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A cytotoxic component(s) was detected in culture filtrates of Klebsiella oxvtoca isolated from patients with antibiotic-associated hemorrhagic colitis. Eleven of 12 isolates exhibited cytotoxicity on HEp-2 cells. The cytotoxic activity of K. oxvtoca strain MH43-1 was stable for the treatment of 60 C for 30 min, but inactivated by the treatment of 100 C for 15 min.This cytotoxicity was not destroyed by the treatment with trypsin or pronase, and the component was filtrable through a membrane filter which cut off molecular weight 5,000.

A total of 111 clinical isolates of Campylobacter jejuni and 10 clinical isolates of Campylobacter coli were characterized by their susceptibility to nine antimicrobial agents and by their plasmid profiles on agarose gel electrophoresis. All of the C. jejuni isolates were susceptible to chloramphenicol, ciprofloxacin, erythromycin, kanamycin, and nalidixic acid, but 55% were tetracycline resistant. In the 10 C. coli isolates, a high prevalence of multiple-antibiotic resistance was noted. Plasmids were found in 82% of the tetracycline-resistant and 15% of the tetracycline-susceptible C. jejuni isolates. Tetracycline resistance in six randomly selected C. jejuni isolates, which contained 50-or 135-kilobase (kb) plasmids, was transferred by conjugation to a Campylobacter fetus subsp. fetus recipient with recovery of a 50-or a 45-kb plasmid from transconjugants. From one multiple-antibiotic-resistant C. coli isolate, resistance to tetracycline, kanamycin, and chloramphenicol was transferred concomitantly with a 58-kb plasmid, pNR9589. Nonconjugative 98-kb plasmids, pNR9131 and pNR9581, from C. coli isolates with resistance to tetracycline, kanamycin, and erythromycin were shown by cloning experiments to code for at least kanamycin resistance. Restriction digests revealed that 50-kb plasmids from tetracycline-resistant C. jejuni isolates were identical, although plasmids from multiple-antibioticresistant C. coli isolates shared partial DNA homology to each other. Cloning of the kanamycin and chloramphenicol resistance genes of pNR9589 into Escherichia coli showed that the two genes are closely linked or clustered. Double-digestion analysis of the fragments encoding the kanamycin resistance of pNR9131, pNR9581, and pNR9589 showed that these three plasmids contain a common fragment related to kanamycin resistance.Campylobacterjejuni is recognized as one of the common causes of acute bacterial enteritis throughout the world (2, 17). More than 200 strains of C. jejuni and a small number of C. coli strains, 60% of which are from children, are isolated every year in Tokyo Metropolitan Toshima General Hospital.Taylor et al. (19, 20) and Tenover et al. (21) demonstrated that tetracycline resistance in C. jejuni is mediated by conjugative R plasmids with a size of 60 kilobases (kb), and more recently, Tenover et al. (22) showed that all tetracycline-resistant C. jejuni harbored R plasmids. Most recently, Taylor (18) mapped the tetracycline resistance plasmid. Studies on plasmid detection in Campylobacter spp.have not yet been carried out in Japan, although clinical and epidemiological studies on Campylobacter spp. have been performed extensively. In the present study, we examined the MICs of nine antimicrobial agents against Campylobacter isolates, the plasmid carriage in these isolates, and the relationship between antimicrobial resistance and plasmid carriage in C. jejuni and C. coli. Moreover, we analyzed three plasmids isolated from multiple-antibiotic-resistant C. coli strains by restriction endonuclease digestion and c...