Colistin Heteroresistance in Acinetobacter baumannii Poses Significant Diagnostic and Treatment Challenges

Multidrug-resistant Gram-negative bacteria, particularly carbapenem-resistant strains, represent a critical global public health threat, severely limiting therapeutic options. This has necessitated the reintroduction of polymyxin antibiotics like colistin as last-resort treatments. However, widespread colistin use has driven an increase in resistance, with heteroresistance emerging as a significant, underrecognized challenge. This phenomenon involves bacterial subpopulations within an isolate exhibiting varying antibiotic susceptibility, complicating both diagnosis and effective treatment of Acinetobacter baumannii infections.

This comprehensive review synthesized current evidence on colistin heteroresistance in Acinetobacter baumannii, focusing on its molecular basis, clinical implications, and diagnostic limitations. The authors analyzed existing literature to highlight the prevalence and challenges associated with this complex resistance mechanism. The review aimed to consolidate knowledge for microbiologists and clinicians, emphasizing the urgent need for improved diagnostic approaches and more effective treatment strategies to combat persistent infections and recurrence.

The review highlights that colistin heteroresistance in Acinetobacter baumannii is characterized by the presence of subpopulations within an isolate that exhibit varying levels of susceptibility to the antibiotic. This intrinsic variability can lead to the selection and expansion of resistant subpopulations during therapy, directly contributing to clinical treatment failure, persistent infections, and disease recurrence. The prevalence of colistin heteroresistance in A. baumannii is noted to vary geographically, underscoring the need for localized surveillance and understanding of its molecular basis. This understanding is crucial for developing targeted interventions and improving patient outcomes. The review emphasizes the critical importance of understanding the molecular basis of this resistance to develop targeted interventions.

A key finding is the inability of routine antimicrobial susceptibility testing methods to reliably detect colistin heteroresistance, resulting in its underrecognition in clinical settings and potentially leading to inappropriate therapeutic decisions.