The effect of temperature and pH on the motility of Listeria sp. J. Islamic Acad. Sci (original) (raw)
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Journal of Applied Microbiology, 1990
Factorially designed experiments have been used to study the growth and survival of Listeria monocytogenes in different combinations of pH and salt concentrations at ambient and chill temperatures. Survival at low pH and high salt concentration was strongly temperature dependent. The minimum pH values that allowed survival after 4 weeks from an initial 104 cells were 4·66 at 30†C, 4·36 at 10†C and 4·19 at 5†C. These limits were salt dependent, low (4–6%) salt concentrations improved and higher concentrations reduced survival at limiting pH values. The lowest pH that allowed a 100-fold increase in cell numbers within 60 d was 4·66 at 30†C but this was increased to 4·83 at 10†C. At 5†C growth occurred at pH 7·0 but not at pH 5·13. Simple predictive models describing the effect of hydrogen-ion and salt concentration on the time for at least a 100-fold increase in numbers at 10†C and 30†C were constructed after analysis of the results for a least squares fit to a quadratic model. The interactions between salt and hydrogen-ion concentration on growth were found to be purely additive.
Listeria ivanovii and L. monocytogenes, are the only pathogenic species of the genus Listeria and share many virulence factors and mechanisms of pathogenicity. L. ivanovii shows host tropism towards small ruminants and rodents and much lower virulence for humans compared to L. monocytogenes. However, severe infections caused by L. ivanovii, resulting in bacteremia, abortion and stillbirth, occasionally occurred in immunocompromised persons and in pregnant women, while in immunocompetent hosts L. ivanovii can cause gastroenteritis. In this review the updated knowledge on virulence aspects and distribution of L. ivanovii in the environment and in food are summarized. Recent research on its virulence characters at genome level gave indications on how pathogenicity evolved in this bacterial species. As for L. monocytogenes, L. ivanovii infections occur after the ingestion of contaminated food, so an overview of reports regarding its distribution in the food products was carried out to o...
Long Term Survival of Listeria monocytogenes in Stress Conditions: High pH and Salt Concentrations
Journal of Research in Medical and Dental Science, 2018
Background: Listeria monocytogenes is a bacterium that is transmitted by food. This bacterium is the cause of Listeria disease, which causes severe symptoms such as meningitis, septicemia and abortion. Determination of the effect of different conditions such as pH, salt and temperature on survival of L. monocytogenes in food seems essential. Methods: A standard strain of L. monocytogenes (ATCC: 19115) was used for this study. The bacteria was added in the concentration of 3 × 108 CFU/ml, to BHI broth medium at pH=4, 5, 6 and 7 and salt concentrations of 0, 7%, 14% and 21%. Temperature was 4°C and 20°C. Samples were collected every 24 hours from the cultured mediums in a special environment of PALCAM agar. This will be done until no colonies grow on the PALCAM agar environment. Results: The effect of independent variable of storage temperature alone on the survival rate of L. monocytogenes in the level of 5% is not significant. Also, the increase in salt concentrations and pH togethe...
Journal of Food Protection, 1989
The effects and interactions of temperature (5, 19, 28, 37°C), initial pH (6.0 and 7.5), atmosphere (aerobic and anaerobic), sodium chloride content (0.5 and 4.5%), and sodium nitrite concentration (0, 50, 100, 200, 1000 μg/ml) on the growth of Listeria monocytogenes Scott A were determined using Tryptose Phosphate Broth. Growth data were analyzed by regression analysis to generate “best-fit” Gompertz equations, which were used subsequently to calculate lag phase duration, exponential growth rate, generation time, and maximum population density values. The data indicated that the growth kinetics of L. monocytogenes was dependent on the interaction of the five variables, particularly in regard to exponential growth rates and lag phase durations. The data suggest that sodium nitrite can have significant bacteriostatic activity against L. monocytogenes and may provide cured meats with a degree of protection against this microorganism, particularly if employed in conjunction with a comb...
The genus Listeria is currently comprised of 17 species, including 9 Listeria species newly described since 2009. Genomic and phenotypic data clearly define a distinct group of six species (Listeria sensu strictu) that share common phenotypic characteristics (e.g., ability to grow at low temperature , flagellar motility); this group includes the pathogen Listeria monocytogenes. The other 11 species (Listeria sensu lato) represent three distinct monophyletic groups, which may warrant recognition as separate genera. These three proposed genera do not contain pathogens, are non-motile (except for Listeria grayi), are able to reduce nitrate (except for Listeria floridensis), and are negative for the Voges-Proskauer test (except for L. grayi). Unlike all other Listeria species, species in the proposed new genus Mesolisteria are not able to grow below 7 °C. While most new Listeria species have only been identified in a few countries, the availability of molecular tools for rapid characterization of putative Listeria isolates will likely lead to future identification of isolates representing these new species from different sources. Identification of Listeria sensu lato isolates has not only allowed for a better understanding of the evolution of Listeria and virulence characteristics in Listeria but also has practical implications as detection of Listeria species is often used by the food industry as a marker to detect conditions that allow for presence, growth, and persistence of L. monocytogenes. This review will provide a comprehensive critical summary of our current understanding of the characteristics and distribution of the new Listeria species with a focus on Listeria sensu lato.
Journal of food protection, 2003
Twenty-one Listeria monocytogenes strains belonging to three different genotypic lineages were evaluated for differences between lineages and between individual strains with respect to thermal inactivation, growth, and survival. Three sets of heat inactivation conditions (60 degrees C, pH 6.0, and 0.5 M lactate; 55 degrees C, pH 6.0, and 0.5 M lactate; and 50 degrees C, pH 4.0, and 0.5 M lactate) were used on strains grown in modified brain heart infusion (BHI) broth with and without glucose. Two sets of growth conditions (35 degrees C, pH 6.5, and 0.1 M lactate and 5 degrees C, pH 6.5, and 0.1 M lactate) were used with modified BHI broths to determine lag phases and exponential growth rates. Two sets of conditions (28 degrees C, pH 4.0, and 1 M lactate and 28 degrees C, pH 4.5, and 0.5 M lactate) were used with modified BHI broth to determine survival times (D-values). Thermal inactivation D-values were consistently lowest for lineage III, but differences were not significant for a...