Objective:To explore the feasibility of rapid detection of AAC(6′)-Ⅰb-cr enzyme-producing Enterobacteriales using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Methods:A total of 55 Enterobacteriales strains isolated from the Department of Clinical Laboratory of Wenzhou TCM Hospital from January to July 2022 were collected. Ciprofloxacin and norfloxacin solutions were used as reaction substrates, incubated with the test strains for 1 hour, followed by centrifugation, and the supernatant was detected by MALDI-TOF MS. In addition, 128 clinical strains isolated from the clinical laboratory of our hospital from March to May 2023 were prospectively collected for the validation study of the method. Results:After ciprofloxacin and norfloxacin were acetylated by the AAC(6′)-Ⅰb-cr enzyme, a mass shift of relative molecular mass 42 occurred, resulting in the appearance of three mass spectral peaks representing the acetylated drugs. No such peak was observed in enzyme-negative strains. Besides, compared with gene sequencing results, the MALDI-TOF MS results of 128 strains used in the validation test showed 100% both in specificity and sensitivity.Conclusion:MALDI-TOF MS can rapidly and accurately detect AAC(6′)-Ⅰb-cr enzyme-producing Enterobacteriaceae bacteria.

Objective:To explore the feasibility of rapid detection of AAC(6′)-Ⅰb-cr enzyme-producing Enterobacteriales using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Methods:A total of 55 Enterobacteriales strains isolated from the Department of Clinical Laboratory of Wenzhou TCM Hospital from January to July 2022 were collected. Ciprofloxacin and norfloxacin solutions were used as reaction substrates, incubated with the test strains for 1 hour, followed by centrifugation, and the supernatant was detected by MALDI-TOF MS. In addition, 128 clinical strains isolated from the clinical laboratory of our hospital from March to May 2023 were prospectively collected for the validation study of the method. Results:After ciprofloxacin and norfloxacin were acetylated by the AAC(6′)-Ⅰb-cr enzyme, a mass shift of relative molecular mass 42 occurred, resulting in the appearance of three mass spectral peaks representing the acetylated drugs. No such peak was observed in enzyme-negative strains. Besides, compared with gene sequencing results, the MALDI-TOF MS results of 128 strains used in the validation test showed 100% both in specificity and sensitivity.Conclusion:MALDI-TOF MS can rapidly and accurately detect AAC(6′)-Ⅰb-cr enzyme-producing Enterobacteriaceae bacteria.