Vol.67 No.1 January 2019

MALDI-TOF mass spectrometry for detection and identification of extended-spectrum β-lactamases

Kazuko Ikegaya^{1, 2)}, Yuriko Matsumura²⁾, Keisuke Shima³⁾, Atsuo Iwasawa²⁾, Satoshi Kimura²⁾ and Ken Tsuchiya¹⁾

¹⁾Department of Clinical Laboratory, Shizuoka City Shimizu Hospital, 1231 Miyakami, Shimizu-ku, Shizuoka, JAPAN
²⁾Division of Infection Prevention and Control, Tokyo Healthcare University
³⁾Shimadzu Corporation

Abstract

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been applied for microorganism identification, and is widely used in the field of clinical microbiology, with economic and diagnostic benefits. Recently, it has been used for the detection of antibiotic resistance by monitoring the hydrolysis of antibiotics. There are many reports of detection of carbapenemase with the MALDI Biotyper, however, there have been no studies using VITEK^Ⓡ MS. The aim of this work was to confirm the hydrolysis of cefotaxime (CTX) using VITEK^Ⓡ MS, in order to detect the extended-spectrum β-lactamases (ESBLs). Escherichia coli ATCC^Ⓡ 25922^TM (sensitive strain), E. coli NCTC 13462 (bla_CTX-M group 2-producing strain) and Klebsiella pneumoniae ATCC^Ⓡ BAA-1705^TM (KPC-producing strain) were used as the test strains. On the MS spectrum, signals at 455.77 Da (proton adduct) and 477.85 Da (sodium adduct) were observed after 60 minutes' incubation of CTX in saline at 36°C. A linear relationship was observed between the amount of CTX and the relative signal intensities at I₄₅₆ and I₄₇₈, where the signal intensities were normalized using that of the dimer of 2-cyano-4-hydroxycinnamate (CHCA). Signals at 369.86 Da and 413.74 Da appeared when a bacterial suspension of E. coli NCTC 13462 was used. These phenomena were observed for the carbapenemase-producing bacteria. It was found that VITEK^Ⓡ MS is useful for detecting ESBLs by monitoring the reaction products of CTX with β-lactamase. It was also suggested that the antibiotic susceptibility of ESBL-producing bacteria to CTX can be estimated from the standardized signal intensities.

Key word

antibiotics, antibiotic resistance, MALDI-TOF MS, cefotaxime, hydrolysis

Received

May 2, 2018

Accepted

August 28, 2018

Jpn. J. Chemother. 67 (1): 29-37, 2019