Protein profile changes in acid adapted Listeria monocytogenes exhibiting cross-protection against an activated lactoperoxidase system in tryptic soybroth

Foodborne pathogens often tolerate and survive environmental stress conditi ons including extreme acidity to varying degrees. One possible reason for t his survival may be the production of protective stress proteins during aci d shock (ASR) and/or tolerance (ATR) responses. The ASR and ATR of Listeria monocytogenes strains V7, V37 and CA in tryptic say broth without dextrose acidified with lactic acid were studied. Possible cross-protection of acid adapted cells against an activated lactoperoxidase system was also determi ned. The strains were either directly challenged at pH 4.0 and 3.5 to study their ASR or initially adapted at pH 5.5 for the equivalent of I generatio n before challenging at pH 4.0 and 3.5 to study their A TR. Adapted and non adapted cells were challenged at pH 4.5 with or without an activated lactop eroxidase system. In all cases viability was determined by enumeration over a period of 24 or 48 h after challenge and the production of stress protei ns analyzed by 2-dimensional gel electrophoresis. While there were some dif ferences in the survival responses for each strain, the acid adapted cells of each strain survived to a greater degree than nonadapted cells at both p H 4.0 (at least 10 fold at 24 h) and pH 3.5 (at least 1000 fold at d h) but not at pH 4.5. The acid adapted cells exposed to the lactoperoxidase syste m survived better (at least 5-fold) than their nonadapted counterparts far all 3 strains at 24 ann 48 h. The 2-dimensional gel analysis for all 3 stra ins showed that the adapted and nonadapted cells underwent a change in thei r physiology, (at pH 4.0 compared to the control at pH 7.0, at pH 4.5 with the addition of lactoperoxidase system components) in that there was induct ion as well as repression of several proteins.