Microbiological examination of sputum

Microbiological research is the most important link in the diagnostic search and verification of the pathogen of pneumonia. It involves not only the isolation of the pathogen, but also the study of its properties, including sensitivity to various medications that have bactericidal and bacteriostatic effects.

For this purpose, the method of sputum culture on various nutrient media is used. In a sample of phlegm delivered to the laboratory, purulent lumps are collected and thoroughly washed in a Petri dish with an isotopic sodium chloride solution, which to a certain extent allows them to be released from the microflora of the upper respiratory tract. Crops of purulent lumps of sputum produce various nutrient media, the composition of which is described in special manuals on microbiology. Mediums with inoculations are incubated at 37.5 ° C for 24 hours. From the grown colonies, pure cultures are isolated, identified by known microbiological methods, and determine susceptibility to antibiotics.

To quantify the content of microorganisms, sputum is homogenized, mixed with nutrient broth, and sequential tenfold dilutions are prepared from the mixture, which are plated on petri dishes with blood agar. After 24 hours of incubation at 37.5 ° C, the results are taken into account, counting the colonies of the same type in appearance and taking into account the degree of dilution of the material. Smears are prepared from the colonies and microscopic.

Interpretation of results

The interpretation of the results of microbiological sputum examination is rather complicated, which is explained by a number of factors. We have already mentioned the constant contamination of the bronchial contents with the microflora of the upper respiratory tract and oral cavity and the frequent presence in the normal tracheobronchial contents of healthy people of most of the most common causative agents of respiratory diseases (pneumococci, streptococci, staphylococcus, etc.). In connection with this, the isolation of various microorganisms in sputum during microbiological studies, most of which are conditionally pathogenic in this particular case, makes it extremely difficult to establish a causative agent of the disease. Therefore, in order to interpret the results of the microbiological examination of sputum, the quantitative predominance of one or another type of bacteria should be taken into account (more than 10 ⁶ -10 ⁷ m.ks / ml), the appearance of certain microorganisms in the exacerbation phase and their disappearance during the remission period. It is very important to take into account the clinical picture of the disease.

The main and possible pathogens of various clinical forms of pneumonia

Clinical form of pneumonia	Major pathogens	Possible pathogens
Croupous	Pneumococci	Streptococci, clebesioplasts
Postgrippoznaya	Staphylococci, pneumococci, Klebsiella	Hemophilus influenzae, streptococci
Abscessing	Staphylococci, bacteroides, mixed flora	Klebsiella, Pseudomonas aeruginosa
Aspiration	Bacteroides, anaerobic streptococci	Staphylococci, pneumococci
Postoperative	Staphylococci	Pneumococci, Klebsiella
Interstitial	Mycoplasma	Pathogens of ornithosis, psittacosis
Secondary pneumonia in hospital patients without prior antibiotic therapy	Staphylococci, pneumococci, Klebsiella, bacteroides	E. Coli, serrations, etc.
Secondary pneumonia, developed against the background of antibiotic therapy	Optional pathogenic microorganisms	Pseudomonas, Serratia, Klebsiella, Staphylococcus, Proteus, and others.
In patients with chronic bronchitis	Pneumococcus, haemophilus influenzae	Staphylococci, streptococci
In patients with alcoholism	Pneumococci, hemophilic rod, Klebsiella	E. Coli, protozoa
In the syndrome of acquired immunological failure	Pneumocysts, mushrooms	Cytomegalovirus
Patients whose care is performed by outsiders	Pneumococci, staphylococcus, hemophilic daddy	Klebsiella, E. Coli

Estimating quantitatively the results of the study of microbial contamination in patients with pneumonia, one should remember about the extremely high sensitivity of this indicator to the appointment of antibiotics. Even short-term treatment with antibacterial drugs can lead to a sharp decrease in microbial contamination, which does not allow to adequately assess the results of sputum examination. Therefore, it is advisable to take sputum before prescribing antibiotics.

It should also be noted that for the cultivation of intracellular pathogens pneumonia (mycoplasma, legionella, chlamydia, rickettsia) use special selective nutrient media. Routine microbiological testing using conventional nutrient media (agar-agar) never yields positive results. Therefore, the choice of specific methods of microbiological research should be conducted with the participation of the attending physician, who is obliged to inform the laboratory technician about his suspicions about the possible role of intracellular pathogens in the onset of pneumonia in this patient.

It should be added that in real clinical practice even a technically perfect microbiological examination of sputum reveals the causative agent of the disease no more often than in 40-60% of cases. Therefore, other modern methods of investigation can be used to verify the causative agent. The informativeness of bacteriological research can be significantly increased by using not as a sputum as a biological material but as a tracheobronchial aspirate, a fluid obtained from bronchoalveolar lavage (JVAL), bronchoscopy, and the like.

In addition, for the detection of pathogens of pneumonia, the method of immunofluorescence of various biological materials (bronchoscopy material, blood, pleural contents, etc.), methods of PCR diagnostics, and the study of the level of specific antibodies in blood serum can be used. Unfortunately, up to now, these methods of diagnosis have not found wide clinical application and are still used only in large specialized centers and laboratories.

[1], [2], [3], [4], [5], [6], [7]