Superiority of SDS lysis over saponin lysis for direct bacterial identification from positive blood culture bottle by MALDI-TOF MS.

PURPOSE: Fast species diagnosis has an important health care impact, as rapid and specific antibacterial therapy is of clear benefit for patient's outcome. Here, a new protocol for species identification directly from positive blood cultures is proposed.

EXPERIMENTAL DESIGN: Four in-house protocols for bacterial identification by MS directly from clinical positive blood cultures evaluating two lytic agents, SDS and saponin, and two protein extraction schemes, fast (FP) and long (LP) are compared. One hundred and sixty-eight identification tests are carried out on 42 strains.

RESULTS: Overall, there are correct identifications to the species level in 90% samples for the SDS-LP, 60% for the SDS-FP, 48% for the saponin LP, and 43% for the saponin FP. Adapted scores allowed 92, 86, 72, and 53% identification for SDS-LP, SDS-FP, saponin LP, and saponin FP, respectively. Saponin lysis is associated with a significantly lower score compared to SDS (0.87 [0.83-0.92], p-value < 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE: This study supports the use of SDS lysis instead of saponin lysis and the application of this rapid and cost-effective protocol in daily routine for microbiological agents implicated in septicemia.