Evidence of genomic instability in Campylobacter jejuni isolated from poultry

Abstract

Poultry isolates of Campylobacter jejuni derived from a survey of meat processing batches were genotyped by pulsed-field gel electrophoresis (PFGE) of chromosomal DNA to establish the clonal relationships between single-colony isolates. In the majority of batches studied, one or two genotype patterns predominated. However, in one batch (batch A), 21 single-colony isolates gave 14 different PFGE genotypes. The banding patterns obtained with SmaI were sufficiently different to distinguish between genotypes, although the patterns also produced many common bands. The question of whether these isolates represented different clones or had a common clonal ancestry was addressed by additional genotypic and phenotypic methods. Restriction length polymorphism of PCR products obtained from the flagellin genes showed an identical flagellin genotype for all of these isolates. In contrast, unrelated control isolates resulted in different flagellin genotypes. Moreover, all 14 different PFGE genotypes of batch A had identical Penner serotypes and identical or similar biotypes and phage types. It was concluded that the isolates were of clonal origin and that the diversity in the PFGE banding patterns had most likely originated from genomic rearrangements. However, the PFGE genotypes were shown to be stable upon subculturing in vitro and after in vivo passage in chickens, and natural transformation between isogenic mutants carrying antibiotic markers did not occur in vivo in a chick colonization model. The possible mechanisms for the hypothesized genomic recombinations and the conditions that allow, induce, or select for such events are discussed.

FIG. 1

PFGE of chromosomal DNA of C. jejuni isolates from poultry batch A digested with SmaI. Isolates are designated above the lanes. The genotypes (gt) are given below the lanes. M, molecular mass marker (in kilobase pairs).

FIG. 2

PFGE of SmaI digests of isolates from batch B (302, 303, 307, and 308), batch C (317 and 318), and batch D (331).

FIG. 3

PCR-RFLP profiles of amplified flagellin products digested with DdeI (D) and HinfI (H). (A) A subset of eight isolates (lanes 1 to 8: 123a, 123b, 123c, 124a, 124c, 125a, 125d, and 125c, respectively) from batch A is shown. All other isolates from this batch displayed identical profiles. (B) Isolates 318 (lane 1) and 317 (lane 2) from batch C; 307 (lane 3), 303 (lane 5), and 302 (lane 6) from batch B; and 331 (lane 4) from batch D. M, marker.