Overview When local infection spreads to the whole body and systemic infection occurs, bacteria can appear in blood and bone marrow, that is, bacteremia, toxemia or septicemia. Clinically, when patients have fever, hemogram and infection symptoms, bacterial culture of blood and bone marrow can be carried out. Blood and bone marrow bacterial culture is used to detect microorganisms in blood of patients with bacteremia and mycosis. Most bacteremia is intermittent, and it needs multiple cultures to be diagnosed.
The traditional broth enrichment method and automatic blood culture instrument are commonly used in blood and bone marrow bacterial culture.
Normal values of bacterial culture in blood and bone marrow; Normal human blood and bone marrow grow aseptically.
Clinical significance of bacterial culture in blood and bone marrow 1. Bacteria that may be infected in blood: Blood and bone marrow should be sterile. Once bacteria are detected, it should be regarded as bacteremia and drug sensitivity test should be carried out. Common bacteria in blood and bone marrow mainly include the following kinds.
(1) Gram-positive cocci: Staphylococcus, especially drug-resistant Staphylococcus aureus (such as MRSA), followed by Staphylococcus epidermidis and Streptococcus hemolyticus B; α hemolytic streptococcus (such as Streptococcus viridis and Streptococcus pneumoniae) can often be detected in subacute endocarditis. Suppurative pericarditis can be caused by pathogenic staphylococcus, hemolytic streptococcus B, streptococcus pneumoniae and anaerobic bacteria.
(2) Gram-negative bacilli: common non-fermentative bacteria such as Pseudomonas aeruginosa; Typhoid fever, paratyphoid fever and other enterobacteriaceae bacteria. Bacteroides and Fusobacterium can be detected in anaerobic culture.
2. When rare bacteria are detected, or the clinical manifestations are too different to be confirmed as infection, they should be regarded as positive under the following circumstances.
(1) is submitted for inspection again, and it is strictly sterile. If the same bacteria are still growing, they should be considered positive.
(2) 2-3 weeks after the symptoms of infection appear, the corresponding antibody titer in blood is obviously increased, which is of great significance, and the culture result should be regarded as positive.
(3) When necessary, blood samples are taken from two different parts at the same time, or venous blood and arterial blood, and the same bacteria are detected, which should be regarded as positive.
(4) The same pathogen was detected in blood culture and sputum, urine, pus, chest and ascites culture.
(5) When pathogenic bacteria are detected in blood culture and there are clinical manifestations of bacteremia, sensitive antibiotics should be selected for effective treatment according to the results of drug sensitivity test.
3. Possible causes and treatment when repeated cultures are negative due to typical infection:
(1) The timing was inappropriate, and there were high concentrations of antibiotics in the blood during the examination. Blood sampling at high drug concentration time or using culture medium containing antibiotic adsorbent (neutralizing agent) should be avoided.
(2) It may be L-shaped bacteria, anaerobic bacteria, virus infection, etc. Special cultivation methods or other inspection methods should be adopted.