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.
