LAUSR

Background Treatment of infections in the ICU represents a great challenge, especially infections caused by Gram-negative organisms. Rapid introduction of appropriate antimicrobial therapy is crucial to reduce mortality, and resistance rates in the ICU can be elevated due to antimicrobial selection pressure. Objectives To evaluate the frequency and antimicrobial susceptibility of Gram-negative bacteria isolated from patients with pneumonia hospitalized in ICUs. Methods A total of 6091 bacterial isolates were consecutively collected from 75 US medical centres in 2015-17 as part of the International Network for Optimal Resistance Monitoring (INFORM) programme and tested for susceptibility to multiple antimicrobial agents at a central laboratory by reference broth microdilution methods. Results The most common organisms were Staphylococcus aureus (30.0%), Pseudomonas aeruginosa (20.7%), Klebsiella spp. (11.8%), Enterobacter spp. (8.3%), Escherichia coli (7.1%) and Stenotrophomonas maltophilia (5.1%). Colistin (99.8% susceptible), ceftazidime/avibactam (96.8% susceptible in 2015-17 and 96.2% in 2017) and ceftolozane/tazobactam (96.5% susceptible in 2017) were the most active compounds against P. aeruginosa. Ceftazidime/avibactam (100.0% susceptible), amikacin (99.4% susceptible) and meropenem (97.6% susceptible) were the most active compounds against Enterobacteriaceae. S. maltophilia and Acinetobacter baumannii exhibited high resistance rates to most antimicrobials tested. Conclusions Gram-negative bacteria were isolated from 67.1% of the patients and P. aeruginosa and Enterobacteriaceae represented >80% of these organisms. Ceftazidime/avibactam and amikacin provided the best coverage against Gram-negative organisms overall.