Flumequine, a fluoroquinolone in disguise

Abstract

Fluoroquinolone resistance in E. coli isolates from livestock in Europe remains high despite EMA restrictions on fluoroquinolone use in animals. However, flumequine, a quinolone not classified as a fluoroquinolone by various regulatory bodies, is still used in livestock in the Netherlands, Belgium, Greece and France. We investigated whether flumequine selects for the same resistance mechanisms in E. coli. Resistant and non-resistant E. coli isolates were obtained from caecal fermentation assays and broilers exposed to concentrations of flumequine and enrofloxacin. Flumequine usage leads to an approximately 3-fold increase in resistant E. coli in the caecal fermentation, similar to enrofloxacin. In vitro exposure to both flumequine and enrofloxacin revealed the same amino acid substitutions (S83L, D87G) in GyrA. Additionally, the same resistance-causing substitutions were found in phenotypically resistant E. coli isolates from broilers treated with either enrofloxacin or flumequine. Flumequine induces similar resistance mechanisms as enrofloxacin, warranting equivalent restrictions on its use.

Fig. 1. Percentage of surviving E. coli isolates after stepwise exposure per timepoint the maximum could be 10 isolates resistant (n = 10).

A represents the curve after the enrofloxacin treatment and (B) after the flumequine treatment. r = correlations coefficient (Kendalls correlation test). P = the p value which shows that the null hypothesis is rejected.

Fig. 2. Resistant E. coli colonies isolated from the caecal fermentations.

Graph (A) Caecal fermentation treated with enrofloxacin. Graph (B) Caecal fermentation with flumequine. Error bars are representing standard errors of the mean. **** p ≤ 0.0001.

Fig. 3. Percentage resistant E. coli colonies after exposure of clinical concentrations of flumequine.

T = 0 is before initiating the treatment and T = 1 directly after termination of the treatment. A represents the control group which was not treated with flumequine and (B) the group that was treated with flumequine. On the x-axis the concentrations in the control plates are displayed. ECOFF concentration (2 mg/L flumequine and 0.125 mg/L enrofloxacin) and clinical breakpoint concentrations (8 mg/L flumequine and 2 mg/L enrofloxacin). Error bars are representing standard errors of the mean. **** p ≤ 0.0001.