Microbiology: Agar Media Characteristics

MSA (Mannitol Salt Agar)

• Selective: High salt concentration (7.5% NaCl) inhibits the growth of many bacteria except for halophiles.
• Differential: Differentiates between pathogenic and non-pathogenic Staphylococcus aureus.
• Yellow growth: Indicates mannitol fermentation.
• Pink/orange growth: Indicates non-mannitol fermenter.

EMB (Eosin Methylene Blue Agar)

• Differential: Differentiates bacteria based on lactose fermentation ability.
• Pink/lavender growth: Gram-negative bacteria that are weak lactose fermenters.
• Red growth: Gram-negative bacteria that are non-lactose fermenters (same characteristics as the medium).
• Metallic green growth: Gram-negative bacteria that are rapid lactose fermenters.
• Use: Identifying fecal coliforms.

HE (Hektoen Enteric Agar)

• Differential: Differentiates bacteria based on lactose fermentation and sulfur reduction. Uses additives such as thiosulfate and ferric ammonium citrate.
• Yellow growth: Lactose fermenters (e.g., E. coli).
• Blue/green growth: Breakdown of proteins to alkali products (e.g., Salmonella and Shigella).
• Black growth: Sulfur reduction (e.g., Salmonella).
• Differentiates: Salmonella and Shigella from other bacteria that EMB cannot differentiate.

B vs. T Lymphocytes

• B cell origin: Bone marrow.
• B cell maturation: Bone marrow.
• T cell origin: Thymus.
• T cell maturation: Thymus.
• Regulatory cells: Produced by T cells.
• B cell activation: Activation via interaction with MHC-II
• T cell activation: Activation via interaction with MHC
• Apoptosis: Not all self-reactive B and T cells undergo apoptosis.

Tuberculosis (TB)

• Bacteria: Mycobacterium tuberculosis.
• Primary TB: Contained within the lung.
• Secondary TB: Tubercle breaks open.
• Tertiary/Disseminated TB: Mycobacterium spreads from lungs to other parts of the body.
• Antibiotics: Isoniazid and Rifampin (and possible others) are used.

Effector B Cell

• Name: Plasma cell.
• Job: Release antibodies.

Glycocalyx

• Examples: Endothelial cells and digestive system cells.
• Role in bacterial survival: Creates a mechanical barrier that protects against antibiotics and helps evade host defense systems.
• Biofilm role: Biofilms can protect bacteria from immune system actions and antimicrobials.

Cell Wall Makeup

• Gram-positive: Thick layer of peptidoglycan.
• Gram-negative: Thin cell walls.
• Acid-fast: Used in identifying Mycobacterium.

Gram Stain

• Gram-positive result: Purple.
• Gram-negative result: Pink/red.
• Primary stain: Crystal violet.
• Decolorizer: Ethyl alcohol.
• Counterstain: Safranin.
• False positive: Gram-negative incorrectly staining purple (too little alcohol).
• False negative: Gram-positive incorrectly staining pink/red (too much alcohol).
• Counterstain purpose: Differentiates Gram-positive from Gram-negative.
• Gram-positive after decolorization: Purple.
• Gram-negative after decolorization: Clear (alcohol removes crystal violet).

Endotoxin vs. Exotoxin

• Gram-positive Endotoxins: Lipoteichoic acid (LTA) released during cell lysis.
• Gram-negative Endotoxins: Lipopolysaccharide (LPS) released upon bacterial death.
• Exotoxins: (3 main types): diverse types of proteins.

Lyme Disease

• Disease Causative Agent: Borrelia burgdorferi.
• Classification: Spirochetes.

Cell Wall Differences (Mycobacterium vs. Mycoplasma)

• Mycobacterium: Thick, protective, waxy cell wall.
• Mycoplasma: Lacks a cell wall.

Hemolysis

• Alpha hemolysis: Greenish/brownish zone around bacterial colony (partial RBC destruction).
• Beta hemolysis: Clear zone around bacterial colony (complete RBC destruction).
• Gamma hemolysis: No visible zone change (no RBC disturbance).

Sporulation

• Genera: Bacillus (aerobic/facultative anaerobic), Clostridium (anaerobic)
• Process: Formation of spores.
• Conditions for sporulation: Unfavorable growth conditions.
• Oxygen concentration: Bacillus sporulates in high oxygen environments to increase survival.
• Germination: Spore returns to vegetative form.

Anti-Retroviral Medications

• Viral targets: HIV, possibly others (e.g., COVID-19, herpes, hepatitis).

Breath Test

• Diagnosis: Helicobacter pylori.
• Complications: Causes pain, inflammation, and ulcers in the upper digestive tract.

Antigens

• H antigen: Flagellar antigen (variable).
• K antigen: Capsular antigen (protection from immune response).

