The effects of sub-inhibitory concentrations of antibiotics on V. vulnificus cytotoxicity and rtxA1 transcription.

A. Cytotoxicity assay. The impaired cytotoxicity of ΔrtxA1 compared with that of the WT strain shows that cytotoxicity at 120 min is due principally to RtxA1. V. vulnificus cytotoxicity is inhibited more markedly by 1/4 MIC of ciprofloxacin than by 1/4 MICs of cefotaxime or minocycline (n = 12 per group). B. Transcriptional reporter assay. The transcription of rtxA1 is more efficiently inhibited by 1/4 MIC of ciprofloxacin than by 1/4 MICs of cefotaxime or minocycline (n = 4 per group). WT, MO6-24/O; ΔrtxA1, CMM770 (MO6-24/O background with a deletion mutation in the rtxA1 gene); CTX, cefotaxime; CIP, ciprofloxacin; MCL, minocycline. *P<0.05 compared to the values for ciprofloxacin (Student’s t-test).