POSTANTIBIOTIC EFFECTS OF OFLOXACIN ON ESCHERICHIA-COLI, KLEBSIELLA-PNEUMONIAE, STAPHYLOCOCCUS-AUREUS, AND STREPTOCOCCUS-PYOGENES

A viable counting technique was used to determine the post-antibiotic effect (PAE) of ofloxacin against four bacterial species, treated with either once of four times the minimum inhibitory concentration for 1 or 3 h. Similar to the results obtained previously with ciprofloxacin, ofloxacin gave PAE values with Escherichia coli, Staphylococcus aureu s, and Streptococcus pyogenes. Cell division of Klebsiella pneumoniae was inhibited on removal of ofloxacin, but no clear PAE was demonstrat ed with this species because once replication recommenced, the mean ge neration times of drug-treated cultures were much shorter than those o f untreated controls. Therefore, although the results obtained with ci profloxacin and ofloxacin imply a consistency of PAE for 4-quinolones within a species, the response to DNA damage induced by 4-quinolones i s multifaceted and species dependent. 4-quinolones inhibit both DNA re plication and cell division, whilst at the same time stimulating DNA r epair pathways. Thus, in some cases PAEs result from an increased post -treatment lag phase which may be followed by nearly normal multiplica tion, whereas in other cases a long lag may be followed by abnormally rapid cell division, with the generation times of treated cultures bei ng shorter than those of corresponding drug-free controls. The PAE of a drug-induced lag may thus be masked by rapid cell division once grow th resumes.