Selection of Resistant Bacteria in Mallards Exposed to Subinhibitory Concentrations of Ciprofloxacin in Their Water Environment

Emergence and selection of antibiotic resistance following exposure to high antibiotic concentrations have been repeatedly shown in clinical and agricultural settings, whereas the role of the weak selective pressures exerted by antibiotic levels below the MIC (sub-MIC) in aquatic environments due to anthropogenic contamination remains unclear. Here, we studied how exposure to sub-MIC levels of ciprofloxacin enriches for Escherichia coli with reduced susceptibility to ciprofloxacin using a mallard colonization model. Mallards were inoculated with two isogenic extended-spectrum-beta-lactamase (ESBL)-encoding E. coli strains, differing only by a gyrA mutation that results in increased MICs of ciprofloxacin, and exposed to different levels of ciprofloxacin in their swimming water. Changes in the ratios of mutant to parental strains excreted in feces over time and ESBL plasmid spread within the gut microbiota from individual birds were investigated. Results show that in vivo selection of gyrA mutants occurred in mallards during exposure to ciprofloxacin at concentrations previously found in aquatic environments. During colonization, resistance plasmids were readily transferred between strains in the intestines of the mallards, but conjugation frequencies were not affected by ciprofloxacin exposure. Our results highlight the potential for enrichment of resistant bacteria in wildlife and underline the importance of reducing antibiotic pollution in the environment.

Nykvist, MarieUppsala universitet,Institutionen för medicinsk biokemi och mikrobiologi,Natl Vet Inst, Uppsala, Sweden.(Swepub:uu)marny745 (author)
Lustig, UlrikaUppsala universitet,Institutionen för medicinsk biokemi och mikrobiologi(Swepub:uu)ulu03860 (author)
Andersson, Dan I.Uppsala universitet,Institutionen för medicinsk biokemi och mikrobiologi(Swepub:uu)dan19789 (author)
Järhult, Josef D.,1975-Uppsala universitet,Infektionsmedicin(Swepub:uu)josja939 (author)
Sandegren, LinusUppsala universitet,Institutionen för medicinsk biokemi och mikrobiologi(Swepub:uu)lisan839 (author)
Uppsala universitetInfektionsmedicin (creator_code:org_t)

In:Antimicrobial Agents and Chemotherapy: American Society for Microbiology65:30066-48041098-6596

By the author/editor: Atterby, Clara; Nykvist, Marie; Lustig, Ulrika; Andersson, Dan I ...; Järhult, Josef D ...; Sandegren, Linus

About the subject

MEDICAL AND HEALTH SCIENCES: MEDICAL AND HEAL ...; and Basic Medicine; and Microbiology in ...

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