Antimicrobial Resistance of Bacteria Isolated From Patients With Cancer

Cancer patients are at high risk of developing infections caused by multidrug-resistant (MDR) microorganisms. Monitoring antimicrobial resistance (AMR) is essential for guiding treatment in this vulnerable population. This study aimed to evaluate AMR patterns and temporal evolution among clinical bacterial isolates-comparing pre-pandemic (2016-2019) versus pandemic (2020-2021) periods and care settings (outpatient vs. inpatient)-recovered from cancer patients at a tertiary care center in Guerrero, Mexico.

An observational, cross-sectional, retrospective study was conducted between 2016 and 2021. A total of 1,019 strains were analyzed using WHONET 2023 software, following the Clinical and Laboratory Standards Institute (CLSI) M100 cut-off values. Categorical variables were compared using Pearson's chi-squared test (χ²). For antibiotics with absolute frequencies less than 5, Fisher's exact test was applied using STATA statistical software version 14.2 (StataCorp LLC, College Station, TX, USA).

Enterobacteriaceae accounted for 73.1% of the isolates, with Escherichia coli (42.3%, n = 431) and Klebsiella pneumoniae (14.0%, n = 143) being the predominant strains. The overall prevalence of extended-spectrum beta-lactamases (ESBLs) was 22.6%. In E. coli, an increase in resistance was observed starting in 2019, with resistance rates > 80.0% for ampicillin and cefixime. When comparing the 2020 period with 2021, resistance in E. coli increased significantly for ciprofloxacin (χ² = 4.144, p = 0.042) and ceftriaxone (χ² = 4.100, p = 0.043). Regarding MDR, 51.0% of E. coli isolates were MDR, while 32.2% of K. pneumoniae strains exhibited extensive drug resistance (XDR). In addition, possible pandrug-resistant (PDR) phenotypes were identified in 14.3% of Acinetobacter spp. isolates. Isolates from hospitalized patients showed higher resistance rates compared to those from outpatients with regard to E. coli for ampicillin/sulbactam (χ² = 4.422, p = 0.035), piperacillin/tazobactam (χ² = 17.519, p < 0.001), and cefazolin (χ² = 6.746, p = 0.009).

The results demonstrate a high predominance of Enterobacteriaceae among clinical bacterial isolates from the evaluated oncology population. E. coli exhibited the highest proportion of MDR phenotypes (51.0%), whereas K. pneumoniae showed the highest frequency of XDR (32.2%). The high level of resistance observed among isolates from hospitalized patients could help guide empirical treatment toward alternative therapeutic options.