Primary Intestinal Pathogens of Enterobacteriaceae
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p313
2025-07-08
580
Salmonella (All Serotypes)
Salmonella are facultative anaerobic, motile gram-negative rods commonly isolated from the intestines of humans and animals. Identification is primarily based on the ability of the organism to use citrate as the sole carbon source and lysine as a nitrogen source in combination with hydrogen sulfide (H2S) production. The genus is comprised of two primary species, S. enterica (human pathogen) and S. bongori (animal pathogen). S. enterica is subdivided into six subspecies: subsp. enterica, subsp. salamae, subsp. arizonae, subsp. diarizonae, subsp. houtenae, and subsp. indica. S. enterica subsp. enterica can be further divided into serotypes with unique virulence properties. Serotypes are differentiated based on the characterization of the heat-stable O antigen, included in the LPS, the heat-labile H antigen flagellar protein, and the heat-labile Vi antigen, capsular polysaccharide. A DNA sequence-based method has been developed for molecular identification of DNA motifs in the flagella and O antigens.
Shigella spp. (S. dysenteriae, S. flexneri, S. boydii, S. sonnei)
Shigella spp. are nonmotile; lysine decarboxylase–negative; citrate-, malonate-, and H2S-negative; non–lactose fermenting; gram-negative rods that grow well on MacConkey agar. The four subgroups of Shigella spp. are: S. dysenteriae (group A), S. flexneri (group B), S. boydii(group C), and S. sonnei (group D). Each subgroup has several serotypes. Serotyping is based on the somatic LPS O antigen. After presumptive identification of a suspected Shigella species based on traditional biochemical methods, serotyping should be completed, especially in the case of S. dysenteriae. Suspected strains of Shigella sp. that cannot be typed by serologic methods should be referred to a reference laboratory for further testing.
Yersinia spp. (Y. pestis, Y. enterocolitica, Y. frederiksenii, Y. intermedia, Y. pseudotuberculosis)
Yersinia spp. are gram-negative; catalase-, oxidase-, and indole-positive, non–lactose fermenting; facultative anaerobes capable of growth at temperatures ranging from 4° to 43°C. The gram-negative rods exhibit an unusual bipolar staining. Based on the composition of the LPS in the outer membrane, colonies may present with either a rough form lacking the O-specific polysaccharide chain (Y. pestis) or a smooth form containing the lipid A-oligosaccharide core and the complete O-polysaccharide (Y. pseudotuberculosis and Y. enterocolitica). Complex typing systems exist to differentiate the various Yersinia spp., including standard biochemical methods coupled with biotyping, serotyping, bacteriophage typing, and anti biogram analysis. In addition, epidemiologic studies often include pulsed-field gel electrophoresis (PFGE) studies.
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