also inhibited strains of L. monocytogenes serogroup 1, however, NP117, 325 and 6-165
inhibited only strains of L. monocytogenes serogroup 4. The number of growth inhibited
strains in L. monocytogenes serogroup 4 was significantly larger than in serogroups 1 and
3. The effects of generation times of the two Listeria species in the combinations were
evaluated at three different incubation times during culture. L. monocytogenes could not be
isolated at 24 h from 12/52 (23.1%), at 48 h from 24/52 (46.2%), and at 7 days from 30/52
(57.7%) combinations after enrichment culture. L. monocytogenes showed a faster
generation time in 31/52 combinations, while L. innocua showed a faster generation time
in the remaining 21/52 combinations. No statistically significant differences could be
related to the generation times of either of the Listeria species when cultured in 31
combinations with L. monocytogenes generation times less than L. innocua and 21
combinations with the L. monocytogenes generation times greater than L. innocua. In the
enrichment cultures of 31 combinations that showed a faster generation time for L.
monocytogenes, at 24 h 7/31 (22.6%) cultures were negative for L. monocytogenes, at 48 h
15/31 (48.9%), and at 7 days 16/31 (51.6%) were negative. In the remaining 21
combinations, 5/21 (23.9%) failed to yield L. monocytogenes at 24 h, 9/21 (42.9%) were
negative at 48 h and at 7 days 14/21 (66.7%) were negative.