Rapid identification of bacteria directly from positive blood cultures by a modified method using a serum separator tube and matrix-assisted laser desorption ionization – time of flight MS

Abstract

Introduction. Several studies have used matrix-assisted laser desorption ionization-time of flight MS (MALDI-TOF) with a serum separator tube (SST) to perform rapid identification of microorganisms directly from positive blood cultures (BCs), with different performances and methodologies. Hypothesis / Gap Statement. The use of TSS could significantly reduce the time of identification of microorganisms that produce bacteremia. Aim. Our goals were to evaluate bacterial identification by MALDI-TOF using a method based on an SST and compare it with MALDI-TOF after subculture for 18–24 h. Methodology. BCs no more than 1 h after a positive growth signal were included in the study. Analysis of results was expressed as a score. Information about time to a positive signal and number of microorganisms was collected. Results. In total, 253 BCs were analysed; 45.5 % gave a reliable result, 23.3 % an unreliable result and 31.2 % an error in identification. In gram-negative and gram-positive bacteria, the percentages of reliable results were 83.5 and 21.8 %, respectively. According to time to positive signal, the percentages of correct identification and mean score were 81.1 % (99/122) and 1.89±0.30 in Group 1 (<15 h); and 57.2 % (75/131) and 1.70±0.32 in Group 2 (>15 h), respectively (P <0.001). According to the number of microorganisms, the corresponding percentages of correct identification and mean scores were: Group 1 [≤50 microorganisms observed per field (MOF)], 50/94 (53.19 %) and 1.72±0.32; Group 2 (51–100 MOF): 44/66 (66.67 %) and 1.85±0.34; Group 3 (>100 MOF): 79/93 (84.94 %) and 1.84±0.31. Conclusion. This method allowed us to obtain a high percentage of the aetiological agent of bacteraemia in less than 30 min after a positive BC.

Parallel Validation of the NG-Test Carba 5 and the Xpert Carba-R for Detection and Characterization of Carbapenem-Resistant Enterobacterales Causing Bloodstream Infections

“…A score above 99.9 was considered acceptable. 12,13 To determine carbapenem susceptibilities phenotypically, bacterial isolates and BCB specimens were inoculated on blood agar plates in three-phase streaking, followed by incubation at 35 C AE 2 C for 18 to 24 hours. Identification and antimicrobial susceptibility testing were performed using the Vitek 2 Compact automated microbial identification system (bioMérieux).…”

Rapid and precise identification of bloodstream infections using a pre-treatment protocol combined with high-throughput multiplex genetic detection system

“…Next, the centrifugation adopting a serum separation tube (SST) can enrich pathogens from up to 5-10 mL samples, yielding an equivalent of 5-10 mL sample input volume per PCR, and the removal of the supernatant after centrifugation can also reduce potentially interfering factors efficiently, through which the pathogen load assayed was increased directly and the pathogen was preliminarily purified. This approach had been successfully applied for the enrichment of pathogens from blood culture samples for subsequent identification by MALDI-TOF MS, which proved to be able to capture bacteria effectively out of such a substrate and no side effect was reported [29][30][31]. Finally, despite the depletion of factors that interfere with PCR, inhibition was still observed after the above process, which resulted in relatively low peaks in the detection of positive samples and even false negative results.…”

Rapid and precise identification of bloodstream infections using a pre-treatment protocol combined with high-throughput multiplex genetic detection system

“…Next, the centrifugation adopting a serum separation tube (SST) can enrich pathogens from up to 5-10 mL samples, yielding an equivalent of 5-10 mL sample input volume per PCR, and the removal of the supernatant after centrifugation can also reduce potentially interfering factors e ciently, through which the pathogen load assayed was increased directly and the pathogen was preliminarily puri ed. This approach had been successfully applied for the enrichment of pathogens from blood culture samples for subsequent identi cation by MALDI-TOF MS, which proved to be able to capture bacteria effectively out of such a substrate and no side effect reported [29][30][31]. Finally, despite depletion of factors that interfere with PCR, inhibition were still observed after the above process, which resulted in relatively low peaks in the detection of positive samples and even false negative results.…”