[Effect of antibiotics on autochtonous intestinal E. coli population in SPF mice and on planktonic phase isolates]

Representatives of different groups of antibiotics were tested on the autochtonous Escherichia coli of mice being in biofilm mode of growth, as well as on their isolates in planktonic phase. Aminoglycoside antibiotics, chloramphenicol, oxytetracycline, erythromycin, lincomycin-clindamycin, and polymyxins showed a very reduced effectivity on Escherichia coli embedded in the biofilm matrix. On the other hand, beta-lactam antibiotics were equally effective both for sessile and planktonic bacteria. Derivates with broader, or broad spectra showed an increased biofilm activity. Testing the possibilities of penetration or concentration on mouse colonic pieces exposed to 2 Minimal Bactericidal Doses--polymyxin B showed no sign of penetration into the colonic mucus, while 2.9% of streptomycin and 60% of the exposed quantity of carbenicillin was detected in the intestinal mucus. Ampicillin, however, has concentrated about three-four times in the intestinal matrix.