MICR101A LESSON 8 Antibacterials and AMR (Salem)

Page 1: Introduction

  • Course: MICR 101 General Veterinary Microbiology

  • Instructor: Andrei John T. Salem, MSc, RMicro

  • Focus Areas: Antibacterial Agents and Antimicrobial Resistance (AMR)

  • Key Method: Antimicrobial susceptibility tested via Kirby-Bauer disk diffusion method

Page 2: Fair Use Notice

  • Purpose: Material is for educational and informational use only.

  • Compliance: Prepared in accordance with Section 185 Fair Use of Copyrighted Work (R.A. 8293).

  • Reproduction: Further communication of materials may be legally restricted.

Page 3: Chemical Control of Bacterial Growth

  • Antimicrobial Types:

    • Bacteriostatic: Inhibits growth without killing bacteria (e.g., sulfa drugs). Growth resumes upon removal.

    • Bactericidal: Kills bacteria without causing cell lysis; total cell counts remain constant (e.g., formaldehyde).

    • Bacteriolytic: Kills and lyses cells, reducing viable and total cell counts (e.g., detergents, penicillin).

Page 4: Assaying Antibacterial Activity

  • Minimum Inhibitory Concentration (MIC):

    • Smallest amount needed to inhibit bacterial growth.

    • Methods:

      • Broth Medium: Broth dilution method.

      • Agar Medium: Kirby-Bauer, Etest, Agar dilution test.

    • Observations vary based on medium and setup used.

Page 5: Kirby-Bauer Disk Diffusion Method

  • Simplest method for antimicrobial susceptibility testing.

  • Procedure:

    • Place antibiotic-impregnated paper discs on agar inoculated with bacteria.

    • Antibiotic diffuses to create a gradient.

    • Measure zone of inhibition for susceptibility interpretation per CLSI guidelines.

Page 6: Broth and Agar Dilution Method

  • Broth Dilution:

    • Twofold dilutions of antibiotics in nutrient broth.

    • MIC determined by observing growth.

  • Agar Dilution:

    • Antibiotic incorporated into agar plates.

    • Bacteria spot-inoculated to determine susceptibility.

Page 7: Chemical Control Agents

  • Types of agents:

    • Sterilants: Kill all microorganisms including endospores.

    • Disinfectants: Kill most microorganisms; may not affect endospores; used on surfaces.

    • Sanitizers: Reduce microbial numbers without sterilization.

    • Antiseptics: Kill/inhibit growth on living tissues (e.g., iodine, alcohol).

Page 8: Common Chemical Control Agents

  • Ethanol/Isopropyl Alcohol (70%): Antiseptic/disinfectant; denatures proteins.

  • Sodium Hypochlorite (Zonrox): Disinfectant; oxidizing agent.

  • Hydrogen Peroxide (3%): Antiseptic/disinfectant; breaks down into water and oxygen.

  • Benzalkonium Chloride (Lysol): Disinfectant; disrupts cell membranes.

Page 9: Antibiotics Overview

  • Function: Kill/inhibit bacterial growth; classified by structure and action mechanism.

  • Selective Toxicity: Effective against pathogens without harming the host.

  • Spectrum:

    • Narrow-spectrum: E.g., penicillin (effective against Gram-positive).

    • Broad-spectrum: E.g., tetracycline (effective against both Gram-positive and negative).

Page 10: Targets of Antibiotics

  • Major targets include:

    • Nucleic Acid Synthesis: Interference with DNA replication and RNA synthesis.

    • Protein Synthesis: Inhibit bacterial ribosomes (30S and 50S subunits).

    • Cell Wall Synthesis: Disruption of peptidoglycan formation (e.g., beta-lactams).

Page 11: Antibiotic Resistance Mechanisms

  • Mechanisms include:

    • Modification of Drug Targets: Mutations that change antibiotic binding sites.

    • Enzymatic Inactivation: Chemical modification of the antibiotic (e.g., beta-lactamase).

    • Efflux Pumps: Remove antibiotics, decreasing intracellular concentrations.

    • Metabolic Bypasses: Alternative pathways bypassing antibiotic targets.

Page 12: Classes of Antibiotics

  1. Cell Wall Synthesis Inhibitors:

    • Beta-lactams (e.g., penicillin, cephalosporins).

