Isolation and characterization of lytic bacteriophages of Salmonella Typhimurium and their therapeutic application

Abstract

Salmonella Typhimurium is an important bacterial pathogen of gastroenteritis revealing multidrug resistance and has zoonotic implication. In an approach towards alternatives to antibiotics, lytic bacteriophages were isolated against Salmonella Typhimurium from sewage effluent using double agar overlay method. The isolated bacteir ohages, viz. fST1, fST2, fST3, fST4 and fST5 were characterized microbiologically and revealed host range 85–92% individually and 100% collectively within the genus. Biophysical characterization revealed that the phages were stable at 16°, 37°, 42°C and pH 4, 7 and 9 for 3h, supporting their therapeutic application. Electron microscopic examination of the fST1 showed icosahedral head (52.5nm), contractile tail (220–250nm) belonging to the family Myoviridae and order Caudovirales. Further, molecular characterization of fST1 revealed 38kb nucleic acid and digested by restriction endonucleases i.e., EcoRI, Bam HI and Hae III. The therapeutic application of the isolated phage cocktail was ascertained in Swiss albino mice models by infecting the control and treatment groups with 3×108 cfu/ml of the organism intramuscularly and orally. Following challenge the treatment group administered with 3×109 pfu/ml of phage mixture showed significant decrease in number of colony forming units of bacteria in vivo.