Download
1 / 27
270 likes | 320 Views
Explore the methods and terminology involved in controlling microbial growth, including physical, chemical, and biological approaches. Learn about factors influencing effectiveness, such as microbial populations, environmental influences, and time exposure. Discover various control methods like sterilization, disinfection, antisepsis, and more. Gain insights into the importance of prevention and different types of disinfectants used. Enhance your knowledge of biocides, germicides, bacteriostasis, and asepsis for optimal microbial control.
E N D
Control of microbial growth Some terms to start with.
terms • Biocide: kills biologicals • Germicide: Kills bacteria • Bacteriostasis: stops growth • Asepsis: absence of growth
Some terms. • Sterilization: destruction of all life • Disinfecting: destruction of vegetative pathogens • Antisepsis: disinfection of living tissue • Sepsis: refers to microbial contamination. • Aseptic surgery techniques prevent microbial contamination of wounds.
Factors that influence effectiveness • Number of microbes • Environmental influences • Time exposure • Microbial characteristics
Bacterial populations die at a constant logarithmic rate. Figure 7.1a
Methods of Control • Physical • Chemical • Biological • Why is prevention best?
Physical Controls: • Not for use on living organisms • Somehow, alter membrane permeability and / or structure of proteins and nucleic acids
The autoclave: Moist heat and pressure • 15psi, 121’c, 15 minutes • Thermal death point (TDP): Lowest temperature at which all cells in a culture are killed in 10 min. • Thermal death time (TDT): Time to kill all cells in a culture • Decimal reduction time (DRT): Minutes to kill 90% of a population at a given temperature
Other controls • Heat, dry heat takes longer • Low temperature • Desiccation • Osmotic Pressure • Radiation • Ionizing • No ionizing (UV)
Radiation damages DNA • Ionizing radiation (X rays, gamma rays, electron beams) • Nonionizing radiation (UV) • (Microwaves kill by heat; not especially antimicrobial)
Chemical Methods of Control • May be used on living organisms • Factors that may effect disinfecting • Concentration of the disinfectant • What is to be disinfected • pH • Organic materials • Contact with microbe • time
Testing • Use dilution test • Three microbes are used Salmonella choleraesuis Staphylococcus aureus Pseudomonas aeruginosa • Metal carriers dipped and dried • Standard conditions 10 min at 20’C
Types of disinfectants • Phenol and Phenolics • Halogens (iodine, chlorine) bind to aa of enzymes • Betadine iodophor (iodine bound to organic molecules)
Types of Disinfectants • Phenol • Phenolics. Lysol • Bisphenols. Hexachlorophene, Triclosan • Disrupt plasma membranes Figure 7.7
Alcohol’s usually by protein denaturizing • Heavy metals • Oligodynamic action • Denature proteins
Surface active Agents (detergents) Soap Degerming Acid-anionic detergents Sanitizing Quarternary ammonium compoundsCationic detergents Bactericidal, Denature proteins, disrupt plasma membrane • Antibiotics • Worry about resistance • Not many used as preservative (Nisin, Natamycin)
Gaseous Chemostaerilizers • Ethylene oxide denatures proteins • Resistance to these methods depends on the microbe.
Types of Disinfectants • Peroxygens • Oxidizing agents • O3, H2O2, peracetic acid
Types of Disinfectants • Aldehydes • Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH) • Glutaraldehyde, formaldehyde
Types of Disinfectants • Chemical Food Preservatives • Organic Acids • Inhibit metabolism • Sorbic acid, benzoic acid, calcium propionate • Control molds and bacteria in foods and cosmetics • Nitrite prevents endospore germination • Antibiotics. Nisin and natamycin prevent spoilage of cheese
