Abstract
BackgroundCampylobacter (C.) jejuni is the leading cause of human campylobacteriosis worldwide. We performed a molecular epidemiological study to investigate the genetic relationship among C. jejuni strains isolated from human diarrhoeal patients, broiler products and dairy cattle in Lithuania.MethodsThe C. jejuni isolates from human clinical cases, dairy cattle and broiler products were genotyped using multilocus sequence typing (MLST). Allele numbers for each housekeeping gene, sequence type (ST), and clonal complex (CC) were assigned by submitting the DNA sequences to the C. jejuni MLST database (http://pubmlst.org/campylobacter). Based on the obtained sequence data of the housekeeping genes a phylogenetic analysis of the strains was performed and a minimum spanning tree (MST) was calculated.ResultsAmong the 262 C. jejuni strains (consisting of 43 strains isolated from dairy cattle, 102 strains isolated from broiler products and 117 clinical human C. jejuni strains), 82 different MLST sequence types and 22 clonal complexes were identified. Clonal complexes CC21 and CC353 predominated among the C. jejuni strains. On ST-level, five sequence types (ST-5, ST-21, ST-50, ST-464 and ST-6410) were dominating and these five STs accounted for 35.9% (n = 94) of our isolates. In addition, 51 (19.5%) C. jejuni strains representing 27 (32.9%) STs were reported for the first time in the PubMLST database (http://pubmlst.org/campylobacter). The highest Czekanowski index or proportional similarity index (PSI) was calculated for C. jejuni strains isolated from human campylobacteriosis cases and broiler products (PSI = 0.32) suggesting a strong link between broiler strains and human cases. The PSI of dairy cattle and human samples was lower (PSI = 0.11), suggesting a weaker link between bovine strains and human cases. The calculated Simpson’s index of all C. jejuni isolates showed a high genetic diversity (D = 0.96).ConclusionOur results suggest that broiler products are the most important source of human campylobacteriosis in Lithuania. The study provides information on MLST type distribution and genetic relatedness of C. jejuni strains from humans, broiler products and dairy cattle in Lithuania for the first time, enabling a better understanding of the transmission pathways of C. jejuni in this country.
Highlights
Campylobacter (C.) jejuni is the leading cause of human campylobacteriosis worldwide
This C. jejuni strain collection was composed of 43 strains isolated from dairy cattle at farm level between May 2012 and August 2012, 102 strains isolated from retail broiler products collected between October 2011 and October 2012 and 117 clinical human C. jejuni strains that were collected at the Microbiological Laboratory of Kaunas Clinical Hospital between September 2011 and October 2012
Forty (15.3%) strains were assigned to 19 sequence type (ST) which did not match any of the clonal complex (CC) of the Multilocus Sequence Typing (MLST) database
Summary
Campylobacter (C.) jejuni is the leading cause of human campylobacteriosis worldwide. We performed a molecular epidemiological study to investigate the genetic relationship among C. jejuni strains isolated from human diarrhoeal patients, broiler products and dairy cattle in Lithuania. C. jejuni can be detected in other food animals as well [4, 5], with growing evidence that sources other than poultry products, such as cattle, might be a significant reservoir for human infections [6, 7]. Multilocus Sequence Typing (MLST) displays a reasonable level of heterogeneity of Campylobacter sequence types (STs) among the different sources and has become one of the most extensively used molecular typing methods for C. jejuni population analysis and can be applied for source attribution studies [8,9,10,11]
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