PDF《Hong Kong》

Epidemiol.

Infect. (2001), 126, 173C179. Printed in the United Kingdom #

2001 Cambridge University Press The prevalence and characterization of verotoxin-producing Escherichia coli isolated from cattle and pigs in an abattoir in Hong Kong P. H. M. LEUNG , W. C. YAM#, W. W. S. NG$ ??? J. S. M. PEIRIS#* Department of Nursing and Health Sciences, The Hong Kong Polytechnic Uni ersity, Hung Hom, Hong Kong SAR, China # Department of Microbiology, Queen Mary Hospital, The Uni ersity of Hong Kong, Hong Kong SAR, China $ School of Professional and Continual Education, The Uni ersity of Hong Kong, Pokfulam Road, Hong Kong SAR, China (Accepted

5 December 2000) SUMMARY The aim of the study was to de?ne the prevalence of verotoxin-producing Escherichia coli (VTEC) in cattle and pigs in a Hong Kong abattoir. Faecal and carcass samples collected from

986 cattle and

487 pigs from an abattoir were tested for verotoxin (VT) by PCR and cytotoxicity assays. VTEC was isolated from 41n5 and 1n8% of cattle faecal and carcass samples and from 2n1 and 0n2% of porcine faecal and carcass samples, respectively. Amongst

409 VTEC isolates from cattle,

9 were serotype O157:H7 and eaeA+. The most prevalent t genotype among bovine VTEC was t1+ t2+ (73n8%) and in porcine VTEC was t2e+ (30%). None of the porcine VTEC isolates and 9n3% of the bovine VTEC isolates was eaeA+. The non-O157 serogroup VTEC isolates carrying eaeA and EHEC-hlyA belonged to serogroups O172, O15, O84, O91, O110 and O121. The local dietary preference for pork or chicken (rather than beef), the low VTEC carriage in pigs, the rarity of additional virulence factors (eaeA) in VTEC isolated from cattle may explain the apparently low incidence of human diarrhoeal disease associated with VTEC in Hong Kong hitherto. However, the presence of non-O157 VTEC strains carrying the eaeA virulence marker in cattle highlights the fact that sole reliance on sorbitol-MacConkey agar for screening human VTEC isolates may underestimate the human disease burden. The changing dietary habits of the population in Hong Kong reinforce the need for continued vigilance. INTRODUCTION Verocytotoxin (VT) is a potent cytotoxin that inhibits eukaryotic protein synthesis and is a well-established virulence factor for Escherichia coli (VTEC) associated with human disease [1]. VTEC are geo- graphically widespread and have been found to be associated with human disease ranging from bloody diarrhoea to the haemolytic-uraemic syndrome (HUS) [1]. The pathogenicity of VTEC is associated with additional virulence factors, the best known being the attaching-and-e?acing (eae) A gene that encodes * Author for correspondence. intimin, a

94 kDa outer-membrane protein [2]. Intimin enables VTEC to cause attaching-and-e?acing lesions in the microvilli of the host intestine. Another virulence factor, the enterohaemorrhagic E. coli haemolysin A (EHEC-hlyA) gene, is encoded on a

60 MDa plasmid and is associated with EHEC strains [2]. Although Sandhu and colleagues reported that EHEC-hlyA was present in almost all eaeA-positive VTEC isolates obtained from animals [3], its role in the pathogenicity of VTEC is poorly understood. VTEC is a naturally occurring organism in the gut ?ora of cattle [4] and has been isolated from the gut of other animals such as sheep, goats and pigs [1].

174 P. H. M. Leung and others Outbreaks are associated with consumption of con- taminated undercooked ground beef and vegetables or unpasteurized milk [2]. Serotype O157: H7, the best-known serotype of VTEC associated with human disease, was responsible for the foodborne outbreak that occurred in Japan in