Chapter 11 Controlling Microorganisms

Topics • Microbial agents - Controlling Microorganisms • Sanitation - Physical Control • Effectiveness • Mode of action - Chemical control

Microbial agents -static agents

• -static agents • Temporarily preventing the • -cital agents growth of microbes • Resistance – Bacteriostatic • Terms – Fungistatic • Effectiveness • Mode of action

-cidal A chemical substance is bacteriostatic if it inhibits the growth of organisms . • Killing or destroying a A chemical substance is bacteriocidal if microorganism it kills the organisms – Germicide In like manner viro, sporo and fungi can – Bactericide be substituted for bacterio in the terms bacteriocidal and bacteriostatic.

1 Resistance

• Highest resistance - bacterial spores and S. aureus prions • Moderate resistance - some bacteria, protozoan cysts, fungal sexual spores, naked viruses • Least resistance - most bacteria, fungal E. coli nonsexual spores and hyphae, enveloped viruses, yeast, protozoan trophozoites

Disinfectants are typically applied to Terms inanimate objects to reduce the number of pathogenic organisms. • Sterilization Antiseptics are generally applied to living • Disinfection organisms to destroy microorganisms or • Antisepsis limit their growth. Sterilization is the complete killing of all microorganisms in a material or on an object. A substance is either sterile or not sterile - there is no intermediate.

Effectiveness Disinfection or Sterilization • Number of microorganisms Figure 11.2 shows the ways in which • Target population (bacteria, fungi, spores, viruses) disinfection or sterilization are affect • Temperature and pH by time and 'load' of microorganisms • Concentration of agent • Mode of action A concept - the number of • Interfering agents (solvents, debris, organisms present at the beginning saliva, blood, feces) affects the time needed to achieve disinfection.

2 Factors that influence the effectiveness of Modes of action of agents that antimicrobial agents kill microorganisms • Cell wall • Cell membrane • Nucleic acid synthesis • Protein synthesis • Protein function

THESE WILL BE DISCUSSED IN DETAIL IN THE NEXT CHAPTER AS THEY RELATE TO CHEMOTHERAPEUTIC AGENTS. WE'LL NOTE THE SIMILARITIES AS WE DISCUSS ANTIMICROBIALS

Dry heat Physical Control Useful for substances not damaged by moist heat - 171 oC for one hr. • Heat Moist heat • Radiation Autoclave - 121 oC for 20 min - time is • Filtration dependent on configuration of the materials to be sterilized - a one liter flask of broth is easy - a 30 gal bag stuffed with insulating materials may require 1hr or more.

Mode of action Steam and pressure

• Moist heat • Pressure above normal atmospheric – Coagulation of proteins pressure will result in temperatures – Denaturation of proteins above 100˚C • Dry heat • Effectively destroys spores – Dehydration • Sterilizes inanimate objects (glassware) – Denaturation – Oxidation (burning to ashes) • Ex. Autoclave and home pressure cooker

3 Pasteurization

Cartoon of an • Disinfection of beverages AUTOCLAVE • Exposes beverages to 71.6 ˚C for 15 seconds – Stops fermentation • Prevents the transmission of milk-borne If you would come to diseases my office hours, and – Salmonella, Campylobacter, Listeria, discovered where my Mycobacteria office is - you could see an actual • Examples: Milk industry, wineries, breweries autoclave!!!!!

Boiling water Effects of cold and desiccation

• Decontaminates at 100 ˚C for 30 • Cold temperatures reduce the activity of minutes some microbes, not psychrophiles • Kills most non-spore forming pathogens • Not a disinfection or sterilization method • Examples: home sanitizing and • Dessication or dehydration kill some disinfecting, disinfecting unsafe water microorganisms – Lyophilization – freezing and drying method used to preserve microbes

Refrigeration, freezing excellent to preserve food and other materials - retards microbial Radiation growth, but does not effectively kill microorganisms. Microorganisms can be • Types of radiation stored in this way. • Modes of action Drying - many microorganisms are sensitive to • Applications drying - but, many are not. For example, Treponema pallidum dies if dried. Thus, if toilet seats are dried, there is little chance of spread of syphilis by that route. Freeze drying is used for storing many microorganisms.

4 Types of radiation Mode of actions

• Ionizing • Ionizing radiation ejects orbital electrons – Gamma rays (High energy) from an atom – X-rays (Intermediate energy) – High energy • Penetrates liquids and solids effectively – Cathode rays (least energy) • Nonionizing radiation raises atoms to a • Nonionizing higher energy state – Ultraviolet – Low energy • Less penetration capability • Pyrimidine dimers

The effects of ionizing and nonionizing Ionizing radiation is an effective radiation on DNA sterilizer. It damages DNA and generates peroxides in the cells. Both effectively sterilize the material. The material does not become radioactive. Gamma rays and x-rays pass through the material without causing the material to become radioactive. Very effective for the preservation of food.

UV radiation of a bacterial lawn on agar Ultraviolet (UV) radiation can cause the formation of pyrimidine dimers on DNA

Repair Process?

5 Applications Filtration • Ionizing radiation – Alternative sterilization method • Removes microbes and spores from – Materials sensitive to heat or chemicals liquids and air – Some foods (fruits, vegetables, meats) • Perforated membrane • Nonionizing radiation – Pore sizes vary – Alternative disinfectant • Applications – Germicidal lamp in hospitals, schools, food – Liquids that are sensitive to heat preparation areas (inanimate objects, air, • Serum, vaccines, media water)

An example of a filtration system Filtration is an effective way to remove microorganisms from a liquid. However, the porosity of What was in that water? the filter is very important. To effectively remove bacteria, a pore size of 0.45 µm is essential, 0.22 µm is preferred.

Applications Chemical control • Halogens • Phenolics • Widely used agents • Alcohols • Applications • Surfactants • Hydrogen peroxide • Detergents and soaps • Heavy metals • Aldehydes • Gases • Dyes, acids, and alkalis

6 Structural formulas of some Surfactants disrupt the cell membrane - detergents are surfactants important disinfectants

Fig. 11.4 Modes of action affecting protein function

Halogens Phenolics • Chlorine – Disinfectant and antiseptic • Vary based on functional groups • Disrupt sulfhydryl groups in attached to the aromatic ring amino acids • Examples: Hexachlorophene, Triclorsan • Iodine – Microcidal – Ingredient in soaps to kitty litter – Topical antiseptic • Disrupts cell walls and membranes, • Disruption is similar to chlorines

7 Phenolics contain a basic phenolic aromatic ring with different functional groups A method of expressing efficacy is the phenol coefficient. The phenol coefficient is determined by testing dilutions of the disinfectant relative to that of phenol.

Hydrogen peroxide Alcohols - note that we are NOT talking about weekend parties!! • Colorless and caustic liquid • Ethyl alcohol, isopropyl (rubber alcohol) • Form hydroxyl free radicals – 70% concentration dissolve membrane – Effective against anaerobes lipids, disrupt cell surface tension, denatures proteins • Skin and wound cleaner • Germicidal and skin degerming • Quick method for sterilizing medical equipment

Heavy metals - note that here we are Heavy metals - silver nitrate NOT talking about Iron Maiden or Metallica solution in infants eyes to prevent • Mercury, silver, infection by Neisseria during – Inactivate proteins – Preservatives in cosmetics and delivery. Tincture of merthiolate is ophthalmic solutions an organomercury compound used as an antiseptic.

8 Demonstration of the effects silver and gold have on microbial growth

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