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Control of Microbial Growth

Control of Microbial Growth. Tim Ho University of Alberta, Canada * The materials are mostly based on Dr. Brian Lanoil’s Microb 265. Part I. Objectives. Physical agents Mechanical removal methods Chemical agents. Know 3 methods of microbial control

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Control of Microbial Growth

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  1. Control of Microbial Growth Tim Ho University of Alberta, Canada * The materials are mostly based on Dr. Brian Lanoil’s Microb 265 Part I tim3@ualberta.ca

  2. Objectives • Physical agents • Mechanical removal methods • Chemical agents tim3@ualberta.ca Know 3 methods of microbial control Know the strategies on how drugs control the growth of microorganisms. Understand how do bacteria become resistant to antibiotics.

  3. Terminology of Microbial Control • Sterilization: • The complete destruction or removal of all viable organisms, except bacteria endospores, from an environment. • - Autoclave or high energy ionizing radiation (x ray, gamma) • Disinfection: • Killing, inhibition, or removal of viable microorganisms from inanimate objects. • - Phenolics, boiling water, UV irradiation tim3@ualberta.ca • Sanitization: • Reduction of microbial population to a safe level. • - Soaps • Antisepsis: • Prevention of infection of host tissue. • - Iodine, ethanol

  4. 6 Factors that Affect Antimicrobial Activities Exposure (time): longer exposure lead more organisms get kill Temperature: Higher temperature usually increases effectiveness in killing Environment: Environmental factors play an important role in affecting effectiveness of antimicrobial agents pH, humidity, concentration of organic matter tim3@ualberta.ca • Population size: • larger populations require longer time to kill • Population composition: • different microorganisms have different range of sensitivity to antimicrobial agents • G- bacteria vs. G+ bacteria • Concentration of antimicrobial agent: • higher concentrations of agents have greater efficient in killing microorganisms

  5. D value • Time at which kill 90% of • the original population • - Applies to all methods • Z value • Increase in temperature • needed to reduce the original • D value by one log (90%) tim3@ualberta.ca 20 5 Z value of (i) = 89-75, or 14 degree Z value of (ii) = 95-85, or 10 degree Decimal reduction time (D)

  6. 3 Methods of Microbial Control Moist heat is more effective than dry heat • 15 min. at 2 atm at 121°C • Effective against vegetative and endospore cell • Serilize glassware tim3@ualberta.ca The temperature of 100 °C is effective against vegetative cells and eukaryotic spores • Twice boiling • First boiling: kill vegetative cells, but not spores • Remaining spores germinate to form new vegetative cells after incubation • Second boiling: kill remaining vegetative cells -> nearly sterilized • - 15 sec. at 71°C • Used for heat-sensitive materials eg. Wine, and milk • Not effective against gram positive pathogens due to endospores

  7. 3 Methods of Microbial Control • Sterilization • Produce oxygen radicals that react with DNA • Disinfection (surface sterilization only) • Thiamine dimer formation • Works best near 260 nm to destroy pyrimidine bases tim3@ualberta.ca Corrin, N. Damage to DNA from Toxins. Washngton: Nicholas Corrin. 2012 Jul. [Cited 2013 Dec 22]. Available from: http://radiation-remedies.com/inflammation-and-double-break-dna-rupture/why2/

  8. 3 Methods of Microbial Control • Remove (but not kill) microorganisms from serum containing media • Membrane filters can remove most bacteria but not viruses tim3@ualberta.ca • Remove microorganisms in laminar flow biological safety cabinets and clean rooms Figure. HEPA filter eliminates over 99% of microorgansims and allergens. Image: CleanCraft Products, Inc.

  9. 3 Methods of Microbial Control eg. Ethylene oxide, Vapor-phase hydrogen peroxide To kill or inhibit microorganisms within host tissue tim3@ualberta.ca • Antibiotics • Antifungals • Antivirals 9 1 More information about chemotherapy can be found in Control of Microbial Growth – Part II.

  10. Phenolics • - denature parteins • - target sites: cell wall and membrane • - used as disinfectants • Alcohols • - denature proteins; do not kill endospores • - target sites: membrane • - used as disinfecants and antiseptics tim3@ualberta.ca • Heavy metals (mercury, silver) • - inactivate proteins • - target sites: ribosomes • - used as antiseptics • Halogens (Cl2 and I2) • - oxidize cell constituents • - target sites: ribosomes • - used as disinfectants and antiseptics 10

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