RESUMO
Since sewage is a hotspot for antibiotic resistance genes (ARGs), the identification of ARGs in environmental waters impacted by sewage, and their correlation to fecal indicators, is necessary to implement management strategies. In this study, sewage treatment plant (STP) influent samples were collected and analyzed using quantitative polymerase chain reaction (qPCR) to investigate the abundance and correlations between sewage-associated markers (i.e., Bacteroides HF183, Lachnospiraceae Lachno3, crAssphage) and ARGs indicating resistance to nine antibiotics (belonging to aminoglycosides, beta-lactams, sulfonamides, macrolides, and tetracyclines). All ARGs, except bla VIM, and sewage-associated marker genes were always detected in untreated sewage, and ermF and sul1 were detected in the greatest abundances. intl1 was also highly abundant in untreated sewage samples. Significant correlations were identified between sewage-associated marker genes, ARGs and the intl1 in untreated sewage (τ = 0.488, p = 0.0125). Of the three sewage-associated marker genes, the BIO-ENV procedure identified that HF183 alone best maximized correlations to ARGs and intl1 (τ = 0.590). Additionally, grab samples were collected from peri-urban and urban sites along the Brisbane River system during base and stormflow conditions, and analyzed for Escherichia coli, ARGs, the intl1, and sewage-associated marker genes using quantitative polymerase chain reaction (qPCR). Significant correlations were identified between E. coli, ARGs, and intl1 (τ = 0.0893, p = 0.0032), as well as with sewage-associated marker genes in water samples from the Brisbane River system (τ = 0.3229, p = 0.0001). Of the sewage-associated marker genes and E. coli, the BIO-ENV procedure identified that crAssphage alone maximized correlations with ARGs and intl1 in river samples (τ = 0.4148). Significant differences in E. coli, ARGs, intl1, and sewage-associated marker genes, and by flow condition (i.e., base vs. storm), and site types (peri-urban vs. urban) combined were identified (R = 0.3668, p = 0.0001), where percent dissimilarities between the multi-factorial groups ranged between 20.8 and 11.2%. Results from this study suggest increased levels of certain ARGs and sewage-associated marker genes in stormflow river water samples compared to base flow conditions. E. coli, HF183 and crAssphage may serve as potential indicators of sewage-derived ARGs under stormflow conditions, and this merits further investigation. Data presented in this study will be valuable to water quality managers to understand the links between sewage pollution and ARGs in urban environments.
RESUMO
Animal fecal contamination in aquatic environments is a major source of zoonotic diseases in humans. While concerns are focused on livestock, companion animals such as dogs can also be a source of a wide range of zoonotic pathogens. Therefore, detection of dog or canine fecal contamination in aquatic environments is important for mitigating risks. In this study, host-sensitivity and specificity of four canine fecal-associated marker genes were evaluated by analyzing 30 canine and 240 non-canine fecal samples. The application of these markers was also tested in water from an urban river under dry weather conditions. The host sensitivity values of the Bacteroides BacCan-UCD, DogBact, DF113 and DF418 were 1.00, 0.90, 0.83, and 0.90, respectively. The host specificity value of the BacCan-UCD, DogBact, DF113 and DF418 were 0.87, 0.98, 0.83, and 0.41, respectively. The mean concentrations of DF418 were highest (7.82 ± 1.13 log10 gene copies (GC)/g of feces) followed by BacCan-UCD (7.61 ± 1.06 log10 GC/g) and DogBact (7.15 ± 0.92 log10 GC/g). The mean concentration of DF113 (5.80 ± 1.25 log10 GC/g) was 1.5 to 2.5 orders of magnitude lower than the other marker genes. The DogBact marker gene was not detected in any other animal feces other than a small number of untreated sewage samples. The BacCan-UCD marker gene cross-reacted with cat, chicken, and pig fecal samples, while the DF113 marker gene cross-reacted with cat, chicken, cattle fecal and untreated sewage samples. The DF418 marker gene was detected in all sewage and animal feces and deemed not suitable for canine fecal contamination tracking in sub-tropical Australia. Canine fecal contamination was infrequently detected in environmental water samples. Based on the results obtained in this study, we recommend that at least two canine feces-associated marker genes should be used in field studies.