Microbiology B.E Pruitt & Jane J. Stein AN INTRODUCTION EIGHTH EDITION TORTORA FUNKE CASE Chapter 7 The Control of Microbial Growth

Sepsis refers to microbial contamination. Asepsis is the absence of significant contamination. Aseptic surgery techniques prevent microbial contamination of wounds.

Sterilization: Removal of all microbial life –Commercial Sterilization: Killing C. botulinum endospores Disinfection: Removal of pathogens Antisepsis: Removal of pathogens from living tissue Degerming: Removal of microbes from a limited area Sanitization: Lower microbial counts on eating utensils Biocide/Germicide: Kills microbes Bacteriostasis: Inhibiting, not killing, microbes Bacteriocidal: Kills bacteria Terminology

Bacterial populations die at a constant logarithmic rate. Figure 7.1a

Number of microbes Environment (organic matter, temperature, biofilms) Time of exposure Microbial characteristics Condition of microbes - lag, log or sport Effectiveness of antimicrobial treatment depends on: Figure 7.1b

Mechanisms of action for Antimicrobial control agents Alternation of membrane permeability Damage to proteins Damage to nucleic acids Interfere with metabolic pathways Actions of Microbial Control Agents Methods may be Physical or Chemical Physical like heat Chemical like disinfectants

Heat is very commonly used, heat may be moist or dry. Heat –Thermal death point (TDP): Lowest temperature at which all cells in a culture are killed in 10 min. –Thermal death time (TDT): Time to kill all cells in a culture –Decimal reduction time (DRT): Minutes to kill 90% of a population at a given temperature Physical Methods of Microbial Control

Moist heat denature s proteins Autoclav e: Steam under pressure Moist Heat Figure 7.2

Pasteurization reduces spoilage organisms and pathogens Equivalent treatments –63°C for 30 min –High-temperature short-time 72°C for 15 sec –Ultra-high-temperature: 140°C for <1 sec –Thermoduric organisms survive Physical Methods of Microbial Control

Dry Heat Sterilization kills by oxidation –Flaming –Incineration –Hot-air sterilization Physical Methods of Microbial Control Hot-airAutoclave Equivalent treatments170˚C, 2 hr121˚C, 15 min

Filtration removes microbes Low temperature inhibits microbial growth –Refrigeration –Deep freezing –Lyophilization High pressure denatures proteins Desiccation prevents metabolism Osmotic pressure causes plasmolysis Physical Methods of Microbial Control

Electromagnetic spectrum, shorter wavelength means great energy and can penetrate further. Radiation damages DNA Two types used: –Ionizing radiation (X rays, gamma rays, electron beams) –Non-ionizing radiation (UV) –(Microwaves kill by heat; not especially antimicrobial) Physical Methods of Microbial Control

Figure 7.5 Electromagnetic Spectrum

Principles of effective disinfection –Concentration of disinfectant –Organic matter –pH –Time Often chemical methods are compared to Phenol. If more effective given a phenol coefficient of >1. If less effective give a phenol coefficient of <1. Chemical Methods of Microbial Control

Evaluating a disinfectant –Use-dilution test 1. Metal rings dipped in test bacteria are dried 2. Dried cultures placed in disinfectant for 10 min at 20°C 3. Rings transferred to culture media to determine whether bacteria survived treatment Chemical Methods of Microbial Control

Figure 7.6 Evaluating a disinfectant Disk-diffusion method

Types of Disinfectants Figure 7.7 Phenol Phenolics. Lysol Bisphenols. Hexachlorophene, Triclosan Disrupt plasma membranes

Biguanides. Chlorhexidine –Disrupt plasma membranes Types of Disinfectants

Halogens. Iodine, Chlorine –Oxidizing agents –Bleach is hypochlorous acid (HOCl) Types of Disinfectants

Table 7.6 Alcohols. Ethanol, isopropanol Denature proteins, dissolve lipids

Heavy Metals. Ag, Hg, Cu –Oligodynamic action –Denature proteins Types of Disinfectants

Surface-Active Agents or Surfactants Types of Disinfectants SoapDegerming Acid-anionic detergentsSanitizing Quarternary ammonium compounds Cationic detergents Bactericidal, Denature proteins, disrupt plasma membrane

Chemical Food Preservatives –Salts –Sugar –Dry –Organic Acids Inhibit metabolism Sorbic acid, benzoic acid, calcium propionate Control molds and bacteria in foods and cosmetics –Nitrite prevents endospore germination –Antibiotics. Nisin and natamycin prevent spoilage of cheese Types of Disinfectants

Aldehydes –Inactivate proteins by cross-linking with functional groups (–NH 2, –OH, –COOH, — SH) –Glutaraldehyde, formaldehyde Types of Disinfectants

Gaseous Sterilants –Denature proteins –Ethylene oxide - not Ethyl oxide Types of Disinfectants

Peroxygens –Oxidizing agents –O 3, H 2 O 2, peracetic acid Types of Disinfectants

Microbial Characteristics and Microbial Control Figure 7.11

Microbial Characteristics and Microbial Control Chemical agentEffectiveness against EndosporesMycobacteria PhenolicsPoorGood QuatsNone ChlorinesFair AlcoholsPoorGood GlutaraldehydeFairGood