[Effect of suprainhibitory (supra-MIC) concentration of clindamycin on endotoxin release from Bacteroides fragilis]

The aim of this work was to determine the influence of clindamycin at concentration 100 x MIC on the growth of culture and the induction of endotoxin release from the cells of standard B. fragilis IPL E 323 strain. The antibiotic was added to 24-hour culture of the strain in BHI medium (time 0), its final concentration was 12.5 mg/l. The samples for further examinations were collected at time 0 and after 1, 2, 3 and 24 hours of continued incubation. At the same time the strain was cultured in a medium without the antibiotic. The optical density (OD 420 nm) of each sample was determined, they were centrifuged (2000 x g, 10 min), the supernatants were filtered (0.45 micron filters) and concentrated three times (5000 D ultrafilters). Two serological methods were applied to detect the presence of endotoxin in filtrates of culture medium: immunoelectroprecipitation (IEP) and immunoenzymatic assay (dot-ELISA) with rabbit anti-IPL E 323 immune serum. The results of experiments performed with filtrates of culture without the antibiotic indicate that standard B. fragilis IPL E 323 strain liberates endotoxin spontaneously to the culture medium. Single suprainhibitory dose of clindamycin at concentration 100 x MIC inhibits the growth of examined strain and does not cause augmented release of endotoxin from B. fragilis cells in vitro.