Direct antimicrobial susceptibility testing from the blood culture pellet obtained for MALDI-TOF identification of Enterobacterales and Pseudomonas aeruginosa

  • J. M. López-Pintor
  • C. Navarro-San FranciscoEmail author
  • J. Sánchez-López
  • A. García-Caballero
  • E. Loza Fernández de Bobadilla
  • M. I. Morosini
  • R. Cantón
Original Article


To standardize the methodology for conducting direct antimicrobial susceptibility testing (AST) of Enterobacterales and Pseudomonas aeruginosa causing bacteremia from positive blood culture pellets. Two methods for processing positive blood cultures with Enterobacterales and P. aeruginosa were compared: a conventional method for identification and AST versus a direct method obtaining a pellet for both matrix-assisted laser desorption/ionization–time of flight (MALDI-TOF) identification and direct AST. A total of 157 (145 Enterobacterales, 12 P. aeruginosa) positive blood cultures were included. Microorganism identification showed 100% concordance between both methods at species and genus level. Definitive AST results were obtained 24 h earlier with the rapid method than the conventional one (p < 0.001). Of the 2814 MICs generated, there were discrepancies with respect to the conventional method in 47 (1.7%), 0.3% being very major (VME) and 1.3% major (ME) errors. Better results for AST were obtained when colony counts with the pellet were ≥ 105 cfu/ml. The essential agreement (EA) for antibiotics tested in Enterobacterales was at least 97%, except for ampicillin (95%). Regardless of colony count, the greatest discrepancies were observed for first/s-generation cephalosporins and aminoglycosides. In P. aeruginosa, EA was at least 92%, except for piperacillin-tazobactam (84%) and cefepime (76%). No VME occurred except for ceftazidime (8%). ME occurred in piperacillin/tazobactam (16%), ticarcillin, ceftazidime, tobramycin, amikacin, and colistin (8% each). Direct use of the blood culture pellet permits fast AST in bacteremia of Enterobacterales, enabling the clinicians to perform an early treatment adjustment. However, for Pseudomonas aeruginosa, the data needs expanding to improve the reliability of this technique.


Bacteraemia Gram-negative bacilli Blood culture pellet Direct antimicrobial susceptibility testing MALDI-TOF 



RC research is partially supported by Plan Nacional de I+D+i 2013–2016 and Instituto de Salud Carlos III, Subdirección General de Redes y Centros de Investigación Cooperativa, Ministerio de Economía, Industria y Competitividad, Spanish Network for Research in Infectious Diseases (REIPI RD16/0016/0011)—co-financed by European Development Regional Fund “A way to achieve Europe”, Operative program Intelligent Growth 2014–2020, and Fundación Soria Melguizo (Madrid, Spain).

We thank Mary Harper for English correction of the manuscript. Also, we thank Francisca Pérez, Maria Isabel Moya, and Isabel Soler for their daily work.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

The study was approved by the local ethics committee as it stated in the record number 332 of this committee.

Supplementary material

10096_2019_3498_MOESM1_ESM.docx (20 kb)
ESM 1 (DOCX 19 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • J. M. López-Pintor
    • 1
  • C. Navarro-San Francisco
    • 1
    • 2
    Email author
  • J. Sánchez-López
    • 1
  • A. García-Caballero
    • 1
  • E. Loza Fernández de Bobadilla
    • 1
    • 2
  • M. I. Morosini
    • 1
    • 2
  • R. Cantón
    • 1
    • 2
  1. 1.Servicio de MicrobiologíaHospital Universitario Ramón y Cajal, Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS)MadridSpain
  2. 2.Red Española de Investigación en Patología Infecciosa (REIPI)Instituto de Salud Carlos IIIMadridSpain

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