Integration of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in blood culture diagnostics: a fast and effective approach.

Sepsis is a major cause of mortality in hospitalized patients worldwide, with lethality rates ranging from 30 to 70 %. Sepsis is caused by a variety of different pathogens, and rapid diagnosis is of outstanding importance, as early and adequate antimicrobial therapy correlates with positive clinical outcome. In recent years, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) fingerprinting has become a powerful tool in microbiological diagnostics. The direct identification of micro-organisms in a positive blood culture by MALDI-TOF MS can shorten the diagnostic procedure significantly. Therefore, the aim of the present study was to evaluate whether identification rates could be improved by using the new Sepsityper kit from Bruker Daltonics for direct isolation and identification of bacteria from positive blood cultures by MALDI-TOF MS compared with the use of conventional separator gel columns, and to integrate the MALDI-TOF MS-based identification method into the routine course of blood culture diagnostics in the setting of a microbiological laboratory at a university hospital in Germany. The identification of Gram-negative bacteria by MALDI-TOF MS was significantly better using the Sepsityper kit compared with a separator gel tube-based method (99 and 68 % correct identification, respectively). For Gram-positive bacteria, only 73 % were correctly identified by MALDI-TOF with the Sepsityper kit and 59 % with the separator gel tube assay. A major problem of both methods was the poor identification of Gram-positive grape-like clustered cocci. As differentiation of Staphylococcus aureus from coagulase-negative staphylococci is of clinical importance, a PCR was additionally established that was capable of identifying S. aureus directly from positive blood cultures, thus closing this diagnostic gap. Another benefit of the PCR approach is the possibility of directly detecting the genes responsible for meticillin resistance in staphylococci and for vancomycin resistance in enterococci, which is of high importance for early adequate treatment. Both of the described methods were finally integrated into a protocol for fast and effective identification of bacteria from positive blood cultures.

Difficulties of interpreting Borrelia serology in patients with uveitis.

PURPOSE: We aimed to review all uveitis patients with a positive Borrelia serology to evaluate positive results in uveitis subtypes. Further we wanted to test a self-assembled Interferon gamma release assay (IGRA) as a possible supplement method in these patients. METHODS: Patients where serology for Borrelia was ordered from September 2005 to May 2008, were identified by database search. Patients with positive results in ELISA and Western Blot were retested by a self-assembled IGRA. Bayes Theorem was applied. RESULTS: Testing for Borrelia was ordered for 184 patients. 18 patients (9,8%) showed positive results. 11 were positive for IgG (5,9 %), 3 were positive for IgG and IgM (1,6 %) and 4 for IgM (2,1%). Applying Bayes Theorem, we calculated a posttest-probability of 9% in case of a positive test result. 16 of the 18 patients were retested by IGRA. None of them showed a positive result. CONCLUSIONS: A positive serology with uveitis as the only clinical symptom is not sufficient to confirm Borreliosis as 5,9 % of patients with uveitis and a positive IgG serology correspond to the normal spread of Borrelia in the population. Looking at posttest-probability shows a lot of false-positive test results when testing all uveitis patients for Borrelia routinely.