Occupational exposure to Staphylococcus aureus in the wastewater treatment plants environment

The aim of the study was to assess the occupational exposure to Staphylococcus aureus bacteria, including methicillin- resistant S. aureus (MRSA) and other antibiotic-resistant strains in the municipal wastewater treatment plants (WWTPs) environment.

In 16 WWTPs in Poland, 33 wastewater and 253 air samples were collected in the spring-summer season. The microbiological analysis was carried out using a chromogenic medium. Species identification was carried out using the matrix assisted laser desorption ionization time-of-flight method, while the antibiotic-resistance analysis was performed with an automatic method.

Among 2805 bacterial isolates from the air and wastewater, 574 were identified as S. aureus species (20.5%). The presence of S. aureus species was found in 11 WWTPs (69%), among them in 11 WWTPs in raw wastewater and in 1 WWTP additionally in treated wastewater. The concentrations of S. aureus in wastewater ranged 2-1215 colony-forming units per milliliter (CFU/ml). In the air, 2 S. aureus isolates were identified in concentrations of 5 and 10 CFU/m³; both samples were collected at the stage of mechanical wastewater treatment. The results revealed the following trend: the higher the outdoor temperature, the bigger the number of WWTPs with confirmed S. aureus presence. Among 149 S. aureus isolates (2 from the air and 147 from wastewater, including 2 MRSA), 100 isolates were resistant only to penicillin, while 34 isolates showed multi-antibiotic resistance (to penicillin and other drugs). It was found that isolated bacteria were resistant almost strictly to critical and highly important antibiotics in veterinary medicine.

In general, WWTPs workers are occupationally exposed to S. aureus, including MRSA, and other antibiotic- and multi-antibiotic-resistant strains. The highest risk of infection concerns the activities carried out in direct contact with wastewater or devices through which wastewater flows, particularly at the stage of mechanical treatment. A significant source of S. aureus seems to be intensive livestock farming located in the area of the WWTPs under analysis. The study confirms the necessity to disinfect the wastewater discharging into WWTPs. Med Pr. 2020;71(3):265-78.