Microbial Stress Response In The Food Environment PDF

1 MICROBIAL STRESS RESPONSE IN THE FOOD ENVIRONMENT MIC 322 Songsirin Ruengvisesh, PhD  2 Microbial stress response Foodborne microorganisms are usually exposed to different physica...

1 MICROBIAL STRESS RESPONSE IN THE FOOD ENVIRONMENT MIC 322 Songsirin Ruengvisesh, PhD  2 Microbial stress response Foodborne microorganisms are usually exposed to different physical and chemical environments during production and processing (stressed environment). Bacterial cells become stressed and manifest several types of altered characteristics I. Stress adaptation II. Sublethal stress and injury III. Viable-but-nonculturable (VBNC) 3  4 I: Stress adaptation  5 Stress adaptation A situation whereby a brief exposure of a bacterial population to a suboptimal physical or chemical growth environment enables the cells to resist subsequent exposure to the same or other type harsher environments Cold and warm temp Low aw Low hydrostatic pressure UV light High salt concentration Preservatives Antibiotics  6 I: Stress adaptation Examples: An exposure of cells for an extended period to mild acidic environment (pH 5.0 to 5.8) enables them to develop resistance to subsequent exposure to pH ≤ 2.5. A brief exposure of E. coli cells to 50°C enables them to survive better at 60-72°C. Heat resistance of L. monocytogenes, Salmonella spp., E. coli O157:H7 that were initially acid adapted  7 Mechanism of stress adaptation Synthesis of shocked proteins or stress proteins Stress proteins provide protection to structures that could be otherwise adversely affected by the stress  8 https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of- dna-into-rna/a/overview-of-transcription  9 Sigma factor binds to RNA pol (core) so RNA pol (core) turn in to holoenzyme. A sigma factor (σ factor) (specificity factor) = a protein needed for initiation of transcription in bacteria. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase (RNAP) to gene promoters RNA pol binds to promoter Correct promoter recognition is the function of the holoenzyme form of RNA polymerase. Promoter = specific DNA region that initiates transcription  10 Regulon σ factor enables specific (𝜎32 ) binding of RNA polymerase to a promoter. 11  12 Importance of stress-adapted microorganisms in foods Stress-adapted bacteria can become resistant to lower pH and other treatments and survive in foods. Stress-adapted bacteria can become resistant to stomach acid and other treatments and survive in the stomach and cause diseases. Enhancing viability of starter cultures and probiotic bacteria Exposing the cultures to mild stress to release stress protein may enable cells to survive subsequent stress conditions.  13 II. Sublethal stress and injury  14 Sublethal stress and injury Sublethal stress occurs following exposure of bacterial cells to unfavorable physical and chemical environments (beyond the growth range but not in the lethal range) Low heat, low aw, radiation, UV, high hydrostatic pressure, low pH, preservatives cause reversible alterations in the functional and structural organization of the cells (e.g. inability to multiply) can repair their injury and initiate multiplication in an appropriate environment (e.g. using an enrichment medium)  15 Importance of sublethally-injured microorganisms in foods Detection of undesirable microorganisms Injured microorganisms may not be detected. As a result, foods containing viable but injured pathogens, indicators or spoiler above the acceptance limit can be sold. These products can be hazardous and have short shelf life. Enhancing shelf life of foods Injured cells are susceptible to many physical and chemical environments Preservation of foods can be done more effectively by killing injured cells or spores  16 III. Viable-but-nonculturable (VBNC)  17 VBNC Under unfavorable environments, some cells in a bacterial population remain viable but are not able to multiply in many microbiological media. They can be present in food and food environment and can potentially cause foodborne diseases and spoilage. https://www.hindawi.com/journals/isrn/2013/703813/ 18  19 References Ray B., 2003. Fundamental Food Microbiology.Taylor & Francis