Carbapenemase-mediated resistance to carbapenems in Enterobacteriaceae has become the main challenge in the treatment and prevention of infections recently. The partially unnoticed spread of OXA-48-type carbapenemase producers is usually assigned to low minimum inhibitory concentrations (MICs) of carbapenems that OXA-48-producing isolates often display. Therefore, there is an urgent need of specific and sensitive methods for isolation and detection of OXA-48 producers in clinical microbiology diagnostics. The influence of bicarbonates on carbapenem MICs against carbapenemase-producing Enterobacteriaceae was tested. We also checked whether the addition of bicarbonates to liquid media supplemented with meropenem may facilitate the selective enrichment of various carbapenemase producers in cultures. Furthermore, the sensitivity of carbapenemase confirmation by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) and spectrophotometric hydrolysis assays upon the addition of NH4HCO3 was examined. The addition of NaHCO3 significantly increased MICs of ertapenem and meropenem for OXA-48 producers. Furthermore, liquid media supplemented with NaHCO3 and meropenem were reliable for the selective enrichment of carbapenemase producers. The presence of NH4HCO3 in buffers used in the spectrophotometric and MALDI-TOF MS carbapenemase detection increased the sensitivity of that assay. Our results demonstrate that bicarbonates in media or reaction buffers can enhance the sensitivity of screening methods and diagnostic tests for carbapenemase producers.

• MeSH
• Bacterial Proteins analysis   secretion   MeSH
• beta-Lactamases analysis   secretion   MeSH
• Enterobacteriaceae enzymology   isolation & purification   MeSH
• Enterobacteriaceae Infections diagnosis   microbiology   MeSH
• Bicarbonates diagnostic use   MeSH
• Culture Media chemistry   MeSH
• Microbial Sensitivity Tests methods   MeSH
• Buffers MeSH
• Sensitivity and Specificity MeSH
• Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization MeSH
• Publication type
• Journal Article MeSH
• Evaluation Study MeSH
• Research Support, Non-U.S. Gov't MeSH

A comparison of a matrix-assisted laser desorption ionization-time of flight mass spectrometric (MALDI-TOF MS) meropenem hydrolysis assay with the Carba NP test showed that both methods exhibited low sensitivity (approximately 76%), mainly due to the false-negative results obtained with OXA-48-type producers. The addition of NH4HCO3 to the reaction buffer for the MALDI-TOF MS assay dramatically improved its sensitivity (98%). Automatic interpretation of the MALDI-TOF MS assay, using the MBT STAR-BL software, generally agreed with the results obtained after manual analysis. For the Carba NP test, spectrophotometric analysis found six additional carbapenemase producers.

• MeSH
• Electronic Data Processing MeSH
• Bacterial Proteins analysis   MeSH
• beta-Lactamases analysis   MeSH
• Bicarbonates * MeSH
• Hydrolysis MeSH
• Automation, Laboratory MeSH
• Humans MeSH
• Buffers MeSH
• Sensitivity and Specificity MeSH
• Software MeSH
• Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization methods   MeSH
• Thienamycins metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Evaluation Study MeSH
• Research Support, Non-U.S. Gov't MeSH

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is a potentially useful tool for the detection of antimicrobial resistance, especially that conferred by β-lactamases. Here we describe a modification of a previously reported MALDI-TOF MS meropenem hydrolysis assay. The modified method was validated on 108 carbapenemase-producing members of the Enterobacteriaceae, two NDM-1-producing Acinetobacter baumannii isolates, and 35 carbapenem-resistant enterobacteria producing no carbapenemase. The detection of carbapenemases by MALDI-TOF MS seems to be a powerful, quick, and cost-effective method for microbiological laboratories.

• MeSH
• Acinetobacter baumannii enzymology   MeSH
• Bacterial Proteins metabolism   MeSH
• beta-Lactamases metabolism   MeSH
• Enterobacteriaceae enzymology   MeSH
• Enterobacteriaceae Infections microbiology   MeSH
• Hydrolysis MeSH
• Humans MeSH
• Microbial Sensitivity Tests methods   MeSH
• Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization methods   MeSH
• Thienamycins metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Validation Study MeSH