Wild Boars Carry Extended-Spectrum β-Lactamase- and AmpC-Producing Escherichia coli

Abstract

Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA) represent major healthcare concerns. The role of wildlife in the epidemiology of these bacteria is unclear. The purpose of this study was to determine their prevalence in wild boars in Germany and to characterize individual isolates. A total of 375 fecal samples and 439 nasal swabs were screened for the presence of ESBL-/AmpC-E. coli and MRSA, respectively. The associations of seven demographic and anthropogenic variables with the occurrence of ESBL-/AmpC-E. coli were statistically evaluated. Collected isolates were subjected to antimicrobial susceptibility testing, molecular typing methods, and gene detection by PCR and genome sequencing. ESBL-/AmpC-E. coli were detected in 22 fecal samples (5.9%) whereas no MRSA were detected. The occurrence of ESBL-/AmpC-E. coli in wild boars was significantly and positively associated with human population density. Of the 22 E. coli, 19 were confirmed as ESBL-producers and carried genes belonging to bla_CTX-M group 1 or bla_SHV-12. The remaining three isolates carried the AmpC-β-lactamase gene bla_CMY-2. Several isolates showed additional antimicrobial resistances. All four major phylogenetic groups were represented with group B1 being the most common. This study demonstrates that wild boars can serve as a reservoir for ESBL-/AmpC-producing and multidrug-resistant E. coli.

Keywords: AmpC; ESBL-producing Escherichia coli; MRSA; multidrug resistance; wild boars.

Figure 1

Geographic distribution of sampled hunting locations within Germany. Counties, where sampling took place are shaded in darker grey and the individual hunting locations are represented by circles. Black circles represent locations where ESBL/AmpC-producing E. coli were detected, white circles represent locations where all samples tested negative. The fat black line indicates the division between the North German Lowlands and the region of Middle and Southern Germany, including higher altitudes.

Figure 2

Characteristics of E. coli isolates collected in the course of the present study. ^a Dendrogramm depicting the relatedness of the isolates and the percentage of similarity based on PFGE band patterns after XbaI digestion. ^b Multilocus sequence types and clonal complexes according to genome sequences. These data are only available for isolates subjected to genome sequencing. None: ST does not belong to a defined clonal complex. ^c Includes ESBLs, AmpC-β-lactamases and additional non-extended-spectrum β-lactamases (TEM-1, TEM-116, TEM-135). ^d Resistance phenotype based on MICs determined by broth macrodilution susceptibility testing and evaluation according to CLSI breakpoints for E. coli. AMP = ampicillin, CAZ = ceftazidime, CHL = chloramphenicol, CTX = cefotaxime, NAL = nalidixic acid, SMX = sulfamethoxazole, TET = tetracyclines, TMP = trimethoprim. ^e Resistance genes other than β-lactamase genes detected in the isolates by PCR.