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CIostridium chau woei strain 0 ki nawa produced spontaneous non-mot i I e variants at an unusually high rate (approx. conditions without mutagen. Revertants of non-motile variants were detected at a rate of approximately lo-'. Biochemically, every variant corresponded well with the parental strain. By transmission electron microscopy, three of nine non-motile variants of strain Okinawa were found to be flagellate, while the other six were found to be aflagellate. These phenotypes were confirmed by Western blot analysis using monoclonal antibodies directed against the flagella of C. chauvoei. Moreover, the parental flagellate strain and non-motile flagellate variants were significantly more virulent in mice than non-motile, aflagellate variants. Our results demonstrated that phase variation in motility and flagellation occurs in C. chauwoei, and that the flagella are associated with the full expression of virulence. per generation) under normal

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ABSTRACT. A total of 101 Actinobacillus pleuropneumoniae isolates from diseased pigs taken from across Japan during 2002 to 2005 were examined for antimicrobial susceptibility. All isolates were susceptible to ceftiofur, erythromycin, florfenicol and enrofloxacin. Antimicrobial-resistant isolates to oxytetracycline (OTC) (27.7%), dihydrostreptomycin (10.9%), thiamphenicol (10.9%), kanamycin (5.9%), trimethoprim (4.0%) and ampicillin (2.0%) were recognized. OTC-resistant isolates taken from 1986 to 2005 were examined for the tetracycline resistance gene. In OTC-resistant isolates, tetB has been the most frequently isolated gene in Japan. It is likely that the dissemination of tetB has contributed to the increased OTC resistance of A. pleuropneumoniae in Japan.

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