Colorimetric in vitro susceptibility testing of penicillins, cephalosporins, macrolides, streptogramins, tetracyclines, and aminoglycosides against Borrelia burgdorferi isolates

The spectrum of antibiotic susceptibility of Borrelia burgdorferi has been only partially defined. In the present study the effectiveness of 12 antimi crobials, belonging to six different antibiotic classes have been tested ag ainst Borrelia burgdorferi s.s. (N = 3), Borrelia garinii (N = 3), Borrelia afzelii (N = 3), Borrelia valaisiana (N = 1), and Borrelia bissettii (N = 1) isolates. These isolates were analysed by a new standardised colorimetri c minimal inhibitory concentration (MIC) method based upon colour changes t hat result from actively metabolizing spirochaetes after 72 h of incubation . Piperacillin (MIC90: 0.08 mg/l), ceftriaxone (MIC90: 0.04 mg/l), cefotaxi me (MIC90: 0.15 mg/l), azithromycin (MIC90: 0.015 mg/l), roxithromycin (MIC 90: 0.05 mg/l) and quinupristin/dalfopristin (MIC90: 0.12 mg/l) gave the lo west MIC values. Minimal inhibitory activity of amoxycillin (MIC90: 1.04 mg /l), cefixime (MIC90: 1.33 mg/l), cefoperazone (MIC90: 0.83 mg/l) tetracycl ine (MIC90: 0.29 mg/l) and minocycline (MIC90: 0.30 mg/l) was slightly lowe r, whereas borrelia were resistant to amikacin (MIC90: >128 mg/l). Mean min imal borreliacidal concentrations (MBCs) were representatively determined f or piperacillin (MBC: 1.8 mg/l), ceftriaxone (MBC: 2.0 mg/l), azithromycin (MBC: 0.82 mg/ml), roxithromycin (MBC: 1.8 mg/l), quinupristin/dalfopristin (MBC: 5.0 mg/l), minocycline (MBC: 5.8 mg/l), and amikacin (MBC: >128 mg/l ) by using conventional subculture for three weeks in combination with dark -field microscopy. B. garinii proved to be the most susceptible of the geno species tested. Our study showed excellent in vitro antimicrobial activity of all classes of antibiotics tested, except the aminoglycosides and hence their suitability for therapy of Lyme disease. (C) 2000 Elsevier Science B. V. and International Society of Chemotherapy. All rights reserved.