EFFECTS OF SUBINHIBITORY CONCENTRATIONS OF ANTIBIOTICS ON BIOLOGICAL PROPERTIES OF SALMONELLA-TYPHIMURIUM

We followed the effects of subinhibitory concentrations (sub-MICs) of 7 antibiotics (ticarcilin, cefotaxim, streptomycin, gentamicin, ciprof loxacin, pefloxacin, mitomycin C) on the sensitivity of a Salmonella t yphimurium strain to standard bacteriophages, on the phage DNA as well as on the factors of virulence (permeability and cytotoxic activity). The phage type was not changed by the sub-MICs of the tested antibiot ics. However, differences were found in culture filtrates prepared fro m the bacterial suspensions of the strain cultivated with the sub-MICs . Marked inducing effects on phage DNA were exhibited by mitomycin C ( 1/2, 1/4, 1/8 of the MIC), pefloxacin (1/2, 1/4, 1/8 of the MIC) and c ipronoxacin (1/2, 1/4, weakly also 1/8 of the MIC). Ticarcilin (1/2 of the MIC), like the aminoglycosides streptomycin and gentamicin (1/2, 1/4, 1/8 of the MIC), had a weak effect. Sub-MICs of the studied antib iotics (with the exception of 1/8 of the MIC of ciprofloxacin and 1/4 of the MIC of ticarcilin) decreased the permeability reaction in rabbi t skin. Most effective was streptomycin (1/2 of the MIC). Sub-MICs of the tested antibiotics (with the exception of 1/4 and 1/8 of the MIC o f ciprofloxacin and 1/4 of the MIC of pefloxacin) caused also an inhib ition of the factor responsible for morphological changes on Vero cell s. Gentamicin and streptomycin were effective at all the sub-MICs test ed.