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Dna-Based Detection Of Food Isolates Of Bacillus Cereus And Its Behavioural Pattern In Selected Foods

Shivalingsarj, V. Desai (2010) Dna-Based Detection Of Food Isolates Of Bacillus Cereus And Its Behavioural Pattern In Selected Foods. PhD thesis, University of Mysore.

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Abstract

Bacillus cereus is an opportunistic foodborne pathogen that contaminates a wide variety of foods. There are mainly two types of illness caused by B. cereus in human beings namely diarrhoeal and emetic types. The recent studies reporting the foodborne illness being caused by all the members of B. cereus have made the specific identification of B. cereus all the more important. The study of the organism has gained significance due to its endospore forming nature, which are resistant to heat, nutrition depletion, desiccation and other such factors. India being a vast and subtropical country with plethora of food varieties being prepared at household and commercial level provides an ideal situation for an organism like B. cereus to survive and grow leading to health hazards. In the background of Indian scenario, The present Ph.D. programme attempts to assess the prevalence of toxigenic and non-toxigenic isolates of B. cereus in selected foods and understand the behavioural pattern of this bacterial species in culture and food systems. The native isolates of B. cereus obtained from a diverse range of foods revealed the occurrence of B. cereus as evidenced by conventional and molecular biology methods. Isolates in varied percent were positive for target genes of 16S rDNA and phosphatidylinositol phospholipase C (pi-plc), haemolysin BL (hbl) and sphingomyelinase (sph). The selected toxigenic food isolates of B. cereus revealed a high degree of sequence homology with earlier established selected strains of B. cereus and other species of B. cereus cluster as evidenced in sequence homology of partial nucleotide sequences of respective PCR amplicons of target genes. Genetic relatedness among selected potent toxigenic native isolates of Bacillus cereus based on RAPD-PCR using 4 selected arbitrary primers resulted in a dendogram with 3 clusters covering almost all the isolates except for one isolate, which was of non-cluster type. The cluster patterns could distinguish the isolates of B. cereus based on source of isolation, growth temperature and prevalence of toxigenic traits like haemolysin and sphingomyelinase. The experimental trials undertaken to evaluate the behaviour of vegetative cells and spores of four potent native toxigenic food isolates of Bacillus cereus as affected by selected time-temperature combinations used in Indian traditional foods revealed a thermal inactivation pattern, which indicated that the death rate was not constant during the process of heat treatment. a Abstract of Ph.D. thesis b In the present experimental trials, an attempt was made to model the behaviour of vegetative cells and spores of a potent toxigenic native food isolate of B. cereus CFR 1534 in terms of LPD and GR. The culture of B. cereus which exist as vegetative cells and spores have better survival and growth ability in a diverse range of food matrices as a function of temperature, pH and sodium chloride concentration. The generated lag phase duration (LPD) and growth rate (GR) values did reveal the versatility of this native toxigenic food isolate B. cereus. The model derived in the study was found to be significant and the predicted values were found to be in good agreement for LPD and moderately fitting for GR values. The same native isolate was also studied for its behaviour in two food systems namely (i) a traditional cereal legume based dehydrated nutritious food product based on millet and legume, locally known as Ragi hurittu and (ii) a ready-to-use chocolate milk, which is a cocoa-based beverage with reasonable total solids. The bacterial species tend to remain in the product, whether introduced as vegetative cells and/or spores and subsequently, do increase in a slow paced manner. Such a product profile with no visual changes, but harbouring viable population of B. cereus is of high risk from the viewpoint of causing potential health hazards. The research findings of this Ph.D. thesis did indicate that the diversified genetic relatedness of toxigenic traits are well spread within B. cereus cluster and have become stable traits among food isolates of B. cereus prevalent in the food chain. Being an opportunistic foodborne pathogen, the thermal inactivation pattern and behavioural pattern in culture system and food matrices would enable to develop HACCP protocols in the food chain towards providing microbiologically safe foods to the human population.

Item Type: Thesis (PhD)
Uncontrolled Keywords: Bacillus cereus, foods, PCR-based detection, toxins, microbial food safety
Subjects: 600 Technology > 08 Food technology > 18 Processed foods
600 Technology > 08 Food technology > 13 Quality control > 02 Safety
500 Natural Sciences and Mathematics > 07 Life Sciences > 03 Biochemistry & Molecular Biology > 04 Biosynthesis
Divisions: Human Resource Development
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 01 Mar 2011 11:31
Last Modified: 01 Jul 2015 12:47
URI: http://ir.cftri.com/id/eprint/9959

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