Postantibiotic effect of CI-960, enoxacin and ciprofloxacin on Escherichia coli: effect on morphology and haemolysin activity

Abstract

The postantibiotic effect (PAE) has been classically defined as the suppression of bacterial growth that persists after limited exposure of organisms to antimicrobial agents. Morphology and haemolysin activity during the PAE of three quinolones on Escherichia coli were examined in this study. A one hour exposure to the quinolones, CI-960, enoxacin and ciprofloxacin, produced a PAE of 0.5-2.0 h. When determinated by Coulter counter, at 0.5 x MIC of enoxacin or CI-960 after 1 h exposure, 58% or 42% cells, respectively, of the treated cells were filamentous (cell length greater than 12 microns). After drug removal, the population of the filamentous cells decreased, however, after even 4 h, 12% and 2% of the cells were still filamentous after exposure to enoxacin or CI-960. Further morphological studies during the PAE showed that the first division of the filamentous cell was asymmetrical, and both bacterial cell division and septation were delayed after exposure to 0.5 MIC of CI-960. Following quinolone removal, the treated E. coli did not exhibit normal activity of haemolysin for at least 2 h. Internal haemolysin activity was adversely affected for 1 h. The results of this study suggest that any consideration of postantibiotic effects should include the residual antibiotic effects on bacterial morphology and virulence factors, in addition to the defined suppression of bacterial regrowth.

Evaluation of in vitro antibacterial activity of some disinfectants on Escherichia coli serotypes.

“…Cell filamentation was observed when the exposure time to this concentration increased to 15 min. A further increase in exposure time to 60 min resulted in extensive filamentation, which in Gram-negative rods is usually followed by a delay in septum formation and in cell division (Guan and Burnham, 1992). A similar effect was observed when E. coli was exposed to cryptolepine (Sawer et al, 1995).…”

Isolation and in-vitro and in-vivo characterisation of a mutant of Pseudomonas aeruginosa PAO1 that exhibited a reduced postantibiotic effect in response to imipenem

“…The tendency of CM41 cells to resume a normal cell size distribution after exposure to imipenem was consistent with its shorter PAE: it should be pointed out that 3 h after antibiotic removal (after the end of the PAE as defined in equations 1, 2, 3 and 4) the cells of both PAO1 and CM41 remained smaller than those in control cultures. Discrepancies between the PAE measured by viable counts and the period before which cells resumed normal morphology were also noted by Guan & Burnham (1992). They found that E. coli cells did not resume normal cell size for at least 4 h after treatment with the quinolone enoxacin, whose PAE was 0-7 h. Thus changes in cell size should be considered in addition to inhibition of bacterial growth, when studying the PAE.…”

Cell surface hydrophobicity and adherence of a strain of group B streptococci during the post-antibiotic effect of penicillin

“…Such a delay in turbidity development was observed by BIGGER 6 after the addition of penicillinase in staphylococcal and streptococcal cultures that had been previously exposed to penicillin G in vitro. This post-antibiotic effect (PAE) has thus been the purpose of many studies during the last decades, because of morphological, ultrastructural and biochemical changes that it produces in bacteria 18 . Regarding streptococci of groups A an C exposed to inhibitory concentrations of penicillin during growth in vitro, changes were observed in the elaboration of bacterial antigens, such as enzymes, toxins and cellular components 2,15 in the cell-surface hydrophobicity and also adherence capabilities 2,16 .…”