Postantibiotic effects and postantibiotic sub-MIC effects of ciprofloxacin, pefloxacin and amikacin on the biological properties ofSalmonella strains

The postantibiotic effect (PAE) and the postantibiotic sub-MIC effect (PASME) of ciprofloxacin, pefloxacin and amikacin were studied forSalmonella typhimurium andS. enteritidis strains. PAE was induced by 2× and 4×MIC of antibiotics studied for 0.5 h. After PAE and PASME their effect on prophage induction of a lysogenicS. typhimurium strain and on Congo red binding for both strains as a marker of their surface hydrophobicity was examined. The longest PAE was found after treatment with ciprofloxacin, higher values being observed withS. typhimurium. PAEs of pefloxacin and amikacin were much lower, except for the suprainhibitory concentration 4×MIC of amikacin withS. enteritidis (6.9 h). PASMEs of ciprofloxacin did not allow any regrowth of either strain. For other antibiotics the PASME's were different while concentrations of 2×MIC+0.2×MIC and 0.3×MIC, and of 4×MIC+0.1×MIC, 0.2×MIC and 0.3×MIC of amikacin did not allow any regrowth ofS. enteritidis. PAEs of the antibiotics tested did not affect the Congo red binding by bothSalmonella strains, but the PAEs of ciprofloxacin and pefloxacin expressively induced a prophage of lysogenicS. typhimurium strain. We noted the influence of Congo red binding after applying 4×MIC+0.1×MIC, 0.2×MIC and 0.3×MIC of amikacin forS. typhinurium and 2×MIC+0.1×MIC forS. enteritidis.