ABSTRACT
AIMS: To assess low-pressure ultraviolet light (LP-UV) inactivation kinetics of Mycobacterium avium complex (MAC) strains in a water matrix using collimated beam apparatus. METHODS AND RESULTS: Strains of M. avium (n = 3) and Mycobacterium intracellulare (n = 2) were exposed to LP-UV, and log(10) inactivation and inactivation kinetics were evaluated. All strains exhibited greater than 4 log(10) inactivation at fluences of less than 20 mJ cm(-2). Repair potential was evaluated using one M. avium strain. Light repair was evaluated by simultaneous exposure using visible and LP-UV irradiation. Dark repair was evaluated by incubating UV-exposed organisms in the dark for 4 h. The isolate did not exhibit light or dark repair activity. CONCLUSIONS: Results indicate that MAC organisms are readily inactivated at UV fluences typically used in drinking water treatment. Differences in activation kinetics were small but statistically significant between some tested isolates. SIGNIFICANCE AND IMPACT OF THE STUDY: Results provide LP-UV inactivation kinetics for isolates from the relatively resistant MAC. Although UV inactivation of Mycobacterium species have been reported previously, data collected in this effort are comparable with recent UV inactivation research efforts performed in a similar manner. Data were assessed using a rigorous statistical approach and were useful towards modelling efforts.
Subject(s)
Disinfection/methods , Microbial Viability , Mycobacterium avium Complex/radiation effects , Mycobacterium avium/radiation effects , Ultraviolet Rays , Colony Count, Microbial , HumansABSTRACT
Three species of Bacillus were evaluated as potential surrogates for Bacillus anthracis for determining the sporicidal activity of chlorination as commonly used in drinking water treatment. Spores of Bacillus thuringiensis subsp. israelensis were found to be an appropriate surrogate for spores of B. anthracis for use in chlorine inactivation studies.
Subject(s)
Bacillus anthracis/drug effects , Bacillus anthracis/physiology , Bacillus cereus/drug effects , Bacillus cereus/physiology , Bacillus thuringiensis/drug effects , Bacillus thuringiensis/physiology , Chlorine/pharmacology , Colony Count, Microbial , Disinfection/methods , Spores, Bacterial/drug effects , Spores, Bacterial/growth & developmentABSTRACT
Drinking water regulations under the Final Coliform Rule require that total coliform-positive drinking water samples be examined for the presence of Escherichia coli or fecal coliforms. The current U.S. Environmental Protection Agency-approved membrane filter (MF) method for E. coli requires two media, an MF transfer, and a total incubation time of 28 h. A newly developed MF method, the MI agar method, containing indoxyl-beta-D-glucuronide and 4-methylumbelliferyl-beta-D-galactopyranoside for the simultaneous detection of E. coli and total coliforms, respectively, by means of their specific enzyme reactions, was compared with the approved method by the use of wastewater-spiked tap water samples. Overall, weighted analysis of variance (significance level, 0.05) showed that the new medium recoveries of total coliforms and E. coli were significantly higher than those of mEndo agar and nutrient agar plus MUG (4-methylumbelliferyl-beta-D-glucuronide), respectively, and the background counts were significantly lower than those of mEndo agar (< 5%). Generally, the tap water source, overall chlorine level, wastewater source, granular activated carbon treatment of the tap water, and method of grouping data by E. coli count for statistical analysis did not affect the performance of the new medium.
