Incidence of colistin heteroresistance among carbapenem-resistant Acinetobacter baumannii clinical isolates in a tertiary care hospital in Pakistan

Purpose The emergence of colistin-resistant and heteroresistant strains of carbapenem-resistant Acinetobacter baumannii (CRAB) complicates treatment and exacerbates the global health crisis of drug-resistant bacteria. This study aims to investigate the incidence and clinical implications of colistin heteroresistance in carbapenem-resistant Acinetobacter baumannii isolates from a tertiary hospital in Pakistan. Materials and methods A total of 130 CRAB isolates were collected from December 2022 to December 2023. Colistin susceptibility was assessed using broth microdilution, and heteroresistance was detected through population analysis profiling. Results Heteroresistance (HR) was identified in 31.5% (41/130) of the isolates, while 7.7% were colistin-resistant, despite initial susceptibility indicated by broth microdilution. Clinical data revealed that HR was associated with significant 14-day clinical failure but not with 30-day all-cause mortality. Heteroresistant strains showed extensive multidrug resistance, posing a serious threat to effective treatment. Conclusions The study highlights the critical need for accurate detection of colistin HR to prevent treatment failure and improve patient outcomes. The prevalence of colistin HR underscores the necessity for revised diagnostic and treatment strategies in Pakistan, emphasizing the importance of recognizing and addressing this emerging threat in healthcare settings.