Abstract
McNemar’s test and the Pearson Chi-square were used to assess the co-detection and observed frequency, respectively, for potentially virulent E. coli genes in river water. Conventional multiplex Polymerase Chain Reaction (PCR) assays confirmed the presence of the aggR gene (69%), ipaH gene (23%) and the stx gene (15%) carried by Enteroaggregative E. coli (EAEC), Enteroinvasive E. coli (EIEC) and Enterohermorrhagic E. coli (EHEC), respectively, in river water samples collected from the Berg River (Paarl, South Africa). Only the aggR gene was present in 23% of samples collected from the Plankenburg River system (Stellenbosch, South Africa). In a comparative study, real-time multiplex PCR assays confirmed the presence of aggR (EAEC) in 69%, stx (EHEC) in 15%, ipaH (EIEC) in 31% and eae (EPEC) in 8% of the river water samples collected from the Berg River. In the Plankenburg River, aggR (EAEC) was detected in 46% of the samples, while eae (EPEC) was present in 15% of the water samples analyzed using real-time multiplex PCR in the Plankenburg River. Pearson Chi-square showed that there was no statistical difference (p > 0.05) between the conventional and real-time multiplex PCRs for the detection of virulent E. coli genes in water samples. However, the McNemar’s test showed some variation in the co-detection of virulent E. coli genes, for example, there was no statistical difference in the misclassification of the discordant results for stx versus ipaH, which implies that the ipaH gene was frequently detected with the stx gene. This study thus highlights the presence of virulent E. coli genes in river water and while early detection is crucial, quantitative microbial risk analysis has to be performed to identify and estimate the risk to human health.
Highlights
In South Africa water abstracted from rivers is used for irrigation and domestic purposes, often without treatment
A Pearson Chi-square test was used for the comparison of results obtained by the conventional and real-time multiplex Polymerase Chain Reaction (PCR) for the detection of virulent E. coli genes throughout the sampling period (Table 2)
These results correlate with the fecal coliform counts observed in previous studies conducted, where water samples collected from the Berg and Plankenburg River systems were analyzed for the fecal indicator groups [1, 16, 17, 27]
Summary
In South Africa water abstracted from rivers is used for irrigation and domestic purposes, often without treatment. It has been shown that certain surface water sources contain high levels of fecal contamination. Most strains of the E. coli group are non-pathogenic members of the normal intestinal flora, certain strains contain virulent genes that may cause various human-related illnesses, such as urinary tract and respiratory infections, diarrhea and pneumonia. Lateral gene transfer from pathogenic microorganisms to E. coli strains may lead to the emergence of new pathogenic strains [5] They cause different types of diarrheal diseases due to the presence of specific genes associated with pathogenicity, colonization factors and other virulence factors that are generally absent in non-pathogenic strains of this typical indicator organism
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