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Control of Microbial Growth - Coggle Diagram
Control of Microbial Growth
Methods of Microbial Control
Physical
Heat
Moist heat(autoclave) sterilizes media
Dry heat → Incineration, flaming
Pasteurization → 72°C for 15 sec (kills pathogens, not sterilization)
Filtration
Removes microbes from liquids/gases (0.2 µm filters; HEPA 0.3 µm)
Low temperature
(Bacteriostatic) → Slows growth (Listeria survives refrigeration)
Osmotic pressure
Salt/sugar curing, dehydration
Radiation
Ionizing (X-rays, gamma) → Destroys DNA
Non-ionizing (UV) → Thymine dimers; poor penetration
Chemical
Disinfectants (Non-living surfaces)
Phenols/Bisphenols → Lysol, Triclosan
Halogens → Iodine, Chlorine, Betadine
Alcohols → 70% most effective
Quaternary compounds → Zephiran, Cepacol
Antimicrobial Drugs (Used in host)
Antibiotics → Produced by microbes (Penicillin, Streptomyces spp.)
Antifungal → Azoles, Amphotericin B
Antiviral → AZT, Tamiflu, Acyclovir
Mechanisms
Alteration of membrane permeability
Damage to proteins (enzymes)
Damage to nucleic acids (DNA/RNA)
Antimicrobial Drug Actions
Bactericidal: Kills (99.9% reduction)
Bacteriostatic: Inhibits growth
Spectrum of Activity
Broad-spectrum: Acts on many types (risk: superinfection, e.g. C. difficile)
Narrow-spectrum: Specific to Gram + or Gram – bacteria
Evaluating Effectiveness
Broth Dilution Test → Determines MIC/MBC
Kirby-Bauer (Disk Diffusion) → Zone of inhibition
E-Test → MIC only
Antimicrobial Safety
Toxic dose vs. Therapeutic dose
Therapeutic Index = Toxic dose / Therapeutic dose
Larger index = safer drug
Resistance Mechanisms
Enzymatic drug destruction (β-lactamase)
Prevent drug entry
Alter target site
Efflux pumps
Resistance genes → plasmids/transposons
Applications
Food preservation (osmotic, heat)
Medical sterilization (autoclave, radiation)
Disinfection (surface cleaning)
Chemotherapy (antibiotics, antivirals, antifungals)