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Microbial Growth &
Microbial Growth & I
| Question | Answer |
|---|---|
| Biofilms: | communities of microorganisms that form on surfaces and are encased in a protective matrix of extracellular polymeric substances (EPS). This provides significant protection to the microbes within, allowing them to thrive in various environments. |
| Quorum Sensing: | allows microbes to detect what other organisms are in the environment. Helps them start group-behavior and secrete viral factors. A form of cell-to-cell communication that allows bacteria to monitor and respond to the popular density. |
| Quorum Sensing Example: | bobtail squid squid goes hunting at night, illuminated so there’s no shadow and they’re undetected. In morning, it purges the bacteria from light organ so quorum sensing doesn't allow organ to light, at night, the opposite happens. |
| Why Do We Incubate Bacteria At A Temperature of Around 30 Degrees Instead of Putting It In the Fridge? | It slows down the growth; it does not kill the bacteria. When it’s at a higher temperature, you do kill it, because the bacteria becomes denatured. |
| Mesophile: | organisms that grow from around 10 degrees celsius to around 45 degrees celsius (average of 39). Most pathogens are in this group. |
| Psychropile: | organisms that grow from around -5 to 10 degrees celsius (average of 4 degrees). They can be found near glaciers, and they wouldn’t cause any diseases because they wouldn’t be able to survive in our natural body temperature. |
| Psychrotroph: | grow from around 10 degrees celsius to 35 degrees celsius, grow best at room temperature. An example is listeria, which is a food pathogen, can be found in un-pasterized milks and cheeses, and can cause diseases. |
| Acidophiles: | organisms that grow best in acidic environments (low pH, usually pH < 5). |
| Neutrophiles: | organisms that grow best in neutral pH environments (around pH 6–8). |
| Alkaliphiles: | organisms that grow best in alkaline (basic) environments (high pH, usually pH > 9). |
| H. Pylori: | neutrophile, but special because it can survive in the stomach’s acidic environment (pH ~2) by producing enzyme urease. Can colonize stomach lining and cause gastritis, ulcers, and cancer. To prove this, scientist drank a concoction and became ill. |
| Osmophiles | live in environments high in sugar. |
| Xerophiles | able to grow in very dry environments. |
| Lowest Water Activity Life Can Survive At: | Life can exist down to aᵥ ≈ 0.61, below which water is too limited for cellular processes. |
| Water activity (aᵥ) → | measure of how much “free” water is available for microbes. Pure water has aᵥ = 1.0. |
| Nonhalotolerant | cannot tolerate much salt (e.g., E. coli). |
| Halotolerant | can tolerate moderate salt but don’t require it (e.g., Staphylococcus aureus). |
| Halophiles | require salt for growth, usually 3–12% NaCl (e.g., Aliivibrio fischeri). |
| Extreme halophiles | need very high salt concentrations (>15–20% NaCl), e.g., Halobacterium salinarum. |
| Which halo-organism is likely to grow on your skin? | Halotolerant organisms (e.g., Staphylococcus aureus). Skin is salty because of sweat (contains NaCl). Not extremely salty, but salty enough to inhibit many nonhalotolerant bacteria. |
| Which halo-organism is likely to grow in your gut? | The gut environment is aqueous, nutrient-rich, and not salty. Nonhalotolerant bacteria thrive here because there’s no osmotic stress from salt. Example: E. coli is a common commensal (and sometimes pathogenic) gut bacterium. |
| Trioglycollate Resazurin: | reduces oxygen, creating an oxygen gradient. Top = oxygen-rich (oxic zone). Bottom = oxygen-poor (anoxic zone). |
| Resazurin dye: | turns pink when oxidized (O₂ present) and colorless when reduced (no O₂). |
| Obligate aerobe: | only grows in the oxic layer, found in aerobic respiration |
| Obligate anaerobe: | only grows in the anoxic layer, found in fermentation/anaerobic respiration |
| Facultative aerobe (anaerobe): | grows in both but mostly oxic, all the bacteria are trying to pack into the oxic zone because it’s more energy favorable. Found in aerobic respiration or anaerobic respiration. |
| Microaerophile: | the name means “loves little oxygen,” can be found in low oxic levels and even anoxic, used in oxygen-reliant mechanisms but only needs small amounts of it. |
| Aerotolerant Anaerobe: | can tolerant oxygen but is mostly anaerobic, strictly fermentative mechanisms |
| Label an organism that lives in the soil around campus → | neutrophile, mesophile |
