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Molecular characterization of toxigenic Staphylococcus spp. for stress responses under simulating conditions of food processing in model food systems

Rohinishree, Y. S. (2015) Molecular characterization of toxigenic Staphylococcus spp. for stress responses under simulating conditions of food processing in model food systems. PhD thesis, University of Mysore.

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Abstract

Street foods have been reported to be highly contaminated with bacteria, fungi and viruses and they can be a cause of food-borne diseases. Food-borne diseases are a major concern worldwide. Two thirds of food-borne diseases are caused by the bacteria, as they are implicated as causative agent in most outbreaks. Staphylococci are Gram-positive, spherical, non-sporulating bacteria with ubiquitous nature. Staphylococcal food poisoning (SFP) is one of the most common foodborne diseases resulting from the consumption of enterotoxins produced by staphylococci. To study the staphylococcal contamination of street foods, different street food samples were collected from various locations in Mysore city. A total of 83 staphylococcal food isolates from these samples were presumptively identified and characterized by conventional biochemical methods. Staphylococcus xylosus was found to be the most dominant species in the street food samples. Polymerase Chain Reaction based Restriction Fragment Length Polymorphism (PCR-RFLP) for 16S rRNA gene was used as a taxonomic marker for the identification of native food isolates. The most diverse Staphylococcus spp. were found in churmuri, rawmilk and peda samples and their pathogenic traits were determined by the presence of regulatory (sarA and agr) and virulence (spa, nuc, hla, hlb, coa) genes. Further, PCR was used to investigate the presence of enterotoxin genes (seasee) and immunological techniques for the quantification of super antigens produced by native food isolates. The results showed that sea, seb and sek were the most abundant genes in food isolates. The enterotoxigenic Coagulase Positive Staphylococci (CPS) as well as Coagulase Negative Staphylococci (CNS) produced more than one type of Staphylocccal Enterotoxins (SEs). PCR based methods were found to be accurate for the identification of staphylococcal contamination in the food matrix- lassi. The role of sigB in staphylococci at stress conditions was investigated by the construction of sigB mutant using targetron technique. The phenotypic properties of wild type (WT) and mutant (sigB-) were characterized and the loss of pigmentation with increased hemolytic and nuclease activities were observed in sigB- strains. The effect of various stresses on growth and virulence of WT and sigB- staphylococcal strains in food model systems was also investigated and it was demonstrated that sigB is important for survival during alkaline (pH 10), saline (8%) and thermal stresses. However, it had no significant influence on toxin production. Transcription profiles of stress and virulence genes were also characterized by using semi quantitative Reverse Transcriptase PCR (RT-PCR). The results establish that sigB is an important component in staphylococcal growth and to the adaptation to stress. Additionally it seems to have a significant role in pathogenicity of staphylococci and it partially represents a key component in the staphylococcal regulatory network.

Item Type: Thesis (PhD)
Uncontrolled Keywords: Staphylococcal food poisoning, Polymerase Chain Reaction, food matrix
Subjects: 600 Technology > 08 Food technology > 10 Food Microorganisms
Divisions: Fruit and Vegetable Technology
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 19 May 2016 07:14
Last Modified: 19 May 2016 07:14
URI: http://ir.cftri.com/id/eprint/12176

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