Chapter 9 Control of Microbial Growth

1. Chapter 9 Control of Microbial Growth

2. IgnazSemmelweis and Joseph Lister developed the first microbial control methods. • Mid 1800s • Before aseptic surgical techniques ~10% of all deaths were due to nosocomial infections • Delivering mothers as high as 25% death rate • During the American Civil War, a surgeon may have cleaned his scalpel by wiping it on his boot sole between incisions.

3. The Terminology of Microbial Control • Sepsis refers to microbial contamination • Asepsis is the absence of significant contamination • Aseptic surgery techniques prevent microbial contamination of wounds

4. The Terminology of Microbial Control • Sterilization: • Disinfection: • Antisepsis:

5. Effectiveness of Microbial Treatment • Depends on: • The more you start with the longer it takes to eliminate • Organic matter (vomit or blood) inhibit certain chemicals • Biofilms cells are protected by polysaccharide matrix • Temperature disinfectants work better under warm conditions • Chemical often requires extended exposure to microbes • Spray, wipe, re-spray • Endospores and Gram negatives are more resistant

6. Microbial Characteristics and Microbial Control • Gram negative more resistant than Gram positive • Pseudomonas highly resistant to biocides • Outer membrane provides protection • Porins are highly selective of molecules that they permit into the cell • Mycobacterium tuberculosis • Mycolic acid • Waxy lipid component in cell wall resists effect of chemicals

8. Microbial Characteristics and Microbial Control • Prions: infectious proteins known to be heat and protease resistant • Autoclave in sodium hydroxide to destroy • Or incineration

9. Figure 7.11 Decreasing order of resistance of microorganisms to chemical biocides.

10. Actions of Microbial Control Agents • Damage results in cell contents to leak from cell • Little bags of enzymes- enzymes are folded proteins unfolding due to chemical treatments makes enzymes not function • Heat, radiation, or chemicals are lethal to cells

11. Physical Methods of Microbial Control

12. Temperature: Heat Sterilization • Moist heat denatures proteins • Heat preserved canned foods, most common method of food preservation • Autoclave: steam under pressure • 15 pounds of pressure per square inch • 121 degrees C • Use: glassware, media, intravenous equipment….

13. Temperature: Dry Heat Sterilization • Kills by oxidation

14. Temperature: Pasteurization • Reduces spoilage organisms and pathogens • High-temperature short-time: • Ultra-high-temperature:

15. Temperature: Low • Low temperature inhibits microbial growth

16. Filtration • HEPA removes microbes • Membrane filtration (liquids) removes • Viruses • Influenza virus: ~ • Rhinovirus common cold:

17. Figure 7.4 Filter sterilization with a disposable, presterilized plastic unit. Flask of sample Cap Membrane filter Cotton plug in vacuum line ensures sterility Sterile filtrate Vacuum line

18. Radiation • Ionizing radiation (X rays, gamma rays) • Damages DNA • Low level radiation approved for use in US on spices, meats, and vegetables • Disposable dental and medical supplies such as plastic syringes and surgical gloves • Postal service uses electron beams to sterilize certain classes of mail • Nonionizing radiation (Ultra Violet) • Damages DNA • Does not penetrate only good for surface applications • Microwaves kill by heat; not especially antimicrobial

19. Figure 9.11 Irradiated and non-irradiated food Non-irradiated Irradiated

20. Chemical methods of microbial control

21. Chemical Disinfection • No single disinfectant is appropriate for all circumstances! • See Lab 26 for clinically important Disinfectants • Affect microbes’ cell walls, cytoplasmic membranes, proteins, or DNA • The chemical compounds are not to be used to treat disease only for controlling growth and preventing disease

22. Chemical Methods of Microbial Control Antimicrobial Soap: To much of a good thing? Page 281 Development of Resistant Microbes Little evidence that products containing antiseptic and disinfecting chemicals add to human or animal health Use of such products promotes development of resistant microbes Use of antimicrobial soaps should be limited to food handlers, caring for newborns, and caring for high-risk patients (immunocompromised) CDC recommends using regular soap and washing with warm water for at least 10-15 seconds

23. Chemical Methods of Microbial Control Development of Resistant Microbes Little evidence that products containing antiseptic and disinfecting chemicals add to human or animal health Use of such products promotes development of resistant microbes Triclosan

24. Bisphenols • Triclosan • Disrupt plasma membranes • Active ingredient in antimicrobial soaps, toothpaste, deodorants • Incorporated into cutting boards and knife handles • Widespread use has resulted in reports of resistance