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Control of Microbial Growth - Coggle Diagram
Control of Microbial Growth
Fundamentals & Definitions
Learning Objective: Understand physical & chemical control methods
Chemotherapy: Use of chemicals to treat disease
Antimicrobial Drugs:
Interfere with microbial growth in host
Types: Antifungal, Antiviral, Antiparasitic
Antibiotic: Produced by microbes; inhibits others
Disinfectants: Destroy microbes on non-living surfaces
Efficacy& Microbial Action
Efficacy Factors
Number of microbes
Environment( organic debris, biofilms, medium)
Time of exposure
Microbial characteristics (acid-fast, endospores)
Bactericidal: Kills bacteria( 99.9% reduction)
Bacteriostatic: Inhibits reproduction (stationary phase)
Modes of Action
Alter membrane permebility
Damage proteins
Damage nucleic acids
Physical Methods of Microbial Control
Autoclave: moist heat; sterilization; bactericidal
Dry Heat: Flaming/incineration; bactericidal
Pasteurization
72 C for 15 sec
Kills pathogens, not sterilization
Thermoduric survivors: Streptococcus, Lactococcus
Filtration
For liquids/gases only
Filters: o.2 um(HEPA=0.3um)
Low temperature: Bacteriostatic
Listeria monocytogenes grows at cold temps-Listeriosis(dangerous in pregnancy)
Osmotic Pressure: Salt/sugar to preserve food
Radiation
Ionizing: (gamma, X-rays) destroys DNA
Non-ionizing:(UV light)- thymine dimers; poor penetration
History, Spectrum, & Safety
1910: Ehrlich-chemotherapy; Salvarsan for syphilis
1928: Fleming- Discovered Penicillin (penicillium notatum)
Selective Toxicity: Kill microbes, not host
Eukaryotic Pathogens: Harder to treat (Fungi, Protozoa, Helminths)
Drug Spectrum:
Broad spectrum: Fast treatment; destroys normal flora- superinfection
Narrow Spectrum: e.g.Penicilling G (Gram + only)
Gram-negative harder to treat (LPS + porins)
Effectiveness Tests:
Broth Boulton: MIC & MBC
Kirby-Bauer: Zone of inhibition
Dosage terms :
Therapeutic dose: Desired effect
Toxic dose: Harmful side effects
Therapeutic index: Toxic + Therapeutic
Resistance& Specific Agents
Antibiotic Resistance Mechanisms:
Enzymatic destruction
Blocked penetration
Altered Target
Drug efflux pump
Resistance Genes
on plasmids/transposon
Antibiotic Producers
Antifungals
Polyenes(amphotericin B)- nephrotoxic
Antivirals:
Neuraminidase inhibitors: Zanamivir, Oseltamivir
Nucleoside analogs: Zidovudine (HIV)), Acyclovir(Herpes)
Antiseptics/ Disinfectants
Bisphenols- Hexachlorophene-neurotoxin
TriclosanL Best vs Gram +
Iodine
Alchol base= antiseptic
Iodphors (betadine)- disinfectand/ surgical scrub
Quaternary Ammonium Compounds *Quats):Zephiran- acne meds
Norovirus
Disease: Gastroneteritis
Transmission-Fecal-oral route
Heat Resistance: survives up to 140F
Disinfection: 25 tbsp bleach/ 1 gallon water