Background: Bloodstream infections (BSIs) cause significant morbidity and mortality. We evaluated the frequency and antimicrobial susceptibility of bacteria causing BSIs in the United States (US).
Methods: A total of 9,210 bacterial isolates were consecutively collected (1/patient) from 33 US medical centers in 2015-2017 and tested for susceptibility by reference broth microdilution methods in a central laboratory (JMI Laboratories) as part of the International Network for Optimal Resistance Monitoring (INFORM) program. Whole genome sequencing was performed on carbapenem-resistant Enterobacteriaceae (CRE).
Results: The most common organisms were S. aureus (SA; 24.3%), E. coli (EC; 20.8%), K. pneumoniae (KPN; 9.1%), coagulase-negative staphylococci (7.3%), E. faecalis (5.5%), P. aeruginosa (PSA; 4.7%), and β-hemolytic streptococci (4.7%). Overall, 50.0% of isolates were gram-negative bacilli (GNB) and 41.4% were Enterobacteriaceae (ENT). All SA were susceptible (S) to dalbavancin (MIC90, 0.03 μg/mL), linezolid, tigecycline (TGC), and vancomycin; >99.9%S to daptomycin, 97.6%S to ceftaroline, and 57.8%S to oxacillin. The most active agents against ENT were CAZ-AVI (99.9%S; Table), amikacin (AMK; 99.7%S), and the carbapenems meropenem (MEM) and doripenem (99.1%S). Ceftolozane-tazobactam (C-T; tested in 2017 only) was active against 96.9% of ENT. Ceftriaxone (CRO)-S rates were 83.0% and 86.5% among EC and KPN, respectively. CRO-non-S KPN exhibited low S rates to most agents, except CAZ-AVI (99.1%S), TGC (93.6%), AMK (93.8%), and colistin (COL; 93.4%). Among 28 CRE isolates (0.7% of ENT), 21 produced a KPC-like, 2 an NMD-like, and 1 a KPC-17 and an NDM-1. COL (100.0%S), C-T (98.7%S), CAZ-AVI (98.2%S), AMK (97.9%S), and tobramycin (95.6%S) were very active against PSA. CAZ-AVI and C-T remained active against most PSA isolates non-S to MEM (93.0 and 95.0%S, respectively) and/or piperacillin-tazobactam (P-T; 88.9 and 91.3%S) and/or CAZ (86.9 and 88.2%S).
Conclusion: GNB represented 50.0% of bacteria isolated from patients with BSIs and the most active agents against these organisms were CAZ-AVI and AMK. Various agents exhibited excellent overall coverage against gram-positives, including dalbavancin, daptomycin, linezolid, and TGC.
H. S. Sader,
M. A. Pfaller, Allergan: Research Contractor , Research support .
M. Castanheira, Allergan: Research Contractor , Research support .