Campylobacter jejuni was isolated from 49 of 100 samples (49.0%) of retail chicken. An MPN procedure was used to determine the change in the level of Campylobacter jejuni in chicken meat on freezing. After freezing at-20° for 7 days, bacterial numbers were reduced a factor of 1/10-1/100, and in 25 out of 49 samples (51.0%) numbers decreased to less than the detection limit (<15/100g) for the MPN method. PFGE analysis of isolates indicated that individual commercial chickens were contaminated with strains of multiple genotypes. In 8 of 24 samples (33.3%), different genotypes were observed among isolates from chicken samples before and after freezing. It is therefore necessary to submit as many isolates for genotyping as possible when investigating the cause of food poisoning. When studying chickens inoculated with C. jejuni, there was a smaller decrease in bacterial numbers in samples that were kept frozen without thawing than in samples which were repeatedly frozen and thawed. This suggests that the elimination of C. jejuni in frozen chicken mainly occurred during the process of freezing or of thawing.
A total of 170 Penner B, D group Campylobacter jejuni strains isolated from humans, chickens and cattle were found to represent 80 different types by PFGE (pulsed-field gel electrophoresis) according to an investigation conducted by three institutes in Akita, Saitama, and Shizuoka prefectures. Fifteen PFGE types were identical between isolates from humans and chickens and one PFGE type was identical between those from humans and cattle. There were some PFGE types which were widespread in time as well as in geography. Our study indicates that there are some Campylobacter strains which spread throughout large areas and become the cause for repeated human infections. The strains examined were grouped into four major clusters (I-IV) on the basis of UPGMA (unweighted pair group method with averages). In group IV, eight PFGE profiles were identical between isolates from humans and chickens. This suggests that isolates from chicken meat and chicken liver, especially those classified into this group, are closely related to those from human Campylobacter infections.