Microbiologic examination may include the following steps or techniques. First of all is the direct examination of the specimen to find out its gross pathology. Direct examination may include microscopy, which may help in identifying the microorganism. Specific microbial antigen can be revealed through procedures like staining the specimen with immuno-peroxidase, immunofluorescence, or with other immunoassays. On the other hand, the DNA or RNA sequences that are genus or species specific can be recognized through the use of genetic probes.
Another technique in microbiologic examination is by doing culture. This procedure requires specialized media for the specimen to grow. A nonselective (noninhibitory) media lets a wide variety of microorganisms to grow, while a selective media permits only selected microorganisms because of the inhibitory substances that it contains. A preliminary microbial identification can be done by the utilization of the morphology of the colony or of the cellular component. It is also necessary in microbial identification the observation of the growth patterns of the specimen under a variety of conditions and other important processes inside the cells.
A serodiagnosis or immunodiagnosis is done to diagnose a certain disease on the basis of the interaction between the antigens and antibodies present on the blood serum. Moreover, an antimicrobial susceptibility test is done to find out if the microorganism is vulnerable to certain antimicrobial agents.
Specimen Selection, Collection and Processing
In microbiologic examinations, the selected specimen must be relevant to the disease that is being studied. The amount of the collected specimen should be sufficient to permit a thorough and complete microbiologic examination. The quantity of microorganisms that is present in a certain measure of the specimen is highly variable. Swabs is one of the very common method in specimen collection, however it usually produces minute specimen to allow a precise microbiologic examination. Thus, it must be only utilized in collecting samples coming from the mucous membranes and the skin.
Both the skin and the mucous membrane are a home to a huge and wide variety of indigenous flora, thus all efforts must be done to eradicate or lessen the contamination of the specimen on the collection process. Many approaches can be applied to avoid contamination. One of this is the disinfection of the skin before aspirating or incising a lesion. Or maybe, the contaminated area can be avoided in taking samples. One example of that procedure is a transtracheal puncture and aspiration of lower respiratory secretions that is usually utilized to identify mycobacterium tuberculosis in patients. It is really impossible to have a specimen that is free of contamination, thus a decontamination technique must be used such as a cultures that has selective media or quantitative media.
Those specimens obtained though the invasive techniques, such as intraoperatively, needs special attention. The quantity of the tissue collected for histopathologic and microbiologic examination must be enough to conduct the following examinations thoroughly. Histopathologic examination is necessary to differentiate between neoplastic lesions as to that of inflammatory lesions and also those acute inflammations from the chronic ones. Histopathologic examination is fundamental in the diagnosis of a certain disease and it can also guide the microbiologic microscopy that should be done on the specimen. One example of this is, if in the histopathologic examination, a caseous granuloma is discovered, then the microbiologic examination that should be done of\n the specimen must include cultures for mycobacteria and fungi. Moreover, the surgeon should also take numerous samples that came from a single big lesion or from many smaller lesions that will be used in microbiologic examinations. In the event that there is an abscess present, the surgeon must take samples of pus in milliliters and also of the abscess wall for the same purpose of microbiologic examination. It should be remembered, however, that the swabs should always be kept out of the operating room.
Moreover, samples should be taken before dispensing antibiotics only if possible. Furthermore, an open line of communication between the clinician and the microbiologist should be established to make sure that the proper specimens are collected and that they are properly examined for the effective and efficient microbiologic examination of the specimen that will result to an accurate and precise diagnosis of a disease.
