Key words : Vero toxin, O157, enterohemorrhagic E. coli, antibiotics

Key words : Vero toxin, O157, enterohemorrhagic E. coli, antibiotics

Table 1 Comparison of minimal growth inhibitory concentration (MIC: pg/ml) of 10 antibiotics against enterohemorrhagic Escherichia coli MICs in parenthesis were determined in anaerobic condition.

Fig. 1 Bactericidal activities and the effect of 10 antibiotics on the extracellular release of verotoxins Number of cells: c,number of inoculated cells, \ \,number of viable cells after 2h. and VT2) measured by RPLA Bars indicate the amount of extracellular verotoxin(vt1.s erially diluted culture supernatant was mixed with anti-vt1 or anti-vt2 coated latex particles and at room temperature overnight. The positive reaction detected left was as agglutination of latex particles. The amount of verotoxin was expressed by the highest dilution of culture supernatant showing positive agglutination.

1) O'Brien AD, LaVeck GD: Purification and characterization of a Shigella dysenteriae 1-like toxin produced by Escherichia coli. Infect Immun 1983 ; 40 : 675-683. 2) Padhye VV, Kittell FB, Doyle MP : Purification and physicochemical properties of a unique Vero cell cytotoxin from Escherichia coli O157 : H7. Biochem Biophys Res Commun 1986 ; 139 : 424-430. 3) Lin Z, Yamasaki S, Kurazono H et al.: Clon- and sequencing of two new Verotoxin ing 2 varient genes of Escherichia coli isolated from cases of human and bovine diarrhea. Microbiol Immunol 1993 ; 37(6) : 451-459. 4) O'Brien AD, Holmes RK : Shiga and shiga- toxins. Microbiol Rev 1987 ; 51 : 206-220. like 5) Walterspiel JN, Ashkenazi S, Morrow AL et al.: Effect of subinhibitory concentration of antibiotics on extracellular Shiga-like toxin 1. Infection 1992 ; 20 : 25-29. 6) Pavia AT, Nichols CR, Green DP et al. : Hemolytic-uremic syndrome during an outbreak of Escherichia coli 0157 : H7 infections for mentally retarded persons : Clinical and

epidemiologic observations. J Pediatr 1990 ; 116 : 544-551. 7) Strockbine NA, Marques LRM, Newland JW, Smith HW, Holmes RK, O'Brien AD: Two toxin-converting phages from Escherichia coli tinct toxins with similar biological activities. Infect Immun 1986 ; 53 : 135-140. 8) Ostroff SM, Kobayashi JM, Lewis JH : Infection with Escherichia coli O157 : H7 in Washington State. The first year of statewide disease surveillance. JAMA 1989 ; 262 : 355-359. 9) Proulx F, Turgeon JP, Delage G et al.: Randomized controlled trial of antibiotic therapy for Escherichia coli O157 : H7 enteritis. J Pediatr 1992 ; 121 : 299-303. Evaluation of Antibiotics Used for Enterohemorrhagic Escherichia coli Teruyo ITO, Emi AKINO & Keiichi HIRAMATSU Department of Bacteriology, Faculty of Medicine, Juntendo University We tested antimicrobial activities of ten oral antibiotics; ampicillin (ABPC), cefdinir (CFDN), cefaclor (CCL), fosfomycin (FOM), norfloxacin (NFLX), nalidixic acid (NA), kanamycin (KM), minocycline (MINO), doxycycline (DOXY), and tetracycline (TC) against eleven enterohemorrhagic Esherichia coli (EHEC) O157 clinical strains. Two strains were resistant to ABPC and TC. Other strains were sensitive to all the ten antibiotics. To investigate the effect of antibiotics on extracellular release of verotoxin (VT), strain EHEC TT10 was grown in 10 ml of LB containing various concentrations of the antibiotics for 2 h. Number of viable cells were counted and the amounts of VT1 and VT2 released in the supernatants were measured with reverse passive latex agglutination (RPLA) using serially diluted sterilized culture supernatants. The amount of VT1 and VT2 was evidently increased with ABPC, CFDN, CCL, and FOM, the inhibitors of cell wall biosynthesis. In the case of quinolons, VT2 was markedly increased, but VT1 was not released to the supernatant. KM killed the bacteria efficiently, but no release of VT1 or VT2 was observed in the supernatant. Tetracyclines (MINO, DOXY, and TC) did not make the bacteria release either VT1 or VT2, but could not kill the bacteria appreciably. These results indicated that the inhibitors of protein synthesis (KM, MINO, DOXY, TC) are the safe antibiotics not causing the release of verotoxin from the cells and thus preventing development of hemolytic uremic syndrome (HUS) or thrombotic thrombocytopenic purpra (TTP), the important sequelae of the enteritis.