Antibiotics

• Antimicrobial drugs


  Chemical substance that destroys pathogenic organisms with minimal damage to host tissues - antibacterial, anti fungal etc
• Antibiotics


  An antimicrobial drug. Produced by microbe, in small amounts inhibits other microbes
• Antibiotics


  • Metabolic products of aerobic spore forming bacteria and fungi
  • Bacteria in genera Streptomyces and Bacillus
  • Molds in genera Penicillium and Cephalosporium
• Antibiotic producing organisms release antibiotics

  1. Inhibits growth of other microbes in same environment

  2. Reduces competition for resources
• Mechanisms of antibiotic drugs

  • Inhibits cell wall
  • Districts cell membrane
  • Inhibits nucleic acid synthesis
  • Inhibits protein synthesis
  • Blocks metabolic pathways
• Narrow spectrum antibiotics


  Effective against a specific group of bacteria, either gram positive or negative, chosen when specific bacteria is known
• Broad spectrum antibiotics


  Effective against wide range of bacteria, both gram negative and positive, used when cause of infection is unknown, higher risk of causing antibiotic resistance
• Empirical therapy


  Starting treatment with antibiotic before specific organism causing the infection is identified
• Narrow spectrum antibiotics


  • Linezolid - gram positive
  • Bacitracin - gram positive, staphylococci
  • Vancomycin, Teicoplanin - gram positive, staphylococci
  • Isoniazid - mycobacterium
• Commonly used broad spectrum antibiotics

  • Tetracyclines
  • Cephalosporins
  • Macrolides
  • Quinolones (ciprofloxacin)
• Bacteriostatic


  Reversible stoppage of bacterial growth
• Bacteriostatic antibiotics


  • Chloramphenicol
  • Erythromycin
  • Clindamycin
  • Tetracylines
  • Trimethoprim
• Bactericidal


  Irreversible killing
• Bactericidal antibiotics


  • Cephalosporins
  • Fluoroquinolones
  • Vancomycin
  • Aminoglycosides
  • Metronidazole
  • Penicillin
• Generations of Cephalosporins


  • Cephalothin, Cefazolin - most effective against gram positive cocci, few gram negative
  • Cefaclor, Cefonacid - more effective against gram negative bacteria
  • Ceftriaxone, Cephalexin - broad spectrum activity against bacteria with beta lactamases
  • Cefepime - BOTH gram negative and gram positive
• Beta lactam drugs


  • Carbapenems (imipenem) - broad spectrum drug for infections with aerobic and anaerobic pathogens
  • Monobactams (aztreonam) - newer narrow spectrum drug for infections with gram negative aerobic bacilli, used by people allergic to penicillin
• Non beta lactam cell wall inhibitors

  • Vancomycin - narrow spectrum, staphylococcal infections
  • Isoniazid - interferes with mycolic acid synthesis, treat infections with mycobacterium tuberculosis
• Drug resistance


  When bacteria become tolerant to an amount of drug that would normally inhibit their growth
• How microorganisms become resistant

  1. Spontaneous mutation - Within chromosomes

  2. Acquisitions of new genes - transfer from another species