1995 Volume 12 Issue 3 Pages 157-163
Fraser broth and HCLA (Hemolytic ceftazidime lithium chloride agar) were evaluated for the recovery of Listeria spp. and L. monocytogens. Fraser broth required 101-105 CFU/ml Listeria spp.for the development of a black color at 35°C for 24 hr. The efficacy of Fraser broth 24 hr incubation transfer from EB and EB 48 hr incubation was not different regardless of injury by testing experimentally contaminated, milk and cheese. Out of 301 naturally contaminated meats and meat environmental swabs tested, Fraser broth gave a false-positive rate of 16.0% and a false-negative rate of 1.6% for 24 hr incubation. However false-negative samples were blackend by 48 hr. 100% (50/50) of L. monocytogenes colonies on HCLA were easily distinguished by narrow zone of β-hemolysis from the samples inoculated L. monocytogenes and L. innocua simultaneously for 24 hr incubation. HCLA recovered L. monocytogenes in 100% of 139 meats and meat environmental naturally contaminated samples without false-positives or false-negatives for 24 hr incubation. When use in combination with Fraser broth and HCLA, The judgement for Listeria-free is obtained by 3 days. And the presence of L. monocytogenes is known for 3-4 days.
