Microbiology
Microbial Nutrition, Environment and Growth
I. Nutrition – Taking in chemicals (nutrients) from the environment
A. After being absorbed, the nutrients are used by the cell for growth and metabolism
1. Metabolism – all chemical reactions in the cell
2. Organic nutrients – carbon based such as lipids, proteins, carbohydrates
3. Inorganic nutrients – water, salts, gases
B. Nutritional classifications
1. Heterotrophs – feed on others
a. Saprophytes (saprobes)
1) Decomposers, live on dead organic matter
b. Parasites
1) Use living host
2) Pathogens
2. Autotrophs – feed themselves
a. Photoautotrophs – use light and CO2
1) Photosynthetic bacteria
b. Chemoautotrophs – use inorganic substances
1) Hydrogen gas, hydrogen sulfide
C. Movement Across Cell Membrane
1. All nutrients must pass cell membrane in order to get into cell
2. Cell membranes are selectively permeable, cell walls are less selective
3. Passive transport
a. Diffusion – movement of particles from high to low concentration
b. Osmosis – movement of water
1) hypotonic, hypertonic, isotonic
2) See Later in Notes
4. Active transport – requires cell to use ATP
a. ATP dependent pumps – membrane proteins that transport substances such as sugars, amino acids, ions, across cell membrane
1) antibiotic drug pumps = antibiotic resistance in bacteria
5. Endocytosis
a. Cell takes in large particles or cells across membrane
b. Phagocytosis – cell eating
1) Phagocytes (macrophages, neutrophils) engulf bacteria
Steps of Phagocytosis
1. Chemotaxis and Adherence of microbe to phagocyte (macrophage)
a. Chemotaxis is chemical attraction of phagocyte to microbe
*chemicals include: Cytokines by WBC’s, damaged tissue, microbes
b. Adherence – phagocytes have TLRs (Toll-like receptors) on their membrane that bind to PAMPs (pathogen-associated molecular patterns) on microbes surface.
*Also, induces phagocyte to release cytokines (Chemotaxis)
2. Ingestion of microbe and formation of Phagosome
3. Phagosome fuses with Lysosome to form Phagolysosome
a. Lysosome contains lysozyme (digests peptidoglycan)
b. Also, Oxidative Burst produces toxic oxygen
1) Superoxide radicals (O2–•), hydrogen peroxide (H2O2), singlet oxygen (1O2-), hydroxyl radical (OH•)
4. Digestion and Discharge of microbe
Microbial Evasion of Phagocytosis (examples)
1. Streptococcus pyogenes – produce M protein on surface that inhibits adherence
2. Streptococcus pneumoniae – thick capsule allows microbe to slide away during adherence
3. Listeria monocytogenes – After ingestion they produce proteins that lyse phagolysosome, then once in the phagocytes cytoplasm they release more proteins that lyse cell membrane of phagocyte and escape.
II. Environmental Factors Influencing Microbes
A. Temperature
1. Minimum temperature – lowest temperature at which a microbe can grow
2. Maximum temperature – highest temperature at which a microbe can grow
3. Optimal temperature – temperature that promotes fastest rate of growth
NOTE:
0° Celsius is -32° F (freezing)
20-25°C is 68°-77° F (room temp)
37°C is 98.6°F (body temp)
100°C is 212°F (boiling)
°C = (°F – 32.) / 1.8
Optimal Temperature Ranges
1. Psychrophiles – love cold; can grow at 0°C and optimum at 15°C
a. Psychrotrophs – can grow slowly in cold, but optimum temp is above 20°C
1) Listeria monocytogenes – grows in refrigerators; food borne illness;
