Characterization of Staphylococcus aureus from Nigeria and South Africa
The detection of methicillin-resistant Staphylococcus aureus (MRSA) in wastewater system from clinical sources has posed a public health challenge in many countries worldwide. Of a greater concern is the discharge of untreated or improperly treated hospital effluents into wastewater, which has been identified as possible hotspot for antibiotic resistance bacteria (ARB) and antibiotic resistance genes (ARGs). MRSA, a distinct form of Staphylococcus aureus (S. aureus) showing resistance to methicillin, is widely reported as a nosocomial pathogen. However, there is paucity of data and limited reporting about its occurrence in non-clinical environments, such as wastewater in Nigeria and South Africa. This present study is on the characterization of S. aureus, MRSA and other staphylococci from clinical and environmental sources in Ile-Ife, Nigeria and Potchefstroom, South Africa. The first part of the thesis emphasized the significance of the genus Staphylococcus and their importance as opportunistic pathogens, causing many diseases and infections in humans. The rationale, aim and objectives of the study were also highlighted. The second part of the study was a systematic review aimed to assess the prevalence of mecA gene in Staphylococcal isolates from clinical and environmental (wastewaters) sources. For this review, 50 peer reviewed full texts (35 clinical and 15 wastewaters) from 19 countries and 5 continents across the globe were selected based on pre-determined criteria. Specifically, there is insufficient information on mecA gene in Staphylococcus spp. from aquatic or environmental wastewaters (30.0%). Further, within the database search period (2000 – 2019), only very few studies (10) on Staphylococcus spp. with reference to mecA gene could be traced and retrieved from developed countries. Data extracted revealed that S. aureus and other Staphylococcus spp. are potential contributors of antibiotic resistance bacterial (ARB) infections from both clinical and environmental settings. In the third part of the study, 76 Staphylococcus spp. were isolated and characterized from hospital and environmental sources in Ile-Ife, Nigeria. These comprised of 40.7% (31/76) coagulase-positive (S. aureus) and (45/76) 59.3% coagulase-negative staphylococci (CoNS) constituting S. sciuri and 3 other rare species - S. xylosus, S. warneri and S. kloosi which have not been widely reported. Furthermore, the study confirmed the presence of resistance and virulence genes of public health importance in the Staph. spp. Sixty-three (63%) of the isolates with these genes originated from clinical samples, while 37% were from environmental sources. Interestingly, the presence of mecA gene was also confirmed in coagulase-negative staphylococci (CoNS) which have been previously considered low-risk or non-pathogenic. This calls for concern since their possession of resistance and virulence genes signal that these species can endanger human health and life. The fourth part of the study also focused on Staphylococcus spp. specifically MRSA and mecA gene detection in a wastewater treatment plant (WWTP) in Potchefstroom, South Africa. In the WWTP, 35 staphylococcal isolates of 7 different species were isolated. These included 3 CoNS which are uncommon: S. cohnii, S. nepalensis and S. arlettae. The study confirmed the presence of MRSA and multidrug resistant (MDR) Staphylococcus spp. at the final effluent point which had undergone chemical treatment by chlorination. It was recommended that a more effective treatment plan or modification procedures should be adopted especially if the water is to be reused. The fifth and final part of the study, reported a high quality draft genomes of 8 CoNS isolates obtained from clinical and environmental settings in Nigeria and South Africa. The isolates were identified as S. lentus (1 from South Africa), S. cohnii (3 from Nigeria and 2 from South Africa) and S. haemolyticus (1 from Nigeria and 1 from South Africa). The isolates possessed an open pan-genome, with a few genetic barriers to horizontal gene transfer. Clustered regularly interspaced short palindromic repeats (CRISPR) associated with Cas protein system (CRISPR/Cas) were identified in one of the 8 isolates. 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.