1994 Volume 42 Issue 10 Pages 1095-1102
“Post-antibiotic sub-MIC effect (PASE)” is defined as growth suppression of a post-antibiotic effect (PAE) phase bacterium by the sub-MIC of an antibiotic. The PASEs of aspoxicillin for Streptococcus pneumoniae, Staphylococcus aureus, Enterococcus faecalis and Escherichia coli and of temafloxacin, ofloxacin, tetracycline and erythromycin for S. aureus were investigated in vitro. A PAE was induced by exposing strains to 2× or 4× the MIC of the antibiotic for 1 h. After removing the antibiotic by washing the bacterial culture, the cells were exposed to different sub-inhibitory concentrations (0.0625, 0.125, 0.25 and 0.5× the MIC) of the same drug, and growth curves were examined later. Unexposed controls were exposed to the sub-MICs of the antibiotic to determine their sub-MIC effects (SEs). In general, the duration of growth suppression of pre-exposed cells was longer than that of unexposed cells. In the case of aspoxicillin and S. pnenmoniae, S. aureus, and E. coli and of temafloxacin and S. aureus, an initial decrease in the viable count of the pre-exposed cells was observed after exposure to the sub-MIC. Pre-exposure to 2× or 4× MIC of the antibiotics enhanced the susceptibility of organisms to sub-MIC levels. Both the PASEs and the PAEs will probably affect the optimal dosing schedules of antibiotics.
