Pharmacodynamic parameters of ofloxacin, tobramycin and ceftriaxone and their effect on the biological properties of salmonellae.

The postantibiotic effect and postantibiotic sub-MIC effect of ofloxacin (CAS 82419-36-1), tobramycin (CAS 32986-56-4) and ceftriaxone (CAS 73384-59-5) on two salmonella serotypes (S. typhimurium and S. enteritidis) were studied. The influence of postantibiotic effect and postantibiotic sub-MIC effect of the antibiotics on prophage induction of the lysogenic S. typhimurium strain and on Congo red binding by both serovars as indicator of their invasive ability was examined. The postantibiotic effect was induced by exposure of the bacteria to the 2x and 4x MIC concentrations of antibiotics studied for 0.5 h. The postantibiotic effects were different; ceftriaxone induced the longest postantibiotic effect against S. enteritidis, and the 4x MIC of tobramycin induced the longest postantibiotic effect against S. typhimurium. The postantibiotic sub-MIC effects lasted longer and in the case of subinhibitory concentrations of tobramycin on S. typhimurium and ceftriaxone on S. enteritidis did not allow any regrowth. The results showed that the postantibiotic effect and postantibiotic sub-MIC effect of ofloxacin induced a prophage of a lysogenic S. typhimurium strain, and the postantibiotic sub-MIC effects of tobramycin influenced Congo red binding by S. enteritidis cells.