Influence of the adaptation of Listeria monocytogenes populations to structured or homogeneous habitats on subsequent growth on chilled processed meat.
The influence of adaptation to habitat structure on the growth of Listeria monocytogenes on processed meats was investigated. Triplicate populations of each of two L. monocytogenes strains were adapted to growth in homogeneous (Tryptic Soy Broth, TSB) or structured (Tryptic Soy Agar) environments by serial transfer in these media incubated at 25 degrees C for 48 h. Adapted (serial transfer for 56 days) and unadapted control (single 48 h growth period) populations were inoculated onto the surface of bologna or farmers' sausage disks, vacuum packaged and stored at 4 degrees C for 4 weeks. Initially and after 4 weeks, L. monocytogenes numbers were determined on Modified Oxford Agar incubated at 25 degrees C for 48 h. Control populations of both strains grown in the structured habitat reached significantly higher levels (1-1.5 log cfu g(-1), P<0.05) on both products than their counterparts grown in homogeneous habitat. Populations of both strains adapted to homogeneous habitats grew to significantly higher levels (0.4-1 log cfu g(-1), P<0.05), while those adapted to growth in structured habitats grew to significantly lower levels (0.3-1 log cfu g(-1), P<0.05), on both products as compared to their unadapted control populations. Populations of both strains adapted to homogeneous habitats grew to significantly higher levels (0.2 to 0.5 log cfu g(-1), P<0.05) on farmers' sausage, and significantly lower levels (0.2 to 0.4 log cfu g(-1), P<0.05) on bologna, than those adapted to structured habitats. Habitat adaptation affected L. monocytogenes growth on processed meats, but the practical significance and reasons for these findings were not established.
Dykes
Gary A
GA
Saskatchewan Food Product Innovation Program, Department of Applied Microbiology and Food Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK, Canada S7N 5A8. gary.dykes@foodscience.afisc.csiro.au
D000222:Adaptation, Physiological; D000818:Animals; D015169:Colony Count, Microbial; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods; D008089:Listeria monocytogenes / Q000254:growth & development / Q000502:physiology*; D008461:Meat Products / Q000382:microbiology*; D013696:Temperature; D013997:Time Factors; D014618:Vacuum