Persistence of MRSA and ESBL-producing E. coli and K. oxytoca in river water

Due to climate change precipitation patterns are changing in terms of frequency and quantity in Germany. As a result, prolonged dry weather can lead to extremely low flow rates in river systems with large portions of treated wastewater. However, storm events and heavy rainfall events are increasing too, which may lead to higher frequencies of combined sewer overflows. Increased microbial pollution (e.g. coliform bacteria, clostridia, faecal streptococci) of waterbodies after heavy precipitation events was demonstrated in several studies. Pathogenic multi-resistant bacteria enter waterbodies via sewer systems. The persistence potential of such pathogens in aquatic environments is mainly still unknown. This study investigated the growth behaviour of Gram-negative extended spectrum beta-Lactamase-producing Klebsiella oxytoca and Escherichia coli and Gram-positive methicillin-resistant Staphylococcus aureus in river water. The concentrations of these antibiotic-resistant bacteria were monitored in batch experiments using river water differently impacted by wastewater. Staphylococcus aureus persisted for at least 3 days at incubation temperatures of 8 and 18 °C. The persistence of K. oxytoca and E. coli was shown for at least 37 days at both temperatures. In the river water at 8 °C, bacteria concentrations decreased slower, suggesting diminished persistence of ARB (antibiotic-resistant bacteria) with increasing temperatures. Initial concentrations of ARB and other pathogens in river water corresponded to the impact of wastewater. However, significant effects on the persistence itself by wastewater impact could not be shown for the bacteria species tested. Further studies should pursue our approaches concerning the persistence of pathogenic ARB in freshwater to assess the health risk for humans and animals.