Lesson 3 Control of Microbial Growth

1. Lesson 3Control of Microbial Growth September 10, 2014

2. Reproduction in Prokaryotes • Binary fission—asexual reproduction by a separation of the body into two new bodies • DNA replication • Cytokinesis—splitting of the cell • Budding—asexual reproduction in which a new individual develops from some generative anatomical point of the parent organism • Yeasts (Candida albicans and Cryptococcus neoformans)

3. Figure 6.12a Binary fission in bacteria. Cell wall Cell elongates and DNA is replicated. Plasma membrane Cell wall and plasma membrane begin to constrict. DNA (nucleoid) Cross-wall forms, completely separating the two DNA copies. FtsZ protein Cells separate. (a) A diagram of the sequence of cell division

4. Budding YEAST AND FUNGI

5. Phases of Bacterial Growth • Bacteria have four distinctive growth phases • Lag—intense activity preparing for population growth but has little to no increase in population • Log—(logarithmic growth) period of growth where cellular reproduction is most active • Stationary—growth rate slows. Number of bacterial death balances the number of new cells. Population stabilizes • Death—number of deaths exceeds the number of new cells formed. Population can die out entirely

6. Figure 6.15 Understanding the Bacterial Growth Curve. Death Phase Population Is decreasing at a logarithmic rate. Lag Phase Intense activity preparing for population growth, but no increase in population. Log Phase Logarithmic, or exponential, increase in population. Stationary Phase Period of equilibrium; microbial deaths balance production of new cells. The logarithmic growth in the log phase is due to reproduction by binary fission (bacteria) or mitosis (yeast). Staphylococcus spp.

7. Question • If a culture of mesophilic bacteria were placed in a refrigerator, what phase of growth would it be in? Incubator (set at 37 degrees)?

8. Terminology of Microbial Control • Sepsis refers to microbial contamination of the body • Septic shock occurs when the body responds to pathogen/toxin contaminating the blood • SIRS—Systemic Inflammatory Response Syndrome • Not specific to infection (burns, pancreatitis, trauma) • Asepsis is the absence of significant contamination • Aseptic surgery techniques prevent microbial contamination of wounds

9. The Terminology of Microbial Control • Sterilization: removing ALL microbial life • Eradicates microbes AND their endospores • Any agent used to sterilized is a sterilant • Steam and pressure (autoclave) • Commercial sterilization: • How do you think can goods are sterilized? • Heated enough to kill C. botulinum endospores • Other thermophilic endospores still persist

10. The Terminology of Microbial Control • Disinfection: destruction of vegetative (growing) pathogens • Endospores still persist • Can be mechanical or chemical • Chemicals, UV radiation, boiling water, and steam • Usually refers to inanimate objects. • Antisepsis: the removal of pathogens from living tissue

11. The Terminology of Microbial Control • Degerming: refers to the removal of microbes from a limited area • Alcohol swabbing before an injection • Mechanical and chemical • Server wiping down table at a restaurant • Sanitization is the practice of lowering microbial counts on public eateries • High-temperature dishwashing and dipping drinking glasses in chemical disinfectant

12. Hotel Room Sanitation?!?! • http://www.youtube.com/watch?v=kLssaWxipN8

13. Names of treatments that cause death of a microbe end in the suffix –cide • Biocide/germicide is the generic name for killing microbes • Bactericide • Fungicide • Virucide • Names of treatments that only stop microbial growth end in the suffix –static/stasis • Once the bacteriostatic agent is removed, growth resumes

14. Factors that affect the efficacy of Antimicrobial Treatments • Number of microbes. More microbes; longer it takes to kill them • Environmental influences. • Time of exposure. Chemical antimicrobials require extended time to function to affect more resistant microbes • Microbial characteristics. Features of the microbe itself determine the effectiveness of antimicrobial agent (constituents of membrane, enzymes, endospores, etc.)

