Background: Sequence type 131 (ST131) O25b serogroup Escherichia coli, producing CTX-M type extended-spectrum β-lactamase (ESBL), is a major clone involved in worldwide pandemic spread in both community- and healthcare-associated infections. Recently, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has become a routine tool for the identification of bacteria in many laboratories. This study aimed to assess the performance of MALDI-TOF MS for the screening of ESBL-producing E. coli ST131 in a rapid, inexpensive, and simple way.

Methods: A total 26 clinical E. coli, isolated from blood between 2013 and 2014, were used. The characteristics are ST131-O25b ESBL producers (n=6), ST131-O16 ESBL producers (n=4), non-ST131 ESBL producers (n=11), and non-ST131 non-ESBL producers (n=5). Specific biomarker peaks to distinguish the ST131 clonal group from others were investigated by MicroIDSys (ASTA, South Korea) and ASTA Tinkerbell 2.0 software.

Results: A peak at 9,713 m/z peak is useful to screen for ST131 E. coli, regardless of serogroup O25 or O16, showing a sensitivity of 100%, specificity of 56.2%, positive predictive value of 58.8%, and negative predictive value of 100% when using a relative intensity cutoff of 15%.

Conclusion: We can screen for ST131 E. coli using MicroIDSys (ASTA), MALDI-TOF MS in a rapid, inexpensive, and simple way. However, other confirmatory tests are needed to confirm ST131 E. coli due to the low specificity of this method. (Ann Clin Microbiol 2016;19:65-69)