Summation of peaks and L34 ribosomal protein in the presence and absence of antibiotics enables susceptibility testing using MALDI-TOF mass spectrometry in 2h from Escherichia coli-positive blood cultures

Enferm Infecc Microbiol Clin (Engl Ed). 2019 Apr;37(4):244-250. doi: 10.1016/j.eimc.2018.06.017. Epub 2018 Sep 17.
[Article in English, Spanish]

Abstract

Introduction: We have developed a MALDI-TOF-mediated phenotypic method, which determines antibiotic susceptibility (AS) from positive blood cultures (BCs) in 2h. We developed a software for process automation. We report results on Escherichia coli-positive BCs with cefotaxime (CTX) and ciprofloxacin (CIP).

Methods: We studied CIP and CTX activity in 18 and 17 real E. coli-positive BCs, and in 56 and 45 spiked BCs, respectively. Positive BCs were incubated for 2h without any antibiotics, and with 2mg/l and 4mg/l of CIP and CTX. The extraction was performed using ethanol/formic acid. Spectra were processed with specifically developed software which compares the peaks' intensity and the size of specific peaks.

Results: The set cut-off point was a 3-fold decrease in the summation of all peaks and/or the 5382m/z peak value (ribosomal protein L34). In simulated BCs, the correlation of CIP 2mg/l and 4mg/l with Etest® was 94.6% and 98.2%, respectively; for CTX 2mg/l and 4mg/l, this correlation was 95.6%. In real BCs, the correlations were 100% for CIP (2mg/l and 4mg/l) and 88.2% and 94.1% for CTX 2mg/l and 4mg/l, respectively. Resistant isolates were always correctly classified.

Conclusion: This method provides accurate, fast and inexpensive AS information. The method can be automated, making it easier to implement in a microbiology laboratory routine.

Keywords: Antibiotic susceptibility; Blood cultures; Espectrometría de masas MALDI-TOF; Hemocultivos; MALDI-TOF MS; Sensibilidad a antimicrobianos.

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Bacteriological Techniques / methods
  • Blood Culture
  • Cefotaxime / pharmacology*
  • Ciprofloxacin / pharmacology*
  • Escherichia coli / drug effects*
  • Humans
  • Microbial Sensitivity Tests
  • Ribosomal Proteins / analysis*
  • Software
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization*
  • Time Factors

Substances

  • Anti-Bacterial Agents
  • Ribosomal Proteins
  • ribosomal protein L34
  • Ciprofloxacin
  • Cefotaxime