An Optimized Bacteriophage Cocktail Can Effectively Control Salmonella in vitro and in Galleria mellonella

Abstract

Salmonella spp. is a leading cause of gastrointestinal enteritis in humans where it is largely contracted via contaminated poultry and pork. Phages can be used to control Salmonella infection in the animals, which could break the cycle of infection before the products are accessible for consumption. Here, the potential of 21 myoviruses and a siphovirus to eliminate Salmonella in vitro and in vivo was examined with the aim of developing a biocontrol strategy to curtail the infection in poultry and swine. Together, the phages targeted the twenty-three poultry and ten swine prevalent Salmonella serotype isolates tested. Although individual phages significantly reduced bacterial growth of representative isolates within 6 h post-infection, bacterial regrowth occurred 1 h later, indicating proliferation of resistant strains. To curtail bacteriophage resistance, a novel three-phage cocktail was developed in vitro, and further investigated in an optimized Galleria mellonella larva Salmonella infection model colonized with representative swine, chicken and laboratory strains. For all the strains examined, G. mellonella larvae given phages 2 h prior to bacterial exposure (prophylactic regimen) survived and Salmonella was undetectable 24 h post-phage treatment and throughout the experimental time (72 h). Administering phages with bacteria (co-infection), or 2 h post-bacterial exposure (remedial regimen) also improved survival (73–100% and 15–88%, respectively), but was less effective than prophylaxis application. These pre-livestock data support the future application of this cocktail for further development to effectively treat Salmonella infection in poultry and pigs. Future work will focus on cocktail formulation to ensure stability and incorporation into feeds and used to treat the infection in target animals.

Bacteriophage Cocktails Protect Dairy Cows Against Mastitis Caused By Drug Resistant Escherichia coli Infection

“…So, the phage mixtures could effective to solve this problem. As expected, our results, which was similar to most reported treatment effects of phage cocktails, exhibited that the symptoms of animals have improved significantly (Tanji et al, 2005b;Jin et al, 2020;Nale et al, 2021). Furthermore, the innate inflammatory response is the initial stage of infection and is a key factor in protecting the body from infectious pathogens (Khan et al, 2015).…”

Development of a Phage Cocktail to Target Salmonella Strains Associated with Swine

“…In contrast, in the co-infection model, the bacterial cells have more of an opportunity to colonise the haemolymph and thus the phages are less effective. Salmonella colonies isolated post-exposure were still sensitive to phage infection, as has been reported in other larvae challenge model studies [32,[49][50][51]. However, it could also be possible the low challenge dose of 10 5 CFU/larva used was insufficient to isolate phage resistant mutants.…”

“…4.9.2. Salmonella Infected G. mellonella Treated with Phage Cocktails For all larvae phage therapy studies, previously described methods were used [32,38,49]. Both the Salmonella strain S01160-12 (LD 50 dose of 10 5 CFU) and phage cocktails at a final concentration of 10 7 PFU (MOI 100 and phages were mixed at equal volumes) were administered to the larvae via the oral route using a Hamilton syringe pump.…”

“…As Galleria mellonella larvae have a similar innate immune response as larger vertebrates [27,28], they have been successfully used to test efficacy of phage lysis in vivo [29][30][31][32]. The infection model is both simpler and cheaper and requires a less complex ethical framework than mammalian studies [33], allowing a larger number of formulations, doses and treatment regimens to be tested [34].…”

Impact of Phage CDHS-1 on the Transcription, Physiology and Pathogenicity of a Clostridioides difficile Ribotype 027 Strain, R20291

“…Having established the expression profiles of CDHS-1 and bacterial genes during interaction we ascertained the virulence of the phage resistant strains and lysogens in G. mellonella larvae. The larval model is inexpensive and can provide useful data on the use of animal infection models of many pathogenic bacteria including C. difficile [17,18,29,51]. The insects are also relatively well established for many bacterial infection, colonization, phage therapy, pathogenesis and virulence assays [17,18,52,53].…”