Heat susceptibility of aquatic mycobacteria

Abstract

An investigation was carried out to measure the heat susceptibility of opportunistic mycobacteria frequently isolated from domestic water supply systems. The study was conducted under standardized conditions designed to resemble those found in oligotrophic aquatic habitats. Strains of the following species were tested: Mycobacterium avium, M. chelonae, M. fortuitum, M. intracellulare, M. kansasii (two strains), M. marinum, M. phlei, M. scrofulaceum, and M. xenopi. Suspensions of the test strains were exposed to temperatures of 50, 55, 60, and 70°C; samples were taken at defined intervals to determine the concentration of survivors. From these data, the decimal reduction times were calculated for each test strain and test temperature. The results indicate that M. kansasii is more susceptible to heat than Legionella pneumophila, whereas the heat susceptibilities of M. fortuitum, M. intracelulare, and M. marinum lie in the same order of magnitude as that of L. pneumophila. The strains of M. avium, M. chelonae, M. phlei, M. scrofulaceum, and M. xenopi were found to be more thermoresistant than L. pneumophila, with the highest resistance being found in M. xenopi. Thermal measures to control L. pneumophila may therefore not be sufficient to control the last five mycobacterial species in contaminated water systems.

Mycobacteria in drinking water distribution systems: ecology and significance for human health

“…This is in accordance with the results of Schulze-Rö bbecke and Buchholtz [300], who found a D 70 value forM. avium of 2.3 s. Schulze-Rö bbecke and Buchholtz [300] concluded from their heat resistance study that thermal measures to control L. pneumophila may not be sufficient to control M. avium, M. chelonae, M. phlei, M. scrofulaceum and M. xenopi in contaminated water systems. In order to reduce the presence of legionellae in hot water distribution systems, it is recommended that hot water should be stored at 60°C and distributed such that a temperature of at least 50°C and preferably 55°C is achieved within one minute at outlets [301].…”

“…Two strains of M. avium and L. pneumophila were killed within 3 min during exposure to hot water at 70°C [294]. This is in accordance with the results of Schulze-Rö bbecke and Buchholtz [300], who found a D 70 value forM. avium of 2.3 s. Schulze-Rö bbecke and Buchholtz [300] concluded from their heat resistance study that thermal measures to control L. pneumophila may not be sufficient to control M. avium, M. chelonae, M. phlei, M. scrofulaceum and M. xenopi in contaminated water systems.…”

“…D 65 values of 4 min or less and D 70 values of 1.5 min or less were found for MAC (swine and human isolates) in phosphate buffer [299]. Schulze-Rö bbecke and Buchholtz [300] found a D 50 value of almost 17 h for M. avium DSM 43216 in sterile water with standardized hardness. At 55°C, a D value of approximately 6 h and 53.5 min was found for M. xenopi NCTC 10042 and M. avium DSM 43216, respectively.…”

Survival of Mycobacterium ulcerans at 37°C

“…For this reason, African strains might be expected to tolerate prolonged incubation at 37°C. Schulze-Rö bbecke and Buchholtz [7] found a D value of 2.33 days at 37°C for a Mycobacterium marinum strain from Philadelphia, USA, which is comparable to the values obtained in the present study for isolates from non-tropical regions (average 3.33 days).…”

“…The slope of the inactivation curves was expressed as decimal reduction time (D), measuring heat resistance and the time needed to inactivate 90% of the bacterial population at a given temperature. A higher D value thus indicates a greater thermotolerance [6,7]. Table 1 shows that a decrease in viability occurred for all isolates after a few days at 37°C, but with large variations for individual isolates.…”