A research team from bioMérieux reports the development of a new method that, they say, could cut hours off the time it takes to diagnose blood infections while also eliminating the need for complicated manual processing and expensive equipment. The scientists reported their study (“Rapid Intrinsic Fluorescence Method for Direct Identification of Pathogens in Blood Cultures”) in mBio®.
The technique combines a selective lysis step in which blood cells in the sample are destroyed, a centrifugation step to collect any bacteria or fungi in the sample, and a fluorescence step that analyzes the particular fingerprint of any pathogens present in the sample. Tests show the method correctly identifies the species of bacteria or fungi in 96.5% of positive blood culture samples, crucial information for doctors to provide the appropriate drugs for their patients.
“A total of 1,121 monomicrobial-positive broth samples from 751 strains were analyzed to build a database representing 37 of the most commonly encountered species in bloodstream infections or present as contaminants. A multistage algorithm correctly classified 99.6% of unknown samples to the Gram level, 99.3% to the family level, and 96.5% to the species level,” wrote the investigators. “There were no incorrect results given at the Gram or family classification levels, while 0.8% of results were discordant at the species level. In 8/9 incorrect species results, the misidentified isolate was assigned to a species of the same genus. This unique combination of selective lysis, density centrifugation, and IFS can rapidly identify the most common microbial species present in positive blood cultures. Faster identification of the etiologic agent may benefit the clinical management of sepsis.”
“The primary benefit of getting a rapid identification is making sure the patient is on the right [antibiotic] therapy and to quickly make any needed adjustments to the initial therapy,” says co-author John Walsh of bioMérieux.
Walsh says the current standard approach to diagnosing bloodstream infections, Gram staining and overnight sub-culture followed by phenotypic ID tests, have limitations that can prevent timely treatment. Gram staining provides early, low-level information about the type of microorganism present, but it sometimes takes hours to deliver a result, and technicians can make mistakes in the process that provide misleading results. Other more specific identification methods are also available for diagnosis, but they can take at least a day or two to produce results and many require expensive equipment.