Quantifying Salmonella Population Dynamics in Water and Biofilms

Abstract

Members of the bacterial genus Salmonella are recognized worldwide as major zoonotic pathogens often found to persist in non-enteric environments including heterogeneous aquatic biofilms. In this study, Salmonella isolates that had been detected repeatedly over time in aquatic biofilms at different sites in Spring Lake, San Marcos, Texas, were identified as serovars Give, Thompson, Newport and -:z10:z39. Pathogenicity results from feeding studies with the nematode Caenorhabditis elegans as host confirmed that these strains were pathogenic, with Salmonella-fed C. elegans dying faster (mean survival time between 3 and 4 days) than controls, i.e., Escherichia coli-fed C. elegans (mean survival time of 9.5 days). Cells of these isolates inoculated into water at a density of up to 10(6) ml(-1) water declined numerically by 3 orders of magnitude within 2 days, reaching the detection limit of our quantitative polymerase chain reaction (qPCR)-based quantification technique (i.e., 10(3) cells ml(-1)). Similar patterns were obtained for cells in heterogeneous aquatic biofilms developed on tiles and originally free of Salmonella that were kept in the inoculated water. Cell numbers increased during the first days to more than 10(7) cells cm(-2), and then declined over time. Ten-fold higher cell numbers of Salmonella inoculated into water or into biofilm resulted in similar patterns of population dynamics, though cells in biofilms remained detectable with numbers around 10(4) cells cm(-2) after 4 weeks. Independent of detectability by qPCR, samples of all treatments harbored viable salmonellae that resembled the inoculated isolates after 4 weeks of incubation. These results demonstrate that pathogenic salmonellae were isolated from heterogeneous aquatic biofilms and that they could persist and stay viable in such biofilms in high numbers for some time.

Detection and Occurrence of Indicator Organisms and Pathogens

“…EHEC E. coli was also identified from different sources in Isamailia, Egypt (Selim et al, 2013 (Sha et al, 2013). Caenorhabditis elegans was fed with Salmonella and a control (E. coli).…”

Substratum‐Associated Microbiota

“…Some aquatic E. coli isolates showed close relationships with strains from human and bovine origins, suggesting that environmental isolates were originally derived from these sources. Sha et al (2013) demonstrated that pathogenic salmonellae could persist over time and stay viable in aquatic biofilms in high numbers. Walczak et al (2013) found that Legionella pneumophila can be found in lakes serving as a natural cooling system of a power plant, since thermally altered aquatic environments provide perfect conditions for the growth of L. pneumophila.…”

Draft Genome Sequence of Salmonella enterica subsp. enterica Serotype Saintpaul Strain S-70, Isolated from an Aquatic Environment

“…Although the mammalian intestine tract is considered its natural habitat (3), Salmonella is constantly being shed into aquatic environments through human and animal feces (4). This pathogen has been detected in a wide range of natural settings, such as water (rivers, lakes, coastal waters, and sewage effluents) (4, 5), soil, and sediments, where it can survive for long periods (6, 7). The wide diversity of Salmonella serotypes and its survival capacity outside a definitive host contribute to its constant presence in aquatic environments (4).…”