# Prophylactic and therapeutic efficacy of Acinetobacter phage RM_A1 against carbapenem-resistant Acinetobacter baumannii with no cytotoxicity to human skin cells

## TL;DR

This study shows that the phage RM_A1 can effectively fight drug-resistant Acinetobacter baumannii without harming human skin cells, offering a potential new treatment for antibiotic-resistant infections.

## Contribution

The study introduces RM_A1 phage as a novel, safe, and effective therapeutic and prophylactic agent against carbapenem-resistant Acinetobacter baumannii.

## Key findings

- RM_A1 phage has a broad host range and effectively inhibits biofilm formation by A. baumannii.
- The phage is stable under harsh conditions and shows no cytotoxicity to human skin cells.
- Genomic analysis confirms RM_A1 lacks genes for antibiotic resistance or pathogenicity.

## Abstract

The rise in multidrug-resistant (MDR) bacteria has rendered common first- and last-line antibiotics ineffective, posing a serious threat to human health. Additionally, the global rise of wound infections caused by carbapenem-resistant Acinetobacter baumannii indicates that the “post-antibiotic” era has begun. Consequently, alternative antimicrobial therapies are urgently required, and the reuse of phages is a promising choice.

Twenty-six strains of A. baumannii were isolated from wound-infected patients, identified by the Vitek 2 automated system, and confirmed by 16 S rDNA sequencing. The strains’ susceptibility to antibiotics and their ability to develop biofilms were then studied. Acinetobacter phage RM_A1 was isolated and characterized, and its lytic activity against A. baumannii was tested in vitro via time-killing curve and antibiofilm formation assays. The phage’s stability was also tested under various conditions. Genomic analysis was performed to characterize the phage and its virulence. Finally, the phage was assessed as a therapeutic and prophylactic agent against carbapenem-resistant A. baumannii in vitro by using human skin cells.

The clinical strains of A. baumannii were found to be resistant to the carbapenem antibiotics, exhibiting high MAR index values and a strong ability to form biofilm. The isolated RM-A1 phage had a myoviral morphology and a 43,994 bp double-stranded DNA genome encoding 84 open reading frames (ORFs), with no genes linked to antibiotic resistance or pathogenicity. This phage possesses a broad host range, with a lysis spectrum of 85% against clinical isolates. It also possesses a large burst size and a short adsorption rate. It was capable of withstanding temperatures as high as 90 °C, was pH-stable, and remained viable for 45 min when exposed to UV light. There was no significant drop in the vitality of HSF cells observed following phage treatment, proving that the phage is safe for use. In vitro results showed that the phage was able to inhibit and eliminate biofilm formation and significantly reduce bacterial growth.

Our research explores the potential use of RM_A1 phage as an alternative therapeutic agent for combating carbapenem-resistant A. baumannii.

The online version contains supplementary material available at 10.1186/s12866-025-04698-7.