R plasmids from Yersinia

Epidemiological, clinical and microbiological features of Yersinia enterocolitica infections in a community during a four-year period

Epidemiological and clinical features of 17 cases (13 children) of yersiniosis treated in a hospital over a four-year period, as well as factors associated with virulence, antibiotic resistance and plasmids in Yersinia enterocolitica strains from these patients were studied. The proportion of Y. enterocolitica was 3.57% of all fecal cultures positive for enteric pathogens, with 13 sporadic episodes and one outbreak. In 11 cases the infection was unimicrobial. The clinical presentation was: gastroenteritis (14 cases), pseudoappendicitis (1 case) and asymptomatic (2 cases). Eight cases needed hospital care, and 8 required antimicrobial treatment. None of the isolated bacterial strains produced pyrazinamidase, hemolysins, elastase, fibrinolysine, colicines or aerobactin. Eight strains showed calcium dependence, 7 of them exhibited autoagglutination, serum resistance, crystal violet binding and carried a 42 MDa plasmid related with virulence. Two strains carried a 3.3 MDa R-plasmid that encoded streptomycin-sulfadiazine resistance. The restriction analysis showed that the virulence plasmids constitute one variety and R-plasmids another.

Antimicrobial susceptibilities of food-isolated strains of Yersinia enterocolitica, Y. intermedia, Y. frederiksenii, and Y. kristensenii

The in vitro antimicrobial susceptibility of Yersinia enterocolitica and newly related species isolated from foods was examined. Only 4 of 375 isolates displayed resistance to non-ss-lactam antibiotics. MICs of ampicillin and carbenicillin determined by agar dilution with respect to 125 isolates showed the high susceptibility of Y. kristensenii and biovar 3 of Y. enterocolitica to carbenicillin (MIC for 90% of the strains, less than or equal to 8 micrograms/ml).

Plasmid-mediated tissue invasiveness in Yersinia enterocolitica

Plasmids have an important role in the pathogenicity of certain bacterial species, and Escherichia coli provides the most complete example of the relationship involved. Enterotoxigenic strains of E. coli, in addition to producing heat-stable and/or heat-labile enterotoxins, may also produce a haemolysin and fimbriate cell surface antigens which facilitate the adherence of the bacterial cell to the mucosa of the small bowel. Numerous studies have shown that these properties are plasmid-mediated and that the plasmids act in concert to confer on the host bacterium the ability to produce enteric disease in man and in animals. Moreover, studies with invasive strains of E. coli have shown that the Col V plasmid, which codes for the synthesis of colicin V, significantly enhances the pathogenicity of its host bacterium. Although the relationship between Col V plasmids and virulence is unclear, reports indicate that Col V-containing strains of E. coli are better able to survive in the alimentary tract and that colicine V itself inhibits macrophage function. It is probable that bacterial virulence is a complex phenomenon involving both chromosomal and plasmid genes. We describe here a virulence plasmid which mediates tissue invasiveness in human pathogenic strains of Yersinia enterocolitica.