Bacteria are very resistant to all environments. A protective coating on the surface helps the bacteria evade the defense mechanisms of the body and generally makes it more durable.Not all bacteria will take on the form of a spores shell-like coating to withstand unfavorable conditions. Bacteria in a spore state remain alive but passive, and they are resistant to the effects of heat, drying, and most bactericidal chemicals. They will remain capable of becoming virulent (strongly pathogenic) again under favorable conditions. However, under unfavorable conditions, they will either die or remain dormant in a spore state until another opportunity for growth presents itself.
Viruses are micro-organisms that are much smaller than bacteria. Viruses vary in size, from being the size of a single protein molecule to the size of a more complicated bacterial cell. They can be so small that they can be seen only through an electron microscope. Viruses cannot live long or reproduce outside of a living body (host). They must be able to enter and live in specific cells. For descriptive purposes, they are customarily divided into three subgroups, based on host specificity:
1. Bacterial viruses
2. Animal viruses (including those that attack humans)
3. Plant viruses
Some of the most common diseases caused by viruses are colds, smallpox, measles, rubella, herpes simplex, AIDS, infectious hepatitis, and serum hepatitis. Viruses are usually not affected by therapeutic treatment with antibiotics. Generally, therapeutic treatment is not used to combat a viral infection, but used to treat a secondary bacterial infection that may develop.
Most viruses are susceptible to immersion in boiling water for at least 20 minutes. There are two major exceptions to this rule, infectious hepatitis and serum hepatitis. Because of these exceptions to heat resistance, autoclaving for a minimum of 20 minutes at 270°F, or dry heat sterilization for 90 minutes at 320°F are the only safe procedures for control of these two viruses. 9-2
Protozoa are single-celled animals that do not have a rigid cell wall. Some protozoa cause parasitic diseases but not all are pathogens. Most species are harmless, living on dead organic matter or bacteria. Protozoa that are pathogenic survive freely in nature and must be spread by a carrier.
Most protozoa pass through a life-cycle, meaning that they have definite stages of development. These stages vary for each species and are usually very complicated. Malaria is an example of a disease that is caused by protozoa.
Fungi, like bacteria, are plants that lack chlorophyll. They are free-living organisms that are smaller than protozoa. Mold and yeast forms of fungi have firm cell walls and resemble plants more than animals.
Molds usually form cells in long chains or threads that grow into tangled masses. Some threads of the mass bear clusters of seedlike spores that, when dry, are easily blown into the air like dust. Each microscopic seed is capable of growing new mold upon settling in a suitable place. Mold spores are easily destroyed by heat. The most common infections in humans because of mold are athletes foot and ringworm. The mold penicillium is very common in nature and contributes to the spoilage of food. The drug penicillium is derived from this mold.
The following terms and their definitions will help you understand the material that is in this chapter and in chapter 10, Sterilization and Disinfection, Volume 1:
Asepsis - The prevention of contact with micro- organisms.
Automated washer processor - Washer, sterilizer, dishwasher, or other mechanical washing device.
Barrier technique - The use of rubber, plastic, foil, or other fluid resistant materials to cover surfaces and protect them from contamination.
Bioburden - The number of micro-organisms contaminating an object. Also known as bioload or microbial load.Continue Reading