Chapter 7: The control of Microbial Growth Flashcards
What is the difference between sterilization and disinfection?
Sterilization is the removal and destruction of all living organisms (heat), and Disinfection is control directed at destroying harmful microorganisms (chemicals, steam, UV radiation.)
Heat as a method of microbial control
Dry heat, and moist heat
Dry heat
Takes longer to kill at higher temps because heat is not as readily transferred through air as it is through liquid. Dry heat kills through oxidative effects. Ex. paper catching fire in the oven, below ignition temperatures.
Moist Heat
Kills by denaturing proteins. BOILING kills vegetative forms of bacteria, pathogens, almost all viruses, and fungi. Not very effective against spores though. Not a good idea for surgical tools. AUTOCLAVING: effective against everything including spores, but not prions. It combines temperatures higher than boiling and pressure. It uses steam, but the steam has to come into contact with all surfaces, to kill on contact (reason for the perforated shelf at bottom). It can be used on anything that will not be damaged by moisture or temperature. Aluminum foil is impervious, oils and vaseline do not permit moisture penetration. PASTEURIZATION: uses mild heating of an entire substance to rid of pathogens. It is less effective in viscous foods, as fats have a protective effect on pathogens.
Filtration
passage of a liquid or gas through a membrane which catches microbes, viruses, and, when small enough, proteins to a vacuum sealed vessel, which creates a pressure differential, pulling the substances through the membrane. It is used to sterilize heat sensitive materials like culture media, enzymes, vaccines, and antibiotic solutions. Air in operating rooms and the rooms of burn patients are filtered like this.
Cold
Refrigeration slows metabolic process of microbes, preventing them from reproducing or synthesizing toxins. Refrigeration has a bacteriostatic effect. Pathogens won’t grow at refrigeration temps, rapid subfreezing causes microbes to go dormant, but not die, slow freezing more effective due to crystals, many eukaryotic parasites are killed by several days of freezing temperatures.
Dessication
The absence of water, preventing normal microbial function. However, they can remain viable for years, and only need the addition of water to hydrate them again. Viruses are generally resistant, but not as resistant as endospores. Important for hospitals because microbes and spores can remain viable in dust, bedding, clothing etc. that contain dried, infectious bodily fluids.
Osmotic Pressure
The salting or sugaring of foods creates a hypertonic environment which pulls the water from microbial cells and stops growth. Molds and yeasts can still grow and spoil.
Radiation
IONIZING: uses gamma, x rays, and/or electron beams. This type of radiation ionizes water, producing highly reactive hydroxyl radicals which react with DNA. balls of energy pass through or close to vital portions of the cell, constituting “hits.” Gamma rays, produced by radioactive elements, penetrate deeply, but are very time consuming. Electron and x rays are similar to one another. They are fast, but have low penetrating power. NONIONIZING RADIATION: is UV light. The wavelength absorbed by DNA is 260nm. It damages by creating thymine dimers in DNA which prevent accurate DNA replication. A disadvantage is that it isnt very penetrating, and organisms must be directly exposed to the light.
What are the examples for oxidizing agents used in microbial control.
Oxidizing agents react with ions in the microbe, and create free radicals that destroy macromolecules. Examples include Halogens like chlorine and peroxygens like hydrogen peroxide and ethylene oxide gas.
What are the examples for antimicrobial agents that disrupt the cell membrane/proteins?
Disrupting the membrane causes lysis andinterfering with proteins destroy enzymes essential to life and function of the microbe. Examples include: PHENOLICS (like Lysol–good for surface disinfection), BISPHENOLS (like triclosan inhibit enzymes needed for the biosynthesis of fatty acids), BIGUANIDES (like chlorhexadine), HALOGENS like iodine form complexes with amino acids and unsaturated fatty acids, ALCOHOLS (like ethanol - an agent in many hand santizers), HEAVY METALS ( like silver and mercury denature proteins, silver used in badages for burn patients, mercury used as anti mildew in paints.)
Antiseptic
used to treat living tissue
cidal agents
causes outright death of microbes with the exception of spores
static agents
inhibit growth and multiplication of bacteria
surfactants (surface acting agents)
soaps and detergents (quats) are not antiseptics , but help degerm through emulsification and washing away. The negatively charged anion reacts with plasma membranes. Quats are ammonium compounds and are cationic detergents with a positively charged cation.