T-helper vs. Cytotoxic T cells (Th vs Tc)

• CD: Tc (CD8), Th (CD4).
• MHC binding: Tc - MHC I; Th - MHC II.
• Effector cell jobs: Tc - kills target cells; Th - activates other immune cells.
• Memory cell jobs: Both remember the specific pathogen.
• MHC I cells: All nucleated cells.
• MHC II cells: Antigen-presenting cells (APCs).
• Treg (regulatory T cells): Regulate immune responses.
• Apoptosis in self-reactive T cells: True for many self-reactive T cells.
• Apoptosis in self-reactive B cells: True for many self-reactive B cells.

Tc Effector Cells & Innate Cells

• Innate Cell Comparison: Similar to natural killer (NK) cells.
• Substances: Perforin and granzymes.

Oxygen Tolerance

• Media: Thioglycolate broth.
• Oxygen tolerance interpretation: Growth location in the medium indicates bacteria's oxygen needs (aerobic, anaerobic, facultative anaerobe).

Coliform vs. Noncoliform

• Coliform: Fecal, aerobic/facultatively anaerobic, lactose fermenters.
• Noncoliform: Lactose non-fermenters, don't originate from the gut.

Enzymes

• Hyaluronidase: Breaks down hyaluronic acid.
• Kinase: Adds phosphate groups to molecules.
• Coagulase: Converts fibrinogen to fibrin (blood clotting).
• Collagenase: Breaks down collagen.

Competitive Inhibitor of PABA

• Antibiotic: Sulfa drugs (Sulfonamides) e.g. Bactrim, Gantrisin.
• Prevents: Production of folic acid.

Syphilis

• Bacteria: Treponema pallidum.
• Stages: Incubation (3-6 weeks), onset of disease (3−6 weeks), (severe organ damage).

Margination, Diapedesis, Chemotaxis

• Causes: Tissue injury triggers inflammation and immune response.
• Margination: WBCs slow down and adhere to injured tissue.
• Diapedesis: WBCs squeeze between endothelial cells into interstitial fluid.
• Chemotaxis: WBCs towards the injury site (following chemical signals).

Pseudomembranous Colitis, Pharyngitis, and Strep Throat

• Pseudomembranous colitis (PC): Clostridium difficile, watery diarrhea, abdominal pain, fever, pseudomembrane in colon.
• Pseudomembranous pharyngitis (PP): Corynebacterium diphtheriae, sore throat, fever, pseudomembrane, swollen neck.
• Strep throat: Streptococcus pyogenes, severe sore throat, fever, swollen tonsils, white exudates.

Charcoal Enriched Media

• Bacteria: Legionella pneumophila and Bordetella pertussis.

Cold/Heat Enrichment

• Cold: Listeria monocytogenes, Yersinia enterocolitica, Campylobacter jejuni, Salmonella.
• Heat: Thermophilic Bacillus, Clostridium, Campylobacter jejuni, Clostridium perfringens, and thermotolerant Enterococcus faecalis.

Anti-Herpes Medication

• Antimicrobial: Acyclovir, Ganciclovir.
• Mechanism: Nucleic acid synthesis inhibitor.

Teeth Staining and Bone Growth

• Antibiotic: Tetracycline (avoid in children due to adverse effects).

Viral Genome

• mRNA-like genome: Double-stranded RNA (dsRNA).

Viral Envelope vs. Capsid

• Viral envelope: Lipid membrane surrounding some viruses.
• Capsid: Protein coat of all viruses.
• Naked: Lacking an envelope.
• Uncoating: Removal of viral capsid.

Epstein-Barr Virus and Cancer

• Cancer: Lymphoma and others.

Beta-Lactam Antibiotics

• Antibiotics: Penicillin, Monobactams, Isoniazid.
• Enzyme inactivation: Beta-lactamase.
• Antibiotic inhibiting the enzyme: Clavulanate, Sulbactam (in combination with beta-lactam drugs).

Hand-Foot-and-Mouth Disease

• Virus: Coxsackie virus.

"Slapped Cheek" Appearance

• Virus: Parvovirus B19.

Rubella, Rubeola, and Roseolovirus

• Rubella: Milder than rubeola, respiratory transmission, fetal malformations.
• Rubeola: Respiratory transmission, Koplik's spots, red hallow, N german measles.
• Roseolovirus: Human herpesvirus 6, fever in infants, roseola-like symptoms.

Common Cold Viruses

• Viruses: Adenovirus and Rhinovirus.

Explore the characteristics of different selective and differential media in microbiology, including Mannitol Salt Agar, Eosin Methylene Blue Agar, and Hektoen Enteric Agar. This quiz tests your understanding of how these media differentiate bacterial species based on fermentation abilities and other criteria.