Multilocus sequence typing, pulsed-field gel electrophoresis, and fla short variable region typing of clonal complexes of Campylobacter jejuni strains of human, bovine, and poultry origins in Luxembourg

Abstract

Campylobacter jejuni is the most common cause of bacterial gastroenteritis in Luxembourg, with a marked seasonal peak during summer. The majority of these infections are thought to be sporadic, and the relative contribution of potential sources and reservoirs is still poorly understood. We monitored human cases from June to September 2006 (n = 124) by molecular characterization of isolates with the aim of rapidly detecting temporally related cases. In addition, isolates from poultry meat (n = 36) and cattle cecal contents (n = 48) were genotyped for comparison and identification of common clusters between veterinary and human C. jejuni populations. A total of 208 isolates were typed by sequencing the fla short variable region, macrorestriction analysis resolved by pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST). We observed a high diversity of human strains during a given summer season. Poultry and human isolates had a higher diversity of sequence types than isolates of bovine origin, for which clonal complexes CC21 (41.6%) and CC61 (18.7%) were predominant. CC21 was also the most common complex found among human isolates (21.8%). The substantial concordance between PFGE and MLST results for this last group of strains suggests that they are clonally related. Our study indicates that while poultry remains an important source, cattle could be an underestimated reservoir of human C. jejuni cases. Transmission mechanisms of cattle-specific strains warrant further investigation.

FIG. 1.

Rarefaction curves of C. jejuni population by origin of isolates.

FIG. 2.

Distribution of ST by origin.

FIG. 3.

Minimum spanning tree of MLST data for the 208 isolates of C. jejuni. Each circle corresponds to a particular ST, and the size of the circle is proportional to the number of isolates sharing the same ST, i.e., the number indicated in the circle (only when the ST is shared by at least three isolates). Inside the circles, the colors reflect the relative number of isolates from each collection: green for cattle, red for human, and blue for poultry. The ST associated to CC as designated on the MLST website from the Oxford database (see Materials and Methods) are linked with the gray areas, and only the main ones are visualized. Designation of these CC are indicates beside. CC206, divided among the ST 46, 122, 290, 572, and 2104, is so close to CC21 that it is not shown as a separate entity on the figure.

FIG. 4.

Epidemic curve of weekly reported human Campylobacter cases during the summer period of 2006 in Luxembourg by sequence types as defined by MLST. Only ST with at least four cases during this period are shown by different colors.