A-279 Comparison of Direct Identification and Short Incubation Time Methods of MALDI-TOF MS from Positive Blood Vials
Authors: Kuo S , Pan L , You H 
Published: September 2023

Abstract

Background
MALDI-TOF analysis after a short incubation time of positive blood culture is currently one of the most widely used methods for rapidly identifying microorganisms. This method can identify most pathogenic bacteria within 4 to 6 h after blood culture. This experiment aims to use direct identification for MALDI-TOF analysis, which can shorten the identification time of bacteria and analyze the advantages and disadvantages of the two methods.

Method
We collected from January 2022 to December 2022, a total of 295 bottles of a single infection. After pretreatment methods such as removing cells and high-speed centrifugation to collect bacteria, carry out direct identification by MALDI-TOF then culture for 5 h for short incubation time method. The culture medium was continued incubated for 18–20 h, to confirm the final identification results of the strains and compare the identification accuracy of direct identification and short incubation time methods. Definition: confidence score cut-off values &gt; = 1.7 of direct identification method.

Result
The identification rate of score &gt; = 1.7 were 67%(199/295). Gram-negative bacilli were identified in 89%, followed by anaerobes in 60% and Gram-positive species in 56%. The yeast could not be identified either by the short incubation time method or the direct identification method. The short incubation time method identified 90% of Gram-negative bacilli, followed by 79% of Gram-positive bacteria and 7% of anaerobic bacteria. The rapid identification of anaerobic bacteria was significantly better than the identification results of the short incubation time method (60%:7%) (P value = 0.01). In addition, the results can be obtained within one hour by direct identification, which can save at least 5-fold times required for the short incubation time method of about 5 h, although the effect is slightly worse than short incubation time method (67 %:76%). Especially for Gram-negative bacilli, there is no statistically significant difference between direct identification and short incubation time methods; it proves that direct identification method can indeed replace short incubation time method.

Conclusion
Patients with septic shock who were treated with antibiotics within one hour had an 80% chance of survival; however, for every hour of delay within six hours of onset, the survival rate decreased by 7.6%. Compared with the short incubation time method, the direct identification method can report the correct strain to clinician 5-fold times earlier. This rapid, simplified extraction direct identification method is cost-effective, time-saving, and easy to use. The SSC sepsis guidelines in 2016 pointed out that extending the course of antibiotic treatment not only has no additional benefits but also is prone to drug resistance, resulting in side effects of antibiotics. Therefore, the direct identification method can significantly improve the optimal utilization of antibiotics for effective targeted treatment and reduce mortality, especially for the identification of anaerobic bacteria, which can provide faster identification results. Therefore, it is recommended that clinical laboratories include a direct identification method for routine identification of blood culture, and if they cannot be identified, they can be supplemented by a short incubation time method, to shorten the time of blood culture identification and effectively improve the treatment of bloodstream infections.