Efficacy of Repeated Applications of Bacteriophages on Salmonella enterica-Infected Alfalfa Sprouts during Germination

Abstract

Nontyphoidal Salmonella enterica is one of the leading pathogens for foodborne outbreaks in a multitude of food commodities, including alfalfa sprouts, which are commonly consumed raw. The food industry has commonly used chlorinated washes, but such methods may not be perceived as natural; this can be a detriment as a large portion of sprouts are designated for the organic market. A natural and affordable antimicrobial method that has been acquiring popularity is the use of bacteriophages. This study compared the efficacy of repeated daily applications and a single application of two separate bacteriophage cocktails (SE14, SE20, SF6 and SE14, SF5, SF6) against four Salmonella enterica (S. enterica) strains on germinating alfalfa sprout seeds from days 0 to 7. The results show S. Enteritidis to be the most susceptible to both cocktails with ~2.5 log CFU/mL decrease on day 0 with cocktail SE14, SF5, and SF6. S. enterica populations on all strains continued to grow even with repeated daily bacteriophage applications but in a significantly decreased rate (p < 0.05) compared with a single bacteriophage application. The extent of the reduction was dependent on the S. enterica strain, but the results do show benefits to using repeated bacteriophage applications during sprout germination to reduce S. enterica populations compared with a single bacteriophage application.

Tailoring the Host Range of Ackermannviridae Bacteriophages through Chimeric Tailspike Proteins

“…Of interest, many of these impacted Salmonella phages (vB_SenA_SM5, Sh19. SE14, and vB-SalM-PM10) are proposed to have commercial utility in food-related industries, although none have been formally evaluated for cross-reactivity against C. sedlakii to our knowledge [ 61 , 62 , 63 , 64 ]. The procedures demonstrated in this study may thus have value in improving the specificity of other phages currently in development.…”

Infectivity responses of Salmonella enterica to bacteriophages on maize seeds and maize sprouts

“…Ye et al (2010) used a phage cocktail and achieved a higher Salmonella population reduction of ∼3.41 log CFU/g ( Ye et al, 2010b ). Furthermore, repeating phage cocktail treatment on alfalfa sprout seeds was found to be more effective on inhibiting the recovery of S. enterica ( Wong and Wang, 2022 ). Aside from phage treatments, the reduction of S. enterica on seeds has also been widely studied by using chemical reagents.…”

“…Maize seeds separately inoculated with S. enterica strains were soaked with the phage cocktail (SF1 + SI1) at MOI 1000 with agitation at 200 rpm for 2 h (phage group) according to previously reported study ( Wong and Wang, 2022 ). After 2 h, the liquids were decanted and the seeds were averagely placed in tip boxes.…”

“…However, researchers have increasingly turned their attention to bacteriophages (phages) as an alternative disinfection method, owing to their high specificity towards pathogens while preserving the native food microbiota ( Sillankorva et al, 2012 ). Previously, specific phages were applied during the sprouting period of alfalfa, mung bean, and lettuce seeds to reduce the population of pathogens such as Salmonella and Escherichia coli ( Ye et al, 2010a ; Zhang et al, 2019 ; Fang et al, 2022 ; Wong and Wang, 2022 ). Although phages are stored under strict conditions like refrigerated temperature (typically 2–8 °C) and limited combination with other chemical reagents to avoid being inactivated, they are naturally occurring, self-replicating and are generally nontoxic to humans ( Moye et al, 2018 ).…”

Transcriptional Response of Salmonella enterica to Bacteriophage Treatments with Differential Multiplicities of Infection

“…However, there was also a population resurgence by day 6, where the bacteriophage-treated alfalfa seeds were <1 log CFU/g compared with the control [14]. Given the Salmonella population resurgence after initial bacteriophage treatments shown in previous research, the authors of [15] implemented repeated daily bacteriophage applications at an MOI of 1000 against S. enterica on alfalfa sprouts during germination and found repeated applications to further reduce S. enterica populations, but the issue of population resurgence still arose [15].…”