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Development of an Anti-Acinetobacter baumannii Biofilm Phage Cocktail: Genomic Adaptation to the Host
L Blasco1,2, I Bleriot1,2, M González de Aledo1,2
1Microbiology Department-Research Institute Biomedical A Coruña (INIBIC); Hospital A Coruña (CHUAC); University of A Coruña (UDC), A Coruña, Spain.
Abstract:
The need for alternatives to antibiotic therapy due to the emergence of multidrug resistant bacteria (MDR), such as the nosocomial pathogen Acinetobacter baumannii, has led to the recovery of phage therapy. In addition, phages can be combined in cocktails to increase the host range. In this study, the evolutionary mechanism of adaptation was utilized in order to develop a phage adapted to A. baumannii, named phage Ab105-2phiΔCI404ad, from a mutant lytic phage, Ab105-2phiΔCI, previously developed by our group. The whole genome sequence of phage Ab105-2phiΔCI404ad was determined, showing that four genomic rearrangements events occurred in the tail morphogenesis module affecting the ORFs encoding the host receptor binding sites. As a consequence of the genomic rearrangements, 10 ORFs were lost and four new ORFs were obtained, all encoding tail proteins; two inverted regions were also derived from these events. The adaptation process increased the host range of the adapted phage by almost 3-fold. In addition, a depolymerase-expressing phenotype, indicated by formation of a halo, which was not observed in the ancestral phage, was obtained in 81% of the infected strains. A phage cocktail was formed by combining this phage with the A. baumannii phage vB_AbaP_B3, known to express a depolymerase. Both the individual phages and the phage cocktail showed strong antimicrobial activity against 5 clinical strains and 1 reference strain of A. baumannii tested. However, in all cases resistance to the bacterial strains was also observed. The antibiofilm activity of the individual phages and the cocktail was assayed. The phage cocktail displayed strong antibiofilm activity.
Insights
Phage therapy offers an alternative to antibiotics against multidrug-resistant bacteria like Acinetobacter baumannii. This study developed an adapted phage, Ab105-2phiΔCI404ad, demonstrating enhanced host range and antibiofilm activity in a cocktail formulation.
Area of Science:
- Microbiology
- Bacteriology
- Genomics
Background:
- The rise of multidrug-resistant (MDR) bacteria, including Acinetobacter baumannii, necessitates alternative treatments to conventional antibiotics.
- Phage therapy, utilizing bacteriophages (viruses that infect bacteria), is being re-evaluated as a viable alternative.
- Phage cocktails can broaden the spectrum of activity against bacterial pathogens.
Purpose of the Study:
- To develop an adapted bacteriophage against Acinetobacter baumannii using evolutionary mechanisms.
- To characterize the genomic and phenotypic changes of the adapted phage.
- To evaluate the antimicrobial and antibiofilm efficacy of the adapted phage, individually and in a cocktail.
Main Methods:
- An lytic phage was adapted to Acinetobacter baumannii through an evolutionary process.
- Whole genome sequencing was performed to identify genomic alterations in the adapted phage.
- Phenotypic characterization included host range determination, depolymerase activity assay, and antibiofilm assays.
- A phage cocktail was constructed by combining the adapted phage with another A. baumannii phage.
Main Results:
- The adapted phage, Ab105-2phiΔCI404ad, exhibited four genomic rearrangements in its tail morphogenesis module.
- These rearrangements led to the loss of 10 ORFs and acquisition of 4 new tail protein-encoding ORFs.
- The adapted phage showed a nearly 3-fold increase in host range and an 81% incidence of depolymerase expression.
- Both individual phages and the cocktail demonstrated significant antimicrobial and strong antibiofilm activity against A. baumannii strains, though bacterial resistance was observed.
Conclusions:
- Evolutionary adaptation can enhance bacteriophage efficacy against multidrug-resistant Acinetobacter baumannii.
- The adapted phage Ab105-2phiΔCI404ad and its cocktail show promise as therapeutic agents.
- Further research is needed to address observed bacterial resistance mechanisms to phage therapy.
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