CHAPTER 9 Flashcards
Physical and Chemical Controls of Microorganisms
Most Resistant to Most Susceptible
prions
bacterial endospores
mycobacteria
cysts of protozoa
active-stage protozoa (trophozoite)
most gram-negative bacteria
fungi
nonenveloped viruses
most gram-positive bacteria
enveloped viruses
Sterilization
process of removing or destroying all microbial life on an object
Intermediate-level germicides
kill fungus spores, protozoa cysts, and viruses (not endospores)
Low-level germicides
kill vegatative cells and some viruses
Antisepsis
reduction in the number of microorganisms and viruses (potential pathogens) on living tissue
ex: iodine or alcohol
Degerming
removing microbes by mechanical means
Disinfection
destruction of most organisms and viruses on nonliving tissue
use of phenolics, alcohols, aldehydes, or soaps on equipment or surfaces
Decontamination
reduction in microbial number from a surface
Antimicrobial Agents: MOA on cell wall
blocks its synthesis
digests it
breaks down its surface
cell becomes fragile and dies of lysis
Antimicrobial Agents: MOA
Cell Membrane
Protein and Nucleic Acid Synthesis
Antimicrobial Agenst: Damage to Proteins
binding to ribosomes to prevent translation
binding irreversibly to DNA to stop transcription and translation
mutagenic agents
some damage proteins by breaking hydrogen and covalent bonds
Methods of Microbial Control
Physical:
heat/cold
radiation (mutate microbe)
dessication
filtration
osmotic pressure
Chemical:
chemical agents
antimicrobial drugs
Dry Heat Sterilization
kills by oxidation;
dry heat
flaming
incineration
hot-air sterilization
Hot Air
170C; 2hr
Autoclave
121C; 15 min
Steam under pressure (most effective pressure-temperature combination for sterilization)
15 psi which yields 121C
Historical (batch) method pasteurization
63C for 30 minutes
Flash pasteurization method
72C for 15 seconds
Ultra-high temperature pasteurization
135C for 1 second
Pasteurization
does not kill prions, endospores, or thermoduric microbes
Three types of radiation
ionizing
ultraviolet light (noninonizing)
microwave radiation
Ionizing Radiation
Gamma rays, X rays, electron beams, higher energy rays;
have short wavelengths (less than 1 nanometer);
dsilodge electrons from atoms;
cause mutations in DNA and produce peroxides;
used to srerilize pharmaceuticals and disposable medical supples;
food industry is interested;
disadvantages: penetrates human tissues; may cause egentic mutations in humans
Ultraviolet (Non-Ionizing) Radiation
wavelength longer than 1 nanometer;
damages DNA by producing thymine dimers, which cause mutations;
used to disinfect operating rooms, nurseries, cafeterias;
disadvantages: damages skin, eyes; doesn’t penetrate paper, cloth, or glass;
ultraviolet light, visible light, infrared light, and radio waves
Ionizing Radiation
DNA breakages
Nonionizing Radiation
DNA (abnormal bonds)
Ultraviolet Light
tool for destroying fungal cells and spores, bacterial vegetative cells, protozoa, and viruses
Microwave Radiation
wavelength: 1 mm to 1 m;
heat is absorbed by water molecules;
HEPA (High Efficiency Particulate Air)
removes microbes > 0.3 micrometers
Membrane Filtration
removes microbes larger than 0.22 micrometers;
composed of cellulose esters
Other Physical Methods of Microbial Control
low temperature inhibits microbial growth;
high pressure denatures proteins;
dessication prevents metabolism;
osmotic pressure causes plasmolysis
Refrigeration between 0C and 7C
halts the growth of most mesophiles (best funtioning in moderate temperature)
Choosing a Microbial Chemical
rapid action in low concentrations;
solubility in water or alcohol and long-term stability;
broad-spectrum microbicidal action without being toxic to human and animal tissues;
penetration of inanimate surfaces to sustain a cumulative or persistent action;
resistance to becoming inactivated by organic matter;
noncorrosive or nonstaining properties;
sanitizing and decolorizing property;
affordability and ready availability
