Medical Technology Department, Faculty of Science, Islamic University-Gaza MB M ICRO B IOLOGY Dr. Abdelraouf A. Elmanama Ph. D Microbiology 2008 Chapter 7 The Control of Microbial Growth

2008 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.

2008 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 Terminology

2008 Bacterial populations die at a constant logarithmic rate. Figure 7.1a

2008 Number of microbes Environment (organic matter, temperature, biofilms) Time of exposure Microbial characteristics Effectiveness of antimicrobial treatment depends on: Figure 7.1b

2008 Alternation of membrane permeability Damage to proteins Damage to nucleic acids Actions of Microbial Control Agents

2008 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

2008 Moist heat denatures proteins Autoclave: Steam under pressure Heat Figure 7.2

2008 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

2008 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

2008 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

2008 Radiation damages DNA Ionizing radiation (X rays, gamma rays, electron beams) Nonionizing radiation (UV) (Microwaves kill by heat; not especially antimicrobial) Physical Methods of Microbial Control

2008 Figure 7.5

2008 Principles of effective disinfection Concentration of disinfectant Organic matter pH Time Chemical Methods of Microbial Control

2008 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

2008 Chemical Methods of Microbial Control Figure 7.6 Evaluating a disinfectant Disk-diffusion method

2008 Types of Disinfectants Figure 7.7 Phenol Phenolics. Lysol Bisphenols. Hexachlorophene, Triclosan Disrupt plasma membranes

2008 Biguanides. Chlorhexidine Disrupt plasma membranes Types of Disinfectants

2008 Halogens. Iodine, Chlorine Oxidizing agents Bleach is hypochlorous acid (HOCl) Types of Disinfectants

2008 Types of Disinfectants Table 7.6 Alcohols. Ethanol, isopropanol Denature proteins, dissolve lipids

2008 Heavy Metals. Ag, Hg, Cu Oligodynamic action Denature proteins Types of Disinfectants

2008 Surface-Active Agents or Surfactants Types of Disinfectants SoapDegerming Acid-anionic detergentsSanitizing Quarternary ammonium compounds Cationic detergents Bactericidal, Denature proteins, disrupt plasma membrane

2008 Chemical Food Preservatives 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

2008 Aldehydes Inactivate proteins by cross-linking with functional groups (–NH 2, –OH, –COOH, —SH) Glutaraldehyde, formaldehyde Types of Disinfectants

2008 Gaseous Sterilants Denature proteins Ethylene oxide Types of Disinfectants

2008 Peroxygens Oxidizing agents O 3, H 2 O 2, peracetic acid Types of Disinfectants

2008 Microbial Characteristics and Microbial Control Figure 7.11

2008 Microbial Characteristics and Microbial Control Chemical agentEffectiveness against EndosporesMycobacteria PhenolicsPoorGood QuatsNone ChlorinesFair AlcoholsPoorGood GlutaraldehydeFairGood