[In-vitro activity of ceftriaxone on Gram-negative bacilli with various resistance phenotypes to cephalosporins. Comparison with cefotaxime, cefmenoxime, moxalactam, ceftazidime].

In vitro activity of ceftriaxone was studied on 245 cephalothin-resistant strains of enterobacteria representing 7 different phenotypes of resistance to cephalosporins and on 130 Gram negative oxidative bacilli. Ceftriaxone was compared to cefotaxime, cefmenoxime, moxalactam and ceftazidime. With modal MICs of 0.015 to 0.25 mg/l, ceftriaxone is active on all phenotypes of enterobacteria not simultaneously resistant to cefamandole and cefoxitin. Among the bacteria with this last phenotype, only K. pneumoniae, C. Freundii and E. cloacae are occasionally found to have intermediate susceptibility or even resistance; ceftriaxone is more active than cefotaxime, cefmenoxime and ceftazidime with inhibition of 95.1% of strains at 4 mg/l. Moxalactam is superior to ceftriaxone against enterobacteria that are intermediate or resistant to both cefamandole and cefoxitin. Activity of ceftazidime is strongest against oxidative bacilli and weakest against enterobacteria regardless of phenotype.