We describe a study on the application of multilocus sequence typing for the analysis of Campylobacter jejuni and C. coli isolates from human domestically acquired infections in the Helsinki-Uusimaa area of Finland in 1996, 2002, and 2003. In addition, isolates from poultry meat and fecal samples of cattle from the seasonal peak (July to September) in 2003 were included in the study. In total, 361 Finnish C. jejuni and C. coli strains were typed. Sequence type 45 (ST-45) (45%), ST-21 (21%), and ST-677 (11%) clonal complexes were the most prevalent. The ST-45 and ST-677 complexes were overrepresented in comparison with previous studies. The longitudinal study revealed an association between C. coli (ST-828 complex) infection and elderly patients (≥60 years). Analysis of exposure factors, determined by a previous case-control study conducted during the seasonal peak in 2002, revealed that the ST-48 complex was significantly ( P < 0.05) associated with the tasting or eating of raw minced meat. New and unassigned STs were associated with swimming in natural bodies of water, whereas the ST-677 complex was related to drinking nonchlorinated water from a small water plant or water from natural sources. The ST-45 complex was associated with contact with pet cats and dogs. In 2003, ST-45 occurrence was significantly associated with poultry whereas ST-50 was associated with isolates from humans. In contrast, ST-53, ST-58, ST-61, and ST-883 were significantly associated with isolates from cattle. Further studies are needed to reveal the significance of the observed associations.

A total of 95 human Campylobacter jejuni isolates acquired from domestic infections and collected from three districts in Finland during the seasonal peak (June to September) in 2012 were analysed by PCR-based multilocus sequence typing (MLST) and by whole—genome sequencing (WGS). Four predominant sequence types (STs) were detected among the isolates: ST-45 (21%) and ST-230 (14%, ST-45 clonal complex (CC)), ST-267 (21%, ST-283 CC) and ST-677 (19%, ST-677 CC). In districts 1 and 3, most infections occurred from early July to middle of August, with a peak at weeks 29—31, but in district 2 the infections were dispersed more evenly throughout three months (June to August). WGS data were used for further whole—genome MLST (wgMLST) analyses of the isolates representing the four common STs. Shared loci of the isolates within each ST were analysed as distance matrices of allelic profiles by the NeighborNet algorithm. The highest allelic variation (>400 different alleles) were detected between different clusters of ST-45 isolates (1,121 shared loci), while ST-230 (1,264 shared loci), ST-677 (1,169 shared loci) and ST-267 isolates (1,217 shared loci) were less diverse with the clusters differing by less than 40 alleles. Closely related isolates showing no allelic variation (subclusters) were detected among all four major STs. In some cases they originated from different districts suggesting that isolates can be epidemiologically connected and may have the same infection source despite being originally identified as sporadic infections.

Campylobacter jejuni is the most common bacterial cause of human gastroenteritis worldwide. Due to the sporadic nature of infection, sources often remain unknown. Multilocus sequence typing (MLST) has been successfully applied to population genetics of Campylobacter jejuni and mathematical modelling can be applied to the sequence data. Here, we analysed the population structure of a total of 250 Finnish C. jejuni isolates from bovines, poultry meat and humans collected in 2003 using a combination of Bayesian clustering (BAPS software) and phylogenetic analysis.

We describe the long-term multilocus sequence typing (MLST) analysis of the population structure and dynamics of 454 Finnish human Campylobacter jejuni isolates, as well as 208 chicken isolates, collected during the mid-1990s to 2007. The sequence type clonal complexes (ST CC) ST-45 CC, ST-21 CC, and ST-677 CC were the most common ones found among all isolates, and they covered 73.9% of all isolates. The ST-283 CC also was found frequently among chicken isolates (8.2%). The predominant STs among all isolates were ST-45, ST-50, and ST-677. ST-137 and ST-230 were common among human isolates, and ST-267 was found more frequently among chicken isolates than human isolates. The ST-45 CC was significantly associated with chicken isolates ( P < 0.01), whereas the ST-21 CC was associated with human isolates ( P < 0.001). The ST-677 CC was not associated with any host ( P = 0.5), and an opposite temporary trend of this complex was seen among chicken and human isolates, with an increase in the former and a decrease in the latter during the study period. Furthermore, the ST-22 and ST-48 CCs were significantly associated with human isolates ( P < 0.01), but neither of the CCs was found in chicken isolates. The annual overlap between STs from human and chicken isolates decreased from 76% at the beginning of the study to 58% at the end. Our results suggest that the importance of chicken as a reservoir for strains associated with human infections has declined despite the consumption of domestic chicken meat increasing during the follow-up period by 83%.

Analysis of 16S rRNA gene sequences has been the method generally used to study the evolution and phylogeny of bacteria. Phylogenetic analysis of the 16S rRNA gene has shown the position of the genus Helicobacter in the ε-subclass of the Proteobacteria. Because 16S rRNA-based phylogeny does not always correspond to the results of polyphasic taxonomy, and the related species cannot always be separated, new phylogenetic markers for Helicobacter species are needed. In this study, conserved partial (600 bp) 60 kDa heat-shock protein (HSP60) sequences were used to study the phylogeny of 37 strains of gastric and enterohepatic Helicobacter species, including type strains of 15 Helicobacter species with validly published names, reference strains of flexispira taxa and Helicobacter felis, Helicobacter bizzozeronii and Helicobacter salomonis and canine flexispira strains. The partial HSP60 gene sequence proved to be a useful phylogenetic marker for the genus Helicobacter, providing a means of differentiating all 15 Helicobacter species analysed. In the resulting phylogenetic tree, gastric Helicobacter species and enterohepatic species with flexispira morphology formed tight, separate clusters. In general, HSP60 sequence similarities between Helicobacter species were significantly lower than the corresponding 16S rRNA gene sequence similarities, indicating a better resolution for species identification. In addition, a specific PCR method for identifying H. salomonis was developed based on the partial HSP60 sequence.