Salmonellae in the intestine of Hypostomus plecostomus in the San Marcos River
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Heavy rainfall events have been associated with outbreaks of many waterborne diseases including salmonellosis. Salmonellosis is caused by members of the genus Salmonella that can enter water systems through sewage contamination, runoff after heavy rainfalls, or flow-through channels through manure fields after heavy rains or flooding. Currently, salmonellae are not closely monitored in regards to water quality. In this study, Hypostomus plecostomus, an invasive, algae consuming fish, was sampled from the San Marcos River (San Marcos, TX), the intestines analyzed for the presence of salmonellae by quantitative real-time polymerase chain reaction (qPCR) after semi-selective enrichment, and results related to precipitation and other ecological factors affecting the river area. Salmonellae were detected in the intestines of H. plecostomus in 40-100% of the fish following most precipitation events, but were not consistently detected in environmental samples (i.e. water and sediments). Other ecological factors affecting the river do not appear to play a significant role in the prevalence of salmonellae in the intestines of H. plecostomus, other than turbidity. This leads us to believe that H. plecostomus is ingesting salmonellae through their food sources and that the amount of salmonellae present in those food sources may be increasing after large rainfall events, but may not be dependent on these events.
Further studies included characterization of Salmonella isolates from positive samples by repetitive polymerase chain reaction (rep-PCR). Unique isolates were then serotyped using Multi-locus Sequence Typing (MLST). Several sampled H. plecostomus were observed to be infected by multiple serotypes of Salmonella, whereas other positive fish were observed to be infected by one serotype only. Some serotypes were observed to be common across multiple sampling dates, which leads us to believe that there may be a common environmental serotype residing in the intestines of infected H. plecostomus. Furthermore, detection of multiple serotypes in the intestines of H. plecostomus was an unexpected observation.