Antimicrobial resistance profiles of selected commensal bacteria isolated from impala (Aepyceros melampus) and their water sources in the Kruger National Park

Abstract

Worldwide there is a growing concern of the emergence and evolution of antimicrobial resistance among bacterial pathogens, which poses a threat to human and animal health. The extensive use and misuse of antimicrobials in human and veterinary clinical therapy and agricultural practices have been a major selective force for the emergence, selection, and dissemination of antimicrobial resistant bacteria and resistant genes. Commensal bacteria constitute a reservoir of resistant genes and their level of resistance is considered to be a good indicator for resistance problems to be expected in pathogens. The monitoring of the prevalence of resistance in indicator bacteria such as faecal Escherichia coli and enterococci in different human and animal populations allows the comparison of the prevalence of resistance and to detect transfer between animals and humans and vice versa. Antimicrobial resistance has however, been found in the bacteria of wildlife not exposed to antimicrobials and living in remote areas of this earth. This has implications for resistance control strategies. Previous studies on antimicrobial resistance in wildlife have yielded contrasting results, such as an almost complete absence of resistance in enterobacteria isolated from moose, deer and vole in Finland compared to a high prevalence of resistance in faecal bacteria from wild rodents living in northwest England, which are possibly due to differences in the ecological systems and the proximity to anthropogenic activities. This study further investigates the phenomenon of antimicrobial resistance in wildlife. A previous study conducted in the conservancy area of Kruger National Park (KNP) within South Africa showed that surface water could be a possible source of antimicrobial resistance in unexposed animal populations and that impala (Aepyceros melampus) were good sentinel animals for the documentation of antimicrobial resistance through rivers. This current study followed on this hypothesis and investigated the prevalence of resistance in commensal bacteria isolated from impala and their water sources in KNP. The following four perennial river systems were selected: the Olifants, the Letaba, the Crocodile, the Sabie-Sand Rivers. Samples of river water (n=11) and faeces (n=165) were collected at 11 different sites along these rivers. Samples were directly plated and resistant colonies were selected by means of discs containing antimicrobials (direct plating method). Resistant colonies that grew in the presence of antimicrobials were cultured and identified. Isolates of E. coli (n=12), Enterobacter cloacae (n=49), Pantoea species (n=9), Enterococcus faecalis (n=59), Enterococcus faecium (n=4) and Enterococcus durans (n=64) were tested for susceptibility to a selection of commonly used veterinary antimicrobial drugs. Susceptibility to 18 antimicrobial drugs was determined by means of minimum inhibitory concentrations (MIC) using a commercial MIC test (Sensititre® Bovine/Porcine plate format BOP06F). Our results allow us to give further support to our working hypothesis that antimicrobial resistance, as evidenced in the impala faeces, may have been due to the impala drinking from the polluted rivers, knowing full well that impala are not routinely subjected to any form of antimicrobial treatment. Although the isolates obtained from the water sources were not as many as those obtained from the faecal samples, a degree of resistance was also observed across all the four river systems that we isolated bacteria from, and this was also evident in the faecal samples as well. Our results also further add to the importance of wildlife as sentinels in environmental antimicrobial resistance studies.