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A low-pathogenicity isolate of Listeria monocytogenes from cow’s milk,as screened in mouseand chicken embryonated egg models,was examined for virulence-related phenotypic traits.Correspondingvirulence genes (iap,prfA,plcA,hly,mpl,actA,plcB,InlA and InlB) were compared with L.monocytogenesreference strains 10403S and EGD to elucidate the possible molecular mechanisms of low virulence.Al-though L.monocytogenes H4 exhibited similar patterns to strain 10403S in terms of hemolytic activity,invitro growth and invasiveness and even had higher adhesiveness,faster intracellular growth and higherphospholipase activity in vitro,it was substantially less virulent than the strain 10403S in mouse and chickenembryo models (50% lethal dose:10~(8.14) vs.10~(5.49) and 10~(6.73) vs.10~(1.9),respectively).The genes prfA,plcA andmpl were homologous among L.monocytogenes strains H4,10403S and EGD (>98%).Genes iap,hly,plcB,InlA and InIB of L.monocytogenes 10403S had higher homology to those of strain EGD (>98%) than isolateH4.The homology of the gene hly between strain 10403S and isolate H4 was 96.9% at the nucleotide level,but 98.7% at the amino acid level.The actA gene of isolate H4 had deletions of 105 nucleotides correspondingto 35 amino acid deletions falling Within the proline-rich region.Taken together,this study presents someclues as to reduced virulence to mice and chicken embryos of the isolate H4 probably as a result of deletionmutations of actA.
A low-pathogenicity isolate of Listeria monocytogenes from cow’s milk, as screened in mouse and chicken embryonated egg models, was examined for virulence-related phenotypic traits. Coactiveding virulence genes (iap, prfA, plcA, hly, mpl, actA, plcB, InlA and InlB ) were compared with L. monocytogenesreference strain 10403S and EGD to elucidate the possible molecular mechanisms of low virulence. Al-though L. monocytogenes H4 with similar patterns to strain 10403S in terms of hemolytic activity, invitro growth and invasiveness and even higher higher adhesiveness, faster intracellular growth and higher phospholipase activity in vitro, it was substantially less virulent than the strain 10403S in mouse and chickenembryo models (50% lethal dose: 10 ~ (8.14) vs. 10 ~ (5.49) and 10 ~ (6.73) (1.9), respectively). The genes prfA, plcA andmpl were homologous among L.monocytogenes strains H4, 10403S and EGD (> 98%). Genes iap, hly, plcB, InlA and InIB of L.monocytogenes 10403S had higher homology to those of strain EGD (> 9 8%) than isolateH4. The homology of the gene hly between strain 10403S and isolate H4 was 96.9% at the nucleotide level, but 98.7% at the amino acid level. The actA gene of isolate H4 had deletions of 105 nucleotides corresponding to 35 amino acid deletions falling Within the proline-rich region.Taken together, this study presents someclues as to reduced virulence to mice and chicken embryos of the isolate H4 probably as a result of deletion mutations of actA.