Antimicrobial resistance and genetic lineages of faecal enterococci of wild birds: Emergence of vanA and vanB2 harbouring Enterococcus faecalis

Abstract

Migrating birds have been implicated in pathogen dissemination over long distances. The lack of data on the intestinal microbiota of birds makes these animals a promising path in order to understand their potential role in the transmission of antibiotic-resistant bacteria. This study aimed to investigate the diversity of enterococcal species, and to analyse the antimicrobial-resistant phenotypes/genotypes, as well as the genetic lineages of isolates obtained from faecal and pellet samples of colonial wild birds in Tunisia. Seventy-nine enterococci were recovered from 150 wild birds, after inoculation of samples in Slanetz-Bartley agar, and were identified as E. faecalis (n = 53), E. faecium (n = 19) and E. casseliflavus (n = 7). Antimicrobial susceptibility was tested, and the following rates of resistance were found: tetracycline (46.8%); erythromycin (34.2%); chloramphenicol (8.8%); gentamicin and streptomycin (2.5-3.8%); ciprofloxacin, trimethoprim-sulfamethoxazole and kanamycin (12.7-21%); and ampicillin and linezolid (0%). The tet(M), tet(L), erm(B), erm(C), aac(6')-Ie-aph(2″)-Ia and cat genes were detected in most tetracycline-, erythromycin-, gentamicin- and chloramphenicol-resistant enterococci, respectively. Three vancomycin-resistant E. faecalis isolates were detected, two with the vanA gene (into Tn1546) and one with the vanB2 gene (into Tn5382); these isolates showed different sequence types determined by multi-locus sequence typing (ST9, ST16 and a new ST848). Seven E. casseliflavus isolates harbouring the intrinsic vancomycin resistance mechanism vanC2 were obtained. The gelE, ace, agg, esp and hyl virulence genes were detected among vanA/vanB2 enterococci. This study provides insight into the possible role of wild birds in the spread of certain antimicrobial resistance genes, particularly vanA/vanB2. To the authors' knowledge, this is the first report of vanB2-containing enterococci in Africa.

Keywords: Antimicrobial resistance; Enterococcus spp.; Tunisia; Virulence; Wild birds.