Flocculation and Re-growth of Mycobacterium avium after ozone exposure
In bench scale reactors dispersed Mycobacterium avium (M. avium) cells rapidly flocculated into aggregates containing hundreds of cells when exposed to ozone in phosphate buffered waters containing 3 mM carbonate alkalinity at pH 6.6 and 7°C. The flocculation response of M. avium cells after ozone exposure was identified using phase contrast and epi-flourescent microscopy. Batch reactors were inoculated with 107 colony forming units per milliliter (CFU/ml) of M. avium and after complete mixing dosed with initial ozone concentrations of 1 and 2 mg/L. M. avium could not be recovered from ozone quenched samples taken from the reactors on Middlebrooks 7H11 agar plates after a CT of 2 mg min L−1. Reactors placed in incubators at 22°C for 5 days after greater than 2 mg min L−1 ozone exposure demonstrated re-growth of M. avium at concentrations of 104 CFU/ml on Middlebrooks 7H11 agar plates. Re-growth of M. avium was confirmed by epi-flourescent microscopy. Nutrient media was not added to the batch reactors after ozone disinfection. The flocculation response observed using epi-flourescent microscopy may provide a protective mechanism against ozone disinfection allowing M. avium to re-grow in what appeared to be completely disinfected batch reactors.
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Document Type: Research Article
Publication date: 2007-01-01
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