An epidemiological study of Swedish Campylobacter jejuni isolates from humans and broilers using multilocus sequence typing

Campylobacter jejuni is the main cause of bacterial diarrhoeal illness in developed countries, with ~7000 cases being reported each year in Sweden. C. jejuni has received growing attention since it’s recognition as a human pathogen in the 1970s, but its epidemiology is complex and much still remains unknown. There are several potential reservoirs for C. jejuni, including environmental sources as water and soil, wild and domesticated animals, particularly poultry, but also other livestock and pets. In this study 348 Swedish C. jejuni isolates from the year 2000 from humans (n = 164) and broilers (n = 184) were characterized with multilocus sequence typing (MLST) with the aim of comparing the population structures and diversity of C. jejuni between isolates from the two hosts. MLST is a method for characterization of bacterial isolates that indexes the variation in DNA sequence of multiple protein encoding housekeeping genes. A secondary aim in this study was to compare populations of C. jejuni from 11 subgroups of isolates based on location of the sampling. The overlap between the populations was analyzed numerically based on genotypes detected and with analysis of phylogeny, gene flow and molecular variation. It was shown that the population structure of C. jejuni isolates from broilers and humans show a high degree of similarity, supporting broilers as an important source of human infection. However, even though the population structure of human and broiler C. jejuni were almost genetically indistinguishable other sources of C. jejuni infections in humans cannot be ruled out since the same genotypes can be found in other sources as well. Analysis of the 11 subgroups suggested that there may be a difference in populations infecting humans in different Swedish regions, and between populations of C. jejuni in broilers from different slaughterhouses. But this could be a result of chance since most of the subgroups were small. Future studies to improve the understanding of C. jejuni epidemiology, for which MLST has proven itself as a valid method, is important to develop control strategies to prevent infection with this common cause of diarrhoeal illness