Lab Exam

Quiz #1 Study Guide:

  1. Laboratory Safety:

    • Follow established safety protocols, wear appropriate protective gear, handle chemicals carefully, and know emergency procedures.

  2. Aseptic Technique:

    • Maintain sterility by sterilizing equipment, working in a clean environment, and avoiding contamination.

    • Do's: Use flame sterilization, work near a Bunsen burner, use sterile techniques.

    • Don'ts: Touch non-sterile surfaces, contaminate sterile materials, leave containers open for long periods.

  3. Streak Plate Technique:

    • Method used to isolate individual colonies on an agar plate.

    • Use an inoculating loop to streak bacteria onto the surface of the agar in a pattern that dilutes the sample.

  4. Microscope Basics:

    • Identify parts such as eyepiece, objective lenses, stage, condenser, and light source.

    • Understand their functions: Eyepiece for viewing, objective lenses for magnification, stage for holding slides, condenser for focusing light, and light source for illumination.

  5. Procedures for Preparing Slides for Staining:

    • Fix bacteria onto a slide, stain with appropriate dyes (such as crystal violet, safranin, or carbol fuchsin), and rinse with water.

  6. Differences between Gram-positive and Gram-negative Bacteria:

    • Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls, retaining crystal violet stain.

    • Gram-negative bacteria have a thinner layer of peptidoglycan and an outer membrane, allowing them to be decolorized by alcohol and stained with safranin.

  7. Appearance of Bacteria after Various Staining Procedures:

    • Gram stain: Gram-positive bacteria appear purple, Gram-negative bacteria appear pink.

    • Capsule stain: Capsules appear as clear halos around stained cells.

    • Endospore stain: Endospores appear green, vegetative cells appear pink.

    • Acid-fast stain: Acid-fast bacteria retain carbol fuchsin stain despite decolorization.

Quiz #2 Study Guide:

  1. Environmental Conditions Affecting Growth:

    • pH: Bacteria have optimal pH ranges for growth, and extremes can inhibit growth.

    • Temperature: Optimal growth temperature varies among bacteria (psychrophiles, mesophiles, thermophiles).

    • Osmolarity and Osmosis: Bacteria adapt to different osmotic environments (hypotonic, isotonic, hypertonic).

    • UV Radiation: UV light can damage DNA, acting as a mutagen.

    • Atmospheric Conditions: Oxygen requirements (aerobic, anaerobic, facultative anaerobic) affect bacterial growth.

    • Bacterial Population Counts: Spread and pour plate methods are used to estimate bacterial populations in a sample.

    • Dilution Problems: Dilution series are used to create known concentrations for counting colonies.

Quiz #3 Study Guide:

  1. Selective and Differential Media:

    • Selective: Allow the growth of specific organisms while inhibiting others.

    • Differential: Allow differentiation of organisms based on specific biochemical reactions.

    • Color Changes: Result from metabolic activities of bacteria growing on the media.

    • Examples: Mannitol salt agar selects for halophiles, blood agar differentiates hemolytic patterns, MacConkey agar selects for Gram-negative bacteria and differentiates lactose fermentation.

  2. Staphylococci:

    • Normal Flora: Found on skin and mucous membranes.

    • Characteristics: Gram-positive cocci in clusters, may exhibit methicillin resistance, produce enterotoxins.

  3. Streptococci:

    • Normal Flora: Found in the throat, mouth, and intestines.

    • Characteristics: Gram-positive cocci in chains or pairs, may cause strep throat or other infections, some individuals are carriers.

  4. Dental Caries:

    • Causative Organisms: Streptococcus mutans and other acid-producing bacteria.

    • Attachment to Teeth: Bacteria adhere to the tooth surface via biofilm formation.

    • Test: Snyder test measures acid production in a medium containing glucose.

    • Color Changes: Medium turns yellow due to acid production.

Quiz #4 Study Guide:

  1. Coliform Testing:

    • Importance: Indicates fecal contamination in water, which may harbor harmful pathogens.

