Survival and proliferation of Listeria monocytogenes in a South African ready-to-eat food factory

Ackermann, Elisma (2017-12)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Listeria monocytogenes is a foodborne pathogen that has the ability to survive within a wide range of conditions found within food processing environments. It is the cause of a potentially life-threatening infection, listeriosis. Its presence is of major concern within ready-to-eat food processing environments and food products. Since no further processing or heat treatment is required by the consumer, post production cross contamination thereof should be minimised. Considering the lack of information about L. monocytogenes in ready-to-eat (RTE) foods in the South African context, the aim of this study was to study the survival and proliferation thereof in a RTE food factory, situated in the Western Cape, South Africa. Presumptive positive samples in the form of inoculated Rapid’L.mono plates (n=434) were collected from the factory’s Listeria management plan. Visual inspection for characteristic black colonies, provided 64 presumptive positive L. monocytogenes species. Polymerase chain reaction protocol was optimised for amplification of target genes iap (Listeria spp.) and lmo2334 (L. monocytogenes), to differentiate positive species. The Rapid’L.mono method was also evaluated for enrichment bias that cause false negatives for L. monocytogenes in the presence of L. innocua. The method was found to be sufficient for detection of L. monocytogenes, if the CFU.g-1 of both species were the same prior to enrichment. Isolates were subtyped through automated EcoRI ribotyping which was conducted using DuPont RiboPrinter® and identified as, DuPont ID 1038, DuPont ID 1041, DuPont ID 1042, and DuPont ID 18596. These strains were previously implicated in human listeriosis cases and international product recalls. DuPont ID 20243, that was isolated from the RTE factory, has not yet been logged on the global Food Microbe Tracker database. From the 29 ribotypes obtained, nine different DuPont ID’s were assigned, which was indicative of the variety of contamination sources within the RTE factory, on par with similar studies conducted. Lineage assignments of L. monocytogenes could be made using the DuPont ID’s and the RTE factory studied was found to host both lineage I and II strains. The cluster analysis revealed contaminated work boots, trolleys and crates to be possible contamination mechanisms. The response of L. monocytogenes biofilms, cultivated under flow conditions, to sanitisers used in the factory environment was evaluated. A protocol was developed using the CO2 evolution measurement system (CEMS) to evaluate the effect of four sanitisers used by the RTE food factory on L. monocytogenes biofilms. In a novel approach, it was found, that even though no bactericidal effect occurred by either sanitiser, the QAC free sanitiser resulted in the best eradication of the biofilm. Peracetic acid and QAC based chemicals had no effect on the biofilm, as recovery of L. monocytogenes was observed after multiple treatments. The RTE factory was advised to use QAC free chemical sanitisers currently available to manage biofilms, specifically in drains. This study not only created more awareness regarding the complexities of L. monocytogenes in the RTE food factory, but also laid the groundwork for further study into the survival and proliferation of L. monocytogenes in the RTE environment.

AFRIKAANSE OPSOMMING: Listeria monocytogenes is ‘n voedselverwante patogeen wat die vermoë besit om in ‘n wye reeks toestande gevind in voedselverwerkingsomgewings, te oorleef. Dit is die oorsaak van ‘n potensieël lewensgevaarlike infeksie, listeriose. Die teenwoordigheid daarvan is van groot kommer binne gereed-om-te-eet (RTE) verwerkingsomgewings en voedselprodukte. Aangesien geen verdere verwerking of hittebehandeling benodig word deur die verbruiker nie, moet na-produksie kruiskontaminasie daarvan geminimiseer word. Aangesien daar ‘n tekort aan inligting rakende L. monocytogenes in RTE voedselprodukte in die Suid-Afrikaanse konteks is, is die doel van hierdie studie om die oorlewing en verspreiding daarvan in ‘n RTE voedselfabriek in die Wes-Kaap van Suid-Afrika, te ondersoek. Vermoedelike positiewe monsters in die vorm van geϊnokuleerde Rapid’L.mono plate (n=434) is ingesamel deur middel van die fabriek se Listeria bestuursplan. Visuele inspeksie van die kenmerkende swart kolonies het 64 vermoedelike L. monocytogenes spesies verskaf. ‘n Polimerase kettingreaksie is geoptimiseer vir die amplifikasie van teikengene iap (Listeria spp.) en lmo2334 (L. monocytogenes), om positiewe monsters te onderskei. Die Rapid’L.mono metode is ook geëvalueer vir verrykingspartydigheid wat vals negatiewes vir L. monocytogenes in die teenwoordighied van L. innocua veroorsaak. Daar is gevind dat die metode voldoende is vir die opsporing van L. monocytogenes mits die KVE.g-1 van beide spesies dieselfde was voor verryking. Isolate was gesubtipeer deur EcoRI ribotipering wat gedoen is deur die gebruik van die DuPont RiboPrinter. Die isolate is geïdentifiseer as DuPont ID 1038, DuPont ID 1041, DuPont ID 1042, en DuPont ID 18596. Hierdie stamme was voorheen geϊmpliseer in menslike listeriose gevalle asook internasionale voedselherroepings. DuPont ID 20243 wat geïsoleer is in OF uit die RTE fabriek is nog nie van tevore aangemeld op die globale “Food Microbe Tracker” databasis nie. Van die 29 ribotipes verkry, was nege verskillende DuPont ID’s aangewys. Hierdie is aanduidend van die verskeidenheid van kontaminasiebronne binne-in die RTE fabriek en dit is in lyn met soortgelyke studies. Linie toekennings van L. monocytogenes kon gemaak word deur gebruik te maak van DuPont ID’s. Daar is gevind dat die fabriek wat bestudeer is, beide linie I en II stamme huisves. Die groepsanalise het gewys dat gekontamineerde werksskoene, trollies en kratte moontlike kontaminasiemeganismes was. Die reaksie van L. monocytogenes biofilms, gekweek onder vloeikondisies, teenoor saniteermiddels wat in dίe fabrieksomgewing gebruik word, is geëvalueer. ‘n Protokol is ontwikkel, deur gebruik te maak van die CO2 Evolusie Metingsisteem (CEMS), om die effek van vier saniteermiddels, gebruik in die RTE voedselfabriek, te evalueer. As eerste van sy soort, is gevind dat al was daar geen bakterieëdodende effek deur enige saniteermiddel nie, het die chemiese saniteermiddels wat geen kwaternêre ammonium samestelling (QAC) bevat het nie, die beste uitwissing van die biofilm veroorsaak. Perasynsuur en QAC-gebaseerde chemikalieë het geen effek op die biofilms gehad nie omdat herstel van L. monocytogenes gesien is na verskeie behandelings. Daar is aanbeveel dat die RTE fabriek gebruik maak van die QAC-vrye chemiese saniteermiddels tans beskikbaar vir die bestuur van biofilms, spesifiek in die dreine. Hierdie studie het nie net meer bewusmaking aangaande die kompleksiteit van L. monocytogenes in die RTE voedselfabriek tot gevolg gehad nie, maar het ook die fondasie gelê vir verdere studies aangaande die oorlewing en verspreiding van L. monocytogenes in die RTE omgewing.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102634
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