Eleven-Year Trends in Antimicrobial Resistance and Isolation Rates per 1000 Patient-Days of Key Gram-Positive and Gram-Negative Bacteria in a Tertiary Care Hospital in Türkiye (2014-2024).

OBJECTIVE: This study examined 11-year trends in antimicrobial resistance and resistant organism isolation rates per 1000 patient-days among key Gram-positive and Gram-negative bacteria in a tertiary-care hospital in Türkiye.

MATERIALS AND METHODS: Microbiology data were obtained from the first isolate per patient per admission between January 2014 and December 2024. Organisms were identified using VITEK MS/matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS). Antimicrobial susceptibility testing was performed using VITEK 2 or BD Phoenix, with disk diffusion used for selected agents. Clinical and Laboratory Standards Institute (CLSI) breakpoints were applied until 2015, and European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints thereafter. Resistance rates (%) and resistant organism isolation rates per 1000 patient-days were calculated.

RESULTS: Enterococcus faecalis remained highly susceptible throughout the study period. In contrast, Enterococcus faecium showed progressive increases in ampicillin and vancomycin resistance, with the isolation rate of ampicillin-resistant bloodstream isolates approximately doubling from 0.405 per 1000 patient-days in 2014 to 0.773 in 2023. Methicillin-resistant Staphylococcus aureus isolation rates increased sharply, from 0.230 per 1000 patient-days in 2014 to 0.945 in 2022 among non-bloodstream isolates. Carbapenem resistance in Acinetobacter baumannii remained persistently high but broadly stable, except for a notable spike in 2021. Both resistance rates and resistant Klebsiella pneumoniae isolation rates increased for carbapenems and third-generation cephalosporins, with carbapenem resistance among bloodstream isolates increasing from 29% to 62% in 2023 and third-generation cephalosporin resistance increasing from 50% to 74%. Ceftazidime-avibactam resistance also emerged during the study period. Third-generation cephalosporin resistance in Escherichia coli initially increased but subsequently stabilized, whereas carbapenem resistance rates and isolation rates of carbapenem-resistant E. coli remained low and stable. Pseudomonas aeruginosa showed increasing resistance trends, with year-to-year fluctuations.

CONCLUSION: Antimicrobial resistance patterns exhibited divergent trends across bacterial species. Increasing resistance rates and resistant organism isolation rates were observed in E. faecium, S. aureus, K. pneumoniae, E. coli, and P. aeruginosa, whereas E. faecalis and A. baumannii showed relatively stable patterns. Monitoring resistance rates helps update local empirical treatment guidelines, while resistant organism isolation rates per 1000 patient-days provide an additional measure for monitoring changes relevant to infection prevention and control programs.

GRAPHICAL ABSTRACT: Graphical Abstract.