Characterization and resistance profiles of selected enteric bacteria isolated from non-human primates at a wildlife-human interface

Abstract

The direct and repeated exposure to antimicrobials in domestic animals and humans has been shown to produce strong selective pressures for the maintenance of antimicrobial resistance in their enteric bacteria. Though wild animal populations are not directly exposed to antimicrobials, antimicrobial resistance has been reported in some wild animal populations. Proximity to humans has been reported to be associated with a higher prevalence of antimicrobial resistance in wild animal populations. In this study faecal samples were screened for indicator and zoonotic bacterial organisms from primate populations (baboons and vervet monkeys) located at two primate rehabilitation centres close to the Kruger National Park, South Africa. For comparison purposes, samples were obtained from non-human primates with 3 distinct levels of exposure to humans. The 1st group had regular human contact and consisted of mostly orphaned juveniles that were fed, bathed and cuddled regularly. The 2nd group had been weaned from frequent contact with humans, but had occasional contact. The 3rd group lived in enclosures similar to their natural habitats with almost no human contact. Antimicrobial susceptibility testing was carried out on all isolates using the Sensititre GPALL1F and GNX2F MIC plates (Trekds, UK). The Gram- positive isolates were tested against 22 antimicrobial drugs while the other Gram-negative bacteria were tested against 21 antimicrobial drugs all in dosages used by humans. In all, 300 fresh faecal samples were collected. Sixty enterococci, 64 Klebsiella spp., and 64 Escherichia coli/E. fergusonii strains were isolated from the baboon samples. From the vervet faecal samples 40 enterococci, 64 Klebsiella spp. and 64 E. coli/E. fergusonii strains were isolated. Over eighty percent of the Gram-negative isolates were resistant to polymyxin B and E (colistin) as well as the carbapenems with occasional resistance recorded against aminoglycosides. Eighty percent of the Gram- positives (all enterococci) were resistant to aminoglycosides, carbapenems and fluoroquinolones. More than 90% of all the Gram-negative isolates were susceptible to penicillins and β-lactamase inhibitor combinations with the exception of the Salmonella spp. in which about 50% of the isolates were resistant. The highest level of antimicrobial drug resistance in the non-human primates was observed in group 1. Comparatively speaking, group 1 had 20% and 23% higher levels of resistance than group 2 and group 3 respectively. This was observed for all the antimicrobials tested, especially polymyxin B and colistin. It was also observed that antimicrobial resistance levels decreased with age; with isolates from older animals being less resistant. This resistance profile was similar in all 3 groups in both rehabilitation centers. Establishing the presence of microbial exchange between human populations and wildlife (especially primates), even in the absence of immediate disease concerns, may identify points of contact where increased surveillance may be justified because of higher risks of novel disease emergence.