Application of Bacteriophages for Biocontrol of Extensively Drug Resistant Salmonella Serovars Isolated from Poultry Farms

Salmonella is one of the most common foodborne pathogens causing diseases in humans and animals. Increased resistance to antibiotics necessitates the need for an alternative control strategy. This study aimed to screen, isolate and evaluate the bacteriophage characteristics for biocontrol of pathogenic Salmonella serovars. Twelve Salmonella isolates, including different Salmonella enterica serovars, were obtained from different sources of poultry farms. All isolates were screened for antibiotic sensitivity and showed multiple antibiotic resistance. Two lytic bacteriophages, vB_SalSph_WW1, and vB_SalM_WW2, were isolated from the sewage and characterized against Salmonella enterica serovar Enteritidis. Morphological analysis by transmission electron microscopy revealed that the vB_SalSph_WW1 phage belonged to the family Siphoviridae while the vB_SalM_WW2 phage belonged to the family Myoviridae. Both phages showed a broad host range within the Salmonella genus. Phages vB_SalSph_WW1 and vB_SalM_WW2 had a lytic effect on 3 (25%) and 4 (33.3%) of the 12 Salmonella isolates, respectively. The lytic cycle of each phage was determined by a one-step growth curve and both phages had the same short latent period (15 min). WW1 phage gave a burst size of 90 PFU/infected cell, while the vB_SalM_WW2 phage gave a higher burst size of 150 PFU/infected cell. The stability test revealed that vB_SalSph_WW1 and vB_SalM_WW2 phages were stable at pH 4–9 and pH 4–10, respectively. Both Phages exhibited high degrees of thermal tolerance with active titer as high as 42◦C. However, they lost their stability and the titers declined when heated at 50◦C for 30 min. This study revealed that vB_SalSph_WW1 and vB_SalM_WW2 phages have the potency to be used as an alternative strategy to control the infection of Salmonella in poultry farms and to prevent transmission of Salmonella infection to humans and spread of the pathogen into environment.