Flocculation and Re-growth of Mycobacterium avium after ozone exposure
Abstract: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.
Document Type: Research Article
Publication date: 2007-01-01
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