1. Controlling Microbes Not Too Hot to Handle 11

2. Looking Ahead On completing this chapter, you should be able to: Summarize factors that influence the effectiveness of agents used for microbial control Explain some of the physical methods of control used to achieve sterilization and destroy all forms of microbes Compare the chemical methods of microbial control to the physical methods with respect to the anticipated objectives Identify some of the important chemical agents used to slow the growth of microbes on skin and on objects

3. Looking Ahead On completing this chapter, you should be able to: Explore the advantages and disadvantages of using antibiotics to control microbes in the body Identify some of the important antibiotics used to treat disease and indicate how these drugs achieve their antimicrobial activity Discuss the problem of antibiotic resistance with reference to its cause and implications

4. Physical Methods of Control Heat is a great sterilizing agent Boiling cannot inactivate spores Radiation is a great sterilizing agent Deinococcus radiodurans resists high levels of radiation, too, though!

5. Physical Methods of Control Heat methods –Denature and inactivate proteins –Drive off necessary water –100 °C steam from boiling water (moist heat) Cannot inactivate spores –Pressure Autoclave 15 psi Allows higher water and steam temperatures 121 °C steam now capable of inactivating spores

6. Physical Methods of Control

7. Heat methods Pasteurization 62.9 °C for 30 minutes (hold method) 71.6 °C for 15 to 30 seconds (flash method) 82 °C for 3 seconds (ultraflash method) Used to kill pathogens in milk, wine, fruit juice Does not inactivate spores Protects against Mycobacterium tuberculosis, Coxiella burnetii

8. Physical Methods of Control Heat methods Dry heat 160 to 170 °C for at least 2 hours Oxidation of proteins Necessary for materials that cannot be autoclaved or pasteurized

9. Physical Methods of Control: Heat

10. Physical Methods of Control Radiation Ionizing radiation X rays Gamma rays About 10,000 times more energetic than UV light Sterilizing Creation of oxygen and hydroxyl free radicals that inactivate proteins and DNA

11. Physical Methods of Control Radiation Electron Beams Room Temperature Treatment Can pass through packaging to sterilize contents Ultraviolet radiation Results in mutations Effective against spores, since no repair mechanism

12. Physical Methods of Control Drying Also known as desiccation Water required for microbes to survive Removal prevents many enzymatic processes Not effective to inactivate spores Effective for storage of Cereals Grains Other foodstuffs normally stored in pantries

13. Physical Methods of Control Drying Lyophilization Osmotic drying Salt Sugar Spices

14. Physical Methods of Control Filtration and refrigeration Filtration Heat-sensitive solution passed through filter Pores in filter prevent passage of microbes Pores can be chosen based on size of microbe 0.2  m to 0.5  m pores prevent passage of many bacteria Does not prevent passage of viruses Solution is not truly sterilized

15. Physical Methods of Control Filtration and refrigeration Refrigeration Slows down enzymatic reactions Only slows microbial growth Refrigerated foods are not sterile

16. Chemical Methods of Control Disinfection and antisepsis Practiced for thousands of years Medicinal chemistry started in the 1800s 1860s: Joseph Lister Principles of antisepsis in surgery Diminished incidence of common infections that occurred during surgery

17. Chemical Methods of Control General principles Disinfectants Kill microbes on inanimate objects Antiseptics Kill microbes on body surfaces Ideal agent Soluble in water Kills all microbes and inactivate infectious agents Stable over time Nontoxic to humans and animals

18. Chemical Methods of Control General principles Ideal agent (cont’d) Uniform composition Combine with organic matter other than microbes Highest efficacy at room or body temperature Efficiently penetrate surfaces Not corrode or rust metals Not damage or stain fabrics Readily available in useful quantities Cost effective

19. Chemical Methods of Control Alcohols and aldehydes Alcohols 70% ethyl alcohol (ethanol) Isopropyl alcohol (isopropanol) Aldehydes Formaldehyde (formalin) Glutaraldehyde

20. Chemical Methods of Control Halogens and heavy metals Halogens Iodine Tincture (2% iodine in ethanol) Iodophor (iodine plus detergent) Betadine® Wescodyne® Chlorine 5% sodium hypocholorite (bleach)

21. Chemical Methods of Control Halogens and heavy metals Heavy metals Silver (as silver nitrate) Mercury (as Merchurochrome®, Merthiolate®, or thimerosal) Copper Copper sulfate Bordeaux mixture (copper sulfate with lime)

