Frequency and antimicrobial susceptibility of Gram-negative bacteria isolated from patients with pneumonia hospitalized in ICUs of US medical centres (2015-17)

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.