Virulence phenotyping and molecular characterization of a low-pathogenicity isolate of Listeria monocytogenes from cow's milk.
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. Corresponding virulence genes (iap, prfA, plcA, hly, mpl, actA, plcB, InlA and InlB) were compared with L. monocytogenes reference strains 10403S and EGD to elucidate the possible molecular mechanisms of low virulence. Although L. monocytogenes H4 exhibited similar patterns to strain 10403S in terms of hemolytic activity, in vitro growth and invasiveness and even had higher adhesiveness, faster intracellular growth and higher phospholipase activity in vitro, it was substantially less virulent than the strain 10403S in mouse and chicken embryo models (50% lethal dose: 10(8.14) vs. 10(5.49) and 10(6.73) vs. 10(1.9), respectively). The genes prfA, plcA and mpl were homologous among L. monocytogenes strains H4, 10403S and EGD (>98%). Genes iap, hly, plcB, InlA and InlB of L. monocytogenes 10403S had higher homology to those of strain EGD (>98%) than isolate H4. 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 some clues as to reduced virulence to mice and chicken embryos of the isolate H4 probably as a result of deletion mutations of actA.
Jiang
Ling-Li
LL
Institute of Preventive Veterinary Medicine, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Zhejiang University, Hangzhou 310029, China.
Xu
Jing-Jing
JJ
Chen
Ning
N
Shuai
Jiang-Bing
JB
Fang
Wei-Huan
WH
D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D002417:Cattle; D002642:Chick Embryo; D017353:Gene Deletion; D005798:Genes, Bacterial / Q000235:genetics; D007928:Lethal Dose 50; D008089:Listeria monocytogenes / Q000145:classification / Q000302:isolation & purification / Q000472:pathogenicity*; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D008892:Milk / Q000382:microbiology*; D008969:Molecular Sequence Data; D010641:Phenotype; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014774:Virulence
D001426:Bacterial Proteins; D008565:Membrane Proteins; C072980:actA protein, Listeria monocytogenes