We quantified in vitro the combined antibacterial effects of two commonly used aminoglycosides, Gentamycin and Tobramycin (GEN and TOB), and two β-lactams, Ampicillin and Cefotaxime (AMP and CTX), for 254 E. We set out to systematically quantify the interactions of the β-lactam/aminoglycoside combination, against an extensive collection of BSI E. In this study, we aimed to characterize the antibiotic interaction profiles in vitro of one of the most commonly prescribed antibiotic combinations consisting of a β-lactam combined with an aminoglycoside for treatment of BSIs. A principle-component analysis on the interaction profile of the strains tested revealed that the interaction of the 2 antibiotics in these combinations largely depends on the choice of the aminoglycoside used. Specifically, the combination of AMP-GEN was antagonistic in approximately 2% of strains followed by the combinations of CTX-GEN and AMP-TOB that were antagonistic in approximately 1% of strains. Alarmingly in a fraction of our isolates we discovered, previously overlooked, significant levels of antagonism between some antibiotics. For most strains we detected an additive interaction between the antibiotics used in combination. coli strains isolated from blood of patients with suspicion of a BSI.
Our study encompasses 254 patient samples of E. To this end, we performed the largest to date systematic quantification of antibiotic interactions in clinical isolates. We chose to test 4 such combinations: Gentamicin (GEN) or Tobramycin (TOB) combined with Ampicillin (AMP) or Cefotaxime (CTX). In this study, we set out to investigate the combinatorial efficacy of the most common antibiotic combination used in the treatment of Blood stream infections.
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