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

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Relation http://ir.cftri.com/12176/
 
Title Molecular characterization of
toxigenic Staphylococcus spp. for stress responses under simulating conditions of
food processing in model food systems
 
Creator Rohinishree, Y. S.
 
Subject 10 Food Microorganisms
 
Description 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.
 
Contributor Negi, P. S.
 
Date 2015
 
Type Thesis
NonPeerReviewed
 
Format application/pdf
 
Language en
 
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Identifier http://ir.cftri.com/12176/1/Rohinishree%20Ph.D%20Thesis.pdf
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.