In vitro and in vivo efficacy of combinations of colistin and different endolysins against clinical strains of multi-drug resistant pathogens

Lucia Blasco,Felipe Fernández-Cuenca,Maria Tomas,Elisenda Miró,Ferran Navarro,Rocio Trastoy,Ines Bleriot,Elena Perez-Nadales,Julian Torre-Cisneros,Tim Kidd,German Bou,Anton Ambroa,Miriam Moscoso,Luis Martínez-Martínez,Laura Fernández-Garcia,Rafael Canton,Jesus Oteo-Iglesias,Alvaro Pascual,Antonio Oliver

doi:10.1038/s41598-020-64145-7

Abstract

The emergence of multidrug resistant (MDR) pathogenic bacteria is jeopardizing the value of antimicrobials, which had previously changed the course of medical science. In this study, we identified endolysins ElyA1 and ElyA2 (GH108-PG3 family), present in the genome of bacteriophages Ab1051Φ and Ab1052Φ, respectively. The muralytic activity of these endolysins against MDR clinical isolates (Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae) was tested using the turbidity reduction assay. Minimal inhibitory concentrations (MICs) of endolysin, colistin and a combination of endolysin and colistin were determined, and the antimicrobial activity of each treatment was confirmed by time kill curves. Endolysin ElyA1 displayed activity against all 25 strains of A. baumannii and P. aeruginosa tested and against 13 out of 17 strains of K. pneumoniae. Endolysin ElyA2 did not display any such activity. The combined antimicrobial activity of colistin and ElyA1 yielded a reduction in the colistin MIC for all strains studied, except K. pneumoniae. These results were confirmed in vivo in G. mellonella survival assays and in murine skin and lung infection models. In conclusion, combining colistin (1/4 MIC) with the new endolysin ElyA1 (350 µg) enhanced the bactericidal activity of colistin in both in vitro and in vivo studies. This will potentially enable reduction of the dose of colistin used in clinical practice.

Highlights

The emergence of multidrug resistant (MDR) pathogenic bacteria is jeopardizing the value of antimicrobials, which had previously changed the course of medical science
Protein homology analysis revealed a high level of homology (>80%) with a group of 9 endolysins from A. baumannii bacteriophages belonging to the same protein family as ElyA120
Endolysins are species or genus-specific enzymes that act by hydrolysing the peptidoglycan layer of the bacterial cell wall

Summary

Introduction

The emergence of multidrug resistant (MDR) pathogenic bacteria is jeopardizing the value of antimicrobials, which had previously changed the course of medical science. The combined antimicrobial activity of colistin and ElyA1 yielded a reduction in the colistin MIC for all strains studied, except K. pneumoniae. These results were confirmed in vivo in G. mellonella survival assays and in murine skin and lung infection models. Combining colistin (1/4 MIC) with the new endolysin ElyA1 (350 μg) enhanced the bactericidal activity of colistin in both in vitro and in vivo studies. This will potentially enable reduction of the dose of colistin used in clinical practice. They can be classified into five groups according to the cleavage site: N-acetyl-β-D-muramidase (lysozymes); N-acetyl-β-D-glucosaminidases (glycosidases); lytic transglycosylase; N-acetylmuramoyl-L-alanine amidases and L-alanoyl-D-glutamate endopeptidases[7,8]

Methods

Results

Conclusion