Specimens may be collected in a number of ways. Each method is designed to ensure that the proper material will be sent to the lab using good aseptic technique. One of the most common tools used to collect specimens is the sterile swab.
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Swabs are used to gather samples from the eye, ear, nose, throat, open wounds, and fecal material. Special handling of the pre-sterilized package is necessary to prevent contaminating the swab. Each manufacturer has its own unique package and provides instructions for its proper use.
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Many swabs have an ampule (small container) of sterile physiological saline solution built into the package. After the specimen is taken and returned to the container, the ampule is squeezed and broken to release the fluid onto the surface of the cotton swab containing microbes.
This is essential since the microbes have been removed from an optimum growth environment- the patient. If the microbes are not protected from drastic changes in moisture content and temperature, they will die before they reach the lab.
For this same reason, specimens should be sent to the lab immediately for culturing. If this cannot be done, most specimens should be refrigerated to limit cell death. Exceptions to this rule are Neisseria gonorrhoeae specimens, which are maintained at room temperature in the lab.
Specimens may also be collected by needle aspiration. The most familiar sample taken using this method is blood. After proper aseptic technique has been followed to prevent infection of the patient and contamination of the hypodermic needle, a sample of venous blood is drawn into a container that has been treated with an anticoagulant such as heparin or potassium oxalate.
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The presence of the anticoagulant prevents the pathogenic microbes from being entrapped in a fibrin clot, which would make a quick isolation impossible. Needle aspiration may also be used to obtain spinal fluid. A modification of the needle aspiration technique involves the use of a long, sterile tube attached to a syringe.
This method is known as intubation and is also used to collect specimens from the stomach, gall bladder, chest, or peritoneal cavities. Tubes used to obtain specimens vary in size, shape, and material. The two most common are the Levin tube and a catheter.
The Levin tube is a soft rubber tube 4-6 mm in diameter and comes prepackaged in a sterile wrap. The Levin tube may be swallowed by the patient or passed through the nostril into the stomach. Specimens may then be withdrawn in small amounts (5-10 ml) every 10 to 15 minutes.
There are three types of catheters used to collect urine specimens. The hard catheter is made of a more firm rubber or plastic material and is used when the urethra has strictures (narrowing of the tube). Special precautions must be taken when using this catheter to avoid tissue damage.
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The French catheter is made of soft material and is the most frequently used to obtain single samples. If urine specimens or drainage are required for an extended period, a Foley catheter (indwelling catheter) is preferred. This is a tube within a tube.
After the catheter has been introduced into the bladder, the tip of the outer tube may be blown up with air or water like a small balloon to prevent it from being removed. Catheterization is one of the hospital procedures most likely to lead to infection.
About 40 per cent of all hospital-acquired infections (400,000 patients in the Unites States annually) occur as a result of catheterization. Urinary tract infections associated with catheters may be caused by such bacteria as E. coli, Klebsiella, Enterobacter, Citrobacter, and Proteus.
These microbes are normally present in the colon or lower portion of the urethra. The bacteria may be moved into the urinary tract and bladder either during or after the catheter is inserted.
Foley catheters are more likely to lead to infections in elderly female patients because of the patients’ inability to properly cleanse them after defecation. The close anatomical position of the anus to the urethal meatus allows for an easy transfer of colon bacteria.
To these difficulties, noncatheterization specimens of urine may be taken from both males and females by the clean-catch method. After the patient has cleansed the tissue surrounding the meatus, a small test tube, cup, or bottle is used to catch the urine sample.
In the clean-catch midstream method, the first portion of the voided urine should not be collected since it will be contaminated with bacteria normally occurring in the lower portion of the urethra.
This first voided urine is discarded and only the second, or midstream, portion is saved for lab analysis, since it will likely contain microbes found in the bladder. The midstream specimens are quickly sent to the laboratory where concentration of organisms is used to determine the presence or absence of a bladder infection.
Sputum is another material that may be taken from a patient without the use special equipment. A distinction must be made between saliva and sputum. Saliva is the clear, alkaline secretion from the salivary glands that serves to moisten the mouth.
Sputum is a thick, heavy material coughed up from the lungs. For instance, when collecting sputum samples for the detection of tuberculosis bacilli, the patient is instructed to rinse the mouth with sterile water and cough up all the material possible. Sputum collected in a special sterile cup will be thick and settle to the bottom.
Specimens collected for laboratory analysis should be properly labeled. In some hospitals, a plastic “charge card” is prepared for each patient and indicates the patient’s name, unit number hospital or case number, room and floor number, and other information.
If such a system is not employed the collection vessel label or a separate form is used to provide the lab with the necessary information. After proper identification, the sample is sent to the lab, where the technician begins a detailed investigation of the specimen.
First, a microscopic check determines the possible nature of the microbe, and culturing follows for more complete identification. In order to perform all the necessary tests, the specimen is cultured in the appropriate media selected and prepared by the technician.
The importance of proper specimen collection cannot be overemphasized. Techniques described here are fundamentally the same as those used in other areas of microbiology and not limited to the medial microbiology.
It is equally essential in the areas of water, food and dairy and industrial microbiology to use proper equipment and aseptic technique to obtain specimens for analysis and identification. In many situations, special collection vessels have been designed to obtain and transport specimens.
For example, sampling for microbes on the deep-ocean bottom is carried out using weighted cylinder samples, which open to let in only certain materials after being triggered with a release cable attached to the research ship.
These containers are then raised to the surface without being contaminated by surface microbes and taken to the laboratory for analysis.