Resistance to imipenem among selected gram-negative bacilli in the United States

Abstract

Objectives: Identification of imipenem resistance among selected gram-negative bacilli, especially Pseudomonas aeruginosa and Enterobacter species.

Methods: We analyzed 1986-1990 National Nosocomial Infection Surveillance (NNIS) data from 3,316 P aeruginosa isolates and 1,825 Enterobacter species isolates for which susceptibility results to imipenem were reported.

Results: For P aeruginosa, 11.1% of the isolates were resistant to imipenem; 16.1% were either intermediate-susceptible or resistant to the drug. A logistic regression model found that resistance was more common among P aeruginosa isolated from the respiratory tract, patients in intensive care units, and in teaching hospitals. Additionally, resistance to imipenem increased by 25% in teaching hospitals from 1986-1988 to 1989-1990. For Enterobacter species, 1.3% of the isolates were resistant to imipenem; 2.3% were either intermediate-susceptible or resistant to the drug. However, imipenem resistance for these isolates did not differ between the two periods and was not more common in patients in an intensive care unit or infections at any specific site.

Conclusions: The frequency of resistance to imipenem is greater among P aeruginosa than among Enterobacter species. Resistance to imipenem among the P aeruginosa isolates is more common from strains isolated from patients with nosocomial infections in an intensive care unit, from the respiratory tract, and from teaching hospitals. Resistance appears to be increasing among nosocomial P aeruginosa isolated in teaching hospitals.