Sensitivity of Human Strains of Oxalobacter formigenes to Commonly Prescribed Antibiotics

OBJECTIVE To determine the sensitivity of 4 strains of Oxalobacter formigenes (Oxf) found in humans-HC1, Va3, CC13, and OxK-to varying concentrations of commonly prescribed antibiotics. Oxf gut colonization has been associated with a decreased risk of forming recurrent calcium oxalate kidney stones. METHODS For each strain and each antibiotic concentration, 100 mu L of an overnight culture and 100 mu L of the appropriate antibiotic were added to a 7-mL vial of oxalate culture medium containing 20 mM oxalate. On the fourth day, vials were visually examined for growth, and a calcium oxalate precipitation test was performed to determine whether Oxf grew in the presence of the antibiotic. RESULTS All 4 Oxf strains were resistant to amoxicillin, amoxicillin/clavulanate, ceftriaxone, cephalexin, and vancomycin, and they were all sensitive to azithromycin, ciprofloxacin, clarithromycin, clindamycin, doxycycline, gentamicin, levofloxacin, metronidazole, and tetracycline. One strain, CC13, was resistant to nitrofurantoin, and the others were sensitive. Differences in minimum inhibitory concentration between strains were demonstrated. CONCLUSION Four human strains of Oxf are sensitive to a number of antibiotics commonly used in clinical practice; however, minimum inhibitory concentrations differ between strains. UROLOGY 79: 1286-1289, 2012. (C) 2012 Elsevier Inc.