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Chapter 2 : Population Biology of Campylobacter jejuni and Related Organisms
Category: Bacterial Pathogenesis
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This chapter explores the contribution that population studies have made to one's understanding of the biology of the Campylobacter, and the authors argue that such studies have a central role to play in understanding the epidemiology and pathogenesis of this important group of gram-negative bacteria. Campylobacter jejuni and Campylobacter coli cause the majority of human cases of Campylobacter-associated gastroenteritis; these two organisms are associated with approximately 90 and 10% of cases, respectively. This chapter discusses variation within the genus Campylobacter. Although human infection is one of the most important practical applications of studies of Campylobacter populations, in terms of Campylobacter population dynamics and evolution, infection is probably irrelevant. Understanding the population biology of Campylobacter is, however, crucial in understanding the transmission to humans and developing means for its control. It is instructive to reflect that the first study of C. jejuni and C. coli population structure by multilocus enzyme electrophoresis provided many insights that have proved to be correct and that have been extended and deepened by multilocus sequence typing (MLST) studies. Ongoing nucleotide sequence-based studies involving large numbers of isolates and improved genealogical analysis tools provide the highly attractive prospect that well within the next 10 years, the population biology of these organisms, at least insofar as it relates to human infection, will be effectively resolved.
Campylobacter MLST databases. (a) The growth of the Campylobacter jejuni and Campylobacter coli database since its inception in 2001. Open squares represent isolates submitted; closed squares, sequence types. (b) The structure of the pubMLST database network, which is used for all of the Campylobacter databases. It allows the integration of data from various sources in a variety of public or private databases, ensuring that a common typing nomenclature is used.
Relationships among the different Campylobacter microbiological species. The phylogeny was reconstructed with concatenated sequences from the alleles common to all of the schemes (gln, gly, and tkt).
Illustration of the Campylobacter clonal complexes with the C. jejuni ST-45 clonal complex. (a) Frequency distribution of sequence types in the database, showing the high frequency of ST-45 to its relatives. (b) Variants of ST-45, with allele changes highlighted with boxes. (c) Heuristic representation of the STs shown in (b), drawn with split decomposition, showing the central position of ST-45.
Correspondence of clonal complexes with genealogies. Clonal complex designations were used to annotate a phylogeny generated by ClonalFrame. The size of the pie charts represents the number of isolates in each clonal complex, with the color indicating the relative contribution of each source: black, human disease; white, chickens and chicken meat; dark gray, ovines and ovine meat; light gray, environmental sources. Data from Dingle et al. (2002) and Parker et al. (2007) .