Abstract
BackgroundMatrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been proved to be a useful tool for identification of pathogens directly isolated from blood cultures in clinical microbiology laboratories. β-Lactam antibiotics are commonly used for treatment of bloodstream infections caused by Enterobacteriaceae strains, and carbapenem is the superlative class of β-lactam antibiotics. Since the carbapenem resistance rate of Enterobacteriaceae strains raised year by year, efficient detection of carbapenemase activity and timely delivery of carbapenem susceptibility reports of Enterobacteriaceae strains isolated from blood cultures is important for clinicians.MethodsWe used 64 simulated blood cultures to establish the method of MALDI-TOF MS based ertapenem hydrolysis assay. The cutoff value of logRQ calculated from the peaks intensity of ertapenem and its hydrolysate was first set to identify the strains with carbapenemase activity. Then, we detected and calculated the logRQ values of 385 Enterobacteriaceae strains from positive clinical blood cultures to distinguish the carbapenemase producers and noncarbapenemase producers.ResultsThe mean logRQ value of 32 noncarbapenemase producers was − 0.85 ± 0.14 in simulated blood cultures, while the logRQ value of 32 carbapenemase producers was 0.87 ± 0.55. Thus, the cutoff value of logRQ was set at − 0.45 with sensitivity of 100% and specificity of 100%. In 385 clinical positive blood cultures, the logRQ values of all carbapenem-susceptible Enterobacteriaceae strains (81.3%, 313/385) were < − 0.45. Comparing with the detection of carbapenemase genes, carbapenem-resistant Enterobacteriaceae strains (18.7%, 72/385) were well distinguished by MALDI-TOF MS based ertapenem hydrolysis assay with a sensitivity of 92.5% and specificity of 100%.ConclusionsOur data show that MALDI-TOF MS based ertapenem hydrolysis assay is a rapid and accurate method to detect carbapenemase activity of Enterobacteriaceae strains from positive blood cultures, and can be routinely performed in clinical microbiology laboratories.
Highlights
Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MS)) has been proved to be a useful tool for identification of pathogens directly isolated from blood cultures in clinical microbiology laboratories. β-Lactam antibiotics are commonly used for treatment of bloodstream infections caused by Enterobacteriaceae strains, and carbapenem is the superlative class of β-lactam antibiotics
Efficiency of MALDI‐TOF MS based hydrolysis assay A total of 385 clinical blood culture bottles contained Enterobacteriaceae strains from different body parts of 218 patients were collected. 81.3% (313/385) were sensitive to carbapenem, including Escherichia coli (207), Klebsiella pneumoniae (68), Enterobacter cloacae (15), Klebsiella oxytoca (6), Serratia marcescens (5), Citrobacter freundii (3), Citrobacter koseri (3), Enterobacter aerogenes (2), Morganella morganii (2), Proteus mirabilis (2)
Comparing with the detection of carbapenemase genes, MALDI-TOF MS based ertapenem hydrolysis assay of carbapenemase detection has a sensitivity of 92.5% (62/67) [95% CI 86.2–98.8%] and specificity of 100% (5/5) [95% CI 100–100%]
Summary
Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been proved to be a useful tool for identification of pathogens directly isolated from blood cultures in clinical microbiology laboratories. β-Lactam antibiotics are commonly used for treatment of bloodstream infections caused by Enterobacteriaceae strains, and carbapenem is the superlative class of β-lactam antibiotics. Β-Lactam antibiotics are commonly used for treatment of bloodstream infections caused by Enterobacteriaceae strains, and carbapenem is the superlative class of β-lactam antibiotics. Since the carbapenem resistance rate of Enterobacteriaceae strains raised year by year, efficient detection of carbapenemase activity and timely delivery of carbapenem susceptibility reports of Enterobacteriaceae strains isolated from blood cultures is important for clinicians. In the past few years, along with the large-scale use of antibiotics, carbapenem resistance of Enterobacteriaceae strains has increased rapidly and become one of the most common global health issues [5], especially for the carbapenem resistance rate of clinical isolated Klebsiella pneumoniae, which has reached up to 10% in 2014 [6, 7]. It’s important for clinical microbiology laboratories to give clinicians timely and believable antimicrobial reports for early anti-infective treatment
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