Evaluation of direct light microscopy for rapid detection of microorganisms in blood cultures

OBJECTIVE: The aim of this study was to evaluate the use of direct light microscopy (x 40 objective) of unstained uncentrifuged blood-broth mixtures for rapid detection of microorganisms in blood cultures.

METHODS: Two thousand two hundred and ninety-four blood cultures were investigated in this study. Blood cultures were processed in the Clinical Microbiology Laboratory, Queen Alia General Hospital, Amman, Jordan from January to December 2001. We compared the results of direct light microscopy and subcultures in 3 stages: macroscopically positive blood culture bottles, macroscopically negative blood culture bottles after 9-17 hours, and macroscopically negative blood culture bottles after 7 days of incubation.

RESULTS: The total positive blood cultures was 434 (18.9%). Three hundred and fifty three (81.3%) were positive by macroscopic examination and direct light microscopy and grew viable organisms, 34 were macroscopically negative blood cultures that grew viable organisms after 9-17 hours of incubation in which 32 (94.1%) were positive by direct light microscopy and 47 macroscopically negative blood cultures that grew viable organisms after 7 days of incubation in which 45 (95.7%) were positive by direct light microscopy.

CONCLUSION: The direct light microscopy methodology proved to be simple, rapid, cost effective, accurate and sensitive technique for the early detection of bacteremia.