Microbiology: Bacterial Organisms and Antibiotics

Bacterial Organisms

• 4 main classes of bacteria:
  • Gram Positive: MRSA, Staphylococci, Streptococci, Enterococcus
  • Gram Negative: E.coli, Haemophilus Influenza, Moraxella Catarrhalis, Pseudomonas, Atypicals, ESBL
  • Anaerobes: Streptococci (Gram +), Clostridia (Gram +), Bacteroides (Gram -)
  • Atypical: Mycoplasma, Chlamydia, Rickettsia, Legionella, Mycobacteria

Antibiotic Agents and Class

• B-Lactams: penicillin, cephalosporin, penicillin beta-lactamase
  • Penicillins: amoxicillin, ampicillin, dicloxacillin, nafcillin, oxacillin, penicillin G, penicillin V, piperacillin
  • Cephalosporins: first generation (cefazolin, cefadroxil, cephalexin), second generation (cefaclor, cefoxitin, cefotetan), third generation (cefotaxime, ceftriaxone), fourth generation (cefepime)
  • Penicillin/Beta-lactamase: amoxicillin/clavulanate, piperacillin/tazobactam
• Other classes: Nitrofurans, Aminoglycosides, Nitroimidazole, Quinolones, Tetracycline, Sulfonamides, Macrolides, Oxazolidinones, Lincosamide, Glycopeptides

Mechanisms of Action

• Inhibition of Cell Wall Synthesis: PCN, Cephalosporins, Imipenem, Meropenem, Aztreonam, Vancomycin
• Inhibition of Bacterial Protein Synthesis: Aminoglycosides, Macrolides, Tetracycline, Linezolid, Clindamycin
• Inhibition of Nucleic Acid Synthesis: Fluoroquinolones, Rifampin
• Inhibition of Folic Acid Synthesis: Sulfonamides, Trimethoprim
• Inhibition of Free Radical Formation: Metronidazole

Mechanisms of Resistance

• Enzymatic Inactivation: Beta-Lactamases, Aminoglycoside-Modifying Enzymes
• Alteration of Target Site: changes to Ribosomes, Penicillin-Binding Proteins (PBPs), DNA gyrase, Topoisomerase
• Decreased Permeability: decreased ability of antibiotic to enter bacterial cell, Porin Channels, Efflux pumps

Antibiotic Adverse Side Effects

• Majority: Nausea/Vomiting/Diarrhea/Rash/Thrush (GI side effects)
• Specific effects:
  • Penicillins: Hypersensitivity/Skin Reactions
  • Cephalosporins: C.Difficile Colitis
  • Macrolides: GI Side Effects/Hepatitis/QT Interval Prolongation
  • Quinolones: QT Prolongation/Tendonitis/Convulsions
  • Aminoglycosides: Nephrotoxicity/Ototoxicity
  • Vancomycin: "Red Man" Syndrome
  • Clindamycin: C.Difficile Colitis
  • Tetracyclines: Hepatotoxicity/Stained Teeth/Photosensitivity/Dysphagia
  • Nitrofurantoin: Peripheral Neuropathy
  • Sulfonamides: Stevens-Johnsons Syndrome (skin type reaction, hypodynamic instability)/Blood Dyscrasias

Antibiotic Drug Interactions

• Enzyme Inhibitors: Erythromycin, Clarithromycin, Metronidazole, Ciprofloxacin
• Enzyme Inducers: Rifampin
• Absorption: Tetracyclines, Quinolones (reduced by Antacids, Calcium)
• Entero-Hepatic Cycling: Broad Spectrum Antibiotics, Oral Contraceptives
• Vitamin K Synthesis: Broad Spectrum Antibiotics, Warfarin
• Metronidazole: Disulfiram-like interaction with alcohol

Renal Adjustment

• Antibiotics that do not require renal adjustment:
  • Nafcillin
  • Oxacillin
  • Ceftriaxone
  • Clindamycin
  • Azithromycin
  • Erythromycin
  • Moxifloxacin
  • Doxycycline
  • Tigecycline
  • Rifampin

Beta-Lactam Antibiotics

• Time Dependent Antibiotics: Beta lactam ring, MOA of Penicillin and Cephalosporin
• Resistance Mechanism: B-Lactamase, PBPs structural changes, Porin structural changes

Penicillins

• Traditional: Narrow Spectrum (Penicillin G, V), Extended Spectrum (Amoxicillin, Ampicillin), Broad Spectrum (Amoxicillin/Clavulanate)
• Coverage: Gram+, Primarily Strep Infections Only! (Staph now resistant)
• Examples: Penicillin G, Penicillin V, Amoxicillin, Ampicillin

Tetracyclines

• Examples: Doxycycline, Tetracycline, Minocycline
• Coverage: Gram+, Gram-, Antiprotozoal properties, and Atypicals
• Concentration Dependent Antibiotic
• Considerations: Doxycycline use more often, Acne, STDs, Pelvic Inflammatory Disease, Rickettsia Disease

Aminoglycosides

• Examples: Gentamicin, Tobramycin, Amikacin
• Coverage: Wide range of bacteria, Most effective = Gram Negative and Pseudomonas
• Concentration Dependent Antibiotic
• Considerations: Not used alone, Typically used with Ampicillin (synergistic), Ototoxicity, Renal Toxicity, Avoid in Pregnancy

Nitrofurantoin

• Example: Nitrofurantoin
• Coverage: Gram+ and Gram-
• Considerations: MOA: Inhibits DNA, RNA, protein, cell wall synthesis, Bacteriostatic/Bactericidal, Urinary Tract Infection Uncomplicated, Urinary Tract Infection Prophylaxis
• Adverse Side Effects: Increased risk for Serotonin Syndrome

This quiz covers the main classes of bacterial organisms, including Gram Positive and Gram Negative bacteria, and considerations for antibiotic treatment of infections.