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Activity of different antibiotics against Borrelia burgdorferi determined by bacterial heat production (microcalorimetry)

Abstract number: P1862

Achermann Y., Vogt M., Trampuz A.

Objectives: Antimicrobial susceptibility testing in Borrelia burgdorferi sensu lato is not routinely performed due to laborious procedure and lacking correlation with treatment outcome. The MIC and MBC values determined by the colorimetric microdilution assay provide no information on the antimicrobial activity over time. Therefore, we evaluated the activity of 4 antibiotics by measurement of heat production using an ultrasensitive real-time instrument (microcalorimeter, detection limit 025 microwatt).

Methods: We used B. burgdorferi sensu stricto (strain 1408/94) isolated from a patient with erythema migrans. Microcalorimetry (detection limit 0.2 mW) was performed in duplicate by adding 0.1 ml of culture containing 106 CFU of B. burgdorferi in 3.9 ml BSK-H medium containing serial 2-fold dilutions of standard antibiotics (amoxicillin, doxycycline, rifampin, levofloxacin). Heat production was measured at 37°C under static conditions for up to 21 days. The minimal heat inhibition concentration (MHIC) was defined as the lowest antimicrobial concentration inhibiting heat production within 14 days after heat was detected in cultures without antibiotics.

Results: Heat of B. burgdorferi was detected in absence of antibiotics after 2 to 8 days and reached a peak of 30 and 50 microwatt. The peak of heat-flow was proportionally delayed with increasing dose of amoxicillin, whereas the peak was also decreased with doxycycline and levofloxacin (Figure). Growth of B. burgdorferi was not affected by rifampin up to 16 mg/ml. The MHIC (mg/ml) was 0.5 (amoxicillin), 1 (doxycycline), 8 (levofloxacin) and >16 (rifampin). At amoxicillin concentrations >0.5 mg/ml, identical heat flow curves were observed even after 14 days delay.

Conclusions: Doxycycline showed the highest activity against B. burgdorferi by microcalorimetry, followed by amoxicillin and levofloxacin, whereas rifampin showed no antiborrelial activity. The MHIC values correlate well with the reported MIC values (Hunfeld et al., 2000). Microcalorimetry is a useful tool for rapid and real-time assessment of growth characteristics of and antimicrobial activity against B. burgdorferi and potentially other slow-growing microorganisms.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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