Antimicrobial Therapy and Mechanisms

Antimicrobial Therapy

• Antimicrobial therapy uses medications to treat bacterial, viral, or fungal infections.
• Antimicrobials target microbes selectively, minimizing harm to host cells.
• Microbial resistance (e.g., conjugation) necessitates continuous development of new antimicrobials.
• Superinfection occurs when antibiotics eliminate normal flora, creating an environment for new, difficult-to-treat infections to develop.

Antimicrobial Mechanisms of Action

• Cell wall destruction: This selectively targets bacteria, not mammals.
• Enzyme inhibition: Inhibition of bacteria-specific enzymes disrupts bacterial survival.
• Protein synthesis impairment: Antimicrobials can disrupt bacterial ribosomes without affecting mammalian cells.
• DNA/RNA interference: These target bacterial DNA/RNA synthesis or function.
• Viral replication inhibition: Disrupts viral reproduction.

Antimicrobial Classification

• Spectrum:
  • Narrow-spectrum: Targets few bacterial types.
  • Broad-spectrum: Targets many bacterial types.
• Mechanism of action:
  • Bactericidal: Directly kills microbes.
  • Bacteriostatic: Inhibits microbe growth, requiring the host's immune response to eliminate the microbe.

Antimicrobial Selection Factors

• Causative agent identification: Crucial for selecting the appropriate antibiotic.
  • Laboratory testing: Body fluids (blood, urine, sputum, wound drainage) examined to identify the infecting microorganism.
    • Gram stain: Direct microscopic identification.
    • Culture: Allows for microbial growth and identification over several days. Specimens must be collected carefully to avoid contamination.
• Microorganism sensitivity: Determining the most effective antibiotic for a particular microorganism.
  • Disk diffusion (Kirby-Bauer): Measuring the zone of inhibition around antibiotic disks to assess sensitivity.
  • Serial dilution: A quantitative method using varying antibiotic concentrations to determine the lowest inhibitory concentration (MIC) and minimum bactericidal concentration (MBC).
  • Gradient diffusion: Uses disks or strips with varying antibiotic concentrations to identify the effective concentration.
• Host factors:
  • Age: Infants and older adults are more susceptible to antibiotic toxicity due to immature/declining organ function.
  • Immune status: Compromised immune systems may need stronger bactericidal antibiotics.
  • Location of infection: Some sites (e.g., brain, heart, abscesses) present barriers to effective antibiotic penetration.
  • Allergies: History of allergies, especially to penicillin, limits antibiotic choices.
• Other host factors: Pregnancy, lactation, and preexisting conditions influence antibiotic choice.

Antimicrobial Combination Therapy

• Combining multiple antimicrobials can:
  • Treat severely resistant infections.
  • Treat mixed infections.
  • Prevent resistance.
  • Possibly reduce toxicity by lowering individual doses.
  • May be more effective than single-antimicrobial therapy.
• However, combining antimicrobials may have negative effects such as increased toxicity, cost, or drug antagonism.

Prophylaxis

• Antimicrobials can be used to prevent infections in specific situations:
  • Pre-surgical procedures (e.g., gastrointestinal, cardiac, vascular, orthopedic, or gynecologic)
  • Sexually transmitted infections (following exposure)
  • Prosthetic heart valves (prior to dental/other procedures)
  • Recurrent urinary tract infections (in specific cases)

Preventing Antimicrobial Resistance

• Perform hand hygiene.
• Use of appropriate infection control measures (aseptic technique, standard precautions, transmission-based precautions).
• Ensure clients/patients complete prescribed courses of antibiotics.
• Monitor patients for improvement and follow up with cultures post treatment to evaluate treatment effectiveness