title: Acid and NaCl limits to growth of Listeria monocytogenes and influence of sequence of inimical acid and NaCl levels on inactivation kinetics.
abstract: Variability in growth limits of Listeria monocytogenes in response to low pH (adjusted with HCl) or high salinity (NaCl) was evaluated for 127 strains in brain heart infusion broth at 25 degrees C. Over 95% of strains habituated at pH 5.0 grew subsequently at pH 4.2, while 25% were able to grow at pH 4.1. More than 85% of strains preadapted to growth at 8.5% NaCl (wt/vol) subsequently grew in the presence of 11.3% NaCl, while 25% were able to grow at 13% NaCl, and 4.7% grew in the presence of 13.9% NaCl. The results extend the generally accepted growth limits for L. monocytogenes in response to these hurdles. Two strains, one of which was relatively tolerant of both hurdles, and another that was less tolerant of both hurdles, were subjected to different sequences of lethal acid (pH 3.5) and NaCl (14%, wt/vol) stresses to determine whether survival was affected by growth limits, or by sequence of application of treatment. There was no significant difference in the inactivation kinetics of the two strains, but inactivation rates were affected by different treatments. For both strains, the inactivation rates, from fastest to slowest, resulted from: (i) lethal pH and then by lethal water activity, or lethal water activity and then by lethal pH; (ii) lethal pH and water activity applied simultaneously; (iii) lethal pH; and (iv) lethal water activity. The results demonstrated that the sequence of lethal stress application strongly influences L. monocytogenes inactivation, and that L. monocytogenes growth limits are not good predictors of survival in inimical environments.
authors.affiliation: Tasmanian Institute of Agricultural Research, School of Agricultural Science, University of Tasmania, Private Bag 54, Hobart, Tasmania 7001, Australia. L.Shabala@utas.edu.au
authors.forename: Lana
authors.initials: L
authors.lastname: Shabala
authors.forename: Shih Hui
authors.initials: SH
authors.lastname: Lee
authors.forename: Pauline
authors.initials: P
authors.lastname: Cannesson
authors.forename: Tom
authors.initials: T
authors.lastname: Ross
mesh_terms: D000143:Acids / Q000494:pharmacology*; D000222:Adaptation, Physiological; D015169:Colony Count, Microbial; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D005506:Food Contamination / Q000032:analysis / Q000517:prevention & control; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008089:Listeria monocytogenes / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology*; D008954:Models, Biological; D009994:Osmolar Concentration; D012965:Sodium Chloride / Q000494:pharmacology*
chemical_list: D000143:Acids; D003470:Culture Media; D012965:Sodium Chloride