Resistance of Escherichia coli to some antibiotics and biocides in the intestinal biofilm of mice.

An artificial monoflora of Escherichia coli in mice, as well as their autochtonous E. coli, exhibited enhanced resistance to streptomycin, chloramphenicol, sodium hypochlorite and silver nitrate. The level of resistance of the monoflora, which was 10-32 times higher than the in vitro determined Minimal Bactericidal Dose (MBCD), reached its maximum on the 7th-9th day after implantation. This latency is a requirement for the stabilization of the monoflora. Formaldehyde and carbenicillin were equally effective in the planktonic and in the biofilm mode of growth. In the case of carbenicillin the pieces of mouse colon contained about 60% of the dose used for exposure, in contrast to the 3% rate of streptomycin, showing the excellent penetrating ability of carbenicillin into the intestinal biofilm.