Accuracy of various matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS)-based rapid identification methods-As a tool to augment diagnostic stewardship in blood culture laboratory, South India.

BACKGROUND

Blood stream infection is a medical emergency associated with high morbidity and mortality. Prompt identification of bloodstream infection-causing microorganisms directly from positive blood culture will significantly enhance patient care by reducing the turnaround time of pathogen recognition.

METHODS

A total of 256 freshly flagged positive blood culture bottles were subjected to Gram staining. Direct MALDI-TOF MS analysis was performed following sample preparation techniques such as lysis centrifugation, lysis filtration and VITEK® MS BC kit to directly identify microorganisms from positive blood cultures. Along with these short-term incubation methods of Choco spot and minute colony(8-10h) were also performed. All those positive bottles were identified by the routine (reference) laboratory method.

RESULTS

177 isolates (69.14 %) were correctly identified by Lysis centrifugation, 163 isolates (63.67 %) were correctly identified by Lysis filtration, 206 isolates (80.47 %) were correctly identified by Choco spot,250 isolates (97.65 %) were correctly identified from minute colony (8-10h) of incubation. Of 162 isolates,115 isolates (70.99 %) were correctly identified by VITEK® MS Blood culture kit, (BioMérieux). VITEK® MS BC kit method revealed higher agreement with the kappa value of 0.697 than lysis centrifugation (0.672) followed by lysis filtration (0.611).

CONCLUSIONS

In house method of lysis centrifugation is found to be equivalent to VITEK® MS BC kit method and superior to lysis filtration method in correct direct identification of bacteria from positive blood cultures by MALDI-TOF MS analysis. As lysis centrifugation requires only 10 min of processing time as compared to overnight incubation, thus it offers a less expensive substitute for the VITEK® MS BC kit in the clinical laboratory. As a consequence of this study, we have implemented direct MALDI-TOF-based identification from positive BCs in our daily routine diagnostic management.