Short CommunicationPrevalence, serotypes and virulence genes of Shiga toxin-producing Escherichia coli isolated from ovine and caprine milk and other dairy products in Spain
Introduction
Shiga toxin-producing Escherichia coli (STEC), also called verotoxin-producing E. coli, is the most important recently emerged group of food-borne pathogens, especially the serotype O157:H7 (Paton and Paton, 1998). STEC elaborate two potent phage-encoded cytotoxins called Shiga toxins (Stx1 and Stx2) or verotoxins (VT1 and VT2) (Paton and Paton, 1998). A number of serotypes belonging to STEC can cause serious diseases in humans, including hemorrhagic colitis (HC), hemolytic uremic syndrome (HUS), and thrombocytopenic purpura (TP), which may prove fatal in immunocompromised patients (Slutsker et al., 1997, Banatvala et al., 2001). It is now generally agreed that the major portion of the histopathological lesions associated with both HC and HUS is a consequence of the interaction of Stx with endothelial cells (Karmali, 1989). In addition to toxin production, another virulence-associated factor expressed by STEC is a protein called intimin, which is responsible for the intimate attachment of STEC to intestinal epithelial cells, causing attaching and effacing lesions in the intestinal mucosa (Jerse et al., 1990). Intimin is encoded by the chromosomal gene eae, which is part of a pathogenicity island termed the locus for enterocyte effacement (LEE) (Donnenberg et al., 1997). A factor that may also affect virulence of STEC is the enterohaemolysin (Ehly), also called enterohaemorrhagic E. coli haemolysin (EHEC-HlyA), which is encoded by ehxA gene (Schmidt et al., 1995).
Since healthy domestic animals, in particular ruminants like cattle, sheep and goats, can harbour STEC and O157:H7 in their faeces, they are regarded as natural reservoirs of these organisms (Beutin et al., 1993, Blanco et al., 2001, Blanco et al., 2004a). Recently, we have demonstrated in our country that a half of the sheep investigated harbour these bacteria (Blanco et al., 2003a, Rey et al., 2003). Transmission occurs through consumption of undercooked meat, unpasteurized dairy products and vegetables, or water contaminated by faeces of carriers. Also, person-to-person transmission has also been documented (Karmali, 1989).
Relatively little information is available about the frequency of isolation of STEC from ill persons in Spain because most laboratories do not routinely culture for this organism (Blanco et al., 2004b).
Given the importance of ovine and caprine livestock in our country, and the fact that many milk products from these species are not treated with any previous bacteriological sterilisation procedures, the aim of the present study was to investigate the prevalence of STEC O157:H7 and STEC non-O157 in ovine and caprine milk and other dairy products in order to determinate the potential risk that the consumption of these products can have from the standpoint of public health and hygiene.
Section snippets
Specimen collection, culture, and STEC screening
Samples were collected monthly in 64 different flocks in Extremadura (Western Spain) between March 2003 and June 2004 and comprise a total of 502 dairy products (DP). The DP included 360 unpasteurised ovine and caprine milk obtained from the bulk tank, 103 fresh cheese curds and 39 cheeses.
According to ISO 16654:2002, a total of 25 g of each sample was added to 225 ml of modified tryptone soya broth (TSB) (CM129, Oxoid, Madrid, Spain) supplemented with novobiocin (20 mg l− 1) (N1628, Sigma,
Results and discussion
Shiga-like toxin E. coli (STEC) implicated in hemorrhagic colitis (HC) and hemolytic uraemic syndrome (HUS), has become a serious health problem in various countries. Although many cases are undoubtedly associated with consumption of undercooked meat and meat products, vegetables and drinking water, a number of studies have also reported outbreaks of HC and HUS associated with consumption of milk and dairy products; sources reported to date include pasteurized and unpasteurized cow's milk (
Acknowledgements
This study was supported partially by the Regional Government Junta de Extremadura-Consejería de Educación, Ciencia y Tecnología (2PRO1A049-2PRO2A007) and the Fondo de Investigación Sanitaria (FIS G03/025-COLIRED-O157). The authors wish to thank A. Echeita (National Centre of Microbiology, Majadahonda, Madrid, Spain) for the phage typing of STEC.
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