Distribution of Campylobacter jejuni multilocus sequence types isolated from chickens in Poland.

Poultry is recognized as the most important source of food-related transmission of Campylobacter jejuni to humans and campylobacteriosis is the most commonly reported zoonotic bacterial disease in the European Union. It has been documented that C. jejuni is genetically diverse and analyses of bacterial isolates usually show a large strain variety. Therefore, molecular typing of strains represents an important tool to study the genetic diversity of isolates and to trace individual strains that cause human infections. The aim of the study was characterization of genetic population structure and antimicrobial resistance (AMR) of C. jejuni isolated from Polish chickens. C. jejuni from chicken ceca and the corresponding carcasses (72 and 61 strains, respectively), originating from 128 flocks in Poland during February 2011 and May 2013, were used in the study. The isolates were tested for their population structure and genetic diversity using a multilocus sequence typing (MLST) scheme with connection to their antimicrobial resistance. The molecular analysis of 133 C. jejuni generated 39 different sequence types (ST); 3 of them were defined for the first time. Additionally, 16 STs were represented by single isolates. The most common STs observed were 6411 (16.5% isolates) and 257 (15.0% strains). The first mentioned ST was resistant to 3 different classes of antibiotics, i.e., quinolones, tetracyclines, and aminoglycosides. Overall, 125 (94.4%) of C. jejuni isolates demonstrated antimicrobial resistance and the most frequent AMR profile observed was ciprofloxacin, nalidixic acid, tetracycline (47.4% strains). Likewise, the clonal complexes CC 257 and CC 353 were defined as the predominant molecular groups covering altogether 37 C. jejuni strains. No associations between CCs and the origin of the samples as well as the place of isolation were found. This study highlights that the C. jejuni population from chickens in Poland was diverse and showed a weak clonal structure.