Postantibiotic effects of imipenem and enoxacin against S-typhimurium and S-enteritidis and the influence on their surface hydrophobicity

The influence of the postantibiotic effect (PAE) and the postantibiotic sub-MICs effect (PA SME) of imipenem and enoxacin on the surface hydrophobicity of S. typhimurium and S. enteritidis strains were studied by evaluating Congo red binding and the aggregation in molar solutions of ammonium sulfate (SAT). A PAE was induced by 2x and 4x MIC of antibiotics tested for 0.5 h. Suprainhibitory concentrations of imipenem against S. typhimurium induced a short PAE (0.3-0.6 h) compared to S. enteritidis (6.0-9.7 h). Suprasubinhibitory concentrations of imipenem did not allow a regrowth of S. enteritidis. Similar results were also found for enoxacin. Evaluation of surface hydrophobic properties of the salmonellas after affecting both PAEs and PA SMEs has shown that imipenem at concentrations 4xMIC and 4xMIC + 0.3xMIC partially influenced the hydrophobicity of S. typhimurium. S. enteritidis was more susceptible toward both antibiotics tested.