Bacterioscopic analysis of sputum
Last reviewed: 23.04.2024
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Timely identification of an infectious agent is very important for the proper choice of an antibacterial drug in order to prevent the development of bacterial resistance during the empirical administration of an antibiotic. Gram staining is the most common method of coloring all types of material obtained from a patient (sputum, bronchoalveolar rinse, etc.) for rapid and indicative establishment of an infectious agent.
Using a sputum smear-smear-microscopy, a preliminary assessment of a possible etiologic agent is carried out. Gram stained smear sputum is examined before sowing it on nutrient media also for the purpose of assessing the suitability for cultivation and identification of a probable pathogen. Sputum is considered suitable if a smear stained by Gram with a small increase in the microscope reveals more than 25 leukocytes and less than 10 epithelial cells in the field of vision. Signs of a quality sputum sample that can be used for cultivation are the prevalence of leukocytes over epithelial cells in it, as well as the presence of bacteria of one species that are located inside or around the leukocytes. Gram-positive bacteria in the preparation have a dark blue color, and gram-negative bacteria have a pink color. The causative agents of atypical pneumonia (mycoplasma, legionella, rickettsia and chlamydia) are not stained by Gram, therefore serological methods are used for their detection.
Spot smears on Tsiol-Nielsen are used to identify acid-fast bacilli, primarily mycobacterium tuberculosis. The preparation is prepared from purulent sputum particles, which are selected from 4-6 different places. The selected particles are carefully triturated between 2 slides to a homogeneous mass, dried in air, fixed over the flame of the burner. Mycobacterium tuberculosis is colored red, all other sputum and bacteria in blue. Mycobacterium tuberculosis has the appearance of thin, slightly curved sticks of various lengths, with thickening at the ends or in the middle, are arranged in groups and singly. Detection of Mycobacterium tuberculosis is the most reliable sign of tuberculosis lesions of the lungs. The method of staining smears according to Tsiol-Nielsen with active forms of pulmonary tuberculosis has a sensitivity of 50% and a specificity of 80-85%.
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