ACTA VETERINARIA ET ZOOTECHNICA SINICA ›› 2014, Vol. 45 ›› Issue (2): 274-280.doi: 10.11843/j.issn.0366-6964.2014.02.016

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Characterization of Listeria monocytogenes Strains with Low Virulence

JIANG Ling-li1,CHEN Jian-shun2,LI Ai-yun3,WAN Jing1,ZHOU Xiang-yang1,QIAN Guo-ying4*,LI Cai-yan4,FANG Wei-huan5   

  1. (1.Zhoushan EntryExit Inspection and Quarantine Bureau,Zhoushan 316021, China; 2.Zhejiang Fisheries Technical Extension Center,Hangzhou 310012,China; 3.Women′s Hospital,Zhejiang University School of Medicine,Hangzhou 310006, China; 4.Zhejiang Wanli University,Ningbo 315100, China;5.Institute of Preventive Veterinary Medicine,Zhejiang University,Hangzhou 310058, China)
  • Received:2013-07-01 Online:2014-02-23 Published:2014-02-23

Abstract:

 Phenotypic and genetic characteristics of two Listeria monocytogenes strains H4 and 54006 with naturally low pathogenicity were carried out to elucidate the possible molecular mechanisms.The two strains,together with other 3 L.monocytogenes strains representing different serovars,were investigated by serotype and lineage identification,virulence to mice,phospholipase activity,adhesion and cytotoxicity assay against HeLa cells,detection of virulence associated genes as well as their transcription levels via real-time PCR.Result were as follows:Strains H4 and 54006 belonged to serovar 4a and lineage Ⅲ,with notable phospholipase activity and increased adhesion to HeLa cells.However,these two strains had decreased pathogenicity to mice,but exhibited significantly higher cytotoxicity against HeLa cells (P<0.05).The virulence associated genes in the two strains were quite homologous to other test strains,with PrfA depicting G145S mutation in strains H4 and 54006.The transcription levels of main virulence genes in strain H4 were significantly higher than those of other strains.Mutant strain H4-ΔprfA (substitution at position 145 from serine to glycine) was constructed by sitedirected mutagenesis and homologous recombination,with abolished phospholipase C activity and increased virulence to mice as compared with its parent strain H4 (105.00 vs 107.18) .The transcription levels of main virulence genes in mutant strain H4-ΔprfA were lower than those of the wild type strain.The study presents some clues that the low virulence of strains H4 and 54006 maybe result from PrfA G145S mutation,and leading to over-expression of PrfA regulated proteins.Hence,the strains might be exposed to the host immune responses with their stronger cytotoxicity.

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