Abstract
The rapid increase in the number of worldwide human infections caused by the extremely antibiotic resistant bacterial pathogen Stenotrophomonas maltophilia is cause for concern. An alternative treatment solution in the post-antibiotic era is phage therapy, the use of bacteriophages to selectively kill bacterial pathogens. In this study, the novel bacteriophage AXL3 (vB_SmaS-AXL_3) was isolated from soil and characterized. Host range analysis using a panel of 29 clinical S. maltophilia isolates shows successful infection of five isolates and electron microscopy indicates that AXL3 is a member of the Siphoviridae family. Complete genome sequencing and analysis reveals a 47.5 kb genome predicted to encode 65 proteins. Functionality testing suggests AXL3 is a virulent phage and results show that AXL3 uses the type IV pilus, a virulence factor on the cell surface, as its receptor across its host range. This research identifies a novel virulent phage and characterization suggests that AXL3 is a promising phage therapy candidate, with future research examining modification through genetic engineering to broaden its host range.
Highlights
Stenotrophomonas maltophilia is an aerobic, Gram-negative bacterium that is ubiquitous in the environment, often found in close association with plants helping to promote plant growth and nutrient breakdown in the rhizosphere [1,2,3]
A novel S. maltophilia phage, AXL3, unrelated to any phages currently sequenced in the National Center for Biotechnology Information (NCBI). We show that this phage recognizes binds to the major pilinPilA. We show that this phage recognizes and bindsand to the major pilin subunit of the type pilus, a virulence factor of many bacterial pathogens, and has potential as a phage therapy a virulence factor of many bacterial pathogens, and has potential as a phage therapy candidate against candidate resistant S. maltophilia
No transmembrane domains were predicted in gp26, analysis with LipoP 1.0 predicted gp26 to be a lipoprotein signal peptide with a predicted signal peptidase II cleavage site between amino acids 17 and 18. This suggests that gp26 acts as an o-spanin, anchored in the outer membrane and spanning the periplasm to reach the cytoplasmic membrane i-spanin protein [53]. These results characterize a novel virulent phage that is active against the multidrug resistant bacterial pathogen S. maltophilia
Summary
Stenotrophomonas maltophilia is an aerobic, Gram-negative bacterium that is ubiquitous in the environment, often found in close association with plants helping to promote plant growth and nutrient breakdown in the rhizosphere [1,2,3]. In addition to inducible chromosomally encoded β-lactamases, multidrug efflux pumps and low outer membrane permeability to defend against antibiotic treatments, S. maltophilia encode several virulence factors These include extracellular enzymes such as proteases, esterases, lipases and haemolysin, and the cell-associated virulence factors lipopolysaccharide and type IV pili that contribute to antimicrobial resistant biofilm formation on abiotic surfaces and host tissues, which aid in the establishment of chronic infections [5]. The tenacity of this pathogen and its extreme multidrug resistance make typical antibiotic treatments ineffective against these infections, emphasizing the need for alternative treatments
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