Beta-Lactam Antibiotics Overview

Beta-Lactam Antibiotics

• Inhibit cell wall synthesis by hindering peptidoglycan.
• Penicillin G and V: Active against Gram-positive bacteria, used to treat streptococcal infections.
• Methicillin/Oxacillin: Active against Gram-positive bacteria, resistant to beta-lactamases.
• Ampicillin/Carbenicillin: Broad-spectrum antibiotics.
• Carbapenems: Broadest spectrum, used for severe infections.
• Vancomycin (Glycopeptide): Interferes with cross-linking, narrow therapeutic index.
• Cephalosporins:
  • 1st Generation (Cephalexin/Cephalothin): Active against Gram-positive bacteria.
  • 2nd Generation (Cefuroxime): Extended spectrum against Gram-negative bacteria.
  • 3rd Generation (Ceftriaxone/Cefotaxime): Used for central nervous system infections.
  • 4th Generation (Cefepime): Covers third-generation resistant bacteria.
  • 5th Generation (Ceftaroline): Effective against MRSA.

Cell Membrane Disruptors

• Bacitracin: Active against Gram-positive bacteria, inhibits peptidoglycan addition.
• Polymyxins: Active against Gram-negative bacteria, disrupts the outer membrane.

Protein Synthesis Inhibitors

• Aminoglycosides: Broad-spectrum, target 30S ribosomes. They have a narrow therapeutic index and require close monitoring for toxicity (e.g., tobramycin, gentamicin).
• Tetracyclines: Broad-spectrum, target 30S ribosomes; known for teeth discoloration.
• Macrolides: Bind to 50S ribosomes; often used for penicillin-allergic patients (e.g., erythromycin).
• Chloramphenicol: Binds to 50S ribosomes; reserved for severe infections; carries a risk of "grey baby syndrome."

Folic Acid Inhibitors

• Trimethoprim/Sulfamethoxazole: Treats UTIs by inhibiting folic acid synthesis.

DNA Synthesis Inhibitors

• Nalidixic Acid: Treats UTIs by inhibiting DNA synthesis.
• Fluoroquinolones: Inhibit DNA gyrase to stop replication.
• Nitrofurantoin: UTI treatment that targets several cellular processes.
• Rifampin: Inhibits DNA polymerase, used for Mycobacterium infections.
• Metronidazole: Causes DNA breaks under anaerobic conditions; has a metallic taste side effect.

Antimycobacterial Agents

• Isoniazid: Inhibits mycolic acid synthesis; can cause hepatitis.
• Ethambutol: Inhibits cell wall formation; can cause optic neuritis.
• Pyrazinamide: Lowers pH, causes gastrointestinal upset.

Antifungal Agents

• Amphotericin B: Drug of choice for severe fungal infections, potential nephrotoxicity.
• Azoles: Inhibit sterol synthesis.
• 5-Fluorocytosine: Effective against Cryptococcus, can depress bone marrow.
• Caspofungin: Effective against Candida and Aspergillus (not Cryptococcus).

Antiviral Agents

• Acyclovir: Effective against Herpes viruses.
• Ribavirin: Effective against Respiratory Syncytial Virus.
• M2 Inhibitor: Inhibits Influenza A.
• Neuraminidase Inhibitors: Inhibit Influenza A and B.

Antimicrobial Resistance Testing

• MRSA: mecA gene leads to altered PBP2a.
• VRSA: Testing with Etest.
• ESBL: Testing with and without clavulanate.
• Clindamycin Resistance: Erm gene.
• Carbapenemase: Modified Hodge Test.
• Glycopeptides: van A PCR.
• Oxacillin Resistance: Cefoxitin disk test.
• Penicillin Resistance: Beta-lactamase testing.

Anaerobes and Growth Requirements

• Anaerobes lack oxidative enzymes (e.g., superoxide dismutase, catalase).
• Intra-abdominal abscesses are a common source of endogenous anaerobic infections.
• Anaerobic Media:
  • Require Vitamin K and Hemin.
  • Thioglycollate Broth: A medium for anaerobes.
  • Phenylethyl Alcohol: Selective for Gram-positive and some Gram-negative anaerobes.
  • Kanamycin-Vancomycin (KV): Selective for Gram-negative anaerobes.
  • Bile-Esculin: Selective for Bacteroides fragilis.
  • Egg Yolk: Identifies anaerobes that break down fats.

Selective Antibiotic Disks (Species Sensitivity Patterns)

• Data provided shows resistance/susceptibility of various species to named antibiotics (Kanamycin, Colistin, Vancomycin).

Gram-Negative Bacilli

• Bacteroides fragilis: Common anaerobic GI tract bacterium, linked to abdominal infections.
• Fusobacterium nucleatum: Pointed, spindle-shaped bacteria, associated with biofilm infections.
• Fusobacterium necrophorum: Pleomorphic, linked to Lemierre's syndrome and Vincent's angina.

Pigmented Gram-Negative Bacilli

• Prevotella melaninogenica: Respiratory and periodontal infections.
• Prevotella intermedia: Gingivitis and oropharyngeal infections.
• Porphyromonas asaccharolyticus: Genital infections.
• Porphyromonas gingivalis: Gingivitis and chronic periodontitis.

Spore-Forming Gram-Positive Bacilli

• Clostridium perfringens: Associated with gas gangrene and food poisoning (double zone of beta-hemolysis).
• Clostridium tetani: Causes tetanus (drumstick-shaped spores).
• Clostridium botulinum: Causes botulism (attacks nervous system).
• Clostridiodes difficile: Causes antibiotic-associated diarrhea and colitis ("horse manure" odor).
• Clostridium septicum: Gas gangrene in malignancies.

This quiz covers the essential characteristics and classifications of beta-lactam antibiotics, including penicillin, cephalosporins, and their mechanisms of action. Test your knowledge on their spectrum of activity and clinical uses. Perfect for students studying pharmacology or related health sciences.