[In vitro effect of acylureido penicillins and mezlocillin on anaerobic sporeless gram-negative rods of genus Bacteroides].

313 anaerobic gram-negative rods of the Bacteroides genus isolated from 295 clinical specimens were tested for their sensitivity to azlocillin and mezlocillin using the dilution method with agar plates. 25 mg/l of azlocillin inhibited 80.2% of the strains and the same concentration of mezlocillin inhibited 86.9%. The somewhat higher in vitro activity of mezlocillin is also seen by the lower mean minimal inhibitory concentration, which is approx. 23.6 mg/l for mezlocillin and 27.6 mg/l for azlocillin. The highest resistance for both drugs were found with B. distasonis (14 strains), followed by B. thetaiotaomicron (63 strains), B. fragilis (161 strains) and B. uniformis (7 strains). The good sensitivity of strains belonging to the B. melaninogenicus group corresponds to the well-known sensitivity of these micro-organisms to penicillins. On the basis of a "break point" of 25 mg/l, a decrease in the proportion of sensitive strains was found between 1974 and 1979. 50 mg/l, a concentration which can be maintained over a longer period of time if applied in a suitable manner, will inhibit 97.4% (azlocillin) and 98.4% (mezlocillin) of the strains. Thus in our opinion azlocillin and especially mezlocillin are suitable drugs for the initial therapy of pyogenous infections in which intestinal Bacteroidaceae are of pathogenic significance.