Effect of nisin on growth boundaries of Listeria monocytogenes Scott A, at various temperatures, pH and water activities.
The effect of nisin on growth boundaries of Listeria monocytogenes Scott A in Tryptone Soy Broth (TSB) under different a(w)s, pH, and temperatures was studied. Growth/no growth turbidity data was modeled using logistic regression. Combinations of various temperatures (5-35 degrees C), pH (4.05-6.70) adjusted with HCl, a(w)s (0.937-0.998) NaCl (0.5-10.5%) and nisin (0-100 IU/ml) were used to monitor the growth/no growth response of L. monocytogenes Scott A for 60 days. The concordance of the logistic regression model was 99.4%, indicating successful data fitting. The minimum pH at which growth was observed was 4.81 at the temperature range of 25-35 degrees C and at a(w) as high as 0.992. Growth was observed at a(w) as low as 0.937, at pH 6.7, at the temperature range of 25-35 degrees C. Increasing nisin concentrations above 25 IU/ml resulted in a more inhibitory environment for L. monocytogenes. Presence of 100 IU/ml resulted in a minimum pH for growth at 5.20, and a minimum a(w) at 0.967 at the temperature range of 25-35 degrees C. It was remarkable that low to medium salt concentrations (2.5-4.5 NaCl% w/v) provided a protective effect against inhibition of L. monocytogenes by nisin. The present study points out the applicability of growth/no growth modeling in order to study any interactions between various factors affecting initiation of growth of micro-organisms, in which its turn helps the understudying of microbe-food ecosystem relations and the development of safer food.
Boziaris
I S
IS
Laboratory of Microbiology and Biotechnology of Foods, Department of Food Science and Technology, Agricultural University of Athens, Votanikos, Greece.
Nychas
G-J E
GJ
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000254:growth & development*; D016015:Logistic Models; D008954:Models, Biological; D009561:Nisin / Q000494:pharmacology*; D013696:Temperature; D014867:Water / Q000378:metabolism
D000900:Anti-Bacterial Agents; D014867:Water; D009561:Nisin