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. Physical Methods • Heat • Dry: kills by oxidation, ex: incineration • Moist: promotes coagulation of proteins • Boiling (100oC) • Autoclave(121oC, 15lbs/sq inch) • Pasteurization • Classic-63oC for 30 minutes • HTST-72oC for 15 seconds • UHT-140oC 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 -80oC • 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 structure of phenols/phenolics

19. 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

20. 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

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

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

23. 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

24. 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

25. Which antiseptic works the best?