Resistotyping of campylobacters: fulfilling a need

Clonal complexes of Campylobacter jejuni identified by multilocus sequence typing correlate with strain associations identified by multilocus enzyme electrophoresis

Multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) with SmaI were used to subtype 55 isolates of Campylobacter jejuni from a diverse range of human and animal sources previously characterized by multilocus enzyme electrophoresis (MEE). MEE and MLST targeted 11 and 7 loci, respectively, and all loci were unique to each method. MEE, MLST, and PFGE identified 40, 37, and 48 discrete subtypes, respectively, with many of the subtypes occurring only once within the data set. Simpson's indices of diversity were calculated to be 0.979, 0.966, and 0.994 for MEE, MLST, and PFGE, respectively, demonstrating that MEE and MLST had similar discriminatory powers but that PFGE was more discriminatory. Allele diversity was higher in the MLST loci; individual single-locus diversities for the 11 MEE loci and the 7 MLST loci were 0.491 and 0.854, respectively. The clonal complexes recognized by MLST correlated with the strain associations previously recognized by MEE and contained some isolates indistinguishable by PFGE. Many clusters contained isolates from diverse geographical regions and from both humans and animals. These results demonstrate the usefulness of MLST for investigation of the global epidemiology of this important pathogen and illustrate its potential to identify indistinguishable strains or clones in geographically distinct regions.

Phenotypic diversity of Campylobacter isolates from sporadic cases of human enteritis in the UK

AIMS

The aim of this study was to identify and subtype a large collection of isolates of Campylobacter spp. to quantify diversity among strains causing human disease from geographically diverse sources in the United Kingdom.

METHODS AND RESULTS

Isolates were characterized by the Penner serotyping scheme, Preston phage typing and biotyping methods. The diversity index calculated from the combined results of all three methods was 0.997 and indicated that isolates from sporadic cases of infection are very diverse. Strong associations between common phagetypes (PG52, PG121 and PG55) and the three most common serotypes (HS1, HS2 and HS4) found in the study were evident.

CONCLUSIONS

Strains of C. jejuni causing human infections in the United Kingdom are very phenotypically diverse. Individual strains characterized by serotype, phagetype and biotype were detected throughout the 7-month study period and from geographically distinct sources, indicating an unrecognized outbreak or other epidemiologically significant source of human infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

The low frequency incidence of most C. jejuni strains should enable easy recognition of outbreaks by strain type surveillance at local, regional and national level in the United Kingdom. The characterization of common strain profiles in this study by simple phenotypic methods could provide the basis for strain specific epidemiological studies for reservoirs of infection and transmission routes for human infection.

A milk-borne campylobacter outbreak following an educational farm visit

After a nursery school trip to a dairy farm, 20 (53%) of 38 children and 3 (23%) of 13 adult helpers developed gastrointestinal infection. Campylobacter jejuni was isolated from 15 primary cases and from 3 of 9 secondary household cases. A cohort study of the school party found illness to be associated with drinking raw milk (relative risk 5.4, 95% confidence interval 1.4-20.4, P = 0.001). There was a significant dose response relationship between amount of raw milk consumed and risk of illness (chi 2-test for linear trend 12.1, P = 0.0005) but not with incubation period, severity of symptoms or duration of illness. All 18 human campylobacter isolates were C. jejuni resistotype 02 and either biotype I (number 16) or biotype II (number 2). Campylobacter was also isolated from samples of dairy cattle and bird faeces obtained at the farm but these were of different resisto/biotypes. Educational farm visits have become increasingly popular in recent years and this outbreak illustrates the hazard of exposure to raw milk in this setting.