# Preheating colistimethate sodium enhances its efficacy against multi/extensively drug-resistant Gram-negative bacilli in preservation fluid

## TL;DR

Preheating colistimethate sodium improves its ability to kill drug-resistant bacteria in preservation fluid during cold storage, without harming kidney cells.

## Contribution

Thermal pretreatment of CMS at 60°C is a novel and safe method for decontaminating preservation fluid from MDR/XDR Gram-negative bacilli.

## Key findings

- Preheating CMS at 60°C for 15–30 min achieved up to 100% inhibition of CRPA, CRKP, and CREC.
- Preheated CMS showed no nephrotoxicity in HK-2 cells during cold storage.
- MRSA was not affected by preheated CMS, indicating limited efficacy against Gram-positive bacteria.

## Abstract

This study aimed to evaluate the efficacy and preliminary safety of preheated colistimethate sodium (CMS) in reducing the load of multidrug-resistant and extensively drug-resistant (MDR/XDR) Gram-negative bacilli in preservation fluid (PF) under simulated static cold storage (SCS) conditions in vitro. CMS was preheated at 37–60 °C for 5 ~ 30 min. The antibacterial effects of preheated CMS were evaluated against five MDR/XDR strains: carbapenem-resistant Pseudomonas aeruginosa (CRPA), Klebsiella pneumoniae (CRKP), Escherichia coli (CREC), Acinetobacter baumannii (CRAB), and methicillin-resistant Staphylococcus aureus (MRSA). Bacterial counts were assessed after 3 h of SCS, and the average inhibition rate (AIR) was calculated. The safety experiment was performed to evaluate the nephrotoxicity of preheated CMS under hypothermic condition. Preheating CMS at 60 °C for 15 ~ 30 min significantly reduced bacterial loads of CRPA, CRKP, CREC, and CRAB, with average inhibition rates (AIR) up to 100%, 96.91%, 98.36%, and 85.06%, respectively. At 37 °C, extended heating (30 min) was required for partial efficacy against CRKP and CRAB, while CREC remained largely unaffected. MRSA showed no susceptibility to preheated CMS. Preheated CMS did not cause significant morphological alterations or reduction in HK-2 cell viability within 3 ~ 6 h of SCS. Thermal pretreatment of CMS at 60 °C represents a novel, practical, and safe strategy for PF decontamination, providing rapid bactericidal activity against frequently encountered MDR/XDR Gram-negative bacilli during the SCS process.