[Molecular epidemiology of Listeria monocytogenes isolates from imported fishery products to China].
OBJECTIVE
We examined the prevalence, molecular characteristics and virulence potential of Listeria monocytogenes isolates from imported fishery products to gain further insights on the public health risk caused by this important food borne pathogen.


METHODS
L. monocytogenes isolates, screened from 1275 batches of fishery products imported from July 2007 to November 2008, were studied by lineage classification, serotyping, in vivo virulence assessment in ICR mouse model and multilocus sequence typing (MLST).


RESULTS
Thirty-three batches were contaminated by L. monocytogenes (33/1275, 2.6%), in which serovar 4b dominated (65.2%), followed by serovars 1/2b (17.4%), 1/2a (13.0%) and 1/2c (4.4%). These isolates were all as virulent as L. monocytogenes reference strains. Of 23 selected L. monocytogenes isolates and 9 reference strains, 23 sequence types (STs) were recognized with discrimination index (D.I.) of 0.97, based on the concatenated gene cluster covering one virulent gene actA, two housekeeping genes hisJ and ribC, and one stress-response gene sigB. Remarkably, 3 isolates from American salmon, Argentina squid and Peru squid respectively belonged to ST9 which represented epidemic clone I (ECI). The isolation rate of L. monocytogenes in imported fishery products (2.6%) was similar to that in domestic fishery products (2.7%). Serovar 4b, which was more virulent than other serovars in humans, was dominant in imported fishery products, and even ECI was recognized.


CONCLUSIONS
All of these isolates were as virulent as L. monocytogenes reference strains, suggesting inspection and quarantine strategies of imported fishery products should be strengthened effectively.
Liang
Qiping
Q
Zhejiang University Institute of Preventive Veterinary Medicine and Zhejiang Provincial Key Laboratory of Prevent Veterinary Medicine, Hangzhou 310029, China. liangqp@nbiq.gov.cn
Chen
Jianshun
J
Chen
Qiaomiao
Q
Lao
Huajun
H
Huang
Shaotang
S
Fang
Weihuan
W
D000818:Animals; D015373:Bacterial Typing Techniques; D002681:China / Q000453:epidemiology; D004269:DNA, Bacterial / Q000032:analysis; D005398:Fisheries; D005506:Food Contamination / Q000517:prevention & control / Q000706:statistics & numerical data; D005516:Food Microbiology / Q000592:standards; D008089:Listeria monocytogenes / Q000235:genetics / Q000472:pathogenicity*; D008088:Listeriosis / Q000453:epidemiology; D051379:Mice; D017720:Molecular Epidemiology; D014774:Virulence / Q000235:genetics*; D037521:Virulence Factors
D004269:DNA, Bacterial; D037521:Virulence Factors