13 microbial control

13 microbial control - CEE 266 ENVIRONMENTAL BIOTECHNOLOGY...

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Unformatted text preview: CEE 266 ENVIRONMENTAL BIOTECHNOLOGY Lecture 13 (Microbial Growth Control) Heat Sterilization   Sterilization   The killing or removal of all viable organisms within a growth medium   Inhibition   Effectively limiting microbial growth   Decontamination   The treatment of an object to make it safe to handle   Disinfection   Directly targets the removal of all pathogens, not necessarily all microbes Heat Sterilization  Heat sterilization is the most widely used method of controlling microbial growth   High temperatures denature macromolecules   Amount of time required to reduce viability tenfold is called the decimal reduction time  Some bacteria produce resistant cells called endospores   Can survive heat that would rapidly kill vegetative cells Heat Sterilization   The autoclave is a sealed heating device that uses steam under pressure   Allows temperature of water to get above 100°C   Not the pressure in an autoclave that kills things, but the high temperature   Pasteurization is the process of using precisely controlled heat to reduce the microbial load in heatsensitive liquids   Doesn’t kill all organisms so it is different than sterilization The Effect of Temperature Over Time on Bacterial Viability Figure 27.1 Radiation Sterilization   Microwaves, UV, X-rays, gamma rays, and electrons can all reduce microbial growth   UV has sufficient energy to cause modifications and breaks in DNA   UV is useful in decontamination of surfaces   Cannot penetrate solid, or light-absorbing surfaces   Radiation is approved by the WHO and is used in the USA for decontamination of foods particularly susceptible to microbial contamination Radiation Sterilization   Ionizing Radiation   Electromagnetic radiation of sufficient energy to produce ions and other reactive molecular species   Generates electrons, hydroxyl radicals, and hydride radicals   Some microbes are more resistant to radiation than others   Microbes tend to be more radiation resistant than multicellular organisms   Sources of radiation include cathode ray tubes, X-rays, and radioactive nuclides Filter Sterilization   Filtration avoids the use of heat for sterilization of sensitive liquids and gases   Pores of filter are too small for organisms to pass through   Pores are large enough to allow liquid or gas to pass through   Depth Filters   HEPA filters   Membrane Filters   Function more like a sieve (i.e., Nucleopore filters) Chemicals for Microbial Control •  SOAP! •  Chlorine •  Ozone •  Peroxide •  Silver compounds •  Ethanol •  Phenol •  Quarternary Ammonium •  Pesticides •  Antibiotics Figure 27.9 Antimicrobial Susceptibility Assay by Dilution Methods Minimum inhibitory concentration (MIC) is the smallest amount of an agent needed to inhibit microbial growth Figure 27.10 Naturally Occurring Antimicrobial Drugs: Antibiotics   Antibiotics are naturally produced antimicrobial agents   Less than 1% of known antibiotics are clinically useful   Can be modified to enhance efficacy (semisynthetic)   The susceptibility of microbes to different antibiotics varies greatly   Gram-positive and gram-negative bacteria vary in their sensitivity to antibiotics such as penicillin   Broad-spectrum antibiotics are effective against both groups of bacteria Antibiotics: Isolation and Characterization   Cross-Streak Method   Used to test new microbial isolates for antibiotic production   Most isolates produce known antibiotics   Most antibiotics fail toxicity and therapeutic tests in animals   Time and cost of developing a new antibiotic is approximately 15 years and 1 billion dollars   Involves clinical trials and U.S. FDA approval   Antibiotic purification and extraction often involves elaborate methods Isolation and Screening of Antibiotic Producers Measuring Antimicrobial Activity Figure 27.11 Modes of Action of Antibiotics Figure 27.12 Antimicrobial Drug Resistance Microbes may be naturally resistant to certain antibiotics!   lack structure the antibiotic inhibits   impermeable to antibiotic   can inactivate the antibiotic   may modify the target of the antibiotic   may develop a resistant biochemical pathway   may be able to pump out the antibiotic (efflux)   Antimicrobial drug resistance   The acquired ability of a microbe to resist the effects of a chemotherapeutic agent to which it is normally sensitive Antimicrobial Drug Resistance  Almost all pathogenic microbes have acquired resistance to some chemotherapeutic agents   A few pathogens have developed resistance to all known antimicrobial agents   Methicillin-resistant S. aureus (MRSA)   Resistance can be minimized by using antibiotics correctly and only when needed   Resistance to a certain antibiotic can be lost if antibiotic is not used for several years Antibiotic Resistance Antibiotic Method of resistance Chloramphenicol reduced uptake into cell Tetracycline active efflux from the cell β-lactams, Erythromycin, Lincomycin eliminates or reduces binding of antibiotic to cell target β-lactams, Aminoglycosides, Chloramphenicol enzymatic cleavage or modification to inactivate antibiotic molecule Sulfonamides, Trimethoprim metabolic bypass of inhibited reaction Sulfonamides, Trimethoprim overproduction of antibiotic target (titration) Antibiotic Resistance Propagation Antibiotic Resistance Propagation 1.  Release of antibiotic-resistance genetic elements from survivors of antibiotic exposure 2.  Uptake into cell cytoplasm of the resistance-conferring genetic elements (plasmids, viruses, vectors) 3.  Intracellular incorporation of the small multidrug-resistance cassettes into larger replicating elements such as plasmids . 4.  Dissemination of the resistance-encoding DNA back to microbial communities that constitute the antibiotic-resistant gene pool. 5.  Always administer antibiotics at a dosage and for a period of time that eliminates the pathogens. Patterns of Drug Resistance in Pathogens Figure 27.28 The Appearance of Antimicrobial Drug Resistance Figure 27.29 ...
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This note was uploaded on 02/02/2012 for the course CEE 266 taught by Professor Shailymahendra during the Fall '11 term at UCLA.

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