Isolation of Bacteriophages from sewage and their molecular characterization and in-vitro antimicrobial activities on contaminated food items collected from Bishoftu town, Oromia Regional State, Ethiopia

Abstract

Foodborne pathogens such as Salmonella and Escherichia coli have become big problem to food industries and human health. Emergence of antibiotic resistant bacteria has limited the opportunities of controlling pathogenic bacteria in food commodities and treating foodborne infections. Bacteriophages are viruses of bacteria that infect and kill bacteria. This study is targeted to isolation, purification, quantification, in-vitro evaluation and molecular characterization of phages. Accordingly, four lytic phages, PS1, PS2, PE1 and PE2, were isolated and characterized. In the result, all the isolated phages have very nice lytic ability phenotypically in spot assay with PS1 and PE2 exhibiting more activity and having higher plaque concentration than PS2 and PE1. Bacteriophages titer was determined within range of 105 to 1012PFU/mL. In phage efficacy test, Phage of PS1 and PE2 was found to be effective in reducing number of bacteria in two different foods (meat and milk) contaminated with Salmonella Enterica (S1) and E. coli O157:H7 (E2), respectively. Which were spiked with 1× 103 CFU of Salmonella Enterica and 1× 105 CFU E. coli 0157:H7 strain and treated with 1× 107PFU of each PS1 and PE2 phage, respectively at 4ºC and 25ºC. In the result of the present study, the inhibitory effect of both phages was better at 25ºC than at 4ºC when the two storage temperature is compared. A significant reduction in bacterial number was observed in both tested foods having p< 0.05 in phage treated food samples when compared with its non-phage treated control compartment. Both Phages incubated at 4ºC in each food samples are relatively stable than the one which is at 25ºC. Molecular analysis of all the four phages using gel-electrophoresis revealed clear band patterns all having greater than 12Kb genome sizes, whereas restriction digestion of phage DNA with MseI has shown no digestion but with HinP1I digestion, low concentrated and cleaved band was observed for PE2. Based on the finding of this study, using bacteriophage as antimicrobial agent to prevent pathogenic bacteria is realistic. Bacteriophages ability of infecting and killing food spoiling microorganisms and capacity of extending shelf life of food makes them potential alternative antimicrobial agent to alleviate the risk of transmitting pathogenic bacteria via food commodities. Accordingly more characterization, in-vivo evaluation and safety investigation study should have to be done to take phage therapy to higher and problem solving stage.