The compound microscope is the most common type of magnification instrument used in the medical office. Microscopes permit visualization of structures that cannot be seen with the unaided eye. Microscopes consist of three main components: the magnification system, the illumination system, and the framework.
The magnification system of the microscope includes the ocular and objective lenses. The eyepiece, or ocular, is located at the top of the instrument and contains a lens to magnify approximately 10 times (10×). The objectives are on the revolving nosepiece. Most microscopes contain three objectives. Each objective provides a different magnifying power. The shortest objective has the lowest power at 10× magnification. This objective is used to bring objects into initial focus. The next objective is the high power, which brings objects into view at 40× magnification. The longest objective is the oil immersion (100×) allowing for the fine focusing of the object and requires the use of special oil that is placed directly on the slide. To determine total magnification, multiply the power of the ocular lens and the objective lens.
Example: 10× (ocular) 10× (lowest objective) = 100× total magnification of the viewed object
The illumination system includes the light source, the condenser, and the iris diaphragm. The light source is on the base of the microscope. Light is directed to the condenser then through the objective lens. The condenser collects and concentrates light rays then directs them up onto the objective lens. The diaphragm regulates the amount of light passing through the specimen. The diaphragm can be located within or beneath the condenser. A lever increases or decreases the light by changing the size of the aperture.
The framework includes stage, arm, and the adjustment knobs. The arm of the microscope connects the objectives and oculars to the base. The stage is a flat, horizontal platform that holds the slide. The stage has a mechanical adjustment knob that allows vertical or horizontal movement of the slide. Just above the base of the microscope are the two adjustment knobs. Coarse adjustment is used to approximate focus quickly and find the object under the low power objective. The fine adjustment allows for precise focus to produce sharp, clear images with high power and oil-immersion lenses.
Focusing the microscope is done through movement of the objective or stage. Stage focus is more common and involves movement of the stage while the body tube is stationary. Movement is controlled by the adjustment knobs located on both sides of the microscope. Proper focusing begins with the lowest power objective, which is used for initial focus and observation. The course adjustment moves the object into approximate focus quickly. Once the specimen is in view, the objective nosepiece is rotated to the high power objective and the fine adjustment knob is used for precise focus.
The following groups of microorganisms are known to contain species capable of causing human disease and include bacteria, viruses, fungi (yeast and molds), protozoa, and parasites.
Bacteria are single-celled microorganisms found throughout the environment. Once a bacterial specimen reaches the laboratory, it will be analyzed for certain criteria used for identification. This criterion includes morphology and staining reaction.
Bacteria can be classified into three basic groups according to morphological shape. Spherical bacteria are called cocci, rod-shaped bacteria are called bacilli, and spiral-shaped bacteria are called spirilla.
Bacilli are rod-shaped bacteria that are frequently found in the soil and air. Some are able to form spores, a characteristic that enables them to resist adverse conditions such as heat and disinfectants. Escherichia coli is a species of bacillus that is found in vast numbers among the normal flora of the intestinal tract.
Spirilla are spiral or curved bacteria. Treponema pallidum is a spirochete (tightly coiled spirilla) and the causative agent of syphilis. Vibrio cholerae causes cholera.
Staphylo- is a Greek term that denotes “bunch of grapes.” Staphylococci are round bacteria that grow in grapelike clusters. The Greek term streptos means twisted. Streptococci are round bacteria that grow in chains. Diplococci are round bacteria that grow in pairs (diplo- means double) and are associated with disease such as pneumonia, gonorrhea, and meningitis.
The chemical composition of a cell wall determines if the bacteria will stain. The most common type of staining is Gram-staining, a solution of dye(s) which imparts a color to the microorganisms.
Viruses are the smallest living organisms and cannot be seen with a regular microscope. Viruses are considered non-cellular and consist of nucleic acid surrounded by a protein coat. Viruses cannot grow independently (without a host).Viruses cause many conditions in people and are classified by diseases they produce. The following list outlines the categories of viral conditions and examples of each.
