In vitro antimicrobial susceptibility of clinical isolates of Borrelia miyamotoi
Objectives: Borrelia miyamotoi is an emerging relapsing fever (RF) Borrelia species that is described to cause human disease in regions where Lyme borreliosis is endemic. We have recently shown that B. miyamotoi tick isolates are resistant to amoxicillin in vitro, however, clinical isolates have not been studied. Therefore, our aim was to show antimicrobial susceptibility of recently obtained clinical isolates of B. miyamotoi
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Methods: A dilution series of various antibiotics was made in MKP-F media. Susceptibility of different clinical B. miyamotoi, B. miyamotoi tick, RF Borrelia and B. burgdorferi sensu lato isolates were tested by measuring MICs through colorimetric change and by counting motile spirochetes by darkfield microscopy after 72 hours of incubation.
Results: The MIC ranges of the six tested clinical B. miyamotoi isolates to ceftriaxone and azithromycin were 0,03-0,06 mg/L and 0,0016-0,0032 mg/L, respectively. This is similar to MICs from RF Borrelia- and B. miyamotoi tick isolates. All tested RF Borrelia were susceptible to doxycycline (microscopic MIC range 0,0625-0,25 mg/L). In contrast to the MIC of the tested B. burgdorferi sl strains and in line with our previous findings, the MICs for amoxicillin (range 8-32mg/L) of all RF Borrelia — including B. miyamotoi clinical isolates — were above the clinical breakpoint for resistance (≤4 mg/L).
Conclusions: Clinical isolates of B. miyamotoi are highly susceptible to doxycycline, azithromycin and ceftriaxone in vitro Interestingly, as earlier described for tick isolates, amoxicillin shows poor in vitro activity against clinical B. miyamotoi isolates.
Source: By Koetsveld J1, Manger A2, Hoornstra D2, Draga RO2, Oei A2, Kolyasnikova NM3, Toporkova MG4, Sarksyan DS5, Wagemakers A2, Platonov AE3, Hovius JW2. In vitro antimicrobial susceptibility of clinical isolates of Borrelia miyamotoi. Antimicrob Agents Chemother. 2018 Apr 16. pii: AAC.00419-18. doi: 10.1128/AAC.00419-18. [Epub ahead of print]