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Control of Microbial Growth - Coggle Diagram
Control of Microbial Growth
Key Definitions
Chemotherapy - use of chemical substances to treat disease
Antimicrobial Drugs - Interfere with microbial growth within the host
Antibiotic - Substance produced by microbes that inhibit others
Disinfectant - Chemical that kills/inactivates microbes on non-living surfaces
Microbial Death Rate
Efficacy depends on:
Number of microbes
Environment (organic matter, biofilms)
Exposure time
Microbial characteristics (spores, acid-fast walls)
Actions of Microbial Control Agents (Modes of Action)
Alteration of membrane permeability
Damage to proteins (enzymes)
Damage to nucleic acids (DNA/RNA)
Physical Methods of Microbial Control
Pasteurization: bactericidal, reduces microbes in milk (not sterile), 72C for 15 sec
Filtration: bacteriostatic, removes microbes from liquids/gasses, HEPA 0.3 μm
Low Temp: bacteriostatic, slows growth, doesn't kill, listeria can survive
Osmotic Pressure: bacteriostatic, dehydrates cells, salted meats, dried fruit
Radiation: bactericidal, damages DNA, ionizing (x-ray, γ) UV light
Heat - Dry: bactericidal, incineration/flame, waste disposal
Heat - Moist (Autoclave): bactericidal, sterilizes media/tools, 121C for 15 minutes
History of Chemotherapy
Ehrlich (1910)
"Magic bullet," coined chemotherapy
Fleming (1928)
discovered penicillin
Florey & Chain (1940)
first clinical trials
Spectrum of Antimicrobial Activity
Broad-spectrum
many types, tetracycline, risk: superinfection (C. difficile, Candida)
Narrow-spectrum
specific group, penicillin G (gram+), less disruption of normal flora
Testing Antimicrobials/Disinfectants
Broth Dilution: MIC & MBC, quantitative
Kirby-Bauer Disk Diffusion: zone of inhibition, qualitative
E-Test: MIC only, combines dilution and diffusion
Antimicrobial Safety
Therapeutic Index = Toxic Dose/Therapeutic Dose
High TI = safer drug
Low TI = higher risk of side affects
Mechanisms of Drug Resistance
Alteration of target site
Efflux pump (drug ejection)
Prevention of drug entry
Resistance genes: plasmids, transposons (transferable)
Enzymatic destruction (β-lactamase)
Types of Antibiotics
Actinomycetes (Streptomyces spp.):
Produce ~50% antibiotics (Streptomycin, Tetracycline, Erythromycin)
Fungi:
Penicillium, Cephalosporium → Penicillin, Cephalothin
Gram+ Bacilli:
Bacillus spp. → Bacitracin, Polymyxin
Types of Antifungal Drugs
Polyenes
membrane sterols, Amphotericin B, nephrotoxic
Azoles
sterol synthlsis, Ketoconazole, Triazoles, topical/orak
Types of Disinfectants
Halogens
Chlorine, Iodine, Fluorine, Iodophors (betadine) for surgery
Alcohols
70% ethanol/isopropanol, concentration-dependant
Bisphenols
Triclosan, Hexachlorophene, Gram+ effective, neurotoxic risk
Quaternary Ammonium Compounds (Quats)
Zephiran, Cepacol, antiseptic/mouthwash
Phenols
Lysol, denatures proteins
Norovirus Case
Resistant: Heat up to 140F
Prevention: 25 Tbsp bleach/gal water, long hot cycles
Transmission: fecal-oral
Treatment: Rehydration
Disease: gastroenteritis
Types of Antiviral Drugs
HIV
nucleoside/nucleotide analogs, AZT, Tenofovir
Herpes
nucleoside analog, Acyclovir
Influenza
neuraminidase inhibitors, Oseltamivir (Tamiflu), Zanamivir