Antibiotic susceptibility profiles of 941 gram-negative bacteria isolated from septicemic patients throughout Canada. The Canadian Study Group.

The choice of antimicrobial therapy for the treatment of bacteremia is often empirical and based on the knowledge of antibiotic susceptibility profiles of the most common bacteria causing such infections. It therefore is crucial to survey the susceptibility of bacteria causing sepsis. This study examines the susceptibility profiles of 941 gram-negative bacteria, isolated from septic patients in 10 Canadian hospitals, to 28 antimicrobial agents. Among the isolates, 30 different species were represented; Escherichia coli dominated, representing 52.5% of isolates. More than 50% of all bacteria were resistant to ampicillin. Only 67% of the E. coli isolates were susceptible to ampicillin, while 30% of all strains were resistant to ticarcillin. Of the cephalosporins, ceftazidime and cefoperazone/sulbactam were the agents to which isolates were the most susceptible (90%). Only 51% of the E. coli strains were susceptible to cephalothin, while 91% were still susceptible to cefazolin. A total of 93% and 98% of the strains were susceptible to aztreonam and imipenem, respectively. Aminoglycosides were highly active against most isolates, in general in the following order: netilmicin greater than tobramycin greater than gentamicin greater than amikacin. Tobramycin was the most active against Pseudomonas aeruginosa. Nearly all isolates were susceptible to the quinolones. Tolerance (MBC/MIC ratio, greater than or equal to 32) was rarely observed. This survey of the susceptibility of gram-negative bacteria causing sepsis provides valuable information for implementing the chemotherapy for gram-negative septicemia and demonstrates that several older and newer agents, alone or in combination, can be used as adequate initial therapy for gram-negative sepsis in Canada.