Control of microbial growth

1. Control of microbial growth Some terms to start with.

2. terms • Biocide: kills biologicals • Germicide: Kills bacteria • Bacteriostasis: stops growth • Asepsis: absence of growth

3. 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.

4. Factors that influence effectiveness • Number of microbes • Environmental influences • Time exposure • Microbial characteristics

5. Bacterial populations die at a constant logarithmic rate. Figure 7.1a

6. Methods of Control • Physical • Chemical • Biological • Why is prevention best?

7. Physical Controls: • Not for use on living organisms • Somehow, alter membrane permeability and / or structure of proteins and nucleic acids

8. 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

11. Other controls • Heat, dry heat takes longer • Low temperature • Desiccation • Osmotic Pressure • Radiation • Ionizing • No ionizing (UV)

12. Radiation damages DNA • Ionizing radiation (X rays, gamma rays, electron beams) • Nonionizing radiation (UV) • (Microwaves kill by heat; not especially antimicrobial)

13. Filtration Removes Microbes

15. 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

16. 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

17. Disk Diffusion Method

18. Types of disinfectants • Phenol and Phenolics • Halogens (iodine, chlorine) bind to aa of enzymes • Betadine iodophor (iodine bound to organic molecules)

19. Types of Disinfectants • Phenol • Phenolics. Lysol • Bisphenols. Hexachlorophene, Triclosan • Disrupt plasma membranes Figure 7.7

20. Alcohol’s usually by protein denaturizing • Heavy metals • Oligodynamic action • Denature proteins

21. 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)

22. Gaseous Chemostaerilizers • Ethylene oxide denatures proteins • Resistance to these methods depends on the microbe.

24. Types of Disinfectants • Peroxygens • Oxidizing agents • O3, H2O2, peracetic acid

25. Types of Disinfectants • Aldehydes • Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH) • Glutaraldehyde, formaldehyde

26. 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

27. Resistance to chemical Biocides