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level: General

Questions and Answers List

level questions: General

QuestionAnswer
Primary sources of microorganisms- soil and water - plants and plant products - food utensils - intestinal tract of humans and animals - food handlers - animal feeds and hides - air and dust - food ingredients - equipment
Cell Wall (structure)- peptidoglycan - encloses cells of most prokaryotes (except for mycoplasma)
Cell Wall (function)- provides shape and protection from bursting - determines cell shape - protection from lysis and harmful chemicals
Gram Stain- differential stain - one of the first steps in ID of bacteria 1) crystal violet, 2) iodine, 3) alcohol, 4) safranin
Gram-negative bacteria- thin peptidoglycan layer - do NOT retain CV - iodine stain when washed with alcohol - stains pink - dual cytoplasmic membrane
Gram positive bacteria- thick peptidoglycan layer - retain CV - iodine stain, not easily removed by acetone/alcohol - stain blue
Cytoplasmic membrane (structure)- lipid bilayer - mainly phospholipids, membrane proteins - fluid structure - hydrophobic barrier - severe damage can cause cell death
Cytoplasmic membrane (function)- enzymes present: ATPase, dehydrogenase - impermeable to protons - facilitates nutrient transport - hydrophobic barrier
Ribosomes (structure)- give granular appearance to cytoplasm - made up of protein and RNA
Ribosomes (function)- synthesize cell protein - 10k per cell
Nucleoid- diffuse nucleus (no nuclear membrane) - single circular DNA molecule - major genetic material of the cell
Flagella (structure)- helical filaments - protein (flagellin) - polar flagellum to 10s, 100s - 3 parts: filament, hooks, basal body
Flagella (function)- rotate to propel the cell - help cell respond to chemical attractants and repellants (chemotaxis)
Pilli (structure)- aka fimbriae - ptrotein (pilin) - straight rods
Pili (function)- no rotation - used for cell attachment - bind to specific receptors - special pili used for conjugation
Fungiyeasts and molds
Yeasts- oval, spherical, or elongated cells - cell wall contains polysaccharides (glycan), protein, and lipids; some chitin - cell membrane - organelles in cytoplasm - well defined nucleus - nuclear membrane - far larger than molds
Molds- filamentous fungi - cell wall of chitin, cellulose, or both! - hyphae: filaments - mycelium: numerous branches of hyphae
Hyphae- filaments of molds - can be vegetative or reproductive - reproductive hyphae: form exospores - aerial hyphae: bear conidia or sporangia - subsurface hyphae: produce enzymes to digest substrate
Classifying microorganisms- species: basic taxonomic group for yeasts/molds/bacteria - genus: several species with similar characteristics - family: several genera with similar characteristics
Microbes in food: bioprocessing- use of food grade microorganisms as a starter culture - different types of fermented foods made - microbial enzymes also used
Microbes in food: biopreservation- using antimicrobial metabolites from desirable microorganisms to preserve food - control pathogens and spoilage organisms - antimicrobial metabolites: lactic acid, acetic acid, propionic acid
Probiotics- viable bacteria that seem to produce health benefits when consumed in foods - specific strains (of Lactobacillus, Bifidobacterium, Lactococcus, Enterococcus) are important
Food spoilage- growth of microbes in foods and/or action of their enzymes - lead to undesirable changes in food texture, taste, flavor, color - discoloration, softening, increased exudate, off-odors, bad taste - causes substantial economic loss
Foodborne disease- pathogenic microorganisms (bacteria, mold, viruses, parasites) - caused by under-processing, cross-contamination, and mishandling of foods - large-scale production of food & increase in foreign importation of food: increase chances of disease outbreaks and new pathogens - most caused by foods of animal origin - common causes: under processing, cross contamination, and mishandling of food
Bacterial spores- endospores: formed inside vegetative cells - exospores: vegetative cells change to cysts
Endospores- one endospore per vegetative cell - produced by some Gram-positive bacteria - highly stress-resistant, dormant structure - resistant to heat, chemical disinfectants, radiation, and desiccation
Destruction of endospores- destroyed by very harsh chemical or physical treatments - 121 deg C at 15psi for 20 minutes in an autoclave - irradiation at 30-40 kGy - Not killed by high pressure practically attainable by current technology ex 600-8800 MPa
Vegetative cells vs. bacterial endospores.
Sporulation- formation of spores in vegetative cells - endospores appear as clear areas in vegetative cells
Germination- formation of vegetative cells from spores - only one veg. cell produced from one spore
Gram positive spore formers- Bacillus spp - Clostridium spp - Alicyclobacillus spp - Sporosarcinia spp (cocci)