22. Chemical Methods of Control Phenols and detergents Phenols Also known as phenolics Ortho-phenylphelnol Hexylresorcinol Hexachlorophene Chlorhexidine Trichlosan Detergents Strong wetting agents Surface tension reducers Dissolves microbial cell membranes

23. Chemical Methods of Control: Phenolics

24. Chemical Methods of Control Ethylene oxide Small molecule Great penetration capacity (gas) Sporicidal Highly toxic Explosive Chemical counterpart of autoclave

25. Antibiotics

26. The first antibacterials Paul Ehrlich Magic bullets Harm bacterial pathogens and not host Arsphenamine Firs syphilis treatment Contains arsenic Gerhard Domagk Prontosil Active ingredient: sulfonilamide

27. Antibiotics: Sulfonilamide

28. Antibiotics The development of penicillin Alexander Fleming Penicillium mold on Staphylococcus plates Clearings where mold was growing Howard Florey and Ernst Chain Industrial production of penicillin Helped fight infections during World War II © Science Source, photo by Dean Pausett/Photo Researchers, Inc. © National Library of Medicine

29. Antibiotics Penicillins Beta lactam core Primarily active against Gram-positive bacteria Block formation of peptidoglycan in cell wall Penicillinase Improved penicillins Penicillin G Amoxicillin Ampicillin Methicillin Carbenicillin Ticarcillin

30. Antibiotics: Penicillins

31. Antibiotics Cephalosporins and aminoglycosides Cephalosporins Like penicillins, contain beta lactam core Produced by Cephalosporium 6-membered ring, as opposed to penicillins’ 5- membered ring Cephalexin ( trade name Keflex) Cephalothin (Keflin) Cefotaxime (Claforan®) Ceftriaxone (Rocephin®) Ceftaxidime (Fortaz®)

32. Antibiotics Cephalosporins and aminoglycosides Aminoglycosides Useful against Gram-negative bacteria Streptomycin Major early weapon against tuberculosis Now most Mycobacterium tuberculosis is resistant Most produced by Streptomyces Inhibit protein synthesis Gentamicin Neomycin

33. Antibiotics Broad-spectrum antibiotics Inhibit or kill many different microbes First one discovered: chloramphenicol Extremely toxic Still used in dire situations Tetracyclines Minocycline Doxycycline Used especially for Gram-negative infections Few side effects Resistance Fungal superinfection Light sensitivity Deposition in teeth

34. Antibiotics Broad-spectrum antibiotics Tetracyclines (cont’d) Few side effects Resistance Fungal superinfection Light sensitivity Deposition in teeth

35. Antibiotics Other antibiotics Macrolides Inhibit protein synthesis Erythromycin Azithromycin (Zithromax ®) Clarithromycin (Biaxin®) Vancomycin Inhibits cell wall synthesis in Gram-positive bacteria Severe side effects Streptogramins Quinupristin + dalfopristin (Synercid®)

36. Antibiotics Other antibiotics Rifampin Inhibits RNA polymerase Synthetic First used against M. tuberculosis Useful against Neisseria, Haemophilus Bacillus-produced antibiotics Only used topically because of toxicity Bacitracin Inhibits cell wall synthesis Effective against Gram-positive bacteria

37. Antibiotics Other antibiotics Bacillus-produced antibiotics (cont’d) Polymyxin B Inhibits outer membranes Effective against Gram-negative bacteria

38. Antibiotics Antiviral and antifungal antibiotics Antiviral chemicals NOT antibiotics Amantadine Acyclovir Antifungal antibiotics Nystatin Useful against Candida albicans Reacts with sterols specifically present in fungal membranes Griseofulvin Ringworm

39. Antibiotics Antiviral and antifungal antibiotics Antifungal antibiotics (cont’d) Amphotericin B (Fungizone®) Fungal infections of internal organs Imidazoles Clotrimazole (Lotrimin®) Miconazole (Monistat®)

40. Antibiotics Antibiotic resistance Spreading through bacterial populations Bacterial pneumonia Streptococcal blood disease Gonorrhea Staphylococcal infections Tuberculosis Means of resistance Destruction of antibiotic Prevention of uptake Alteration of metabolic pathway Mutation that prevents antibiotic binding or efficacy

41. Antibiotics Antibiotic resistance Overuse of antibiotics Overdose of antibiotics Abuse in developing countries Use in animal feeds Resistance gene transfers from one bacterium to another Shigella Salmonella Staphylococcus

42. Antibiotics Antibiotic resistance Alternatives to reduce resistance or increase efficacy New antibiotics Limited antibiotic use Phage therapy