The simultaneous expression of metal tolerance and antibiotic resistance by bacteria from drinking water systems Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/s4655k61g

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  • Previous studies of six Oregon public water supply systems revealed that greater proportions of the standard plate count (SPC) bacteria from distribution waters were multiple antibiotic resistant (MAR) compared to isolates from the corresponding source raw waters. In the present study, two of these water systems were examined further to determine the possible role that metal tolerance has in the selection of MAR bacteria. The first drinking water system examined serves an Oregon coastal resort community. A total of 216 distribution water and 177 raw water isolates were tested for resistance to five antibiotics (chloramphenicol, kanamycin, streptomycin, sulfanilamide, and tetracycline), tolerance to six metals (as salts, Al₂(SO₄)₃, CdC1₂, CuC1₂, Pb(NO₃)₂, SnC1₂, and ZnC1₂), and were identified. Statistically significant associations between multiple antibiotic resistance and tolerance to Cu²⁺, Pb²⁺, and Zn ²⁺ were found among distribution water isolates but not raw water isolates. Significantly greater proportions of the raw water isolates were tolerant to A1³⁺ and Sn²⁺ and were not typically MAR. Tolerance to Cd²⁺ was not associated with the isolates from either water type or with multiple antibiotic resistance. Characteristic patterns of antibiotic resistance and metal tolerance were associated with various taxonomic genera and groups. Of the taxonomic types that were isolated from both raw and distribution waters, greater proportions of the distribution water isolates were resistant to more antibiotics and tolerant to more metals. Resistance to kanamycin and tolerance to Cu²⁺, Pb²⁺, and Zn²⁺ was typical among the distribution but not raw water Acinetobacter, Enterobacter, and Pseudomonas and Alcaligenes groups. The association of multiple antibiotic resistance with tolerance to Cu²⁺, Pb²⁺, and Zn²⁺ was significantly more prevalent among the isolates from near the end of the distribution system while the isolates from near the origin of the system typically expressed phenotypes more similar to those of the raw water isolates. To determine the impact of water treatment and distribution in the selection of MAR and MMT (multiple metal tolerant) SPC bacteria, a drinking water system serving an Oregon community of 40,000 was studied. On four dates, samples were obtained from the source water, treatment waters, distribution waters, and inner surfaces of water pipes. A total of 730 river, 290 flash mix tank, 359 clear well, 629 distribution water, and 298 pipe surface isolates were identified and tested for resistance to the isolates. Significantly greater proportions of the raw water isolates were tolerant to A1³⁺ and Sn²⁺ and were not typically MAR. Tolerance to Cd²⁺ was not associated with the isolates from either water type or with multiple antibiotic resistance. Characteristic patterns of antibiotic resistance and metal tolerance were associated with various taxonomic genera and groups. Of the taxonomic types that were isolated from both raw and distribution waters, greater proportions of the distribution water isolates were resistant to more antibiotics and tolerant to more metals. Resistance to kanamycin and tolerance to Cu ²⁺, Pb²⁺, and Zn²⁺ was typical among the distribution but not raw water Acinetobacter, Enterobacter, and Pseudomonas and Alcaligenes groups. The association of multiple antibiotic resistance with tolerance to Cu ²⁺, Pb²⁺, and Zn²⁺ was significantly more prevalent among the isolates from near the end of the distribution system while the isolates from near the origin of the system typically expressed phenotypes more similar to those of the raw water isolates. To determine the impact of water treatment and distribution in the selection of MAR and MMT (multiple metal tolerant) SPC bacteria, a drinking water system serving an Oregon community of 40,000 was studied. On four dates, samples were obtained from the source water, treatment waters, distribution waters, and inner surfaces of water pipes. A total of 730 river, 290 flash mix tank, 359 clear well, 629 distribution water, and 298 pipe surface isolates were identified and tested for resistance to the antibiotics and tolerance to the metals used in the first study, with the additions of carbenicillin and FeC1₃. Results indicated increases in the incidence of MAR and MMT bacteria when comparing river, treatment plant, and distribution water and pipe surface SPC populations. Distribution water isolates and isolates from inner pipe surfaces exhibited much greater associations of metal tolerance with multiple antibiotic resistance as compared to river isolates or treatment plant isolates. Pipe surface materials were shown to contain high concentrations of metals and large numbers of viable bacteria. The predominant metal tolerance phenotypes of these organisms reflected the metals present, since the copper pipe sample had a high level of Cu²⁺ tolerant bacteria while the galvanized iron pipe samples contained many Zn²⁺ tolerant bacteria. Similarities in taxonomic groups as well as in antibiotic and metal resistance patterns were observed in distribution water isolates and in bacteria from inner pipe surfaces. This suggested that bacteria colonizing pipe surfaces are shed into flowing distribution water.
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