Occurrence of a human-associated microbial source tracking marker and its relationship with faecal indicator bacteria in an urban estuary

One of the main impacts of urban sprawl in rapidly growing countries has been contamination of coastal environments by waterborne pathogens, posing a critical risk to ecosystem and human health. Microbial source tracking (MST) has been a robust tool to identify the origin of these pathogens globally. This study compared the occurrence of a human-associated Bacteroides marker (BT-alpha) with faecal indicator bacteria (FIB) in an urban estuary (Golden Horn, Istanbul, Turkey). Faecal coliform (culture method), enterococci (both culture and qPCR method) concentrations and physicochemical variables were compared with the BT-alpha concentrations in monthly collected samples for a year (n = 108). Enterococci concentrations detected by culture and qPCR were positively correlated (r = 0 center dot 86, P < 0 center dot 01) suggesting that qPCR can be an alternative method for monitoring. BT-alpha marker was positive for 30% of the samples and positively correlated with enterococci (r = 0 center dot 61 and r = 0 center dot 64 for culture and qPCR methods respectively, P < 0 center dot 01). Rainfall had a moderate positive correlation with all faecal/MST indicators suggesting combined sewer overflows also severely impacted estuarine water quality. The high FIB and BT-alpha concentrations at upper estuary suggested that faecal pollution mainly originated from the peri-urban settlements around two creeks entering the estuary.