Disinfectant Susceptibility of Mycobacterium avium
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Mycobacterium avium, an opportunistic human pathogen, infects between 25 and 50% of advanced-stage acquired immuno-deficiency syndrome (AIDS) patients in the United States. M. avium has been isolated from many environmental sources including: natural waters, soils, and aerosols. M. avium has also been recovered from within municipal and hospital drinking water systems. Rhesus macaques (Macaca mulatta) infected with the simian HIV analog, SIV, have been shown to acquire M. avium infections from potable water.
Reduced-aggregate fractions (cell suspensions free of large aggregates) of Mycobacterium avium were exposed to chlorine, monochloramine, chlorine dioxide, and ozone and kinetics of disinfection measured. Chlorine disinfection kinetics was also measured in M. avium cultures grown in biofilms.
M. avium exhibited a high resistance to chlorine compared to E. coli. M. avium CT99.9% (disinfectant concentration x time to 3 logs cell inactivation) values were between 571- and 2318 -times those of E. coli. Clinical isolates of M. avium showed 0.24 and 2.5-fold increase in resistance to chlorine compared to their pulsed-field-gel-electrophoresis- (PFGE) matched environmental isolates.
M. avium strains exhibited a mixed response to exposure to monochloramine. The CT99.9% values of three strains (2 clinical, 1 environmental) were between 6.3- and 23.5- times that of E. coli. Two strains (1 clinical, 1 environmental) exhibited CT99.9% values approximately the same as E. coli, a difference from all the other disinfectants which were much less effective on M. avium than on E. coli.
M. avium strains exhibited a high resistance to chlorine dioxide when compared to E.coli. M. avium CT99.9% values of between 133- and 706- times higher that that of E. coli. In the paired isolates tested, the clinical isolate was 5.3 times more resistant than the matched environmental isolate.
M. avium exhibited a high resistance to ozone when compared to E. coli. M. avium strains exhibited a CT99.9% value of between 52 and 90 times higher that that of E. coli. In the paired isolates tested, the clinical isolate was nearly identical as judged by CT99.9% values. M. avium strain 5002 exhibited an unusual disinfection kinetics curve. Disinfection rate increased by a non-logarithmic factor, indicating that inactivation efficiency was increasing over time.
M. avium strain 1060 showed between a 17% decrease to a 265% increase in CT99.9% value when grown as biofilms as opposed to suspension. Due to the large variance in biofilm density and and CT99.9% values, any conclusions based on these experiments should be considered tentative at best.
M. avium's resistance to chlorine and chlorine dioxide approaches that of the protozoan cysts of Giardia muris and Entamoeba hystolytica. M. avium is much less resistant, relatively, to monochloramine possessing values similar to E. coli. Ozone resistance of M. avium is two orders of magnitude greater than E. coli and one order of magnitude of less than G. muris cysts.
A critical concentration threshold level for chlorine dioxide was found. That is, there was no linear relationship between concentration of chlorine dioxide and cell inactivation. Initial experiments using a range of concentrations from 0.1 ppm to 0.5 ppm chlorine dioxide showed a biphasic curve with the inflection point (indicating the critical concentration) between 0.3 and 0.4 ppm chlorine dioxide.
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