Synergistic in vitro activity between aztreonam and amoxicillin-clavulanate against Enterobacteriaceae-producing class B and/or class D carbapenemases with or without extended-spectrum ß-lactamases.

Introduction. Carbapenemase-producing Enterobacteriaceae have become a major public health concern over the last decade and treatment options are limited.Aims. We evaluated the synergistic activity of the combination of aztreonam (ATM) and clavulanate for 41 ß-lactam-resistant clinical isolates harbouring class B or/and class D carbapenemases combined or not with extended-spectrum ß-lactamases (ESBLs).Methodology. The MICs of ATM, with and without amoxicillin-clavulanate (AMC), were determined. Time-kill assays were performed for three representative strains.Results. The ATM-AMC combination had a synergistic effect on 34/41 (83 %) isolates. The MIC of ATM, in the presence of clavulanate, was ≤1 mg l-1 for 15/41 (37 %) isolates and ≤4 mg l-1 for 29/41 (71 %) isolates. Synergistic activity was observed for 34/37 (92 %) isolates producing ESBLs and carbapenemases, compared to 0/4 (0 %) for ESBL-negative strains. Complete or partial bactericidal activity was obtained when the MIC of the combination was 0.5 mg l-1 and 1.5 mg l-1 or 8 mg l-1, respectively.Conclusion. The combination of ATM and AMC could be an attractive unconventional treatment for infections due to carbapenemase- and ESBL-producing Enterobacteriaceae.

Performance evaluation of the ßLACTA™ Test for rapid detection of ceftazidime resistance in Pseudomonas aeruginosa isolates from cystic fibrosis patients.

The chromogenic ßLACTA™ test was evaluated to detect ceftazidime resistance in P. aeruginosa isolates from patients with cystic fibrosis. Best results were obtained after one hour of incubation with low sensitivity (64.1%), high specificity (98.3%), and negative and positive predictive values of 80.3% and 96.2%, respectively.

In vitro activity of tedizolid and comparator agents against Gram-positive pathogens responsible for bone and joint infections.

Tedizolid, a second-generation oxazolidinone that displays a potent activity against Gram-positive pathogens, could be an interesting option for the treatment of bone and joint infections (BJIs). The aim of the study was to determine minimal inhibitory concentration (MIC) of tedizolid against a collection of 359 clinical isolates involved in clinically-documented BJIs and to compare them to those of comparator agents used in Gram-positive infections. Of the 104 Staphylococcusaureus and 102 coagulase-negative staphylococci (CoNS) isolates, 99 and 92 % were categorized as susceptible to tedizolid, respectively (MIC25=0.12/0.25 µg ml-1 and MIC90=0.25/0.5 µg ml-1), regardless of their methicillin resistance. MIC50 and MIC90 for the 51 enterococci, the 50 Corynebacterium spp. and the 52 Propionibacterium spp. were either equal or inferior to 0.5 µg ml-1. Altogether, tedizolid possessed a potent in vitro activity against most of the BJI Gram-positive pathogens with 95 % of them exhibiting a MIC ≤0.5 µg ml-1.