Evaluation of the Sensitivity and Specificity of Human-Associated Escherichia coli Accessory Genes as Potential Markers for Microbial Source Tracking
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Mentor Information
Valerie Harwood
Description
The human-associated H8 accessory gene in Escherichia coli is one of the potential microbial source tracking (MST) markers used for source identification of human fecal contamination, including sewage, in environmental waters. However, this gene has also been found in Klebsiella, a species ubiquitous to aquatic environments. A second accessory gene, H12, has been proposed as an alternative human marker to H8. In this study, culture and quantitative PCR (qPCR) methods were used to determine the specificity and sensitivity of H8 and H12 genes. Five fecal samples from eight different animals and influent samples from two wastewater treatment plants were tested for presence of these marker genes. Two animal fecal samples (one deer and one chicken) tested positive for the H8 gene, and nine tested positive for the H12 gene (two deer, two chickens, one duck, three horses, and one shore bird). Concentration of the H8 gene was an order of magnitude higher than the H12 gene in sewage. A BLAST search for H12 gene sequence on the NCBI database revealed that it is also found within Salmonella enterica, which is present in human and animal intestinal tracts, and Raoultella planticola, a bacterium ubiquitous in aqueous environments. The H12 gene has lower specificity (76.9%) compared to the H8 gene (94.9%). H8 and H12 genes demonstrated similar sensitivity values (both 100%). Prevalence of the H12 gene (1.67%) in sewage was lower than the H8 gene (15.56%). Based on these results the H12 gene is not a viable marker for source tracking purposes.
Evaluation of the Sensitivity and Specificity of Human-Associated Escherichia coli Accessory Genes as Potential Markers for Microbial Source Tracking
The human-associated H8 accessory gene in Escherichia coli is one of the potential microbial source tracking (MST) markers used for source identification of human fecal contamination, including sewage, in environmental waters. However, this gene has also been found in Klebsiella, a species ubiquitous to aquatic environments. A second accessory gene, H12, has been proposed as an alternative human marker to H8. In this study, culture and quantitative PCR (qPCR) methods were used to determine the specificity and sensitivity of H8 and H12 genes. Five fecal samples from eight different animals and influent samples from two wastewater treatment plants were tested for presence of these marker genes. Two animal fecal samples (one deer and one chicken) tested positive for the H8 gene, and nine tested positive for the H12 gene (two deer, two chickens, one duck, three horses, and one shore bird). Concentration of the H8 gene was an order of magnitude higher than the H12 gene in sewage. A BLAST search for H12 gene sequence on the NCBI database revealed that it is also found within Salmonella enterica, which is present in human and animal intestinal tracts, and Raoultella planticola, a bacterium ubiquitous in aqueous environments. The H12 gene has lower specificity (76.9%) compared to the H8 gene (94.9%). H8 and H12 genes demonstrated similar sensitivity values (both 100%). Prevalence of the H12 gene (1.67%) in sewage was lower than the H8 gene (15.56%). Based on these results the H12 gene is not a viable marker for source tracking purposes.
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