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Microbiological analysis of cerebrospinal fluid
Last reviewed: 23.04.2024
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Microbiological studies
Microscopy of the stained smear of cerebrospinal fluid allows to reveal microbial flora in 10-20% of patients with bacterial meningitis. In bacterial meningitis, meningo-dicococci of the bean-shaped form located intracellularly in the cytoplasm of neutrophils, or pneumococci, which are also diplococci, but have a triangular shape, can be found in bacterial meningitis, and a pair of cocci forms a rhombus (capsule-covered, extracellular). In some cases, visually detect spirochaetes, rod-shaped bacteria, yeast-like fungal cells. The data obtained with microscopy are indicative, and are confirmed by other methods. To detect mycobacteria tuberculosis use the flotation method. To isolate the culture of the pathogen, the cerebrospinal fluid is sown to nutrient media. The results of the study depend on the correctness of the intake and transport of cerebrospinal fluid, the quality of nutrient media. The frequency of isolation of the culture of the pathogen is twice as high, if before the spinal puncture the patient did not receive antibacterial drugs. To isolate the culture of the pathogen from the cerebrospinal fluid, in practice it is possible in 30-50% of patients with purulent meningitis. It is necessary to determine the sensitivity of the isolated culture to antibacterial drugs used to treat meningitis (benzylpenicillin, ampicillin, oxacillin, ceftriaxone, pefloxacin, ciprofloxacin, vancomycin, rifampicin, gentamicin). Cultures of fungi are examined for sensitivity to antifungal agents.
The main rule on which microbiological studies of cerebrospinal fluid is based is that the number of colonies grown depends on the number of sown microorganisms and their viability at the time of sowing. This means that the volume of cerebrospinal fluid directed to a microbiological study, the rapidity of its delivery are directly reflected in the results of the study. Especially large volumes of liquid must be directed to sowing with fungal infections, as the concentration of fungal microorganisms in it is extremely low. Thus, in the study of a patient with chronic meningitis, the minimum volume of cerebrospinal fluid directed to the crop should be 15-20 ml. Another rule of microbiological research is the mandatory conduct of Gram staining in acute bacterial meningitis. The coloring procedure takes about 5 minutes and has a high sensitivity and specificity. The results of this coloring allow immediate selection of adequate antibacterial therapy. Antibiotics prescribed before lumbar puncture can damage bacterial membranes and, thus, significantly reduce the specificity of Gram stains, but even in this case it makes sense. In addition to sowing, Gram stain, coloring for the detection of mycobacteria tuberculosis and staining with mascara for the detection of cryptococci, a number of serological tests for viral, bacterial and fungal antigens are used. So, if a neurosyphilis is suspected in the cerebrospinal fluid, the DAC and RIF should be examined.
Virological methods
The isolation of the culture of the virus is used, as a rule, only for scientific purposes.
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