Antimicrobial activity of oral quinolones against clinical isolates of Bifidobacterium group and Clostridium difficile

Administrations of antimicrobial agent influence human intestinal flora, and sometimes lead to cause Clostridium difficile colitis (CDC). It has been well known that antimicrobial agents, such as clindamycin (CLDM), ampicillin (ABPC) and cephems, frequently cause C. difficile colitis, however, recently some respiratory quinolones, such as garenoxacin (GRNX) and moxifloxacin (MFLX), have paid to attention. Bifidobacterium species would be highly associated with the preservation of normal intestinal flora, while C. difficile would be associated with diarrhea related with antibiotics administration. We investigated antimicrobial activity of GRNX, MFLX and levofloxacin (LVFX) by agar dilution methods based on CLSI recommendations. Forty-seven strains Bifidobacterium species isolated from healthy human intestinal flora and 51 strains of C. difficile isolated from C. difficile colitis patients between 2004 and 2006 were subjected to this study. MIC ranges of Bifidobacterium species for GRNX, MFLX and LVFX were 0.5-16, 0.06-2, and 0.5-8 microg/mL, respectively. MIC50 s of GRNX, MFLX and LVFX against Bifidobacterium species were 2, 0.5 and 4 microg/mL, respectively. MIC90 s of GRNX, MFLX and LVFX against Bifidobacterium species were 8, 2 and 8 microg/mL, respectively. MIC ranges of C. difficile for GRNX, MFLX and LVFX were 0.5 - > 64, 1-64, and 0.125-32 microg/mL, respectively. MIC50s of GRNX, MFLX and LVFX against C. difficile were 2, 2 and 0.5 microg/mL, respectively. MIC90 s of GRNX, MFLX and LVFX against C. difficile were 64, 16 and 8 microg/mL, respectively. LVFX would preserve Bifidobacterium species, and also would be bactericidal for C. difficile, which might lead to the low rate of gastrointestinal disorder in LVFX. GRNX would preserve Bifidobacterium species, however, might be lead to CDC in some cases, since antimicrobial activity for C. difficile has been weak compared with LVFX. Since MFLX would be bactericidal for Bifidobacterium species and antibacterial activity of MFLX for C. difficile would be weak compared with LVFX, we have to pay attention to antibiotics associated diarrhea in MFLX treatment.