Mycology is the study of fungus and the associated diseases. Fungi are a diverse group of microorganisms that produce spores and sometimes filaments. Fungi are present in the soil, air, and water but only some are pathogenic. The two primary forms of fungi are yeasts and molds. Yeasts are single-celled fungi that reproduce by budding. Molds are multicellular forms that depend on plants or animals for food.
Parasitology is the study of parasitic organisms that live on or in the human body. Parasites are transmitted by ingestion during the infective stage, direct penetration of the skin, and inoculation by an arthropod vector. Helminths are parasitic worms and are large enough to see with the naked eye. Roundworms can occur in the intestines (pinworms) or muscle tissue (Trichinella spiralis, a form of roundworm, enters the body in infected meat eaten raw or insufficiently cooked). Tapeworms and flatworms are obtained from ingestion of undercooked meat.
Protozoa are single-celled microorganisms lacking a cell wall and most have some form of locomotion (cilia or flagella). These microorganisms are found in soil and water and most do not cause disease in humans. Pathogenic forms include malaria, amebic dysentery, and Trichomoniasis vaginitis (venereal disease).
The medical assistant should follow standard guidelines for proper specimen collection. The specimen should be collected with great care to avoid causing the patient harm, discomfort, or embarrassment. The specimen should be collected from a site where the organism is most likely to be found and where contamination is least likely to occur. There are site-specific devices to help ensure optimal collection, transportation, and processing of microorganisms. The most common types of cultured specimens include the throat, urine, sputum, wound, and stool.
Throat culture specimens are frequently performed in medical offices. Identification of the microorganism responsible for the infection allows for proper treatment of the patient for upper respiratory, throat, or sinus infections. When obtaining a throat specimen, the medical assistant must avoid touching any other structures inside the oropharynx to avoid contamination.
Sputum specimen collection involves the patient coughing mucus from the lungs into a container. The specimen must not come into contact with saliva and should be refrigerated or cultured immediately. Care must be taken when collecting these items, especially if the patient is coughing. Always use universal precautions.
Wound specimens are collected from infected wounds and lesions by using a sterile swab. The sterile swab is placed deep into the infected area and surface areas of the wound without contaminating the swab by touching any areas outside the suspected area. The medical assistant’s job is to collect the specimen and place it in transport medium.
Medical assistants may assist in the collection of vaginal specimens. Women should not douche within 24 hours of collection of a cervical or vaginal culture. The physician inserts a sterile, cotton-tipped swab into the vagina and samples of fluid are placed on a slide for testing.
Culturing blood requires two or three samples collected 30 to 60 minutes apart. Blood samples can be drawn into sterile, yellow stopper evacuated tubes and transferred to culture media. An anticoagulant must be present in the tube or blood culture bottle to prevent microorganism from being trapped within a clot. The venipuncture technique for collecting blood cultures follows the routine procedure, except for an increase in the antiseptic preparation at the puncture site. There should be at least a 1:10 ratio of blood to culture media as the number of organisms present is usually small.
When the patient is suspected of having certain types of digestive disorders, cancer, bacterial or parasitic infections, a stool specimen may be obtained. The patient must take care not to contaminate with urine or water from the toilet. If a physician requests an Ova and Parasites (O&P), a protozoal or parasitic infection is suspected. Culture collection swabs may be used to collect a rectal specimen or a swab of fecal material, then the swab should be placed in a C&S vial (fecal transport system).
Culture and sensitivity (C&S) testing is a procedure performed on a patient suspected of having a bacterial infection. To identify the microorganism, the medical assistant may perform a culture in which a sample of a specimen is placed in or on a substance (medium) that allows it to grow. For optimal growth, the specimen is placed in an incubator set to a specific temperature and humidity. Sensitivity testing is utilized to isolate the bacterium’s sensitivity to antibiotics. This will assist the doctor in determining which antibiotics might be most effective in treating the infection.