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Control of Microbial Growth - Coggle Diagram
Control of Microbial Growth
Principles & Definitions
Chemotherapy
: use of chemicals to treat diseases
Antimicrobial Drugs
: interfere w microbe growth in host (antiviral, antifungal, antiparasitic)
Antibiotic
: produced by microbes, inhibits others
Disinfectant
: kills microbes on nonliving surfaces
Antimicrobial Agent Impact
: affects microbial growth/survival
Physical Methods of Control
Heat
:
Autoclave
(moist heat) sterilization, preferred if heat/moisture safe),
Dry heat
(incinerator, flame),
Pasteurization
(72C for 15s, kills pathogens, not sterile (thermoduric survive)
Filtration
: 0.2 um filters; HEPA 0.3 um
Low Temp:
Bacteriostatic; Listeria monocytogenes can grow in fridge
Osmotic Pressure:
Salt/sugar preserve meats, fruits
Radiation:
Ionizing
(gamma rays, x-ray) destroys DNA,
Non-ioninzing
(UV 260nm) thymine dimers, poor penetration, harmful to eyes/skin
Microbial Death Rate
(Efficacy Factors)
Number of microbes
Environment (debris, biofilms, medium contents)
Time of exposure
Microbial characteristics (acid-fast, endospores, gram +/-)
Drug Action & Mechanisms
Bacteriostatic
: prevents reproduction
Modes of Action
: alters membrane permeability, damages proteins, damages nucleic acids
Bacteriocidal
: kills bacteria (99.9% reduction)
History of Chemotherapy
1910 Ehlrich
: "magic bullet", coined chemotherapy, salvarsan vs. syphilis
1928 Fleming
: Discovered penicillin (penicillium notaum)
1940 Florey & Chain
: first clinical trials of penicillin
Spectrum of Antimicrobial Activity
Selective Toxicity
: kills microbes, not host
Broad Spectrum
: Saves time (no ID), Risks: destroys flora → Candida, C. difficile
Narrow Spectrum:
Gram (+)
(Penicillin G, Erythromycin),
Gram (-)
(Streptomycin, small hydrophilic drugs cross porins)
Testing & Safety
Broth Dilution Test
: Determines MIC (inhibitory) & MBC (bactericidal)
Kirby-Bauer Disk Diffusion
: Zone of inhibition
E-Test:
MIC only
Safety Terms:
Toxic dose
(causes harm),
Therapeutic Dose
(desired effect),
Therapeutic Index
(toxic/therapeutic, higher=safer)
Resistance
Result
: spread between bacteria → resistant strains
Mechanisms
: enzymatic drug destruction (B-lactamase), prevents penetration, alters target site, efflux pumps)
Causes
: genetic mutations; gene transfer (plasmids/transposons)
Types of Antimicrobial Agents
Antibiotics
:
Bacillus spp
(Bacitracin, Polymyxin),
Streptomyces spp
(Amphotericin B, Chloramphenicol, Tetracycline, Eythromycin, Neomycin, Streptomycin),
Fungi
(Cephalosporium → Cephalothin; Penicillum → Griseofulvin, Penicillin)
Antifungals:
Eukaryotic Cells ()
Amphotericin B:
(systemic, nephrotoxic),
Azoles
: Imidazole (OTC), Ketoconazole (oral/topical), Triazoles
Antivirals
:
Flu
: Zanamivir (Relenza), Oseltamivir (Tamiflu),
HIV
: Zidovudine (AZT), Tenofovir,
Herpes
: Acyclovir
Disinfectants & Example Pathogen
Alcohols
: concentration-dependant
Quats
: Zephiran (acne), Cepacol (mouthwash)
Resistance Order:
Certain microbes resist chemical biocides more than others
Phenols/Bisphenols
: Lysol, Hexachlorophene (staph, neurotoxic risk), Triclosan (plastics, Gram +)
Halogens
: Fluorine, Chlorine, Iodine (Tincture - alcohol base, antiseptic), (Iodophor/Betadine - water base, surgical scrub)
EXAMPLE (Noravirus):
Shed before/after illness (2-3 days before, 2 weeks after)
Treatment
: Rehydration
Gastroenteritis (fecal-oral), heat tolerant (140F)
Prevention
: 25 tbsp bleach/gal water; wash on hot, longest cycle