Genotyping of Campylobacter jejuni strains from Danish broiler chickens by restriction fragment length polymorphism of the LPS gene cluster K.N. Knudsen 1 , D.D. Bang 1 , E.M. Nielsen 2 and M. Madsen 1 1 Department of Poultry, Fish and Fur Animals, Danish Institute for Food and Veterinary Research, Aarhus N, Denmark, and 2 Department of Gastrointestinal and Parasitic Infections, Statens Serum Institut, Copenhagen S, Denmark 2003/0493: received 10 June 2003, revised 1 December 2004 and accepted 9 December 2004 ABSTRACT K.N. KNUDSEN, D.D. BANG, E.M. NIELSEN AND M. MADSEN. 2005. Aims: To apply and evaluate LG (LPS genes) genotyping, which is a genotyping method based on a cluster of genes involved in the synthesis of surface lipopolysaccharides (LPS) in Campylobacter species, for typing of Campylobacter jejuni isolates obtained from Danish broiler chickens. Furthermore, the LG genotyping method was used to study the genetic stability of four C. jejuni strains after gastrointestinal passage through experimentally infected chickens. Methods and Results: In the present study, the LG genotyping method was modified with respect to the restriction enzymes used. To validate the method, 63 Penner serotype reference strains and 107 C. jejuni chicken isolates, representing the most common Penner serotypes of C. jejuni in Danish poultry, were selected for typing. The method was successfully used for typing all isolates and the LG genotype profiles were reproducible. There were no changes in the LG genotype of the C. jejuni strains obtained after experimental passage through chickens. Conclusions: All C. jejuni strains obtained from broiler chickens were typeable by the LG genotyping method. Application of the RsaI restriction enzyme improved the method in terms of ease and consistency of analyses and increase of discriminatory power. Significance and Impact of the Study: The LG genotyping method is a valuable tool for typing C. jejuni isolates obtained from poultry. However, the association between Penner serotyping based on passive haemagglutination of heat-stable antigens and LG genotyping was low when applied to poultry isolates. This is in contrast to previous studies on isolates of human origin that reported a high correlation between results obtained by the two typing methods (Shi et al. 2002). Keywords: broiler chickens, Campylobacter jejuni, genotyping, lipopolysaccharide genes. INTRODUCTION Campylobacteriosis is one of the most common bacterial intestinal infections of humans in many industrialized countries (Altekruse et al. 1999). Although the number of human campylobacteriosis cases in 2003 decreased by 19% in comparison with the year 2002, thermophilic campylo- bacters remain the most important cause of bacterial gastrointestinal disease in Denmark, with 3542 laboratory- confirmed episodes of campylobacteriosis in 2003 (65Æ8 cases per 100 000 inhabitants) (Anon. 2004). Campylobacteriosis in man is mainly caused by the species Campylobacter jejuni. The clinical symptoms range from mild watery diarrhoea to severe dysentery-like illness. In Correspondence to: Katrine Nørrelund Knudsen, Department of Poultry, Fish and Fur Animals, Danish Institute for Food and Veterinary Research, Hangøvej 2, DK-8200 Aarhus N, Denmark (e-mail: kakn@dfvf.dk). ª 2005 The Society for Applied Microbiology Journal of Applied Microbiology 2005, 99, 392–399 doi:10.1111/j.1365-2672.2005.02594.x