# Trends of Colistin MIC Among Acinetobacter Baumannii and Pseudomonas aeruginosa at a First-Class Hospital in Vietnam

## TL;DR

This study tracks how the effectiveness of colistin, a last-resort antibiotic, changed over time against two drug-resistant bacteria in a Vietnamese hospital.

## Contribution

The study identifies a concerning trend of increasing colistin MIC values in Acinetobacter baumannii and Pseudomonas aeruginosa over five years.

## Key findings

- Colistin MIC values for both bacteria increased significantly over time, approaching resistance thresholds.
- MIC values of 1.0 μg/mL became the most common for both bacteria in recent years.
- Carbapenem-resistant strains showed higher colistin MIC values compared to nonresistant strains.

## Abstract

Introduction:
A. baumannii and P. aeruginosa belong to the multidrug-resistant Gram-negative bacteria group, posing significant challenges in treatment. Colistin is considered the last-line antibiotic for treating this bacterium. It is essential to determine the minimum inhibitory concentration (MIC) to adjust the appropriate dosage.

Method: A cross-sectional descriptive study using data from January 2020 to December 2024 was conducted.

Results: The infections caused by A. baumannii and P. aeruginosa showed an increasing trend over the years, accounting for 17.4% and 9.6% of common multidrug-resistant Gram-negative bacteria, respectively. A. baumannii exhibited higher resistance rates than P. aeruginosa with multiple tested antibiotics. Although no Colistin-resistant strains were observed for either bacterium of interest during the observation period, both bacteria of interest showed a statistically significant change during the survey period (p < 0.05). In addition, the MIC value of ≤ 0.75 μg/mL was the most prevalent over 80% from 2020 to 2021, but its percentage declined strongly by 60%–65% in the next 3 years (p < 0.0001). Meanwhile, the MIC value of 1.0 μg/mL became the most common over 70% with a statistically significant difference (p < 0.0001). Regarding the MIC value based on infection types, the MIC value for P. aeruginosa causing septicemia was considerably concentrated at 1.0 μg/mL at 84.6%, while its percentage was lower in A. baumannii at 37.9% (p < 0.0001). Looking into MIC values based on carbapenem-resistant proportions, the MIC values from 1.0 to 2.0 μg/mL were higher in imipenem-resistant strains of both bacteria of interest compared with nonresistant strains (p < 0.0001). This difference was also observed in meropenem-resistant A. baumannii but was not demonstrated in P. aeruginosa.

Conclusions: Although no colistin-resistant strains were observed, A. baumannii and P. aeruginosa showed statistically significant changes in the most prevalent colistin MIC values, which have been approaching the resistance threshold over the years. It is essential to implement control measures of colistin usage before bacteria become completely resistant.