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Oulun yliopiston väitöskirjat

IMPROVED ENRICHMENT CULTIVATION OF SELECTED FOOD-CONTAMINATING BACTERIA, ACTA UNIVERSITATIS OULUENSIS C Technica 370

ISBN-13:	978-951-42-6356-9
Kieli:	englanti
Kustantaja:	Oulun yliopisto
Oppiaine:	Tekniikka, matematiikka
Painosvuosi:	2010
Sidosasu:	pehmeäkantinen
Sijainti:	Print Tietotalo
Sivumäärä:	136
Tekijät:	TASKILA SANNA

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The aim of this work was to assess and improve the enrichment cultivation of food-contaminating bacteria prior to detection by means of RNA-based sandwich hybridization assay(SHA). The examples of beer-spoiling lactic acid bacteria (LAB) and food-borne SalmonellaTyphimurium were selected based on their relevance in Finnish food industry. Also universalchallenges affecting on the selection of the enrichment cultivation procedure are discussed,including some potential possibilities for improved enrichment cultivation. The results of thisstudy may therefore be used for the assessment of the efficiency of bacterial cultivation in otherapplications. The evaluation of the enrichment cultivation procedures prior to SHA lead to followingconclusions: i) the enrichment cultivation procedure is necessary prior to rRNA-based SHA, andit directly influences the accuracy of SHA; ii) the improvement of the enrichment cultivation mayallow faster recovery and growth of bacteria; iii) the improved recovery of bacteria can beachieved by reducing environmental stress factors in the enrichment culture; and iv) the growth ofbacteria may be accelerated by assuring the selectivity of medium and allowing accessibility togrowth factors. Several growth factors were studied by means of full factorial design and responsesurface modeling. Measured cell densities, as well as predicted lag-times and maximum growthrates in the bacterial cultures were used as responses. The results show that small shifts in the cultivation conditions extend the lag-time and decreasethe growth rate of both LAB and Salmonella. Besides adjusting the temperature and pH, thegrowth of LAB was facilitated by reducing osmotic and oxidative stresses in the enrichmentmedium. In this study, a novel enzyme controlled glucose delivery system was used for the firsttime in the enrichment cultivation of food-contaminating bacteria. The glucose delivery systemimproved the growth of LAB in single strain cultures and in actual brewing process samples. Therecovery of injured Salmonella was also enhanced by using the glucose delivery system togetherwith selective siderophore ferrioxamine E, both in terms of reduced lag-times and increasedgrowth rates. Based on the SHA, the adjusted BPW broth enhanced the molecular detection ofheat-injured Salmonella in meat.

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