Phylogenetic diversity of drinking water bacteria in a distribution system simulator.

AIMS: To characterize the composition of microbial populations in a distribution system simulator (DSS) by direct sequence analysis of 16S rDNA clone libraries. METHODS AND RESULTS: Bacterial populations were examined in chlorinated distribution water and chloraminated DSS feed and discharge water. Bacterial strains isolated from DSS discharge water on R2A medium were identified using 16S rDNA sequence analysis. The majority of the bacteria identified were alpha-proteobacteria, ranging from approx. 34% in the DSS discharge water to 94% of the DSS isolates. Species richness estimators Chao1 and ACE (abundance-based coverage estimators) indicated that the chlorinated distribution water sample was representative of the total population diversity, while the chloraminated DSS feed water sample was dominated by Hyphomicrobium sp. sequences. The DSS discharge water contained the greatest diversity of alpha-, beta-, gamma-proteobacteria, with 36% of the sequences being operational taxonomic units (OTUs, sequences with >97.0% homology). CONCLUSIONS: This work demonstrated the dominance of alpha-proteobacteria in distribution system water under two different disinfectant residuals. The shift from chlorine to monochloramine residual may have played a role in bacterial population dynamics. SIGNIFICANCE AND IMPACT OF THE STUDY: Accurate identification of bacteria present in treated drinking water is needed in order to better determine the risk of regrowth of potentially pathogenic organisms within distribution systems.

Molecular characterization of bacteria inhabiting a water distribution system simulator.

The objective of this study was to monitor the impact of chlorination and chloramination treatments on heterotrophic bacteria (HB) and ammonia-oxidizing bacteria (AOB) inhabiting a water distribution system simulator. HB densities decreased while AOB densities increased when chloramine was added. AOB densities decreased below detection limits after the disinfection treatment was switched back to chlorination. The presence of AOB was confirmed using a group-specific 16S rDNA-PCR method. 16S rDNA sequence analysis showed that most bacterial isolates from feed water, discharge water, and biofilm samples were alpha-Proteobacteria or beta-Proteobacteria. The latter bacterial groups were also numerically dominant among the sequences recovered from water and biofilm 16S rDNA clone libraries. The relative frequency of each culturable bacterial group was different for each sample examined. Denaturing gradient gel electrophoresis analysis of total community 16S rDNA genes showed notable differences between the microbial community structure of biofilm samples and feed water. The results of this study suggest that disinfection treatments could influence the type of bacterial community inhabiting water distribution systems.

Evaluation of a DNA probe test kit for detection of Salmonellae in biosolids.

AIMS: Current US regulations (40 CFR 503) for 'Class A' biosolids (treated sewage sludge) requires use of multiple-tube fermentation techniques for fecal coliform or multiple tube enrichment techniques for Salmonella spp. followed by isolation and biochemical and serologic confirmation. The technical difficulties and the time required to complete the procedure for enumeration of Salmonellae in biosolids and sludges has limited the use of this assay. This study was conducted to determine if a commercially available molecular probe system could be used to isolate and enumerate Salmonella spp. in biosolids or sludges in less time than cultural techniques with biochemical confirmation. METHODS AND RESULTS: Several types of treated and untreated municipal sludges were assayed for Salmonellae using a cultural technique with biochemical and serologic confirmation and a DNA probe diagnostic test kit. The results indicate that the molecular probe and the conventional fermentation tube technique yielded equivalent results. Interestingly, the probe technique yielded results within 52 h following initiation of sample analysis compared with the conventional fermentation tube technique with confirmation which required approx. 120 h. CONCLUSIONS: These results suggest that the molecular probe system used for this work may be used to determine the presence or absence of Salmonella spp. in biosolids within a relatively short time frame. SIGNIFICANCE AND IMPACT OF THE STUDY: The ease of using the DNA probe test kit, along with its ability to produce results in less than half the time of conventional culture techniques, suggests that this assay is useful for determining the presence or absence of Salmonellae in biosolids samples.

Effect of UV light disinfection on antibiotic-resistant coliforms in wastewater effluents.

Total coliforms and total coliforms resistant to streptomycin, tetracycline, or chloramphenicol were isolated from filtered activated sludge effluents before and after UV light irradiation. Although the UV irradiation effectively disinfected the wastewater effluent, the percentage of the total surviving coliform population resistant to tetracycline or chloramphenicol was significantly higher than the percentage of the total coliform population resistant to those antibiotics before UV irradiation. This finding was attributed to the mechanism of R-factor-mediated resistance to tetracycline. No significant difference was noted for the percentage of the surviving total coliform population resistant to streptomycin before or after UV irradiation. Multiple drug resistance patterns of 300 total coliform isolates revealed that 82% were resistant to two or more antibiotics. Furthermore, 46% of these isolates were capable of transferring antibiotic resistance to a sensitive strain of Escherichia coli.