| Mycobacterium tuberculosis is a common pathogen that affects the macrophages in the alveoli of patients. It only grows in the presence of oxygen, never in the absence of oxygen → | obligate aerobe, mesophile, neutrophile |
| An organism that lives in Mono Lake (located in Ca, has a pH of 3 and contains 1% NaCl) → | acidophile, halotolerant |
| In terms of oxygen requirements, what type of organism would most likely be responsible for a foodborne illness associated with canned foods → | obligate anaerobic, mesophile |
| Why are jellies never contaminated? | You put a lot of sugar in there, lowering the water level, so that prevents bacterial spoilage. |
| Why Is Oxygen Toxic? | Oxygen is NOT toxic. Exposure to oxygen just yields toxic byproducts, such as superoxide anion (O2), hydrogen peroxide (H2O2), and hydroxyl radical (OH). |
| Superoxide anion (O₂⁻): | Produced when O₂ gains one electron, Strong oxidant; damages macromolecules. Detoxified by superoxide dismutase (SOD) → converts O₂⁻ to H₂O₂. |
| Hydrogen peroxide (H₂O₂): | Detoxified by Catalase → breaks down H₂O₂ → H₂O + O₂ (bubble test for catalase-positive bacteria). |
| Hydroxyl radical (•OH): | Extremely reactive, causes lethal DNA/protein/lipid damage. No enzyme fully detoxifies it → cells must prevent its formation in the first place. |
| Sterile Vs. Aseptic Techniques: | Sterile means completely free of all microorganisms, while aseptic refers to techniques that prevent contamination |
| Pasteurization Vs. Autoclaving: | Pasteurization uses moderate heat to reduce pathogens (doesn't kill all microbes), while autoclaving uses high-pressure steam to achieve sterility |
| Heat, UV Light vs. Gamma radiation, and Filtration: | Different physical methods to kill or remove microorganisms. Additional tips include → moist heat is the best, some bacteria can repair themselves when hit with UV light, a funnel would have to be smaller or equal to 0.4 micrometers. |
| Sterilization | Completely free of all living microorganisms, including bacteria, viruses, fungi, and spores. |
| Aseptic | Techniques and conditions that prevent contamination by microorganisms; maintaining a sterile environment during procedures. |
| Pasteurization | Heat treatment that reduces the number of pathogenic microorganisms to safe levels without achieving complete sterility (typically 63°C for 30 minutes or 72°C for 15 seconds). |
| Autoclaving | Sterilization method using pressurized steam at high temperature (typically 121°C at 15 psi for 15-20 minutes) to kill all microorganisms including spores. |
| Autoclave Function Test | uses Bacillus spores. Failure of spores to be killed indicates a malfunction. |
| Home Equipment | pressure cookers can achieve sterilizing temperatures due to pressure. Ovens use dry heat, which requires longer exposure times. |
| Boiling Water | does NOT sterilize (does not kill spores). Kills pathogens in water. |
| Binary Fission | The primary method of bacterial reproduction where one parent cell divides into two identical daughter cells. |
| Generation Time | The time required for a bacterial population to double in number. |
| Growth | Increase in the number of cells in a bacterial population (not individual cell size). |
| Cell Elongation | The initial stage of binary fission where the bacterial cell increases in length before division. |
| Septum | The partition that forms between dividing bacterial cells during binary fission. |
| Septum Formation | The process of creating a dividing wall between two new daughter cells. |
| Batch Culture | A closed-system microbial culture with a fixed volume of nutrients where no additional nutrients are added during growth. |
| Lag Phase | Initial phase where bacteria adapt to new environmental conditions with little to no cell division. |
| Exponential Phase (Log Phase): | Phase of maximum growth rate where bacteria divide at regular intervals under optimal conditions. |
| Stationary Phase | Phase where the growth rate equals the death rate due to nutrient depletion or waste accumulation. |
| Death Phase (Decline Phase): | Final phase where the death rate exceeds the growth rate, leading to population decline. |
| Planktonic Growth | Growth of free-floating, individual microbial cells suspended in liquid medium. |
| Sessile Growth | Growth of microorganisms attached to surfaces rather than free-floating. |
| Microbial Mats | Thick, multilayered biofilm communities with different types of microorganisms organized in distinct layers based on environmental gradients. |
| Attachment | Initial stage of biofilm formation where planktonic cells adhere to a surface. |
| Colonization | Early biofilm development stage where attached cells begin to multiply and form microcolonies. |