15. Rate of Microbial Death • Bacterial populations usually die at a constant rate. • Different antimicrobial agents have varying microbial death rates • If an antimicrobial agent “x” kills 90% of a microbial population in 1 minute. It will subsequently kill the same amount each additional minute

16. Table 7.2 Microbial Exponential Death Rate: An Example

17. Actions of Microbial Control Agentson Microbes • Microbial agents primarily affect microorganisms via three mechanisms • Alteration of membrane permeability • Plasma membrane is the target of many microbial agents • Damage to ribosomes and/or proteins • Denaturing proteins or abrogating its production results in the inability to carry out metabolic reactions • Damage to nucleic acids • DNA/RNA carry information for replication/metabolism • http://www.ncbi.nlm.nih.gov/books/NBK7986/

18. Control of Microbial Growth • There are two means of controlling microbial growth • Physical • Chemical

19. Physical Methods • Heat • Filtration • Low Temperatures • High Pressure • Dessication • Osmotic Pressure • Radiation

20. Heat • Heat kills microorganisms by inactivating their enzymes • Heat resistance varies among different microbes • Thermal death point (TDP): lowest temperature at which all cells in a culture are killed in 10 min • Thermal death time (TDT): time during which all cells in a culture are killed

21. Moist Heat Sterilization • Moist heat kills microbes by denaturing proteins • Boiling kills vegetative forms of bacteria, most viruses, fungi and their spores in 10’ • Some viruses and endospores may survive • Autoclave: steam under pressure destroys endospores • Most effective use of moist-heat sterilization • Some materials can be damaged by autoclaving

22. Moist Heat Sterilization • Pasteurization—reduces spoilage organisms and pathogens in milk/juices • Raises the temp right below boiling • DOES NOT ERADICATE ALL MICROBES!!!! • High-temperature short-time: 72°C (161°F) for 15 sec • Milk in U.S. Must be refrigerated. Short storage life. • Ultra-high-temperature: 140°C (284°F) for 1-2 sec • Milk became popular in Europe. Can be stored for several months without refrigeration. • Equivalent treatments • As temperature increases, length of time to kill microbes decreases

23. Dry Heat Sterilization • Kills microbes by oxidation effects • Dry heat • Flaming • Incineration • Hot-air sterilization (oven) Dry Heat Moist Heat

24. Filtration • Blocks the passage of microorganisms • HEPA (high-efficiency particulate air) removes microbes >0.3 µm. • Membrane filtration (liquid) removes microbes >0.22 µm

25. 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

26. Physical Methods of Microbial Control • Low temperature inhibits microbial growth • Refrigeration (4°C) • Deep-freezing (-20°) • Lyophilization (freeze-drying) (-80°) • Uses liquid nitrogen • High pressure denatures proteins • Some endospores are resistant. Combined with elevating temps and alternating pressure cycles • Desiccation is the removal of water and prevents metabolism • Osmotic pressure causes plasmolysis

27. Radiation • Ionizing radiation (X rays, gamma rays, electron beams) • Ionizes water to release OH• • Damages DNA, proteins, membranes • Non-ionizing radiation (UV, 260 nm) • Damages DNA by causing thymine dimers • Inhibit DNA replication

28. Figure 7.5 The radiant energy spectrum.

29. Chemical Methods of Microbial Control • Chemical agents are used to control microbial growth on inanimate objects and living tissue • Only a few chemicals achieve “sterility” due to • Endospores • Characteristics of some bacteria resist destruction • NOTE: No single disinfectant is appropriate for all circumstances

30. Principles of Effective Disinfection • Concentration of disinfectant • Greater the concentration, more effective • Organic matter that is being disinfected • pH • Can affect the action of the chemicals • Time • Longer the exposure; more microbes are killed

31. Evaluating a Disinfectant • Use-Dilution Test • Metal/glass cylinders are dipped in test bacteria (broth) are dried at 37°C for a brief period of time • Dried cultures are placed in disinfectant of varying concentrations for 10 min at 20°C • Bacteria from cylinders are transferred to culture media to determine whether bacteria survived treatment

