A rapid and inexpensive protocol to screen for third generation cephalosporin-resistant and non-fermenting Gram-negative rods directly in positive blood cultures

Diagn Microbiol Infect Dis. 2021 Oct;101(2):115428. doi: 10.1016/j.diagmicrobio.2021.115428. Epub 2021 May 16.


Third generation cephalosporins are frequently used in the first-line treatment of Gram-negative rod (GNR) bacteremia but are unsuitable in the case of extended-spectrum-beta-lactamase-producing Enterobacterales (ESBL-E) or non-fermenting GNR infections. The aim of this study was to develop and evaluate a simple and rapid two-test protocol involving oxidase and β-Lacta tests performed directly on positive blood culture broth as a preliminary screen for non-fermenting or third generation cephalosporins-resistant GNR. The diagnostic performance of this approach was evaluated on 294 bottles for the oxidase test and 267 bottles for the β-Lacta Test. The sensitivity and specificity of the oxidase test were respectively 93.1% and 100%, and the sensitivity of the β-Lacta Test for ESBL-E was 100% and the specificity 99.5%. This simple protocol, which can be implemented in all laboratories and performed in only 20 min, may be a valuable tool to optimize first-line antibiotic therapy for bacteremia.

Keywords: Beta-Lacta Test; Gel separator tubes; Gram-negative rods bacteremia; Oxidase; Positive Blood culture; Third-generation cephalosporin resistance.

Publication types

  • Evaluation Study

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Bacteremia / blood
  • Bacteremia / diagnosis*
  • Bacteremia / microbiology
  • Bacterial Proteins / metabolism
  • Blood Culture
  • Cephalosporin Resistance
  • Cephalosporins / pharmacology*
  • Gram-Negative Bacteria / drug effects
  • Gram-Negative Bacteria / enzymology
  • Gram-Negative Bacteria / genetics
  • Gram-Negative Bacteria / isolation & purification*
  • Gram-Negative Bacterial Infections / blood
  • Gram-Negative Bacterial Infections / diagnosis*
  • Gram-Negative Bacterial Infections / microbiology
  • Humans
  • Oxidoreductases / metabolism
  • Prospective Studies
  • Sensitivity and Specificity
  • beta-Lactamases / metabolism


  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Cephalosporins
  • Oxidoreductases
  • beta-Lactamases