Decreasing trend of overlapping multilocus sequence types between human and chicken Campylobacter jejuni isolates over a decade in Finland

Abstract

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%.

FIG. 1.

Overview of the distribution of overlapping ST complexes between human (H) (n = 454) and chicken (C) (n = 208) isolates from 1996 to 2007 (shown as percentages). UA STs are STs that are not assigned to any known CC. Significant host associations are indicated with asterisks, where one asterisk indicates P ≤ 0.01 and two asterisks indicates P ≤ 0.001.

FIG. 2.

Overview of the percentage of overlapping C. jejuni STs/CCs between human and chicken isolates in 1999, 2003, and 2006.

FIG. 3.

Trends of MLST types in chicken isolates from 1999 to 2007. (a) Trend of ST-45 among chicken isolates from 1999, 2003, 2006, and 2007 shown as percentages of isolates with ST-45 in each year. (b) Trend of the ST-45 complex among chicken isolates from 1999, 2003, 2006, and 2007 shown as percentages of isolates with the ST-45 complex in each year. (c) Trend of the ST-677 complex among chicken isolates from 1999, 2003, 2006, and 2007 shown as percentages of isolates with the ST-677 complex in each year. (d) Trend of the ST-283 complex among chicken isolates from 1999, 2003, 2006, and 2007 shown as percentages of isolates with the ST-283 complex in each year.

FIG. 4.

Trends of MLST types in human isolates from 1996 to 2006. (a) Trend of ST-50 among human isolates from 1996, 1999, 2002, 2003, and 2006 shown as percentages of isolates with ST-50 in each year. (b) Trend of the ST-22 complex among human isolates from 1996, 1999, 2002, 2003, and 2006 shown as percentages of isolates with the ST-22 complex in each year. (c) Trend of the ST-677 complex among human isolates from 1996, 1999, 2002, 2003, and 2006 shown as percentages of isolates with the ST-677 complex in each year. (d) Trend of the ST-283 complex among human isolates from 1996, 1999, 2002, 2003, and 2006 shown as percentages of isolates with the ST-283 complex in each year.