    • Glycopeptides (e.g., vancomycin).

  2. Cell Membrane Disruptors:

    • Polypeptides (e.g., polymyxins).

  3. Protein Synthesis Inhibitors:

    • Macrolides, aminoglycosides, tetracyclines.

  4. Nucleic Acid Synthesis Interference:

    • Quinolones, ridampicin.

Page 13: Antibiotics That Inhibit Cell Wall Synthesis

  • Beta-lactams:

    • Penicillin: Effective against Gram-positive bacteria; interferes with peptidoglycan cross-linking.

    • Cephalosporins: Four generations targeting various infections.

    • Vancomycin: Effective against Gram-positive bacteria, particularly resistant strains.

Page 14: Antibiotics That Disrupt Cell Membrane Function

  • Polypeptide Antibiotics:

    • This class is mainly used topically due to potential toxicity.

    • Cyclics (Colistin, Polymyxin): Limited to Gram-negative infections.

Page 15: Antibiotics That Inhibit Protein Synthesis

  • 50S Subunit Inhibitors:

    • Lincosamides and Macrolides.

  • 30S Subunit Inhibitors:

    • Aminoglycosides and Tetracyclines target distinct stages of ribosomal activity.

Page 16: Continued - Protein Synthesis Inhibition

  • Aminoglycosides:

    • Cause misreading of mRNA during protein synthesis.

  • Tetracyclines:

    • Block tRNA attachment, common in veterinary use.

Page 17: Antibiotics That Inhibit Nucleic Acid Synthesis

  • Quinolones and Fluoroquinolones:

    • Bactericidal; interfere with DNA gyrase and prevent supercoiling.

  • Rifampicin: Critical for treating specific bacterial infections.

Page 18: Sulfonamides and Trimethoprim

  • Sulfonamides:

    • Block folic acid synthesis by competing with PABA.

  • Trimethoprim: Works synergistically with sulfonamides by targeting dihydrofolate reductase.

Page 19: Selection of Antibiotics

  • Antimicrobial selection considers:

    • Pathogen type and Gram reaction (e.g., Gram-positive, Gram-negative).

    • Suggested drugs and alternative drug classes for effective treatment.

Page 20: Continued Selection

  • Reference drugs for common pathogens and considerations for resistant pathogens.

Page 21: Antibiotic Drug Interaction

  • Importance of considering interactions between antibiotics to avoid adverse effects.

  • Examples: Synergism vs. Antagonism between combinations.

Page 22: Antimicrobial Resistance (AMR)

  • Global health concern with rising antibiotics ineffectiveness.

  • Resistance mechanisms: innate and acquired properties.

Page 23: AMR Mechanisms

  • Factors contributing to AMR include resistance mechanisms and ecological interactions within bacterial populations.

Page 24: Notable AMR Mechanisms

  • Plasmid and Integron Transmission:

    • Gene exchange and resistance propagation between species.

  • Toxin-Antitoxin Modules: Resilience through dormant states in hostile environments.

Page 25: Persistence and Biofilm Formation

  • Biofilms complicate infections by clustering resistant bacteria, hindering antibiotic action.

Page 26: One Health and AMR

  • Integrated approach to tackle AMR across humans, animals, and the environment.

Page 27: Impact of Companion Animals

  • Rise in companion animals enhances risk factors for AMR traits transmission to humans.

Page 28: Aquaculture Contributions to AMR

  • Increased use of antibiotics in fish farming creates selective pressures for resistance.

Page 29: Domestic Animal Husbandry and AMR

  • Routine antibiotic use in livestock raises AMR risks; emphasis on responsible practices.

Page 30: AMR Microbes in Domestic Animals

  • Campylobacter spp.: Common in reproductive and gastrointestinal infections in various livestock.

Page 31: Antibiotic Resistance in Salmonella spp.

  • Important pathogen in livestock, with significant resistance issues related to AMR mechanisms.

Page 32: Staphylococcus Spp. Resistance

  • Causative agent of various animal infections with significant resistance attributed to SCCmec.

Page 33: Enterococcus Spp. Characteristics

  • Naturally resistant to several antibiotics; potential threats to both humans and livestock.

Page 34: Strategies for Limiting AMR

  • Recommendations for surveillance, laboratory-based prescriptions, hygiene improvements, and withdrawal protocols.