Inhibitory effects of fluoroquinolone antibiotics on Babesia divergens and Babesia microti, blood parasites of veterinary and zoonotic importance

Abstract

Aim: This study aimed to evaluate the inhibitory effects of fluoroquinolone antibiotics, including enrofloxacin, enoxacin, trovafloxacin, norfloxacin, and ofloxacin, on the in vitro and in vivo growth of Babesia divergens and Babesia microti parasites, respectively.

Materials and methods: The in vitro and in vivo inhibitory effects of fluoroquinolone antibiotics against B. divergens and B. microti, respectively were evaluated using fluorescence-based assay. Additionally, combination therapies of highly effective fluoroquinolone antibiotics (enrofloxacin, enoxacin, and trovafloxacin) with diminazene aceturate, luteolin, or pyronaridine tetraphosphate were tested on the in vitro cultures of B. divergens.

Results: Enrofloxacin, trovafloxacin, and enoxacin were the most effective fluoroquinolones against the in vitro growth of B. divergens, followed by norfloxacin and ofloxacin. Furthermore, a combination of enoxacin or trovafloxacin with either diminazene aceturate, luteolin, or pyronaridine tetraphosphate significantly enhanced the inhibitory effect on the growth of B. divergens in in vitro cultures. In mice infected by B. microti, enoxacin and diminazene aceturate combination therapy exhibited a potential antibabesial effect.

Conclusion: These results suggest that safe and cheap fluoroquinolone, such as enoxacin, might be used for the treatment of clinical cases caused by Babesia spp. in animals or humans.

Keywords: Babesia; fluoroquinolones; in vitro; in vivo.

Figure 1

Chemical structures of fluoroquinolone antibiotics used in this study: (A) enrofloxacin, (B) enoxacin, (C) trovafloxacin, (D) norfloxacin, and (E) ofloxacin.

Figure 2

Correlation between relative fluorescence units (RFUs) and the log concentrations of fluoroquinolone antibiotics (nM) in Babesia divergens on the fourth day of treatment. Each value represents the mean of triplicate wells after subtraction of the background fluorescence for non-parasitized red blood cells.

Figure 3

Inhibitory effect of fluoroquinolone antibiotics, diminazene aceturate (DA), and the combination of enoxacin and DA on the growth of Babesia microti. Each value represents the mean ± SD of five mice per experimental group. Asterisks indicate significant differences (*P < 0.05) from day 4 to day 16 post-inoculation between the fluoroquinolone antibiotic-treated and control groups.

Figure 4

Anemia monitoring in mice treated with fluoroquinolone antibiotics: (A) RBCs, (B) hemoglobin (HGB), and (C) hematocrit (HCT). Each value represents the mean ± SD of five mice per experimental group. Asterisks indicate a significant difference (*P < 0.05) between the treated or infected mice and the uninfected mice. Abbreviation: DA, diminazene aceturate.

Figure 5

Changes in mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and red blood cell distribution width (RDW) in mice treated with fluoroquinolone antibiotics: (A) MCV, (B) MCH, and (C) RDW. Each value represents the mean ± SD of five mice per experimental group. Asterisks indicate a significant difference (*P < 0.05) between the treated or infected mice and the uninfected mice. Abbreviation: DA, diminazene aceturate.

Figure 6

PCR of the ss-rRNA gene in different organs of Babesia microti-infected mice treated with DDW (positive control), 25 mg⋅kg^–1 diminazene aceturate (DA), and DA (10 mg⋅kg^–1) combined with enoxacin (50 mg⋅kg^–1). Note: M indicates a 100 bp DNA ladder. Abbreviations: NC, negative control; PC, positive control; DDW, double-distilled water; S, spleen; L, lung; H, heart; K, kidney; DA, diminazene aceturate; PCR, polymerase chain reaction.