Molecular typing and source attribution of Finnish Campylobacter jejuni isolates

Caroline Paula Astrid de Haan

Tutkimustuotos: OpinnäyteVäitöskirjaArtikkelikokoelma


Campylobacter is the main bacterial genus of gastroenteritis in Finland and C. jejuni accounts for more than 90% of the Campylobacter infections. The majority of infections occur during the summertime (June-August). Risk factors associated with the disease are the handling and consumption of undercooked chicken meat, drinking of raw milk or contaminated water and foreign travel. Nevertheless, the source of Campylobacter often remains obscure, due to the sporadic nature of the infection. Multilocus sequence typing (MLST) has been proven to be useful in molecular epidemiology and source attribution studies of this zoonotic food- and water-borne pathogen. Using MLST, we typed 454 C. jejuni isolates from domestically acquired human infections and 208 isolates from chicken meat and caecal samples collected between 1996 and 2006. In this study period, clonal complexes (CCs) ST-45, ST-21 and ST-677 covered 73.9% of all isolates. The annual overlap between STs from human and chicken isolates decreased from 76% in 1999 to 58% in 2006. CC ST-677 occurred with an increasing trend among chicken isolates, but with a decreasing trend among human isolates. A high ST diversity was revealed among 102 Finnish bovine C. jejuni isolates. CC ST-21 alone accounted for 56% of the bovine C. jejuni isolates and encompassed 23 different STs. CC ST-61 was the second largest CC and included 20% of the isolates. Source attribution was determined by the Bayesian Analysis of Population Structure (BAPS) program, which showed that 44.3% of the human isolates were found in the bovine-associated BAPS cluster; 45.4% were found in the chicken-associated BAPS cluster and 10.3% remained unassigned. A high diversity of STs including novel and unassigned STs were found among the 113 C. jejuni isolates sampled from natural water bodies, wild birds and zoo animals. However, the most common ST found among human and poultry isolates, ST-45, was also the most common ST typed among the natural water body isolates. In the BAPS analysis 65.4% of the human isolates grouped into the poultry-associated cluster. A new cluster associated with natural water bodies emerged that largely consisting of uncommon and unassigned STs. Population differentiation revealed that the human and poultry populations and the human and natural water populations were the most similar to each other. The distributions of fspA1 and fspA2 among isolates taken from different sources and STs were studied. The human and poultry isolates, in addition to CC ST-45 and ST-283 were associated with fspA1, whereas the bovine isolates, CC ST-21 and ST-61 were associated with fspA2. FspA1 was highly conserved among the strains in contrast to fspA2, which was profoundly heterogeneous. Sequence analysis of the fspA2 allele in different STs showed that several predicted protein sequences contained premature stop codons. The presence of certain unique metabolic traits was found in some but not all C. jejuni strains. Gamma-glutamyl transpeptidase (GGT) and the gene for periplasmic L-asparaginase (ansBs) were often mutually exclusive with fucose permease (fucP). This particular combination, and also the presence of fucP only was highly ST dependent. The exception to this phenomenon was ST-45, which was very heterogeneous. Total absence of all studied metabolic traits occurred in 22% of the strains. The research conducted here conclusively showed a great diversity of C. jejuni STs among the human, bovine and environmental isolates. The overlap between Finnish human and chicken C. jejuni isolates declined between 1999 and 2006. However, natural waters could be an underestimated source of infection. Pronounced fspA2 diversity was found. The distribution of the secondary metabolic traits GGT, ansBs and fucP was promiscuous among the isolates obtained from different sources which suggests that animal colonization and human infection are not necessarily dependent on these traits.
Painoksen ISBN978-952-10-8237-5
Sähköinen ISBN978-952-10-8237-5
TilaJulkaistu - 2012
OKM-julkaisutyyppiG5 Tohtorinväitöskirja (artikkeli)


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