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Food Microbiology 1. Unit 1 Taxonomy. Historical Perspective. Food Microbiology is extremely important to the safety of our modern food supply. Food produced in mass quantities stored for extended periods distributed nationally & internationally.
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Food Microbiology 1 Unit 1 Taxonomy
Historical Perspective Food Microbiology is extremely important to the safety of our modern food supply Food produced in mass quantities stored for extended periods distributed nationally & internationally Failure of one part of the system effects large quantities of food and thousands of people
Apply basic principles of food microbiology to: • Food production (on the farm) • Food processing • Distribution and retail operations • Food services and home preparations “From stable to table” “From farm to fork” “From gate to plate”
Louis Pasteur • Founder of the Science of Microbiology • Disproved the theory of spontaneous generation of microorganism within food • Prevented spoilage by a process termed “ pasteurization”
I- Classification of Microorganisms • Taxonomy of Microorganisms Not visible without the aid of microscope “micro” Microorganisms Eukaryotic Prokaryotic Viruses Bacteria Molds Yeast Gram - Gram +
Bacteria Grow or multiply in foods Yeasts Molds Parasites Survive but not grow in foods Viruses
Practical Classification of Microorganisms 1- The Good (fermentations) 2- The Bad (Spoilage) 3- Very Bad (pathogens) Food borne Illness
The Good Used in: 1- Food Production Eg. Lactic Acid Bacteria (LAB) Yoghurt, Cheeses Yeasts Bread, Beer, Single Cell Protein (SCP) Mold Cheese (Blue Cheese) 2- Antibiotics 3- Bioremediation
The Bad • Food Spoilage • Eg. Blowing of cans and packaging • Off odors and flavors • Pigmentation • Slime Formation Occurs from the growth of microorganisms and production of undesirable end products Spoiled Not necessary unsafe BUT unpalatable
The Very Bad • Disease Causing (Pathogens) • Food-borne disease: any illness caused by the consumption of foods contaminated with microorganisms, chemicals or metals • Food-borne pathogens: microorganisms that cause illness in humans & were transmitted by consumption of a food • Bacteria (Salmonella, Listeria, Clostridium) • Mold (Aspergillus) • Parasites (Trichinella spiralis, Taxoplasma gondii) • Virus (Rotavirus)
Bacteria • Single-celled organisms • Nuclear region containing DNA is found in the cytoplasm • Cytoplasm is surrounded by a cell membrane usually surrounded by a cell wall • Multiply by a process called Binary fission (two cells arise from one)
Nomenclature of Bacteria • Escherichia coli ATCC 13704 • GENUS SPECIES ID number • Names usually derived from latin or Greek (Eg. coli belonging to colon) • Escherichia named after Escherich who discovered the bacterium in 1895 • Abbreviated to E. coli/E. coli (underlined or italic) • Species name NOT Capitalized
Exceptions • Salmonella • Composed of closely related serovars • Genus Salmonella has only one species (Salmonella enterica) • Therefore, they all are identified by serotypic names • Eg. Salmonella enterica serotype Typhimurium (Salmonella Typhimurium)
How Bacteria are named? • Phenotypic Characteristic: Features and activities of the bacterium which can be determined by observation • Place first detected • Source of original isolation • Person who discovered
Methods of Classification 1- Morphology (microscopic analysis)
2- Differential Stain (Gram stain, capsule stain, etc.) Gram-positive Gram-negative
3- Biochemistry (Catabolic and Anabolic Pathways) • Specific enzymes: Catalase, Oxidase • Metabolic Products: e.g fermentation (lactic acid, acetic acid…) • Sugar Utilization (lactose, mannose, rammnose) API identification kits • Growth characteristics (temperature, anaerobe)
4- Serology (Specific antibodies) (Slide agglutination) • Antigenic structure (Flagella, surface) • test the whole cells or cell extracts for the possession of specific surface antigens by reaction with specific antibodies • Receptors • -- Phage receptors • test bacteria for possession of specific surface receptors by testing for sensitivity to a range of test phages (Phage typing (specific binding and lysis of bacteria) • --Bacteriocin receptors • Toxins
5- Amino Acid Sequencing (SDS-PAGE) 6- Fatty acids 7- Flow cytometry (Differences in electrical conductivity) 8- DNA, Restriction enzyme maps
Development of advanced techniques has led to the re-evaluation of bacterial taxonomy But Bergey’s Manual of Systematic Bacteriology is still regarded as the foundation for classifying bacteria.
Key Questions In Microbiology that will be addressed in the course • What microorganisms are in food? • Do they represent a problem? • How can they be detected and enumerated? • What are the routes by which they enter the food chain? • How can they be controlled and eliminated?
Class Exercise Try to identify if the given microbes are involved in food spoilage, food borne illness and/or food fermentations
1- Salmonella Enteritidis 2- Lactococcus lactis 3- Lactobacillus brevis 4- Saccaromyces cerevicea 5- Listeria monocytogenes