| Development | Maturation stage where biofilm develops complex architecture with channels and layers. |
| Dispersal | Final stage where cells are released from mature biofilm to colonize new surfaces. |
| Effect of Antimicrobial Agents on Growth | antibacterial agents can be classified as bacteriostatic, bacteriocidal, and bacteriolytic by observing their effects on cultures. |
| Bacteriostatic Agents | inhibit important biochemical processes and bind weakly |
| Bactericidal Agents: | bind tightly and kill the cell without lysis. |
| Bacteriolytic Agents | kill by lysis (for example, detergent). |
| Sterilants are → | bactericidal, bacteriolytic |
| Disinfectants are → | the best type is 10% bleach, bactericidal, bacteriolytic, used non-living surfaces because it would damage your cell membrane |
| Sanitzers are → | bacteriostatic |
| Antiseptics (gemicides) are → | bacteriostatic, can be used on living tissue, commonly used is 70% ethanol. |
| Why Didn’t We Use 70% Ethanol as Antiseptic? | Less effective as a disinfectant. Pure ethanol rapidly dehydrates cells → causes proteins to coagulate on the outside of the cell, forming a protective shell that prevents ethanol from penetrating deeper. |
| Antibacterial Drugs: | a naturally produced antimicrobial substance that can kill (bactericidal) or inhibit the growth (bacteriostatic) of other microorganisms. |
| Why Do Some Fungi & Bacteria Secrete Antibiotics? | As a defense mechanism and to fend off competitors for resources. |
| Penicillins: | Inhibits bacterial cell wall synthesis. Specifically binds penicillin-binding proteins (PBPs), preventing cross-linking of peptidoglycan, weakens cell wall, bactericidal, often causing lysis. |
| Cephalosporins: | β-lactam ring fused to a six-membered dihydrothiazine ring (different from penicillin’s five-membered ring). Also inhibits cell wall synthesis by binding PBPs → bactericidal. Generally more resistant to β-lactamases than penicillins. |
| Why Do Some People Think They’re Allergic to Penicillin When They’re Not? | People think they’re allergic because they see a rash on their skin, but this is usually caused by either the original infection or the penicillin's reaction with the original infection. |
| Streptomyces Griseus | discovered at Rutgers, is the state microbe |
| Natural Penicillin G: | The basic structure with a β-lactam ring fused to a thiazolidine ring, creating the characteristic penicillin core. Natural penicillin is effective against gram-positive bacteria but is sensitive to β-lactamase enzymes and acid. |
| Methicillin and Oxacillin: | Resistant to β-lactamase enzymes, making them effective against bacteria that produce these resistance enzymes |
| Ampicillin | Has a broader spectrum of activity, particularly against gram-negative bacteria, but remains sensitive to β-lactamase |
| Carbenicillin | Also broad-spectrum but is acid-unstable and must be given parenterally |
| Blessing in Disguise | the over-use of antibiotics have resulted in microbes gaining a high tolerance to them, making it difficult to overcome newer infections. |
| Why Are Cell Membranes a Good Target For Drugs? | Because humans do not have cell walls, and antibiotics like penicillin usually target peptidoglycan. Some antibiotics work by disrupting bacterial cell membranes rather than targeting specific enzymes or cellular processes. |
| Polymyxin: | Binds to negatively charged membrane components and disrupts membrane integrity. Pink eye. |
| Daptomycin | Used specifically for gram-positive bacterial infections and works by forming pores in the cytoplasmic membrane, leading to cell death. |
| Why Is Protein Synthesis a Good Target For Drugs? | A form of selective toxicity that can disrupt the bacterial metabolism, but won’t affect yours because bacterial ribosomes are different in comparison to the human ones. |
| Examples of Drugs that Target Protein Synthesis | tetracyclines, azithromycin |
| Aminoglycosides | neomycin, tobramycin (eye) |
| Tetracyclines | tetracycline (acne), doxycycline (surgery) |
| Macrolide | erythromycin (respiratory/skin infections), azithromycin (respiratory infections/STIs). |
| How do Drugs Use Nucleic Acids as a Target? | Quinolones are antibacterial compounds that interfere with DNA gyrase, preventing the supercoiling and packaging of DNA in the bacterial cell. For example, ciprofloxacin (used to treat pneumonia) and rifampin (used to treat TB). |
| Growth Factor Analogs | strictly similar to growth factors but do not function in the cell. |
| Optical Density (OD): | using spectrophometer (measures turbidity) |
| Answer The Case Study Questions: | -- |
Created by:
smurtab