In the US, H. pylori vacA shows allelic variation in the signal sequence (which may be type sla, slb or s2) and the mid-region (type ml or m2). Previous PCR-based vacA mid-region typing classified most, but not all, Asian and South American strains tested as ml or m2. We now sought to investigate vacA mid-region diversity further.MotlmodL We studied 13 Japanese, 6 Chinese, 9 Thai, and 8 Peruvian H. pylori isolates. cagA was identified by colony hybridisation (CH), vacA signal sequence was typed by PCR, and vacA mid-region was typed proximally by CH and distally by PCR. Sections of the vacA mid-region from 8 strains were PCR-amplified, sequenced, and compared with known sequences from 8 other strains.Rcuts Of the 36 Asian and South American strains studied, 35 were cagA+ (the cagA-was Peruvian) and 35 were vacA sla (1 cagA + Peruvian was slb). vacA mid-regions from the 13 Japanese strains were not PCR-amplified by ml or m2-specific primers, but hybridised weakly with an ml probe. Sequence analysis of vacA from 1 Japanese strain revealed 91% nucleotide identity with the ml probe but only 71% identity with the m2 probe. The previously equivocal Thai and Peruvian strains also had ml-like mid-region sequences. A Chinese strain was ml in the proximal mid-region and m2 distally, showing a clear crossover site. Final mid-region types were: Japanese, all 13 ml; Chinese, 1 ml, 1 ml/m2, 4 m2; Thai, 3 ml, 6 m2; Peruvian 4 ml, 4 m2. Distal mid-region sequences of 16 strains, compared over 294 bp, clustered into 2 groups, ml and m2. Nucleotide identity between ml and m2 strains ranged from 73-78%. Within groups, m2 strains were less diverse than ml strains (m2 range 94-99.7%, ml 88-99.3%, p<0.001). Sequence analysis of 7 ml and 3 m2 strains over 1.1kb proximally showed maintenance of clustering outside the 294bp region C duions These Asian and South American strains are similar in terms of cagA status and vacA sla genotype, but fall into 2 vacA midregion groups. ml sequences are more diverse than m2, and thus may be phylogenetically older. The vacA sequence of 1 Chinese strain suggests recombination in vivo between ml and m2 alleles. Introduction: H.pylori antimicrobial susceptibility is an important determinant ofthe efficacy of eradication therapies'. The prevalence of antimicrobial resistance varies within the UK and may increase given the increased use of eradication therapy. This multicentre study assesses the prevalence and possible associations ofH.pylon antimicrobial resistance. Methods: H.pylon was isolated from antral biopsies of patients undergoing routine endoscopy and cultured according to standard microbiological methods. Antimicrobial resistance was determined using "E-tests" or disc tests (tinidazole only) with breakpoints defined by previous studies. Results: H.pyloni was isolated from 32% (1222/3823) of patients and antimicrobial susceptibility determined in 90% (1077/1222) Previous case-control studies of IBD have used hospital or community derived controls. There are obvious inherent biases in both metho...
