A multicenter study of antibiotic resistance patterns of bacterial isolates from patients with hematological and solid cancers

BACKGROUND: Antimicrobial resistance (AMR) is a major threat in oncology, where immunosuppression and repeated healthcare exposure increase susceptibility to severe infections. Multicenter data on antibiotic resistance patterns among cancer patients in Iraq remain limited. RESEARCH DESIGN AND METHODS: A multicenter observational study was conducted across three oncology centers in Iraq between January 2024 and March 2025. A total of 125 non-duplicate blood culture isolates from patients with hematological and solid malignancies were analyzed, including 100 resistant and 25 susceptible isolates. Antibiotic susceptibility testing followed Clinical and Laboratory Standards Institute criteria, and categorical variables were analyzed using chi-square tests. RESULTS: Multidrug-resistant and carbapenem-resistant phenotypes were frequent among Klebsiella pneumoniae (35/100, 35%), Escherichia coli (36/100, 36%), and Pseudomonas aeruginosa (29/100, 29%). P. aeruginosa showed the highest burden of advanced resistance phenotypes, including difficult-to-treat resistance. Resistant isolates were more common in patients with hematological malignancies (77/100, 77%) than in those with solid tumors (23/100, 23%). Resistance was prominent for third-generation cephalosporins, fluoroquinolones, and β-lactam/β-lactamase inhibitor combinations, whereas tigecycline and colistin retained greater activity against several resistant isolates. CONCLUSIONS: This study identified substantial antibiotic resistance among bloodstream isolates from cancer patients in Iraq, supporting oncology-specific surveillance and antimicrobial stewardship.