32. Disk Diffusion Test • Disk of filter paper is soaked in a chemical agent • Filters are placed on a “lawn” of bacteria to evaluate growth inhibition • The area where growth is inhibited is called zone of inhibition • Larger the zone, the more effective the chemical agent is at controlling microbes • Antibiotic discs

33. Figure 7.6 Evaluation of disinfectants by the disk-diffusion method. Zone of inhibition Chlorine Chlorine Chlorine O-phenylphenol O-phenylphenol O-phenylphenol Hexachlorophene Hexachlorophene Hexachlorophene Quat Quat Quat Staphylococcus aureus (gram-positive) Pseudomonas aeruginosa (gram-negative) Escherichia coli (gram-negative) Disk Diffusion Method

34. Chemicals in Disinfectants

35. Phenol and Phenolics • Also referred to as carbolic acid • Disrupt plasma membranes and results in cellular leakage • Found in some disinfectants, mouth washes, and throat sprays (1% concentration) • Over the counter throat lozenges are lower concentration • Therefore are not antimicrobial

36. Bisphenols • Derivative of phenol • Two phenols bridge together • Hexachlorophene, triclosan • Disrupt plasma membranes and inhibits enzyme needed for synthesis of fatty acids (lipids) • Used in nurseries • Affects the growth of gram positive staph and strep in newborns • Over use results in resistance

37. Figure 7.7cd The structure of phenolics and bisphenols. (c) Hexachlorophene (a bisphenol) (d) Triclosan (a bisphenol)

38. Biguanides • Broad spectrum of activity • Taken into the plasma membrane and abrogates permeability • Binds to DNA thus affecting transcription • Especially effective against Gram positive bacteria • Not as effective against Gram negative bacteria and viruses • Chlorhexidine disrupts plasma membranes • Used for surgical hand scrubs and pre-operative skin prep in patients

39. Halogens • Iodine • Active against all bacteria • Tinctures: Iodine in aqueous alcohol • Iodophors: Iodine in solubilizing agent such as a surfactant • Alter protein synthesis and membranes • Chlorine • Bleach: hypochlorous acid (HOCl) • Chloramine: chlorine + ammonia • Water treatment facilities • Mode of action is widely debated

40. Alcohols • Kills bacteria and fungi • Ineffective at killing endospores and non-enveloped viruses • Ethanol, isopropanol • Denature proteins, dissolve lipids, disrupts membranes • Requires water to facilitate movement across membrane • 70% more effective than 100% • Certain pathogens that lack a lipid envelope are resistant to alcohols • Clostridium difficile

41. Heavy Metals • Ag (silver), Hg (mercury), and Cu (copper) • Silver sulfadiazine used as a topical cream on burns • Copper sulfate is an algicide(kills algae) • Used in pools • Oligodynamic action—refers to the antimicrobial effect of heavy metals • Method of action is unknown • Silverware (100%) self-sanitize!!!!

42. Figure 7.8 Oligodynamic action of heavy metals.

43. Surface-Active Agents (Surfactants) Surfactants decrease surface tension among molecules of a liquid

44. Food Preservatives • Organic acids • Control molds and bacteria in foods and cosmetics • Inhibit metabolism • Sorbic acid (canned goods), benzoic acid (facial cleaners), and calcium propionate (bread) • Sodium nitrite is added to meats to prevent endospore germination • Antibiotics • Nisin (bacteriocin) and natamycin prevent spoilage of cheese

45. Aldehydes • Inactivate proteins by cross-linking with the functional groups (–NH2, –OH, –COOH, –SH) • Use: Sterilization of medical equipment • Glutaraldehyde and formaldehyde

46. Peroxygens • Oxidizing agents • Use: contaminated surfaces • O3, H2O2, peracetic acid • Especially effective against anaerobic bacteria

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