Wastewater and urban waterways as hotspots for multidrug-resistant Staphylococcus aureus and Staphylococcus epidermidis in Yaoundé, Cameroon

Antibiotic resistance in Staphylococcus is a major public health issue. Wastewater treatment plants and waterways added to urban, hospital and even agricultural discharges are potential reservoirs of resistant bacteria, enabling them to spread into the environment. The aim of this study was to assess the prevalence of antibiotic resistance in Staphylococcus species ( Staphylococcus aureus and Staphylococcus epidermidis ) isolated from a number of wastewater treatment plants and waterways in the city of Yaoundé, as well as the impact of abiotic factors. Water samples were taken at the discharge points of the Wastewater Treatment Plants (WWTP) and in the waterways receiving the WWTP discharges. Staphylococcus strains were isolated on Chapman-mannitol medium and then identified using standard biochemical techniques. Antibiotic susceptibility testing of Staphylococcal isolates was done using the antibiotic disc diffusion method on Müller-Hinton agar. Physicochemical parameters were analysed using appropriate techniques. The results showed that the water was slightly alkaline (pH > 7.5), contained organic matter (nitrates > 8 mg/L, orthophosphates > 4 mg/L) and inorganic salts (electrical conductivity > 380 µS/cm and TDS > 200 mg/L), and harboured species of S. aureus and S. epidermidis that ranged respectively from 1.42 to 1.96 Log 10 CFU/100 µL, and from 1.24 to 2.87 Log 10 CFU/100 µL. The prevalence of antibiotic resistance varied from species to species in the different sampling points and was higher in Staphylococcus strains isolated upstream of waterways receiving wastewater treatment plant discharges. Overall, the Staphylococcus strains were resistant to β-lactam antibiotics (methicillin), glycopeptides (vancomycin) and quinolones (ofloxacin), thus demonstrating the multi-resistant nature of these strains, particularly S. aureus , for which the prevalence rate was 100% with methicillin and ofloxacin, and 99.1% with vancomycin. Significant positive and negative correlations (P < 0.05) were noted between the physicochemical parameters and the inhibition diameters of the various antibiotics. WWTPs and waterways could be hotspots for the dissemination of resistant Staphylococci, requiring optimisation of purification processes and increased monitoring to limit environmental contamination.