Characterization of enterococci isolates from water sources in the North West Province

Abstract

Enterococci are a diverse and complex group of ubiquitous bacteria that can survive extreme conditions. Despite constituting a large portion of the gastrointestinal tract in warm blooded animals and humans, they are responsible for numerous infections and diseases globally. Enterococcal pathogens from point and nonpoint sources such as agricultural runoff and wastewater treatment plants (WWTPs) can be mobilized into receiving water bodies via storm water. This is a cause for concern since epidemiological studies have demonstrated a positive correlation between Enterococcus concentrations and swimmer associated gastroenteritis. Few studies have characterised Enterococcus spp. in South Africa, particularly the North West Province. Thus, there is a paucity of data reporting the prevalence and susceptibility patterns of Enterococcus spp. isolated from surface water systems in the province. In addition, the presence of potentially pathogenic Enterococcus spp. harbouring efflux pumps, plasmids and virulence genes, in surface water systems of the North West Province is unknown. To increase our understanding of Enterococcus spp. in surface water systems of the North West Province, and to highlight their importance in water quality assessments, an overview study was performed in order to determine whether Enterococcus spp. present in environmental water systems of the North West Province were potential pathogens. In the first part of the study, the presence of five clinically relevant virulence genes in six Enterococcus species isolated from environmental water systems was determined. In addition, the presence of virulence genes was correlated with their extracellular enzyme production. Sixty five percent of the isolates were positive for one virulence gene and 13% for two or more. Most frequently detected genes were gelE (32%) and cylA (28%). Enterococcal surface protein was absent in all isolates screened. The results show that a large percentage of these environmental Enterococcus spp. possess virulence factors that could be expressed in vitro. This is a cause for concern and could have implications for individuals using this water for recreational and cultural purposes. It requires further investigation into the sources of these potential pathogenic Enterococcus isolates and measures to minimize their presence in water sources. In the second part of this study the potential source of Enterococcus spp. found in these environmental water systems was determined. The final effluent of three WWTPs and points downstream were analysed for the presence of Enterococcus spp. while their antibiotic susceptibilities and presence of virulence genes were also determined. Furthermore, the multiple antibiotic resistance (MAR) phenotypes were identified for all profiles for pre- and post plasmid curing. The antibiotic inhibition zone diameter data was subject to cluster analysis. Sixty eight percent of the screened Enterococcus spp. were resistant to three or more antibiotics and harboured plasmids. All five virulence genes were detected and six multi-virulence profiles observed. Cluster analysis indicated grouping of isolates from all three WWTPs final effluent together, points downstream together, and between plants one and two together. The findings of this study have demonstrated that Enterococcus spp. harbouring virulence factors and plasmids that mediate multiple antibiotic resistance are present in WWTPs final effluent and receiving water systems that support various social needs. This is a cause for concern and it is recommended that Enterococcus be used as an additional faecal indicator when microbiological quality of water is assessed. The third part of the study analysed the antimicrobial susceptibility of Enterococcus species isolated from five surface water systems in the North West Province. In addition, the presence of four efflux pump genes was determined. Thereafter, the presence of virulence genes was determined. Efflux genes mefA and tetK were not detected in any of Enterococcus spp. screened. However, tetL and msrC were detected in 17% of the Enterococcus spp. Virulence determinants were detected in 86% of the Enterococcus spp. harbouring efflux pump genes. Of the screened five virulence determinants (asa1, cylA, esp, gelE and hyl), four were detected. The findings of this study have demonstrated that Enterococcus spp. from South African surface water systems are resistant to multiple antibiotics, some of these are frequently used for therapy. Furthermore, these isolates not only harbour efflux pump genes coding for resistance to antibiotics but also harbour virulence factors which enhance their pathogenicity potential. These genetic determinants may be useful for the survival of these isolates in surface water environments allowing for their dissemination to humans and animals. Data generated in this study is valuable as it indicates the presence of potentially pathogenic Enterococcus spp. harbouring genetic determinants in surface water systems used for a wide variety of activities. In addition, this study has generated readily available information on the local antimicrobial resistance patterns of potential bacterial pathogens which could assist in improved assessments of human health risks while guiding empirical and pathogen specific therapy. Lastly, data produced in this study could be used for making optimal decisions regarding future water quality monitoring practices.