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Heat inactivation of Mycobacterium avium-Mycobacterium intracellulare complex organisms in aqueous suspension
Abstract:
Isolants from swine and from humans representing serotypes 1, 2, 4, 8, and 10 of the Mycobacterium avium-Mycobacterium intracellulare complex were compared for heat tolerance in aqueous suspension. The most heat-resistant isolant found was a serovar 10 isolated from a human. This isolant was examined further to determine the rate of kill at various temperatures and pH's, the effect of meat protein and fat, and the effect of nitrite. Kill rates were not significant at 60 degrees C or below. Decimal reduction values were 4 min or less at 65 degrees C and 1.5 min or less at 70 degrees C. Kill rates were slightly higher at pH values of 6.5 and 7.0 than at 5.5 or 6.0. the water-soluble fraction of wiener emulsion did not alter kill rates, but the saline-soluble fraction protected the organism somewhat. Fat did not affect the survival of the organisms except to eliminate the protective effect of saline extract when the suspension contained 50% fat. The addition of sodium nitrite to the suspension did not alter the heat sensitivity of the organisms.
Insights
Heat resistance of Mycobacterium avium-intracellulare complex (MAIC) varied by serotype and source. A human-derived serovar 10 MAIC showed the highest heat resistance, with significant kill rates only above 60°C.
Area of Science:
- Microbiology
- Food Safety
- Bacterial Pathogenesis
Background:
- The Mycobacterium avium-intracellulare complex (MAIC) is an opportunistic pathogen found in environmental and food sources.
- Understanding MAIC heat tolerance is crucial for food safety and preventing human infections.
Purpose of the Study:
- To compare the heat tolerance of MAIC isolates from swine and humans.
- To determine the thermal inactivation kinetics of the most heat-resistant MAIC isolate.
- To investigate factors influencing MAIC heat resistance, including pH, meat components, and nitrite.
Main Methods:
- Comparison of heat resistance in aqueous suspension for MAIC serotypes 1, 2, 4, 8, and 10 from swine and humans.
- Determination of decimal reduction values (D-values) at various temperatures (≥60°C).
- Assessment of MAIC survival under different pH conditions and in the presence of meat protein, fat, and sodium nitrite.
Main Results:
- A human-derived serovar 10 MAIC isolate exhibited the highest heat resistance.
- Significant kill rates were observed only at temperatures above 60°C, with D-values ≤4 min at 65°C and ≤1.5 min at 70°C.
- Higher kill rates were noted at pH 6.5-7.0 compared to pH 5.5-6.0. Meat fat and saline-soluble fractions offered some protection, while nitrite had no effect.
Conclusions:
- MAIC serovar 10 from humans is notably heat-resistant.
- Standard pasteurization temperatures may not be sufficient to eliminate certain MAIC strains.
- Food processing parameters like pH and fat content can influence MAIC inactivation, necessitating careful control for effective pathogen reduction.