Antimicrobial activity of amikacin combinations against Enterobacteriaceae moderately susceptible to third-generation cephalosporins

Enterobacteriaceae strains having elevated minimal inhibitory concentrations (greater than or equal to 2.0 to less than or equal to 32 micrograms/ml) of cefoperazone, cefotaxime, ceftazidime, and moxalactam were synergistically inhibited by amikacin combinations (54.1 to 69.6% occurrence). Indifference was rare (8.1% for moxalactam), and true antagonistic interactions were not observed. Strains resistant or susceptible to these new cephalosporins were also synergistically inhibited by the addition of amikacin, reducing resistant cephalosporin minimal inhibitory concentrations to clinically achievable levels.