Estimation of Colistin Resistance Among Multidrug-Resistant Gram-Negative Bacilli: An Observational Study

Area of Science:

• Microbiology
• Infectious Diseases
• Clinical Diagnostics

Background:

• Antimicrobial resistance, especially in Gram-negative bacilli (GNB), is a critical global health threat.
• Colistin, a last-resort antibiotic, faces increasing resistance, limiting treatment options for multidrug-resistant GNB (MDR-GNB).

Purpose of the Study:

• To determine the prevalence of colistin resistance in MDR-GNB isolates.
• To evaluate and compare the performance of three phenotypic methods: broth microdilution (BMD), colistin broth disk elution (CBDE), and colistin agar test (CAT) for colistin resistance detection.

Main Methods:

• An observational study involving 100 MDR-GNB isolates from a tertiary care hospital.
• Colistin susceptibility testing using BMD (gold standard), CBDE, and CAT according to CLSI guidelines.
• Assessment of sensitivity, specificity, and categorical agreement of CBDE and CAT against BMD.

Main Results:

• Prevalent MDR-GNB included Klebsiella pneumoniae (41%), Escherichia coli (35%), Acinetobacter baumannii (13%), and Pseudomonas aeruginosa (11%).
• Overall colistin resistance by BMD was 4%. CBDE showed 100% sensitivity, 98.96% specificity, and 99% categorical agreement.
• CAT exhibited lower sensitivity (75%) and a higher very major error rate (25%).

Conclusions:

• Accurate susceptibility testing for colistin resistance in MDR-GNB is urgently needed.
• CBDE is a practical and reliable alternative to BMD for routine laboratory detection of colistin resistance.
• Regular surveillance and judicious use of colistin are vital to preserve its efficacy.