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Effect of inoculum size on the combined temperature, pH and aw limits for growth of Listeria monocytogenes.
Int J Food Microbiol. 2005 Sep 25; 104(1):83-91.IJ

Abstract

The growth/no growth responses of Listeria monocytogenes inoculated at four levels (0.90, 2.58, 4.20 and 6.81 log cfu/well; 300 microl medium/well) into tryptic soy broth (TSB) were monitored at different combinations of temperature (4 to 30 degrees C), pH (3.76 to 6.44) and aw (0.888 to 0.997) for 60 days. The study was conducted in 96-well microtiter plates and growth was monitored visually and by recording the turbidity of the medium with an automated microplate reader. The growth limits of the pathogen and hence the position of the growth boundary were found to be affected by the size of the inoculum. For example, at 25 degrees C and aw 0.997 the minimum pH values that allowed growth were 4.45 and 3.94 for inoculum levels of 0.90 and 6.81 log cfu/well, respectively. Similarly, at 25 degrees C and pH 6.44 the minimum aw values where growth was observed ranged from 0.900 to 0.928 depending on the inoculum level. The results showed that at temperatures from 10 to 30 degrees C the difference in the growth limits between the tested inoculum levels was higher in environments where a single factor (pH or aw) was inhibitory than in environments where pH and aw together were inhibitory. The data were used to develop a growth/no growth interface model for each inoculum level tested, using logistic polynomial regression. The concordance indices of the models ranged from 99.8% to 99.9% and showed a good fit to the observed data in all models. This study indicates the importance of inoculum size for microbial growth initiation and provides quantitative data that show how the combinations of hurdles which prevent growth vary with inoculum size.

Authors+Show Affiliations

Koutsoumanis KP
Center for Red Meat Safety, Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523-1171, USA.
Sofos JN
No affiliation info available

MeSH

Colony Count, MicrobialFood ContaminationFood MicrobiologyFood PreservationHydrogen-Ion ConcentrationListeria monocytogenesLogistic ModelsModels, BiologicalTemperatureWater

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

16005535

Citation

Koutsoumanis, Konstantinos P., and John N. Sofos. "Effect of Inoculum Size On the Combined Temperature, pH and Aw Limits for Growth of Listeria Monocytogenes." International Journal of Food Microbiology, vol. 104, no. 1, 2005, pp. 83-91.
Koutsoumanis KP, Sofos JN. Effect of inoculum size on the combined temperature, pH and aw limits for growth of Listeria monocytogenes. Int J Food Microbiol. 2005;104(1):83-91.
Koutsoumanis, K. P., & Sofos, J. N. (2005). Effect of inoculum size on the combined temperature, pH and aw limits for growth of Listeria monocytogenes. International Journal of Food Microbiology, 104(1), 83-91.
Koutsoumanis KP, Sofos JN. Effect of Inoculum Size On the Combined Temperature, pH and Aw Limits for Growth of Listeria Monocytogenes. Int J Food Microbiol. 2005 Sep 25;104(1):83-91. PubMed PMID: 16005535.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effect of inoculum size on the combined temperature, pH and aw limits for growth of Listeria monocytogenes. AU - Koutsoumanis,Konstantinos P, AU - Sofos,John N, PY - 2004/07/09/received PY - 2004/11/27/revised PY - 2005/01/10/accepted PY - 2005/7/12/pubmed PY - 2005/11/8/medline PY - 2005/7/12/entrez SP - 83 EP - 91 JF - International journal of food microbiology JO - Int J Food Microbiol VL - 104 IS - 1 N2 - The growth/no growth responses of Listeria monocytogenes inoculated at four levels (0.90, 2.58, 4.20 and 6.81 log cfu/well; 300 microl medium/well) into tryptic soy broth (TSB) were monitored at different combinations of temperature (4 to 30 degrees C), pH (3.76 to 6.44) and aw (0.888 to 0.997) for 60 days. The study was conducted in 96-well microtiter plates and growth was monitored visually and by recording the turbidity of the medium with an automated microplate reader. The growth limits of the pathogen and hence the position of the growth boundary were found to be affected by the size of the inoculum. For example, at 25 degrees C and aw 0.997 the minimum pH values that allowed growth were 4.45 and 3.94 for inoculum levels of 0.90 and 6.81 log cfu/well, respectively. Similarly, at 25 degrees C and pH 6.44 the minimum aw values where growth was observed ranged from 0.900 to 0.928 depending on the inoculum level. The results showed that at temperatures from 10 to 30 degrees C the difference in the growth limits between the tested inoculum levels was higher in environments where a single factor (pH or aw) was inhibitory than in environments where pH and aw together were inhibitory. The data were used to develop a growth/no growth interface model for each inoculum level tested, using logistic polynomial regression. The concordance indices of the models ranged from 99.8% to 99.9% and showed a good fit to the observed data in all models. This study indicates the importance of inoculum size for microbial growth initiation and provides quantitative data that show how the combinations of hurdles which prevent growth vary with inoculum size. SN - 0168-1605 UR - https://www.unboundmedicine.com/medline/citation/16005535/Effect_of_inoculum_size_on_the_combined_temperature_pH_and_aw_limits_for_growth_of_Listeria_monocytogenes_ DB - PRIME DP - Unbound Medicine ER -