Can food-related environmental factors induce different behaviour in two key serovars, 4b and 1/2a, of Listeria monocytogenes?

Listeria monocytogenes isolates (81 in total; 42 isolated from cases of hum an listeriosis; 39 isolated from food), belonging to serovars 1/2a or 4b, w ere studied for any group differences between serovars to selected factors associated with foods (two bacteriocins and mild heat treatment). growth ki netics at 37 degreesC and pathogenicity for chick embryos. The isolates wer e tested for sensitivity to two bacteriocins at 4 degreesC and 37 degreesC, and were tested for the remaining parameters both before and after exposur e to cold storage (4 degreesC) with starvation. In addition, the isolates w ere typed using pulsed field gel electrophoresis (PFGE), multilocus enzyme electrophoresis (MEE) and phage typing to find any correlation between the types and group differences in the chosen parameters. Considerable strain d iversity within each L. monocytogenes serovar with respect to the chosen pa rameters was observed, especially after exposure to cold storage. Neverthel ess, the serovar 1/2a isolates, as a group, tended to be more resistant to the two antilisterial bacteriocins at 4 degreesC than the group of serovar 4b isolates. In contrast, after cold storage at 4 degreesC, L. monocytogene s serovar 4b isolates, as a group, tended to be more resistant to heat trea tment at 60 degreesC than the group of 1/2a isolates. In addition, the sero var 4b group tended to have shorter lag phases and higher pathogenicity, wh en transferred from cold storage to body temperature (37 degreesC), than th e group of serovar 1/2a isolates. No correlation between PFGE-, MEE- and ph age-types and the tested parameters was found. Although the above serovar-r elated differences were observed only when mean values of the groups were c ompared (not all isolates within each group followed the group pattern), th e results indicate interesting directions for further research. (C) 2001 El sevier Science B.V. All rights reserved.