Insights Into The Mechanisms For Host Range Of Pseudomonas Aeruginosa Phages

Due to the overuse of antibiotics and limited development of new antimicrobial agents,treating patients with superbugs is extremely difficult.Bacteriophages(phages)therapy,as an important tool against superbugs,has broad application prospects.However,the natural phage host range is narrow and the specific mechanism of action is not yet clear,which limits the clinical application of phage therapy.Therefore,research on the phage-bacteria interaction is needed to elucidate the determinants of phage host range and promote the development of phage therapy in clinical applications.We chose the superbugs as our research object and isolated 130 strains of P.aeruginosa from clinical samples.From these,we isolated 30 P.aeruginosa phages.Using next-generation sequencing and genome analysis,we identified 13 O-antigen types in the bacteria and 9 phage species with three different morphologies:myovirus,podovirus,and siphovirus.These biological materials were representative.Then we established a network of interactions between the 30 phages and 130 bacteria through cross-infection experiments,and analyzed the mechanisms determining phage host range from both extracellular and intracellular perspectives of phage-bacteria interactions.Extracellularly,phages preferentially bind to the bacterial lipopolysaccharide(LPS)as a receptor.Mutations in the bacterial LPS or phage tail fiber proteins significantly affect the host range,indicating that they are critical factors influencing phage host range.Intracellularly,the bacterial defense system further limits the phage host range.The number of bacterial defense systems is negatively correlated with the number of sensitive phages and positively correlated with the bacterial genome size.Moreover,these defense systems are mainly located in variable genes,suggesting that bacteria primarily rely on the high mobility of defense systems to acquire resistance to phages.Finally,based on the above mechanisms and phage characteristics,we screened and established four phage cocktails.In vitro antibacterial experiments showed that these cocktails could inhibit the growth of randomly selected P.aeruginosa strains from clinical samples in 8 hours,indicating their effectiveness in controlling multidrug-resistant bacteria.In conclusion,this study elucidated the determinants of P.aeruginosa phage host range through phage-bacteria interactions and established efficient and broad-spectrum phage cocktails,which have significant implications for the clinical treatment of bacterial infections using phage therapy.