gulls (Larus delawarensis), a ubiquitous and wide-ranging species in North America[17], with two strains of mcr-1 positive E. coli. We were interested in the question: If gulls are readily colonized with mcr-1 positive E. coli, do they exhibit shedding patterns suggestive of maintenance or bridge hosts16? We addressed the second research question by assessing whether uninoculated, co-housed individuals became colonized with mcr-1 positive E. coli in a shared environment with inoculated gulls, and by measuring the deposition of the two strains into the environment via feces, which allowed us to assess whether ring-billed gulls exhibited patterns suggestive of maintenance or bridge hosts. We used curve fitting under an information-theoretic approach[18] to provide evidence that gulls are more likely to be bridge or maintenance hosts under the assumption that shedding of mcr-1 positive E. coli would peak and decline to or near zero during the experimental period if gulls were bridge hosts or increase to some asymptote that remained at a relatively constant level if gulls were maintenance hosts

Methods

Results

Conclusion