Detection of Enteric Bacteria in Raw Food Samples from Vietnam ...

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CHAPTER 1: INTRODUCTION
Virulence plasmids of nontyphoidal serotypes are associated with systemic infection in both
humans and animals (Jones et al., 1982; Terakado et al., 1983; Gulig and Curtiss III, 1987;
Barrow and Lovell, 1988; Danbara et al., 1992; Fierer et al., 1992; Wallis et al., 1995; Libby
et al., 1997; Rotger and Casadesus, 1999; Bakshi et al., 2003). Among more than 2500
Salmonella serotypes, the virulence plasmid was detected in only a small number of
serotypes, including S. Abortusovis, S. Abortusequi, S. Choleraesuis, S. Dublin, S. Enteritidis,
S. Gallinarum-Pullorum, S. Typimurium, S. Sendai and S. Paratyphi C (Chiu and Ou, 1996;
Rotger and Casadesus, 1999; Chu and Chiu, 2006). The virulence plasmid appears to be
specific to its host, such as the pSEV plasmid with 60 kb in size in S. Enteritisis, pSDV of 80
kb in S. Dublin, 86-kb pSPV of S. Gallinarum-Pullorum, and 95-kb pSTV plasmid in
S. Typhimurium and S. Abortusequi (Chu et al., 1999; Chu and Chiu, 2006).
1.2.2. The virulence genes in E. coli
Most E. coli are normal components of the intestinal flora, but certain pathogenic strains carry
virulence genes enabling intestinal colonising and inducing either intestinal or extra-intestinal
disease (Orskov and Orskov, 1992; Schroeder et al., 2004). The most frequent clinical
syndromes caused by a number of pathogenic clones of E. coli are urinary tract infections,
bacteremia, meningitis and diarrhoeal disease (Bopp et al., 2003; Dobrindt, 2005; Germon et
al., 2005). In contrast to diarrhoeagenic E.coli, extraintestinal pathogenic E. coli (ExPEC)
strains are incapable of causing enteric disease but responsible for most extraintestinal
infections. The infections are caused by three pathotypes: (i) urpathogenic (UPEC) strains that
cause urinary tract infections in humans, dogs and cats (ii) strains involved in neonatal
meningitis (NMEC) and (iii) strains that cause septicemia in humans and animals (Kuhnert et
al., 2000; Russo and Johnson, 2000; Johnson and Russo, 2002; Bekal et al., 2003).