Doctoral Degrees (Food Science)

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Browsing Doctoral Degrees (Food Science) by Subject "Bacteriophages -- Control -- Environmental aspects"

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    The efficacy of bacteriophages FO1a and S16 in the reduction of Salmonella on chicken carcasses in a South African poultry processing environment
    (Stellenbosch : Stellenbosch University, 2022-12) Wessels, Kirsten; Gouws, Pieter Andries; Rip, Diane; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Much of the research surrounding bacteriophages (phages) as a processing aid for the control of Salmonella on chicken meat has been conducted in vitro in the laboratory. Information about the efficacy and application of bacteriophages as part of a hurdle concept in the chicken processing environment is limited. In South Africa, the use of certain antibiotics in live broilers and the use of chlorine-containing antimicrobials in the processing environment, are still permitted as Salmonella control methods. The incidence of Salmonella in chicken meat in South Africa is unclear, but previous research has repeatedly shown that the use of antibiotics and/or chlorine selects for resistance in Salmonella. The aim of this study was to determine the efficacy of a commercial phage cocktail PhageGuard S™ (PGS) (FO1a and S16 phages) in the reduction of Salmonella on chicken carcasses through a validated spraying system in a South African chicken processing plant. This study also investigated the incidence and antibiotic susceptibility profiles of Salmonella isolated from chicken carcasses in the plant. The PGS was applied at a 1% (v/v) concentration onto chicken carcasses via a spraying system (validated specifications: 530 µm nozzle diameter, 200 mesh strainer and 3 Bar pump pressure) after the chlorine spin chilling step. Neck skins samples were collected before the inside- outside wash step (N= 80) and after the PGS application step (N= 160). The neck skin samples were tested for Salmonella presence/absence (EN ISO 6579/A1 (02/2006)) and confirmed using Vitek®. Confirmed Salmonella isolates were screened for antibiotic susceptibility using the Kirby-Bauer disk diffusion method according to M100 from the Clinical and Laboratory Standards Institute (CLSI, 2020). Confirmed Salmonella isolates from neck skin samples collected after PGS application were re-exposed to PGS in the laboratory via a killing assay (Micreos Food Fafety, NL) to determine if the isolates were resistant to the PGS. Before the inside-outside step the Salmonella incidence was 60% with a large portion of these isolates showing resistance to tetracycline (56.3%) and sulfonamide (43.8%). After the combination of the inside-outside wash step, chlorine spin chilling and PGS application, the Salmonella incidence decreased to 23.75%, where more than half of these isolates showed resistance to tetracycline (63.2%) and sulfonamide (55.3%). For the killing assay, all isolates which survived PGS in the processing environment were reduced by 100% in the laboratory, highlighting that the phages were unable to reach the Salmonella via the spray application, and not that the Salmonella was resistant to the phages. The results in this study showed that the multi-drug resistant Salmonella in the chicken neck skins survived a complete immersion in chlorine but were successfully reduced by PGS, making phages a potential solution to many persistent microbial problems. This study also provides valuable insight into implementing phages into the large-scale hurdle concept of a processing environment and highlights the importance of the application method to ensure safe delivery of the phages to the target bacteria for a high efficacy.