    • Method: Use selective media such as MacConkey agar, which selects for coliforms.

  2. Testing Foods for Bacterial Content:

    • Procedure: Use sterile techniques to sample food, plate onto appropriate media, and incubate to assess bacterial growth.

  3. Gram-Negative (Unknown) Tests:

    • Motility: Determine if bacteria are capable of movement.

    • Carbohydrate Fermentation: Assess the ability to ferment specific sugars.

    • Methyl Red, Voges-Proskauer, Indole, Urea, Kligler’s Iron agar, Citrate, Phenylalanine Deaminase, Decarboxylase, Red Pigment Test: Various biochemical tests to identify metabolic capabilities of bacteria.

Quiz #5 Study Guide:

  1. Antiseptics and Disinfectants:

    • Antiseptics: Chemicals used on living tissues to kill or inhibit the growth of microorganisms.

    • Disinfectants: Chemicals used on inanimate objects to kill or inhibit the growth of microorganisms.

  2. Bacteriostatic vs. Bactericidal:

    • Bacteriostatic: Inhibit bacterial growth without killing bacteria.

    • Bactericidal: Kill bacteria outright.

  3. Bacteriophage:

    • Viral Life Cycle: Attachment, penetration, replication, assembly, and release.

    • Parts of the Virus: Capsid, nucleic acid (DNA or RNA), and sometimes an envelope.

    • Plaques: Clear zones on a bacterial lawn where phages have lysed cells. They represent areas of viral replication and cell death.

Study Guide for Labs 13-14:

  1. Antibiotics:

    • Terms: Antibiotics (chemical substances that inhibit the growth of bacteria or kill them), synergism (enhanced effectiveness of two antibiotics used together), additive (effect of two antibiotics together equals the sum of their individual effects).

    • Kirby-Bauer Procedure: A method for determining the sensitivity of bacteria to antibiotics by measuring the diameter of the inhibition zone on an agar plate. Interpretation is done using a zone interpretive table.

    • Synergism Procedure: Testing the combined effect of two antibiotics to see if they enhance each other's effectiveness.

    • Interpretation of Synergism Test: Synergy is indicated if the combined effect of two antibiotics is greater than the sum of their individual effects.

  2. Penicillin Sensitivity/MIC:

    • Terms: MIC (Minimum Inhibitory Concentration, the lowest concentration of an antibiotic that inhibits the visible growth of bacteria), β-lactam ring (a characteristic structure of penicillin antibiotics).

    • Procedure: MIC testing involves exposing bacteria to serial dilutions of an antibiotic and determining the lowest concentration that inhibits growth.

    • Interpretation of MIC: The lower the MIC value, the more sensitive the organism is to the antibiotic. A resistant organism will have a higher MIC value.

    • Appearance for a Resistant Organism: A resistant organism will have a higher MIC value, indicating that it requires a higher concentration of the antibiotic to inhibit its growth.

  3. Slide Agglutination:

    • Correlation with Other Tests: Slide agglutination correlates with serological tests such as coagulase test.

    • Reactive Components in S. aureus: S. aureus has surface antigens and antibodies that react with the latex particles in the test.

    • Lock and Key Principle: In agglutination tests, the antigen on the bacterial surface must combine with the corresponding antibody on the latex particle.

    • Appearance of Results: Positive result: clumping or agglutination of latex particles on the slide; negative result: no clumping, latex particles remain dispersed.

  4. Synthetic Epidemic:

    • Terms: Infectious disease (caused by pathogenic microorganisms), communicable (capable of being transmitted from one individual to another), epidemiology (study of the distribution and determinants of health-related states or events in specified populations), epidemic (occurrence of more cases of a disease than expected), pandemic (an epidemic occurring worldwide).

    • Methods of Pathogen Spread: Direct contact, airborne transmission, fecal-oral transmission, vector-borne transmission.