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Chapter 11 : Isolation, Identification, Subspecies Differentiation, and Typing of Campylobacter fetus
Category: Bacterial Pathogenesis
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This chapter presents an overview of the historic classifications and nomenclature of Campylobacter fetus. The current recognized nomenclature for Campylobacteraceae was officially accepted in 1980, published in the approved list of bacterial names, and in accordance with that used in Bergey’s Manual of Systematic Bacteriology. During 1950s to 1970s, identification, subspecies differentiation, and typing results were based on phenotypic methods that are limited in both reliability and interpretation. Screening programs aiming to control bovine genital campylobacteriosis and limit the economic impact are performed by veterinary health services. The majority of the molecular methods are sensitive and can be used to identify C. fetus. However, one study has investigated the use of animal models for subspecies differentiation, on the premise that C. fetus subsp. venerealis and C. fetus subsp. fetus have differences in their preference for host and niche. The use of animals for subspecies differentiation purposes is not practical and has never been publicly evaluated. Phenotyping of C. fetus has been confined to serotyping. The currently accepted serotyping scheme is based on the heat-stable O antigens and consists of only two serotypes, A and B. Multilocus sequence typing (MLST) results showed that C. fetus has a more clonal structure compared with most other species within the genusCampylobacter. MLST in combination with a C. fetus subsp. venerealis–specific PCR may be applied. Currently, the best method for typing purposes is pulsed-field gel electrophoresis (PFGE).
Lack of genetic diversity in the C. fetus glnA locus compared with other Campylobacter species. Radial neighbor-joining tree comparing 477 nt sequences at the glnA locus of C. fetus with those of five other Campylobacter species. Alleles are numbered as in the MLST databases at http://pubmlst.org/ and prefixed by a letter to indicate the species. Bootstrap values are shown. Reprinted from the Journal of Clinical Microbiology ( van Bergen et al., 2005a ).
Dendrogram showing the AFLP banding patterns of 69 C. fetus strains. Cluster analysis was based on the similarity levels among bands in region 841 to 879 of the banding patterns (arrow). The different clusters of C. fetus subsp. fetus and C. fetus subsp. venerealis are indicated. The percentage of genetic similarity among banding patterns is shown. Reprinted from the Journal of Clinical Microbiology ( Wagenaar et al., 2001 ).
Congruence of sequence type (ST), sap type, and subspecies. Analysis of concatenated MLST sequences by split decomposition. The three STs identified in association with C. fetus subsp. venerealis are indicated by the dotted line, the remainder being C. fetus subsp. fetus. The correlation among ST and sap type is marked; solid line, sapA; dashed line, sap B. A radial neighbor-joining tree constructed by using the same data (inset) is shown to indicate the corresponding treelike phylogenies obtained by both methods. This supports the idea that C. fetus subsp. fetus and C. fetus subsp. venerealis evolved recently, with little (if any) evidence of recombination, and that genetic changes have accumulated by the vertical transmission of point mutations, yielding a clonal structure to the population. Reprinted from the Journal of Clinical Microbiology ( van Bergen et al., 2005a ).
Schematic of proposed ancestral relationships and pathogenicities for C. fetus based on previous and recent studies. C. fetus strains colonize a variety of animals and/or are pathogens of these species. Infection of humans usually reflects direct contact with such animals or exposure to C. fetus–contaminated foods. The widths of the arrows indicate the relative frequencies of human infection with these strains. Reprinted from the Journal of Clinical Microbiology ( Tu et al., 2005 ).
Overview of the subspecies and their host preference and their clinical importance a
Comparison of historic classification and nomenclature of Campylobacter fetus a