Antibiotic resistance in enteric Escherichia coli and Enterococcus spp. isolated from ungulates at Marwell Zoo England

Abstract

Antimicrobial resistance (AMR) has diminished the effectiveness of many antibiotics used to treat human and animal infectious diseases. AMR in bacteria is considered one of the most important emerging threats to animal and human health worldwide (Dobiasova et al. 2013). Understanding the dynamics of AMR in different populations is key to minimising the emergence of resistance to preserve the efficacy of existing and newly developed antimicrobial drugs (Holmes et al. 2016, Sundqvist et al. 2010). This project investigated AMR in the commensal enteric microflora of animals at Marwell Zoo, United Kingdom. Although AMR has been studied in domesticated animals and free-ranging wildlife, there are few studies describing AMR in captive wild animals. In this project, faecal samples were collected from 17 species of healthy ungulates weekly for three weeks which yielded a total of 39 Escherichia coli and 55 Enterococcus spp. isolates. Antibiotic sensitivity was investigated using agar disk diffusion methods. The E. coli isolates were resistant to ampicillin (28.2%), streptomycin (17.9%), spectinomycin (17.9%), trimethoprim sulphamethoxazole (17.9%), neomycin (12.8%), doxycycline (12.8%), tetracycline (12.8%), amoxicillin-clavulanic acid (10.3%), cefotaxime (2.6%), cefpodoxime (2.6%), ceftazidime (2.6%) and amikacin (2.6%). All E. coli isolates were susceptible to apramycin, enrofloxacin, chloramphenicol and florfenicol and none tested positive for extended-spectrum beta-lactamase (ESBL) or AmpC activity using a disk diffusion screening kit. Seven out of 39 (18%) E. coli isolates were resistant to more than three antibiotic classes, the most common pattern of resistance was: penicillins, tetracyclines, aminoglycosides and sulphonamides. The E. coli isolates were further analysed using multi-locus sequence typing (MLST) which identified four pairs of identical sequence type (ST) isolates and 27 diverse strains. The Enterococcus spp. isolates were resistant to cefpodoxime (95%), erythromycin (67%), tetracycline (33%), ciprofloxacin (40%), imipenem (11%), trimethoprim sulphamethoxazole (5%) and streptomycin (4%). All Enterococcus spp. isolates were susceptible to ampicillin, gentamicin, chloramphenicol and vancomycin. This study identified multi-drug resistant phenotypes in the E. coli isolates that were similar to those commonly found in domestic ungulates. The resistance phenotypes were plotted on a map which did not show any significant spatial association between resistance traits in different species. Review of the medical records of individual animals showed previous use of penicillins, sulphonamides and tetracyclines in this population. Resistance to antibiotics that were rarely or never used may have been due to co-selection of resistance genes which were linked with other genes on the same genetic element (Acar & Moulin 2012).