TMSS Medical College Journal

Background: Bacterimia, septicaemia and sepsis remain a significant health problem in many developing countries due to its considerable morbidity and mortality. Hence, blood cultures have become critically important and frequently performed test in clinical microbiology laboratories for diagnosis and treatment. Objective: To compare the conventional blood culture with the lysis centrifugation method for isolation of causative bacteria in cases of bacterimia, septicaemia and sepsis. Methodology: Fifty nonduplicate blood samples for culture from cases of septicaemia and sepsis were analyzed using two blood culture methods concurrently for recovery of bacteria from patients diagnosed clinically with septicaemia and sepsis — in conventional blood culture method using trypticase soy and broth-brain heart infusion broth and the lysis centrifugation method using saponin, SPS, PABA and centrifuging at 3000 g for 30 minutes followed by streaking on solid media. Result: Overall bacteria recovered from 50 blood cultures were 32%. The conventional blood culture method had a higher yield of organisms, especially gram positive cocci and the lysis centrifugation method was comparable with the former method with respect to gram negative bacilli especially facultative intracellular. The sensitivity only lysis method was 28%, conventional method 24% and both methods in same specimen was 32%. Conclusion: Combination of the lysis centrifugation and conventional methods is more sensitive than use of either conventional or lysis method for isolation of bacteria causing blood infection if sample processing in biological safety cabinets for reduces contamination.

Invasion of the blood-stream by living microorganism causes significant morbidity and mortality, a fact well recognized before the dawn of modern medicine. Hence, blood cultures have become and still remain an essential requisite for diagnosis of sepsis. A positive blood culture not only suggests a definitive diagnosis but also guides specific therapy and prognosis. The final identification of a microorganism by the conventional blood culture method takes about 3 10 4 days, provided the organism grows in the first subculture done 48 hours after the receipt of the sample.’ The lysis centrifugation method concentrates and separates microorganism from plasma and cells then subculture done, thereby getting result carlier than conventional method. | The presence of actual colonics after initial | incubation for direct identification, not only makes it rapid but one can also quantify the colony forming units. Based on clinical impression, special media can be chosen for the initial culture setup. It has been found to be an excellent method for intracellular organisms including yeasts and thermal dimorphic fungi. Processing specimens in biological safety cabinets significantly reduces contamination rates, a drawback well known of this method apart from being labor intensive. It is not an optimal method for recovering anaerobes, Haemophilus influenza and listeria.‘ There are few | international studies on the lysis centrifugation method that showed it to be a better method than the conventional one.** Few Indian reports using lysis centrifugation method for brucella'’, mycobacteria’! and fungi” are available. One documented study done in Mymensingh Medical College Bangladesh for recovery of commonly encountered bacteria in blood cultures by lysis centrifugation method was 22% isolation rate’ Hence, this study was undertaken with the intention of comparing the lysis centrifugation method with the conventional blood culture method in terms of yield and recovery rate of ‘bacteria.