Control of Microbial Growth

1. Control of Microbial Growth Chapter 7

2. History Humans vs. Microbes infections diseases plagues epidemics pandemics

4. Bubonic Plague or the Black Death Epidemic swept thru Europe in the Middle Ages (13th and 14th centuries) 40 million people were killed About 1/3 of the population of the continent Etiological agent: Yersinia pestis Gram (-) rod 2 Vectors Rat Flea

6. Bubonic Plague Infection 1. Flea bite with Yersinia pestis 2. Bacteria multiply in the bloodstream Bacteremia 3. Bacteria localize in lymph nodes, especially axillary and groin areas

8. Bubonic Plague Infection 5. If untreated, about 50 % Mortality Rate 6. If bacteria spread to the lungs, it becomes Pneumonic Plague and is now highly contagious (Almost a 99 % Mortality Rate)

11. Humans vs. Microbes 1. Most of History, microbes have been winning the battle 2. In the last 100 yrs or so the battle has swung in our favor Why? Because of our increasing knowledge of how to Control Microbial Growth

13. Methods to Control Microbial Growth 1. Physical 2. Chemical

14. Terms used: Sterilization vs. Disinfection Sterilization destroying all forms of life Disinfection destroying pathogens or unwanted organisms

15. Disinfectant vs. Antiseptic Disinfectant antimicrobial agent used on inanimate objects Antiseptic antimicrobial agent used on living tissue

16. cidal vs. static Bactericidal - kills bacteria Bacteristatic - inhibits bacterial growth Fungicidal Fungistatic Algacidal Algastatic

17. Factors that effect Antimicrobial Activity 1. Temp 2. Time 3. Concentration of Antimicrobial agent 4. Type of Microbe 5. Activity of Microbe 6. Presence of organic matter

18. Targets of Antimicrobial Agents 1. Cell membrane 2. Enzymes & Proteins 3. DNA & RNA

19. Physical Methods of Microbial Control 1. Heat works by denaturing enzymes and proteins A. Thermal Death Point (TDP) lowest temp. at which all microorganism in a liquid culture are killed in 10 minutes B. Thermal Death Time (TDT) minimum length of time in which all microorganisms in a liquid culture are killed at a given temperature

20. Moist Heat 1. Boiling Water kills vegetative bacterial cells, Fungi and many viruses not effective for endospores and some viruses Hepititis (20 min) Some spores may survive boiling water for up to 20 hrs

21. Moist Heat 2. Autoclave (Steam under pressure) preferred method of sterilization Water boils at 100 C Increasing the pressure raises the Temp. 15 lbs./ per sq. inch (psi) ------> 121 C 121 C for 15 min.

22. Kilit Ampule Spores of Bacillus stearothermophilus fermentable sugar pH indicator basic - red acid - yellow

23. Dry Heat 1. Direct Flaming Inoculating Loop and Needle 100% effective 2. Incineration disposable wastes (paper cups, bags, dressings) 3. Hot Air Sterilization Oven ( 170 C for 2 hours) used on substances that would be damaged by moist heat sterilization gauzes, dressings or powders

24. Filtration Removes microorganisms from solutions that might be damaged by heat culture media enzymes vaccines antibiotics

25. Radiation 1. Ionizing Radiation gamma rays & x-rays penetrates most substances Used on substances that could be damaged by heat plastic petri dishes plastic syringes catheters surgical gloves

26. Radiation 2. Non-Ionizing Radiation UV Light does not penetrate plastic, glass or proteinaceous matter Used to reduce microbial populations hospital rooms nurseries operating rooms

27. Pasteurization Disinfection - not sterilization (removes unwanted organisms) Mycobacterium tuberculosis 63 C for 30 minutes 72 C for 15 seconds (HTST) Thermodurics able to survive high temps.

28. Methods used to control Microbial Growth 1. Heat Moist Heat Boiling Water Steam Heat (Autoclave) Dry Heat Direct Flaming Incineration Hot Air Sterilization (Oven) 2. Filtration 3. Radiation Ionizing Radiation Non-Ionizing Radiation 4. Pasteurization (Heat)