Using the Galleria mellonella burn wound and infection model to identify and characterize potential wound probiotics

Carbon source competition within the wound microenvironment can significantly influence infection progression

It is becoming increasingly apparent that commensal skin bacteria have an important role in wound healing and infection progression. However, the precise mechanisms underpinning many of these probiotic interactions remain to be fully uncovered. In this work, we demonstrate that the common skin commensal Cutibacterium acnes can limit the pathogenicity of the prevalent wound pathogen Pseudomonas aeruginosa in vivo. We show that this impact on pathogenicity is independent of any effect on growth, but occurs through a significant downregulation of the Type Three Secretion System (T3SS), the primary toxin secretion system utilised by P. aeruginosa in eukaryotic infection. We also show a downregulation in glucose acquisition systems, a known regulator of the T3SS, suggesting that glucose availability in a wound can influence infection progression. C. acnes is well known as a glucose fermenting organism, and we demonstrate that topically supplementing a wound with glucose reverses the probiotic effects of C. acnes. This suggests that introducing carbon source competition within the wound microenvironment may be an effective way to prevent or limit wound infection.

Genomic analysis of vB_PaS-HSN4 bacteriophage and its antibacterial activity (in vivo and in vitro) against Pseudomonas aeruginosa isolated from burn

The most frequent infections caused by Pseudomonas aeruginosa are local infections in soft tissues, including burns. Today, phage use is considered a suitable alternative to cure infections caused by multi-drug-resistant (MDR) and extensively drug-resistant (XDR) bacteria. We investigated the potential of a novel phage (vB_PaS-HSN4) belonging to Caudoviricetes class, against XDR and MDR P. aeruginosa strains in vivo and in vitro. Its biological and genetic characteristics were investigated. The phage burst size and latent were 119 and 20 min, respectively. It could tolerate a broad range of salt concentrations, pH values, and temperatures. The combination with ciprofloxacin significantly enhanced biofilm removal after 24 h. The genome was dsDNA with a size of 44,534 bp and encoded 61 ORFs with 3 tRNA and 5 promoters. No virulence factor was observed in the phage genome. In the in vivo infection model, treatment with vB_PaS-HSN4 increased Galleria mellonella larvae survival (80%, 66%, and 60%) (MOI 100) and (60%, 40%, and 26%) (MOI 1) in the pre-treatment, co-treatment, and post-treatment experiments, respectively. Based on these characteristics, it can be considered for the cure of infections of burns caused by P. aeruginosa.