Implications of faecal indicator bacteria for the microbiological assessment of roof-harvested rainwater quality in southeast Queensland, Australia

The study aimed to evaluate the suitability of Escherichia coli, enterococci, and Clostridium perfringens for assessing the microbiological quality of roof-harvested rainwater and assessing whether the concentrations of these faecal indicators can be used to predict the presence or absence of specific zoonotic bacterial or protozoan pathogens. From a total of 100 samples tested, 58%, 83%, and 46% of samples were found to be positive for, respectively, E. coli, enterococci, and Clostridium perfringens spores, as determined by traditional culture-based methods. Additionally, in the samples tested, 7%, 19%, 1%, 8%, 17%, and 15% were PCR positive for Aeromonas hydrophila lip, Campylobacter coli ceuE, Campylobacter jejuni mapA, Legionella pneumophila mip, Salmonella invA, and Giardia lamblia β-giardin genes, respectively. However, none of the samples was positive for E. coli O157 lipopolysaccharide, verocytotoxin 1, and verocytotoxin 2 and Cryptosporidium parvum oocyst wall protein genes. The presence or absence of these potential pathogens did not correlate with any of the faecal indicator bacterial concentrations as determined by a binary logistic regression model. The roof-harvested rainwater samples tested in this study appeared to be of poor microbiological quality, and no significant correlation was found between the concentration of faecal indicators and pathogenic microorganisms. The use of faecal indicator bacteria raises questions regarding their reliability in assessing the microbiological quality of water and particularly their poor correlation with pathogenic microorganisms. The presence of one or more zoonotic pathogens suggests that the microbiological analysis of water should be performed and that appropriate treatment measures should be undertaken, especially in tanks where the water is used for drinking