Eravacycline: evaluation of susceptibility testing methods and activity against multidrug-resistant Enterobacterales and Acinetobacter.

PURPOSE

Eravacycline is a tetracycline approved for treating intra-abdominal infections caused by multidrug-resistant (MDR) bacteria. Our study aims to compare two methods for determining eravacycline MIC against Gram-negatives and to evaluate its in vitro activity compared with various antibiotics, particularly last-line agents.

METHODS

We performed susceptibility testing of eravacycline against 275 consecutive MDR Gram-negative clinical isolates collected by the Belgian NRC. The tested strains include Enterobacterales (n = 222) and Acinetobacter (n = 53) species, mostly carbapenemase producers. We used consecutively 111 of these strains to perform method comparison. ERV MICs were determined by broth microdilution (BMD) using Sensititre customized panel (ThermoFisher) and by gradient diffusion strip method (Etest Biomérieux).

RESULTS

According to the BMD method, 83.3% of Enterobacterales were eravacycline susceptible (using EUCAST 2024 breakpoints for E. coli and FDA breakpoints) and 56.6% of Acinetobacter spp. below the ECOFF. For Enterobacterales, the CA, VMD, MD and EA were 98.4%, 1.64%, 0% and 100% respectively. For A. baumannii, we obtained 90% of CA, 88% of EA, 0% of VMD and 10% of MD. For Enterobacterales, eravacycline and tigecycline exhibited a MIC50 of 0.25 and 0.5 mg/L respectively. Colistin displayed a MIC50 of 0.5 mg/L while cefiderocol showed a MIC50 of 0.5 mg/L. 83.3%, 78.4%, 92.8% and 89.4% of Enterobacterales were eravacycline, tigecycline, colistin and cefiderocol susceptible respectively. For Acinetobacter spp., MIC50 was 0.25 mg/L for eravacycline; 0.5 mg/L for tigecycline; 1 mg/L for colistin and 0.25 mg/L for cefiderocol. 56.6%, 47.2%, 92.5% and 72.7% of Acinetobacter spp. were eravacycline, tigecycline, colistin and cefiderocol susceptible respectively.

CONCLUSION

Gradient diffusion strip method provides accurate and reproductible eravacycline susceptibility results overall. Eravacycline may be an interesting therapeutical option against MDR Enterobacterales, with activity rate relatively similar to tigecycline and cefiderocol. Against MDR Acinetobacter spp., eravacycline displayed only moderate activity, despite one dilution lower MIC50 than tigecycline.