Molecular Characterization of Campylobacter jejuni Clones: A Basis for Epidemiologic Investigation

Kate E. Dingle, Frances M. Colles, Roisin Ure, Jaap A. Wagenaar, Birgitta Duim, Frederick J. Bolton, Andrew J. Fox, David R.A. Wareing, and Martin C.J. Maiden

Disclosures

Emerging Infectious Diseases. 2002;8(9) 

In This Article

Abstract and Introduction

A total of 814 isolates of the foodborne pathogen Campylobacter jejuni were characterized by multilocus sequence typing (MLST) and analysis of the variation of two cell-surface components: the heat-stable (HS) serotyping antigen and the flagella protein FlaA short variable region. We identified 379 combinations of the MLST loci (sequence types) and 215 combinations of the cell-surface components among these isolates, which had been obtained from human disease, animals, food, and the environment. Despite this diversity, 748 (92%) of the isolates belonged to one of 17 clonal complexes, 6 of which contained many (318, 63%) of the human disease isolates. Several clonal complexes exhibited associations with isolation source or particular cell-surface components; however, the latter were poorly predictive of clonal complex. These data demonstrate that the clonal complex, as defined by MLST, is an epidemiologically relevant unit for both long and short-term investigations of C. jejuni epidemiology.

Campylobacter jejuni is the most frequently reported cause of acute inflammatory gastroenteritis in industrialized countries and a major cause of intestinal disease in children <2 years of age in developing countries.[1,2]C. jejuni infection is widely perceived as an increasing problem; for example, the number of reported cases of C. jejuni-associated enteritis increased sixfold in the United Kingdom from 1977 to 2000.[3,4] The syndromes associated with C. jejuni infection range from mild enteritis to severe invasive disease, and sequelae can occur, including the autoimmune-mediated demyelinating neuropathies Guillain-Barré and Miller Fisher syndromes.[5] The intestines of many feral and commercially reared birds, livestock, domestic pets, and animals are asymptomatically colonized by this bacterium, which is widely distributed in the environment and food. Transmission to humans is thought to occur through food, drinking water, and pets.[6,7]

Elucidation of the epidemiology of this zoonosis is complicated by the sporadic nature of the disease,[8] along with the organism's wide distribution, high levels of genetic and antigenic diversity, and a lack of representative population samples.[9] The absence of precise information on the relative importance of different sources of human infection has hindered the development of effective disease-control measures and is a major challenge in preventing human disease. The characterization of C. jejuni isolates has relied on serologic typing schemes since the 1980s,[10,11] but the data available from these techniques have not resolved the epidemiology of human disease. Consequently, the development of a method for the characterization of C. jejuni isolates that is accurate, reproducible, and comparable among laboratories has been a research priority for many years.[9] While numerous phenotyping and genotyping techniques that discriminate among isolates for short-term epidemiology have been developed, generating data that are comparable among different laboratories and that accurately identify relationships among isolates from diverse sources has proven more challenging.

A multilocus sequence typing (MLST) scheme[12] has been developed and validated for C. jejuni.[13] This approach, which exploits recent technical developments in high-throughput nucleotide sequence determination and combines them with conceptual advances in bacterial population biology, has proved to be successful for a number of bacteria.[12,13,14,15] MLST is especially suitable for the investigation of diverse bacterial populations that have weakly clonal population structures.[13,16,17] In common with multilocus enzyme electrophoresis, MLST indexes variation in housekeeping genes, which evolve slowly as they are under stabilizing selection for the conservation of metabolic function. The use of nucleotide sequence data directly accesses the variation in the targeted gene, and the technology employed is readily disseminated and highly reproducible.[18] Further advantages are that the data are electronically portable, enabling comparison of isolates via the Internet without exchange of biological materials, and amenable to analysis by phylogenetic and population genetic techniques.[19,20]

Initial analysis of C. jejuni populations with MLST confirmed the diverse genetic nature of the C. jejuni species and indicated that the population structure was likely to be weakly clonal.[13,17] Weakly clonal bacterial populations comprise a number of clonal complexes, which correspond to "lineages," i.e., groups of organisms presumed to derive from a common progenitor. However, the phylogenetic relationships among distinct complexes cannot in general be reconstructed because they have been disrupted by lateral gene transfer.[20] The MLST approach has been used to demonstrate that a number of C. jejuni clonal complexes are associated with human disease and that isolates from several of these caused demyelinating neuropathies.[13,21]

We examined the relationships of C. jejuni isolated from a broad range of sources in two countries by MLST, which was used to define clonal complexes. The results of this analysis were compared with variation observed in two cell-surface components that have been previously used for bacterial typing: the heat-stable (HS) serotyping antigen, which was investigated serologically; and the flagella, which was investigated by nucleotide sequencing of the flaA gene short variable region (SVR). We also examined the extent to which different isolation sources and cell-surface component variants correlated with clonal complex.

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