Chapter 9 Micro

Microbial contamination

• an environment or procedure that is free of contamination by pathogens
• antimicrobial chemicals, expected to destroy pathogens but not to achieve sterilization

non-living surface

living tissue

removal of all microbial life (heat, filtration)

for food

for utensils

inhibits bacterial reproduction

• number of microbes
• environment
• time of exposure
• microbial characteristics

• alteration of cell walls and membrane
• alter permeability
• breakdown lipid components

• damage to protein structure
• disrupts structural proteins
• denatured enzymes cause a decrease in cellular activity

• damage to nucleic acids
• loss of genetic information leads to a decrease in metabolic activity
• can produce fatal mutants
• can halt protein synthesis through action on RNA

• ideally, agents should be:
• inexpensive
• fast acting
• stable during storage
• capable of controlling all microbial gowth while being harmless to humans, animals, and objects
• is this feasible? no

• site to be treated
• relative susceptibility of microorganism
• effectiveness of germicides classified as high, iintermediate, or low
• environmental conditions
• temperature
• pH
• organic material

• compare other disinfectants and antiseptics to phenols effectiveness at controlling microbes under standardized conditions
• greater than 1.0=product is more effective than phenol

• expose contaminated cylinders to various dilutions of antimicrobial agents
• incubate cylinder for 48 hours and check growth

• expose bacterium to suitable concentration of disinfectant
• return to growth medium and check turbidity

swabs of object are taken pre/post disinfectant and grown

• effects of high temperatures
• denaturation of proteins
• interference with integrity of cytoplasmic membrane
• disruption of structure and function of nucleus

lowest temperature that kills all cells in broth in 10 minutes

denatures proteins

significant number reduction (esp. spoilage and pathogenic organisms) does not sterilize! Destroyed TB.

63° C for 30 min

72° C for 15 sec. most common in us. thermoduric organisms survive

• 140° C for <1 sec
• technically not pasteurization because it sterilizes

• kills by oxidation
• denatures proteins and oxidizes metabolic and structural chemicals
• used for materials that cannot be sterilized with or damaged by moist heat
• flaming of loop
• incineration of carcasses
• bird flu
• mad cow disease

• decrease microbial metabolsm, growth and reproduction
• chemical reactions occur slower at low temperatures
• liquid water not available
• psychrophilic microbes can multiply in refrigerated foods
• refigeration halts growth of most pathogens
• slow freezing more effective than quick freezing
• organisms vary in susceptibility to freezing
• exceptions: listeria monocytogenes
• refrigeration: 0-7° C
• freezing: below 0° C

• Air filtration uses high efficiency particulate air (HEPA) filters. effectie to 0.3 um
• Membrane filters for fluids
• pore size for bacteria: 0.2-0.4 um
• pore size for viruses: 0.01 um

• high concentrations of salt or sugar in foods to inhibit growth
• cells in a hypertonic solution of salt or sugar lose water; cell desiccates
• fungi have greater ability than bacteria to survive hypertonic environments

radiation damages DNA: sterilization of medical equipment and foods

• affect microbes cell walls, cytoplasmic memebranes, proteins, or DNA
• effect varies with temperature, length of exposure, and amount of organic matter
• also varies with pH, concentration, and age of chemical
• tend to be more effective against enveloped viruses and vegetative cells of bacteria, fungi, and protozoa

• disrupts cell membranes
• effective in presence of organic matter and remain active for prolonged time
• commonly used in health care settings, labs and homes
• pheno (carbolic acid) historical significance
• phenolics: creosol (lysol)
• bisphenolics
• hexachlorophene: pHisoHex
• triclosan: toothpaste, antibicterial soaps

• are bactericidal, fungicidal, and virucidal against enveloped viruses
• ineffective against fungal spores and bacterials spores
• denature proteins and disrupt cytoplasmic membranes
• evaporate rapidly and inactivated by organic debris
• 70%(optimal concentration) more effective than 90%
• used in hand santizers and cosmetics

• intermediate- level antimicrobial chemicals
• iodine
• chlorine
• bromine
• fluorine
• iodine: medically used as a tincture or iodophores
• betadine
• sodium hypochlorite (bleach)
• chlorine treatment of drinking water

• peroxide kill by oxidation of microbial enzymes
• effective against anaerobic microorganisms of deep wounds
• hydrogen peroxide can disinfect and sterilize surfaces of objects
• 3% or higer
• catalase neutralizes; not useful for treating open wounds
• staphylococcus aureus

"surface active" chemicals that reduce surface tension of solvents to make them more effective at dissolving solutes

• ions are antimicrobial because they alter the 3-D shape of proteins, inhibiting or eliminating their function
• low-level bacteriostatic and fungistatic agents
• 1% sliver nitrate to prevent blindness caused by N gonorrhoeae
• thimerosal used to preserve vaccines
• copper controls algal growth in reservoirs, fish tanks, swimming pools, and water storage tanks; interferes with chlorophyll

• inactivate proteins by cross-linking with their function groups (-NH₂, -OH, -COOH, -SH)
• compounds containing terminal -CHO groups
• glutaraldehyde
• formalin used in embalming and disinfection of rooms and instruments

kills bacteria

A constant rate

microbial death rate

time to sterilize volume of liquid at set temperature

• steam under pressure
• most dependable sterilzation method
• steam must directly contact material to be sterilized
• pressurized steam reaches higher temperatures
• normal autoclave conditions: 121.5 C for 15 min
• prion destruction: 132 C for 4.5 hours

x rays, microwave

• UV
• most effective wavelength~260 nm
• actively dividing organisms are more susceptible
• used to limit air and surface contamination
• germicidal lamps

good degerming agents but not antimicrobial

• quaternary ammonium compounds
• colorless, tasteless, harmless to humans, and antimicrobial; ideal for many medical and industrial application
• most effective against gram +
• pseudomonads live in them