A Bacteriophage Cocktail Reduces Five Relevant Salmonella Serotypes at Low Multiplicities of Infection and Low Temperatures

Abstract

Salmonella are important pathogenic bacteria and, following Campylobacter, they are the second most common cause of bacterial foodborne infections worldwide. To reduce the presence of bacteria along the food chain, the application of bacteriophages (phages) may be a promising tool. In this study, the lytic properties of six phages against five relevant Salmonella serotypes (S. Enteritidis, S. Typhimurium, S. Infantis, S. Paratyphi B and S. Indiana) were analyzed. Three phages were able to lyse all five serotypes. We determined the lytic potential of each phage on indicator strains in vitro at room temperature (RT) and at 37 °C using low multiplicities of infection (MOIs). Most phages reduced their host more efficiently at RT than at 37 °C, even at the lowest MOI of 0.001. Following this, the lytic activity of a cocktail comprising five phages (MOI = 0.1) was examined with each of the five serotypes and a mix of them at RT, 15, 12, 10, 8 and 6 °C. All cultures of single serotypes as well as the mixture of strains were significantly reduced at temperatures as low as 8 °C. For single serotypes, reductions of up to 5 log10 units and up to 2.3 log10 units were determined after 6 h (RT) and 40 h (8 °C), respectively. The mixture of strains was reduced by 1.7 log10 units at 8 °C. The data clearly suggest that these phages are suitable candidates for biocontrol of various Salmonella serotypes under food manufacturing conditions.

A bacteriophage cocktail can efficiently reduce five important Salmonella serotypes both on chicken skin and stainless steel

“…The significant reduction of a mixture of the five different Salmonella serotypes at 6°C suggests that the phage cocktail remains active within the cold chain. Resistance against the six phages was not observed, we identified at least one phage to which the bacteria exhibited sensitivity (Gvaladze et al, 2023 ). Thus, it is likely that some bacteria survived the infection not because of resistance, but rather because of the fact that they entered the late logarithmic or even stationary growth phase, in which propagation of phages is limited.…”

“…In a previous study performed under in vitro conditions, reduction of Salmonella strains by the phage cocktail investigated here has been demonstrated (Gvaladze et al, 2023). To examine the reduction on chicken skin, we initially tested two S. Enteritidis strains revealing the highest susceptibility to the phage cocktail.…”

“…In this study, we evaluated the efficacy of a commercially available Salmonella phage product containing six phages on both chicken skin and stainless-steel surfaces. Some properties of the phages have already been described (Gvaladze et al, 2023 ). Four phages exhibited a myoviridal morphology, while the remaining two are siphoviruses.…”