All hope is not lost: development of a bacteriophage cocktail to control Salmonella biofilms under chicken, pig and human gut conditions

Salmonella causes gastroenteritis via consumption of contaminated water, poultry, pork or beef products. Salmonellosis affects ~550 million people, causes ~33 million deaths and costs ~$3.7 billion to treat per year globally. The situation is compounded by rising antimicrobial resistance (AMR) and dwindling antibiotic innovations. Whilst antibiotics may be helpful, they have limited efficacy in biofilms, a protective extracellular matrix produced by many bacteria including Salmonella. To effectively control Salmonella and mitigate the general impending global AMR crisis, effective alternatives are needed to augment or replace antibiotics. Here, we present data to support the use of phages which we show can penetrate biofilms and kill Salmonella. They could therefore be used as a control strategy in water, given to animals pre-harvest or during food processing. We optimised a broad host range six-phage (five myoviruses and a siphovirus) cocktail that effectively lysed important serovars including the monophasic strains. We determined the biofilm properties of representative chicken and pig associated strains aerobically at 37oC, and anaerobically at 37 and 40oC to mimic growing conditions of Salmonella and guts of humans, swine and poultry. Treating established biofilms with the cocktail caused a significant decrease (p