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Cancer / Enterobacteriaceae Infections / Pseudomonas Infections · Journal article
Diagnostic Microbiology and Infectious Disease · August 1, 2026
Early or partial results. Treat as a signal, not a conclusion.
This multicenter surveillance study reports in vitro susceptibility patterns of Gram-negative bacteria from immunocompromised hospitalized patients to novel β-lactam–β-lactamase inhibitor combinations. Aztreonam-avibactam showed superior activity against carbapenem-resistant Enterobacterales (95.8% susceptible, including 100% of carbapenemase producers), while ceftazidime-avibactam was most active against P. aeruginosa (95.7% susceptible). These findings are descriptive and do not establish clinical benefit or treatment outcomes.
Multicenter prospective surveillance study of in vitro antimicrobial susceptibility. Patients hospitalized in hematology, oncology, and transplant units at 75 US medical centres; isolates derived from bloodstream infections (53.6% of Enterobacterales), urinary tract infections (19.9%), and respiratory infections (35.0% of P. aeruginosa) and other sites.. Intervention: In vitro susceptibility testing of bacterial isolates against aztreonam-avibactam, ceftazidime-avibactam, meropenem-vaborbactam, ceftolozane-tazobactam, piperacillin-tazobactam, meropenem, and tobramycin. Compared with: Comparative susceptibility rates across multiple β-lactam–β-lactamase inhibitor combinations and comparator agents. n = 2,892. 75 medical centres across the United States.
Aztreonam-avibactam was highly active against Enterobacterales (99.9% susceptible) and uniquely effective against carbapenem-resistant Enterobacterales (95.8% susceptible) Among carbapenemase-producing CRE isolates, 100% were aztreonam-avibactam-susceptible versus 77.4% ceftazidime-avibactam-susceptible and 67.7% meropenem-vaborbactam-susceptible Ceftazidime-avibactam demonstrated the highest activity against P. aeruginosa (95.7% susceptible), followed by ceftolozane-tazobactam (94.8% susceptible)
In vitro susceptibility data do not establish clinical efficacy, treatment outcomes, or mortality benefit.
These susceptibility data suggest aztreonam-avibactam may have a role in treating multidrug-resistant and carbapenem-resistant Enterobacterales infections in immunocompromised hosts, while ceftazidime-avibactam may be preferred for P. aeruginosa. However, in vitro susceptibility alone does not predict clinical efficacy, pharmacokinetics, tissue penetration, or patient outcomes, and clinical trials are needed to guide treatment decisions.
In vitro susceptibility surveillance from a large multicenter collection in immunocompromised patients; establishes baseline resistance patterns and comparative agent activity but lacks clinical outcome data, treatment efficacy, or validation in patient populations.
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These susceptibility data suggest aztreonam-avibactam may have a role in treating multidrug-resistant and carbapenem-resistant Enterobacterales infections in immunocompromised hosts, while ceftazidime-avibactam may be preferred for P. aeruginosa. However, in vitro susceptibility alone does not predict clinical efficacy, pharmacokinetics, tissue penetration, or patient outcomes, and clinical trials are needed to guide treatment decisions.
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Immunosuppression increases the risks and severity of infections and is associated with a higher incidence of infection with multidrug-resistant (MDR) pathogens. We evaluated the antimicrobial susceptibility of Enterobacterales and Pseudomonas aeruginosa from patients hospitalized in hospital units where the frequency of immunosuppressed patients is very high. Bacterial isolates were consecutively collected (1/patient) from 75 US medical centres in 2019-2024 and susceptibility tested by broth microdilution. Enterobacterales (n = 2,407) and P. aeruginosa (n = 485) from patients hospitalized in hematology, oncology, and transplant units were evaluated. Carbapenem-resistant Enterobacterales (CRE) were screened for β-lactamases by whole genome sequencing. Enterobacterales were mainly from bloodstream infection (BSI; 53.6%) and urinary tract infection (19.9%) and P. aeruginosa were mainly from BSI (37.9%) and pneumonia (35.0%). Aztreonam-avibactam, ceftazidime-avibactam, and meropenem-vaborbactam were highly active against Enterobacterales (99.9-99.4% susceptible), including MDR isolates (99.6-98.1% susceptible), but only aztreonam-avibactam exhibited good activity against CRE (95.8% susceptible). Ceftolozane-tazobactam showed good activity against Escherichia coli (95.7% S) and Klebsiella pneumoniae (92.8% S), but limited activity against Enterobacter cloacae species complex (75.9% susceptible). All (100.0%) carbapenemase (CBase)-producing CRE isolates were aztreonam-avibactam-susceptible while 77.4% were ceftazidime-avibactam-susceptible and 67.7% were meropenem-vaborbactam-susceptible. The most common CBases were KPC (41.7%), NDM (12.5%), and OXA-48 types (10.4%). Metallo-β-lactamases represented 23.5% of CBases and were identified in 16.7% of CREs. The most active agents against P. aeruginosa were ceftazidime-avibactam (95.7% susceptible), ceftolozane-tazobactam (94.8% susceptible), and tobramycin (91.5% susceptible). Piperacillin-tazobactam and meropenem were active against 81.4% and 82.5% of P. aeruginosa, respectively, and aztreonam-avibactam inhibited 78.6% of P. aeruginosa at ≤8 mg/L.
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