10/18/2017 Characteristics of Listeria Listeria monocytogenes Joseph Lister invented Differs from most other pathogens medical disinfection and Widely distributed in nature had a mouthwash and Genus Resistant to adverse environmental named after him conditions Nonpathogenic species are isolated from the same foods and environments as L. Psychotrophic and grows in human monocytogenes macrophages Thirteen serotypes of L.monocytogenes Survives for a long time in or on food, Three serotypes predominate in listeriosis soil,plants,surfaces patients Unclear:the illness is severe but making PulseNet established by the CDC helps all food Listeria free is unrealistic identify strains by DNA fingerprints Susceptibility to physical and Susceptibility to physical and chemical agents chemical agents ·Listeria monocytogenes grows from O°C Survives but does not grow at a pH to 45C but grows slowly at cold below 4.3 temperature Organic acids,such as acetic,citric and Freezing does not reduce the numbers lactic acids,inhibit growth Killed at temps greater than 50C Grows best at water activity of greater Temperature (C)Doubling time than 0.97 and survives at water activity growth (hours) of0.83 4 43 10 6.6 Heat resistance increases as the water 37 activity decreases 10/18/2017 4 Listeria monocytogenes • Differs from most other pathogens • Widely distributed in nature • Resistant to adverse environmental conditions • Psychotrophic and grows in human macrophages • Survives for a long time in or on food, soil, plants, surfaces • Unclear: the illness is severe but making all food Listeria free is unrealistic Characteristics of Listeria • Joseph Lister invented medical disinfection and had a mouthwash and Genus named after him • Nonpathogenic species are isolated from the same foods and environments as L. monocytogenes • Thirteen serotypes of L. monocytogenes • Three serotypes predominate in listeriosis patients • PulseNet established by the CDC helps identify strains by DNA fingerprints Susceptibility to physical and chemical agents • Listeria monocytogenes grows from 0oC to 45oC but grows slowly at cold temperature • Freezing does not reduce the numbers • Killed at temps greater than 50oC Temperature (oC ) Doubling time – growth (hours) 4 43 10 6.6 37 1.1 Susceptibility to physical and chemical agents • Survives but does not grow at a pH below 4.3 • Organic acids, such as acetic, citric and lactic acids, inhibit growth • Grows best at water activity of greater than 0.97 and survives at water activity of 0.83 • Heat resistance increases as the water activity decreases