POSTANTIBIOTIC EFFECTS OF NORFLOXACIN AND NETILMICIN AND THEIR INFLUENCE ON THE BIOLOGICAL PROPERTIES OF SALMONELLA STRAINS

The postantibiotic effect (PAE) and the postantibiotic sub-MIG effect (PA SME) of norfloxacin and netilmicin on two clinical strains - Salmo nella typhimurium and Salmonella enteritidis was investigated. After b oth PAE and PA SME of antibiotics were studied, we determined their ef fect on the induction of a prophage in the lysogenic S. typhimurium an d on Congo red binding by both serovars, as an indicator of invasive a bility in vitro. The PAE was induced by 2 . MIC and 4 . MIC of norflox acin and netilmicin for 0.5 h. Norfloxacin induced a longer lasting PA E on both Salmonella serovars as compared to netilmicin. Supra-subinhi bitory concentrations (PA SMEs) delayed regrowth of tested strains. Th e PA SMEs of norfloxacin as well as of netilmicin (except 2 MIC + 0.1 . MIC concentration) did not allow regrowth of S, enteritidis. The pro phage-inductive ability of norfloxacin was more expressive after PA SM Es than PAE. The PA SMEs of netilmicin caused loss of Congo red bindin g by S. typhimurium cells and decreased this binding by S. enteritidis cells.