1. Control of Microbial Growth

2. A few terms Bacteriostatic: inhibits bacterial growth Bactericidal: something capable of killing bacteria Antiseptic: an agent that is used to inhibit/kill bacterial growth on skin and mucus membranes Disinfectant: an agent that is used to inhibit/kill bacterial growth on inanimate objects

3. History behind microbial control Joseph Lister was the first to introduce the use of carbolic acid to reduce bacterial infections in hospitals (1860s) Ignatz Semmelweis regarded as the “Father of Infection Control”, physicians used chlorinated lime to cleanse hands (1850s)

4. What factors influence the success of microbial control? What type of organism are you targeting? What type of environment are you treating?

5. Are all microbes equally sensitive?

6. What parts of a bacterial cell are sensitive to physical treatments and chemicals? Plasma membrane DNA and proteins

7. Physical Methods

8. Heat –Dry: kills by oxidation, ex: incineration –Moist: promotes coagulation of proteins Boiling (100 o C) Autoclave(121 o C, 15lbs/sq inch) Pasteurization –Classic-63 o C for 30 minutes –HTST-72 o C for 15 seconds –UHT-140 o C for 3 seconds

9. Autoclave

10. Autoclaves work due to steam under pressure

11. Indicators used in autoclaving

12. What if the substance is heat sensitive? Filtration is the best choice Pore sizes can be either.45um or.22um

13. Physical Methods Low temperature: freezing does not kill bacteria, most cultures are stored at -80 o C Dessication: remove the water and bacteria can remain viable

14. Physical Methods Radiation –Ionizing radiation (gamma rays, x-rays) –Non-ionizing radiation (uv rays) –Microwaves

15. Electromagnetic Spectrum

16. Chemical Methods Most are only able to reduce the numbers of organisms, not achieve sterility Types of chemicals –Phenol and phenolics –Halogens –Alcohols –Heavy metals –Soaps –Quaternary Ammonium compounds –Biguanides

17. Evaluation of chemicals: disc diffusion method

18. Chemical Control

19. Chemical structure of phenols/phenolics

20. Chemical Control Phenols and phenolics –Destroy cytoplasmic membranes and denature proteins –Kill most vegetative bacteria and in higher concentrations kill Mycobacterium tuberculosis –Reasonable cost to use, effective in presence of organics

21. Chemical control Halogens 1. Iodine (binds to tyrosine, alters cell membranes) Tincture Iodophore Target: all bacteria, fungi, most endospores, and some viruses -Are all organisms killed by iodine??? 2. Chlorine (strong oxidizing agent) Target: all types of microbes and viruses

22. Chemical Control Alcohols –Mechanism of action is protein denaturation, can also dissolve lipids –Most common are ethanol and isopropanol Target: kill vegetative cells and fungi, do not kill endospores and some naked viruses

23. Chemical control Heavy metals exert oligodynamic action Silver, copper and mercury

24. Chemical control Surfactants (soaps) –Little value as an antiseptic –Acid-anionic surface-active sanitizers are important in cleaning of dairy equipment and utensils

25. Chemical control Quaternary Ammonium Compounds (Quats) –Group of positively charged detergents Action: react with the cell membrane Target: kill many vegetative bacteria and enveloped viruses, do NOT kill endospores, Mycobacteria, or naked viruses

26. Chemical control –Biguanides (chlorhexidine) Used in antiseptic products Adheres to skin and mucus membranes, low toxicity Action: membrane disruption Target: wide range of bacteria, fungi, and some enveloped viruses

27. Which antiseptic works the best?