Micro Bio – Microbiology Flashcards with Answers
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Introduction Microbial Growth Requirements
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oGrowth measured by number of cells not size oNutrients àrapid growth §Escherichia coli doubles in 30 min §Single cell àone billion in 15t hours §50 hours to cover Pittsburgh (the city of champions) in 1 foot layer of sludge oUnchecked growth §Disease §Food spoilage §Destruction of materials oControlled by identifying and controlling factors allowing growth
Requirements- Physical and chemical
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Physical Factors |
o Temperature o pH o Osmotic Pressure o Hydrostatic Pressure |
Temperature |
o Minimum, optimum, and maxiumum o 4 major groups § Pyschrophiles -- -4 – 20 C, 8 – 12 optimal § Mesophiles – 14 – 46 C, 34 – 39 optimal (most are mesophiles) § Thermophiles – 43- 80 C, 65 – 70 optimal § Hyperthermophiles – 67 – 106 C, 92 – 98 optimal o Microbes spoiling refrigerator food § 0-30 C, 15 – 25 optimal § Suggested they called pychotrophs because between psychrophiles and meophiles o Maximum temperature determined by enzyme stability to heat o Minimum temperature determined by § Stability of enzymes to cold § Efficiency of enzymes in cold o Food prep § Common food contaminants § Often present before cooking and could be introduced while or after cooking § Most bacteria killed at 62 C – cooking used to preserve § Few grow in refrigerate (0 – 4 C) § Rapid growth between 16 – 50 C · Moist food stored at several hours can spoil and harm eater § Example · Rice contaminated with Bacillus cereus endospores that cause diarrhea · Cooking rice does not kill endospores · Cooked in large pot à put in refrigerator à stays above 15 C for a while (5 hours) |
pH |
o Internal and external pH important o Tertiary structure and functional activity of biomolecules pH dependent § Require near neutral pH § Internal pH needs to be close to 7 o External pH can be key limiting growth factor for most bacteria § Optimal 7 – 7.4 § Can do 6-7.8 § Stop growing at 5 § Fungi can grow 4-5 o Affects regulation of internal pH § Acid fermentation can eventually inhibit or kill bacteria § Export acid byproducts extracellular § 2 pH different makes regulation difficult (100x) § pH below 6 starts affecting inside cell § Can help preserve (cheese, sauerkraut, pickles) o Acidogenic § Microbe ferments sugars into acid o Acidophilic § Tolerates low pH § AKA aciduric § Not common § Virulence property for dental plaque o Alkalinophiles § Tolerate pH up to 11.5 o Clinical Application – dental carries § Etiologic agents · Mutans streptococci · Lactobacilli § Mutans strepotococci · Primary initiators of dental caries · 7 species · Streptococcus mutans and Streptococcus sobrinus most important varieties to humans · Mutans streptococci more aciduric than other strep o Survive low as 4.2 whereas others 5.2 § Lactobacilli expand caries, do not begin · Survive as low as 3.7 |
Water |
o Crucial for cell growth § Solvent for nutrient and enzyme dissolution § Participant in reactions § Help folding of biomolecules o Cells die in absence of water except § Mycobacteria have high lipid content to retain water § Clostridia and Bacillus form endospores that cease most metabolic activity and can survive for years § Parasitic protozoans form cists with thick coat that can cease most metabolic activity |
| Osmotic pressure |
o Pressure required to halt osmosis through membrane § Proportional to solute concentration difference o Hypertonic media § Cells can take up ions § Too high – lose water and shrivel à plasmolysis ceases growth o Isotonic § 0.86% NaCl or equiv o Hypotonic § Animal cells pump out ions § Protoza discharge water in vacuoles § Can cause hypotonic lysis § Antibiotics inhibiting cell wall synthesis result in hypotonic lysis o Halophiles – adjusted to high salt environments § Obligate halophiles – only in high salt (up to 20%) and lyse in low salt § Facultative halophiles – can tolerate but do not require · Grow on surgace of skin o Staphylococci o Micrococi o Proprionibacterium o Corynebacterium
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Hydrostatic pressure
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o Water pressure according to depth § 10 meters of depth, 1 more atmosphere in water § Deep sea organisms – barophiles · Die rapidly in low pressure |
Chemical requirements
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o Some simple like carbon and inorganic ions, others extensive o Commonly essential elements compounds with carbon, oxygen, nitrogen, hydrogen o Categories § Carbon and energy source § Oxygen § Nitrogen § Hydrogen atom § Inorganic ions § Organic growth factors |
Carbon and Energy source
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o All organisms require energy and carbon § Carbon makes up all organic components which are 50% of dry weight of cell § Sometimes carbon source is also energy source o Carbon types § Autotrophs -- Use inorganic carbon like CO2 § Heterotrophs – Use organic carbon as carbon source o Energy type § Phototroph – use light as energy source § Chemotrophs – use chemicals as energy source (organic or inorganic) |
Oxygen Requirements
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o Component of compounds o 20% of dry weight o Most obtain oxygen used in components from CO2 or carbon source o Some require molecular oxygen as final electron acceptor or cofactor o Oxygen deadly poison for obligate anaerobes § O2 itself not dangerous but reactive oxygen species § Toxic oxygen metabolites kill cells without inactivating mechanisms o 4 reactive metabolic derivatives from O2 § H2O2 § Superoxide anion (O2-) § Hydroxyl free radical (OH*) § Singlet oxygen (1O2) § All four are strong oxidizing agents · Steal electrons and cause chain of oxidizing oxidations damaging lipids, nucleic acids, and proteins · Damage to membrane, DNA and enzymes can cause cell aging and death |
H2O2 |
