Evaluation of antibiotics used for enterohemorrhagic Escherichia coli O157 enteritis--effect of various antibiotics on extracellular release of verotoxin

Abstract

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.