chapter 9 microbiology

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 untensils

bacteriostatic (inhibits bacterial reproduction), bactericidal (kills bacteria), fungicide, sporicide, germicide

• bacterial populations subjected to heat or antimicrobial chemicals die at a constant rate
• effectiveness depends on number of microbes, environment, time of exposure, and microbial characteristics
• evaluation of antimicrobial efficacy:
• microbial death rate

• 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

• methods for evaluating disinfectants and antiseptics
• phenol coefficient
• 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

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

• heat is very effective (fast and cheap)
• thermal death point-lowest temperature that kills all cells in broth in 10 minutes
• thermal death time-time to sterilize volume of liquid at set temperature

• denatures proteins
• autoclave: 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

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

destruction of M. tuberculosis

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 using 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
• ionizing radiation (x rays, microwave)
• nonionizing radiation (UV)
• most effective wavelength~260 nm
• actively dividing organisms are more susceptible
• used to limit air and surface contamination
• germicidal lamps

• 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 ceells 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% 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
• soap and detergents
• good degerming agents but not antimicrobial
• Quats= 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

• 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