Control of Antibiotic-Resistant Salmonella enterica Serovar Typhi in Water and Milk Using Phage Cocktail

Abstract

THE RISE of clinical concern about antibiotic-resistant Salmonella enterica serovar Typhi is mainly attributed to the frequent contamination of food and drinking water. The aim of this study is to assess the sensitivity of S. Typhi to antibiotics as well as isolation of lytic bacteriophages specific to the bacterium and investigate their ability to enhance the safety of tap water and milk. S. Typhi clinical isolates recovered from infected blood specimens were included in this study. The bacterial isolates were identified by conventional biochemical tests; Vitek analyzer in addition to Widal test to determine the serotypes of Salmonella isolates. Four lytic bacteriophages specific to S. Typhi were isolated and characterized using TEM and designated as vb_StyM,EN-1, vb_StyM,EN-2, vb_StyS,EN-3 and vb_StyP,EN-4. The results showed resistance of S. Typhi isolates to various antibiotics. Phage cocktail was prepared and applied for controlling S. Typhi growth in milk and drinking water at 4⁰C and room temperature. After treatment, complete eradication of bacterial growth was observed in broth medium at 4°C and room temperature after 24hrs. In addition to that, phage cocktail showed complete inhibition of S. Typhi growth in treated tap water at 25°C after 24hrs and in milk at 4°C. A significant reduction; nearly five log reductions was observed in skim milk while one log reduction was obtained in full fat milk at 25°C. These results indicate that S. Typhi is resistant to some antibiotics and bacteriophages could be promising antimicrobial alternatives.