# Status of Antibiotic Susceptibility of Polymyxin B And Colistin in the Treatment of Carbapenem Resistant Gram Negative Bacterial Infections: An Observational Study

## TL;DR

This study found that Polymyxin B and Colistin are fully effective against carbapenem-resistant Gram-negative bacteria, which are a major global health threat.

## Contribution

The study provides current empirical evidence on the 100% susceptibility of carbapenem-resistant Gram-negative bacteria to Polymyxin B and Colistin in a Nepalese setting.

## Key findings

- 100% of carbapenem-resistant Gram-negative bacteria were susceptible to Polymyxin B and Colistin.
- Klebsiella species were the most common carbapenem-resistant bacteria found in the study.
- Routine susceptibility testing and judicious use of these antibiotics are recommended to preserve their efficacy.

## Abstract

The emergence and rapid spread of multidrug-resistant gram-negative bacteria is a global concern. Polymyxin B and Colistin have gained significance due to the scarcity of new antibiotics and the high morbidity and mortality associated with carbapenem-resistant gram-negative bacteria. This study aims to assess the antibiotic susceptibility of Colistin and Polymyxin B against carbapenem-resistant gram-negative bacteria.

This was a descriptive cross-sectional study conducted in a tertiary center of Nepal, from June to August 2025. Specimen resistant to any of the carbapenem drugs at the Clinical Laboratory was evaluated. The incidence of susceptibility or resistance of the Polymyxin and Colistin in the carbapenem-resistant gram-negative bacteria was recorded and assessed.

A total of 1,412 Gram-negative bacterial samples were analyzed within the predetermined study period. Among these samples, the prevalence of 395 (27.97%) was from carbapenem-resistant Gram-negative bacteria. There were 185 (46.84%) carbapenem-resistant Klebsiella species, followed by 105 (26.60%) Acinetobacter species. Both Polymyxin B and Colistin showed 100% susceptibility across all carbapenem-resistant gram-negative bacteria species and sample sources evaluated.

Polymyxin B and Colistin continue to be vital last-line treatments for carbapenem-resistant gram-negative bacteria. This study found a susceptibility rate of 100% to colistin and polymyxin B among carbapenem-resistant gramnegative bacteria. To maintain the efficacy and reliability of these antibiotics, it is essential to use them judiciously, conduct routine susceptibility testing, and implement ongoing surveillance.