Spectrum of activity, mutation rates, synergistic interactions, and the effects of pH and serum proteins for fusidic acid (CEM-102).
Fusidic acid (CEM-102) is a steroidal antimicrobial agent with focused Gram-positive activity that acts by preventing bacterial protein synthesis via interacting with elongation factor G. A collection of 114 wild-type isolates (> 80 species) was used to define the contemporary limits of fusidic acid spectrum against Gram-positive and Gram-negative species. Reference broth microdilution and anaerobic agar dilution methods were performed. Modifications of standardized test methods included adding 10% human serum and adjusting the medium pH to 5, 6, and 8. Synergy was assessed by the checkerboard method and time-kill studies. Mutational rates to resistance were determined at 4 x, 8 x, and 16 x MIC. Against Gram-positive pathogens, fusidic acid MIC values ranged from 0.06 to 32 microg/mL with the greatest potency against Staphylococcus aureus, Corynebacterium spp., and Micrococcus luteus (MIC results, 0.25, < or = 0.12, and < or = 0.5 microg/mL, respectively). Enterococci and streptococci were less susceptible (MIC ranges, 2-8 and 16-32 microg/mL, respectively). Fusidic acid activity against Gram-negative species was more limited (all MIC values, > or = 2 microg/mL) except for Empedobacter brevis, Moraxella catarrhalis and Neisseria meningitidis. A 4-fold increase in fusidic acid MIC results was observed when 10% serum was added to the broth. Decreasing medium pH to 5.0 to 6.0 negated the protein binding effects. Among the 8 antimicrobial combinations tested, gentamicin and rifampin enhanced the activity when combined with fusidic acid (no antagonism). Fusidic acid in vitro activity was most improved when combined with rifampin. Single-step mutational rates ranged from 1.2 x 10(-6) for 4x MIC to 9.8 x 10(-8) for 16 x MIC. In conclusion, these in vitro results for fusidic acid tested against contemporary strains confirm a persisting antimicrobial spectrum, especially against staphylococci and some other Gram-positive species.
JMI Laboratories, North Liberty, IA 52317, USA. douglas-biedenbach@jmilabs.com
Douglas J
DJ
Biedenbach
Paul R
PR
Rhomberg
Rodrigo E
RE
Mendes
Ronald N
RN
Jones
D000890:Anti-Infective Agents / Q000494:pharmacology*; D001798:Blood Proteins / Q000378:metabolism*; D003470:Culture Media / Q000737:chemistry; D004357:Drug Synergism; D005672:Fusidic Acid / Q000494:pharmacology*; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000235:genetics; D006094:Gram-Positive Bacteria / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests / Q000379:methods*; D050296:Microbial Viability / Q000187:drug effects; D009154:Mutation
D000890:Anti-Infective Agents; D001798:Blood Proteins; D003470:Culture Media; D005672:Fusidic Acid