1 of 4 reactive metabolic derivatives from O2 · Flavoproteins and oxidases lose 2 electrons to O2
· H2O2 dissociates to peroxide anion (O22-) and 2 protons
· Hydrogen peroxide inactivated by catalase and peroxidases
· Normal product of superoxide dismutase
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Superoxide anion (O2-)
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1 of 4 reactive metabolic derivatives from O2 · Formed by incomplete reduction of O2 by ETC and by flavoproteins and oxidases transferring 1 electron to O2 · Inactivated by superoxide dismutase
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Hydroxyl free radical (OH*)
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1 of 4 reactive metabolic derivatives from O2
· Hydroxide loses electron to superoxide anion or to peroxide
· Most reactive of oxygen derivatives
· Also formed by ionizing radiation
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Singlet oxygen (1O2) |
1 of 4 reactive metabolic derivatives from O2 · Oxygen with electron in higher energy state · Unstable, can lose electron · Electron can damage nearby macromolecules · Formed by o Oxygen absorbing energy from sunlight (carotenoids in photosynthetic organisms dissipate this)
o Formed in phagolysosomes to kill ingested microbes |
Cells using O2 have evolved protective enzymes to deactivate these 4 reactive metabolic derivatives from O2
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§ Catalase · H2O2 à 2 H2O + O2 § Superoxide dismutase · O2- + O2- + 2 H+ à H2O2 + O2 § Peroxidases · Transfers electrons from O2- and H2O2 to organic acceptor molecules like glutathione · Large family of enzymes |
| Bacteria requiring O2 produce...... |
o catalase and/or superoxide dismutase but not peroxidases (only eukaryotes) § Eukaryotes produce all three |
Clinical correlation of Oxygen requirements
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§ Fruit flies and nematodes with elevated levels of superoxide dismutase live 1.5 to 3 times longer § Used genetic engineering § Calorie restricted diets (70% of normal) live 1.5 times longer · Reduced Calorie Society testing on humans · Think less calories produce less oxygen metabolites § Antioxidants like Vitamin C and E are also thought to protect |
Oxygen classification of Microorganisms
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o5 Groups §Obligate aerobes §Facultative anaerobes §Microaerophilic §Aerotolerant anaerobes §Obligate anaerobes |
Obligate aerobes |
§ Grow only in presence of oxygen
§ Produce catalase and superoxide dismutase
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Facultative anaerobes |
§ Grow with or without oxygen § Ferment when needed § Catalase and superoxide dismutase |
Microaerophilic organisms |
§ Grow only in lowered oxygen content (2-10% rather than 21% in air) § Need small amount of oxygen for metabolism § Lack ETC § Low levels of superoxide dismutase and catalase |
Aerotolerant anaerobes |
§ Grow in presence or absence of oxygen but have no ETC
§ Low levels of superoxide dismutase and catalase
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o Obligate anaerobes |
§ Can’t grow in oxygen § No catalase or superoxide dismutase § Some rapidly killed by oxygen, others can tolerate brief exposures |
Different growth patterns in agar deeps
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§ Obligate aerobes – grow on top only § Obligate anaerobes – grow on bottom § Facultative anaerobes – grow throughout, but more at top § Aerotolerant anaerobes – grow throughout evenly § Microaerophilic – grow a little down from surface but nowhere else |
Clinical correlation for classification of microorganisms |
§ Obligate anaerobes are predominant steady state flora on mucous membranes except those in contact with air § Can’t penetrate due to oxygen from capillaries underneath § Facultative anaerobes can penetrate and cause infection |
Nitrogen |
o 14% of cells dry weight o Required for § Proteins § Nucleic acids § Other components o Comes from organic and inorganic § Can also recycle § Many microbial species use NH4+ (ammonium ions), nitrate ions (NO2-) or nitrate ions NO3-) as nitrogen source § Some use organic source like amino acids § Few can use nitrogen gas (N2) and convert it to NH3 · Nitrogen fixation · Crucial process of converting nitrogen into useable substance for other organisms |
Hydrogen Atom source
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o Constitutes 8% of dry weight o Present in water and all organic compounds o Most get it from water and carbon source |
Organic Growth factors
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o Anything organic microbe is unable to synthesize o Synthesis abilities differ from species o If compound needed, microbe can only grow if present in medium |
Inorganic ions |
· Phosphate o Required for carbohydrate metabolism, DNA, RNA, phospholipids, hi energy storage compounds, structural components o 3% of dry weight · Sulfur o Required to make some amino acids and vitamins o 1% of dry weight · Mg++, Ca++, K+, Cl-, Na+ o Cofactors, stabilize negative charged macromolecules o 3% of dry weight · Mn, Co, Zn, B, Se, Mo, Cu o Trace minerals needed as cofactors · Silicon o Cell walls of algae · Iron o Essential for all organisms o Cytochromes, catalase, other proteins o 0.25% dry weight o Iron assimilation by Microbes § Common ferric form insoluble § Iron and ferrous ions oxidize by oxygen to ferric hydroxide (rust) which is very soluble § Aerobic bacteria and fungi secrete siderophores that solubilize ferric ions by chelation § Transported into cells and iron released § Siderophores virulence factors because they strip host of ions § Clinical correlation · Iron in animals bound tightly to proteins o Ferritin in liver o Transferrin in serum o Lactoferrin in milk · Bacteria battles for this iron · During infections, liver produces elevated iron binding proteins. Malnutrition, hemolytic anemia, or anything that elevates iron concentration in serum predispose one to infection
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