MICRO BIO EXAM NOTES STUDY GUIDE

1. Antibiotics and Their Use

• Penicillin:

  • Bacterial cidal: Kills bacteria.

  • Penicillinase-resistant: Only works for staph, not MRSA (Methicillin-resistant Staphylococcus aureus).

  • First-generation penicillins: Great for surgical infections, simple UTIs, skin infections.

  • Amoxicillin: Commonly used for ear infections in children, pharyngitis in children, and other mild infections.

• Chloramphenicol:

  • Extremely toxic and used very rarely due to toxicity.

  • Never the ideal option for most infections.

• Aminoglycosides:

  • Used for severe infections like bacteremia caused by puncture wounds.

  • Often paired with other antibiotics for broader coverage.

• RIPES:

  • For tuberculosis (TB), the first-line treatment includes RIPES: Rifampin, Isoniazid, Pyrazinamide, Ethambutol, and Streptomycin.

• Other Antibiotics:

  • Bactrim (Trimethoprim-Sulfamethoxazole): Effective for gram-negative UTIs.

  • 3rd & 4th Generation Cephalosporins: Good for bacteremia or serious infections.

  • Vancomycin: Effective for MRSA, used when dealing with serious gram-positive infections.

2. Specific Infection Treatments

• UTIs:

  • Common in females, especially 20-year-old: Bactrim or Trimethoprim-Sulfamethoxazole.

  • For elderly patients, especially those in nursing homes, Bactrim or similar drugs are also used.

• Tuberculosis (TB):

  • Use RIPES for treatment (Rifampin, Isoniazid, Pyrazinamide, Ethambutol, Streptomycin).

• Bacteremia:

  • Caused by puncture wounds: Treat with Aminoglycosides, Bactrim, Anti-pseudomonal Penicillins.

  • Use 3rd and 4th generation cephalosporins for resistant strains.

• Bronchitis (16-year-old male):

  • Use Penicillin or Amoxicillin for uncomplicated cases.

• Pharyngitis (8-year-old):

  • Use Penicillin or Aminopenicillin.

• Ear Infections (2-year-old):

  • Penicillin or Amoxicillin.

3. Mechanisms of Action of Antibiotics

• Penicillins:

  • Inhibit cell wall synthesis by targeting peptidoglycan.

• Aminoglycosides:

  • Inhibit protein synthesis by binding to the bacterial ribosome.

• Vancomycin:

  • Inhibits cell wall synthesis, primarily for gram-positive organisms.

• Macrolides:

  • Inhibit protein synthesis by binding to the bacterial ribosome.

• Fluoroquinolones:

  • Inhibit DNA synthesis by targeting topoisomerase.

4. Gram-Positive vs. Gram-Negative Bacteria

• Gram-Positive:

  • Thicker cell wall (peptidoglycan).

  • Example: Staphylococcus and Streptococcus.

• Gram-Negative:

  • Thinner cell wall, lipopolysaccharide outer membrane.

  • Example: Escherichia coli (E. coli), Pseudomonas.

5. Infections and Toxins

• Endotoxins:

  • Found in gram-negative bacteria. Released when the bacterial cell is destroyed.

  • Can cause severe reactions like sepsis.

• Exotoxins:

  • Released actively by both gram-positive and gram-negative bacteria.

  • Can cause severe damage (e.g., tetanus toxin).

• Superantigens:

  • A type of exotoxin that can cause a hyperimmune response, leading to toxic shock syndrome.

6. Viral Infections and Hepatitis

• Hepatitis Types:

  • Hepatitis A: Fecal-oral transmission, RNA virus, no cure.

  • Hepatitis B: Bloodborne, DNA virus, can lead to liver disease.

  • Hepatitis C: Bloodborne, RNA virus, curable with antiviral treatments.

• Treatment of Hepatitis:

  • Antivirals for B and C.

  • Vaccines available for Hepatitis A and B.

7. Fungal Infections

• Mycoses:

  • Systemic: Bloodstream infections, can spread throughout the body.

  • Dimorphic fungi: Molds inside the body, yeasts outside (or vice versa).

• Treatment of Fungal Infections:

  • Antifungals: Examples include Azoles and Echinocandins.

8. Gram Staining and Cell Wall Composition

• Gram-Positive Bacteria:

  • Thick peptidoglycan layer, which retains the crystal violet stain during Gram staining.

• Gram-Negative Bacteria:

  • Thinner peptidoglycan layer, surrounded by an outer lipid membrane, which does not retain the crystal violet stain.

9. Phage Infection Cycle

• Lytic Cycle:

  • Attachment: Phage attaches to the host.

  • Entry: Phage injects DNA into the host.

  • Replication: Phage DNA is replicated.

  • Assembly: New phage particles are assembled.

  • Lysis: Host cell breaks open, releasing new phages.

10. Mechanisms of Resistance

• Penicillin Resistance:

  • Penicillinase: Enzyme that breaks down penicillin.

  • MRSA: Resistant to methicillin, uses alternative pathways.

• Carbapenem Resistance:

  • Carbapenems are broad-spectrum antibiotics, but some bacteria, like Enterobacteriaceae, are becoming resistant.

11. Therapeutic Concepts

• Therapeutic Index:

  • Measures the safety of a drug; a higher index means the drug is safer (larger gap between effective dose and toxic dose).

• MIC (Minimum Inhibitory Concentration):

  • The lowest concentration of an antibiotic that inhibits bacterial growth.

• Empiric Therapy:

  • Treatment started based on the most likely infection before results from cultures are available.

12. Key Microbiology Concepts

• Eukaryotic vs. Prokaryotic Cells:

  • Eukaryotic: Have organelles, including a nucleus.

  • Prokaryotic: No nucleus or membrane-bound organelles.

• Bacteria vs. Viruses:

  • Bacteria: Cellular organisms that can reproduce on their own.

  • Viruses: Non-living, require a host cell to reproduce.

• Viruses:

  • RNA viruses (e.g., HIV, Hepatitis C) and DNA viruses (e.g., Hepatitis B).

13. Infection Prevention and Control

• Community vs. Hospital-acquired Infections:

  • Hospital-acquired infections are often more resistant to antibiotics, such as MRSA.

• Transmission via Arthropods:

  • Ticks transmit Lyme disease.

  • Mosquitoes transmit malaria, dengue, and other diseases.

14. Final Tips

• Be sure to understand:

  • Antibiotic mechanisms of action and their indications.

  • The differences between bacterial and viral infections.

  • Host microbial response to infections.

  • The differences between Gram-positive and Gram-negative bacteria.