ready-to-go deli meat
2. Mesophiles – optimal growth of 20-40°C
a. Most pathogenic bacteria have optimal temp. of 37°C
b. Clinical cultures incubate at 37°C
3. Thermophiles – optimal at 50-60°C
a. Thermoduric – microbes that are usually mesophiles but can survive high temps
1) Spore formers, Clostridium and Bacillus
B. Oxygen
1. Obligate aerobes – require O2 to grow
a. Bacillus subtilis
2. Facultative anaerobes – grow better with O2, but can grow without it too (anaerobic)
a. E. coli
3. Obligate anaerobes – cannot grow in O2 (poisoned by it)
a. Clostridium
b. Do not produce superoxide dismutase (SOD) or catylase
4. Aerotolerant anaerobes – cannot use O2 to grow, but can tolerate it.
a. lactobacilli ferment sugar to lactic acid
b. Contain superoxide dismutase (SOD) – can neutralize toxic O2
5. Microaerophiles – aerobic, require O2
a. Require oxygen, but at lower levels than is air
b. At high [O2], will produce high amounts of superoxide radicals
Toxic forms of Oxygen – steal electrons from other compounds and cause damage (oxidize)
1. Singlet oxygen, 1O2–
a. Molecular oxygen (O2) boosted into higher energy state, very reactive
2. Superoxide radicals (O2–•)
a. Highly reactive and toxic, formed during normal aerobic cellular respiration
b. Aerobic, facultative anaerobes and aerotolerant bacteria produce superoxide dismutase (SOD) to convert it to hydrogen peroxide and oxygen.
O2–• + O2–• + 2 H+ —–SOD——-à H2O2 + O2
3. Hydrogen peroxide (H2O2) – contains peroxide anion (O22-) which is toxic
a. Catalase neutralizes H2O2 to water and oxygen
b. Hydrogen peroxide bubbles when you put it on a wound because our cells have
catalase; you see the oxygen bubbling off.
2 H2O2 —–Catalase———-à 2 H2O + O2
c. Peroxidase also breaks down H2O2
4. Hydroxyl radical (OH•)
C. pH
1. Bacteria and other organisms have optimal pH ranges in which they grow best at, as well as pH ranges that inhibit their growth.
2. pH scale
3. Neutrophiles – bacteria that grow best at pH = 6.5 – 7.5
a. Most bacteria
b. Blood and body fluid pH = 7.35 – 7.45
4. Acidophiles – bacteria that love acidic habitats
a. Many fungi prefer lower pH
b. Helicobacter pylori – live in stomach; ulcers
5. Alkalinophiles – bacteria that love alkaline habitats
a. Vibrio cholera – grows best in water with pH = 9
D. Osmotic Pressure (osmoregulation)
1. Osmotic pressure is related to dissolved solutes in solution, ex) electrolytes, sugar
2. Water moves to where the concentration is greater, i.e. there are more solutes
a. Hypotonic
b. Hypertonic
1) Plasmolysis – cell membrane shrinks away from cell wall
c. Isotonic
1) 0.9% NaCl is isotonic to our cells
3. Facultative Halophiles – can tolerate higher levels of salt
a. Staphylococcus aureus – grows in Mannitol Salt Agar (7.5% NaCl)
1) Normal agar is 1.5% NaCl
2) Staph skin infections – can grow on our salty, sweaty skin
4. Salts and sugars preserve foods
a. Hypertonic environment will draw water out of microbes / prevent growth
b. Osmotically preserved foods; beef jerky, salted fish, honey
E. Microbial Relationships and Biofilms
1. Antagonistic relationships – one organism harms or kills another
a. Antibiotics are released by one microbe to inhibit the growth of another
2. Synergistic relationships – all members benefit from relationship more than they could without the relationship, but each can live alone.
a. In Soil: Cellulomonas breaks down cellulose to glucose. Azotobacter uses
glucose for energy and fixes nitrogen gas (N2) into ammonia (NH3) for Cellulomonas.
3. Symbiotic relationships – at least one organisms depends on relationship to live
a. Mutualism – both members benefit
b. Commensalism – one benefits, other unharmed
c. Parasitism – one benefits, other harmed
1) Viruses use cellular host to replicate itself, then kill host cell to be
released
III. Growth of Bacterial Cultures
