Analysis of antimicrobial resistance among gram-negative bacilli and antimicrobial use in intensive care unit patients for 5 years in a Veterans Affairs medical center.

Background: Gram-negative bacilli antimicrobial resistance remains a significant problem for patients in the intensive care unit (ICU). Patterns of antimicrobial use may be a contributing factor.

Methods: Gram-negative bacilli from ICU patients of a Veterans Affairs (VA) medical center were tested to determine in vitro antimicrobial susceptibility (205 isolates in 1995 and 209 in 1999). Antimicrobial use was calculated from 1995 through 1999.

Results: For Pseudomonas aeruginosa, significant declines in susceptibility to ciprofloxacin (medical ICU [MICU] individually and all units) and aztreonam (all units) were noted. For gram-negative bacilli that was non-P aeruginosa, significant increases in susceptibility to ceftazidime (MICU, surgical ICU, and all units), gentamicin (all units), and ticarcillin/clavulanate (MICU) were noted. The most notable trends in antimicrobial usage were sharp increases in fluoroquinolone use in the MICU and surgical ICU and substantial decreases in the use of third-generation cephalosporins, monobactams, and aminoglycosides. In each instance of significant change in the susceptibility of a group of organisms to an antibiotic, there was a corresponding inverse change in the use of the antibiotic and/or its antimicrobial category (except for aztreonam).

Conclusions: Significant changes in antimicrobial use may affect certain gram-negative bacilli antimicrobial susceptibilities in ICUs.