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Susceptibility testing of Danish isolates of Capnocytophaga and CDC group DF-2 bacteria
A Bremmelgaard1, C Pers, J E Kristiansen
1Department of Clinical Microbiology, Frederiksberg Hospital, Copenhagen, Denmark.
Abstract:
Twelve Capnocytophaga and seven DF-2 strains were tested for their susceptibility to 14 antimicrobial agents using an agar dilution and an agar diffusion method. Twenty-three other antibiotics were evaluated using the diffusion test only. All strains were fully susceptible to penicillin, ampicillin, cefuroxime, cefotaxime, erythromycin, clindamycin, chloramphenicol, doxycycline, rifamycin and ofloxacin using both methods. Clindamycin, rifamycin and cefotaxime were most active. Using agar dilution some strains were susceptible to gentamicin, but agar diffusion showed total resistance. One Capnocytophaga strain was susceptible and another moderately susceptible to metronidazole, other strains were resistant. The agar diffusion test showed that both Capnocytophaga and DF-2 were resistant to most other aminoglycosides, to fosfomycin, polymyxin and trimethoprim. All strains of both taxa were fully susceptible to piperacillin, cefoxitin, imipenem and fusidic acid and showed different susceptibilities to the other agents. Susceptibility testing by means of agar diffusion using an enriched chocolate agar and 5% CO2 atmosphere could be used to test Capnocytophaga and DF-2 strains and gives sufficient accuracy for routine use, when revised inhibition zone breakpoints are employed.
Insights
Capnocytophaga and DF-2 bacteria show full susceptibility to several key antibiotics including penicillin and erythromycin. Revised agar diffusion testing methods offer accurate routine susceptibility testing for these challenging pathogens.
Area of Science:
- Microbiology
- Infectious Diseases
Background:
- Capnocytophaga and DF-2 are bacteria that can cause opportunistic infections.
- Accurate antimicrobial susceptibility testing (AST) is crucial for effective treatment.
Purpose of the Study:
- To evaluate the in vitro susceptibility of Capnocytophaga and DF-2 strains to a broad range of antimicrobial agents.
- To assess the suitability of agar diffusion methods for routine AST of these bacteria.
Main Methods:
- Agar dilution and agar diffusion methods were used to test 12 Capnocytophaga and 7 DF-2 strains against 14 and 23 antimicrobial agents, respectively.
- Testing was performed on enriched chocolate agar under a 5% CO2 atmosphere.
Main Results:
- All strains were fully susceptible to penicillin, ampicillin, cefuroxime, cefotaxime, erythromycin, clindamycin, chloramphenicol, doxycycline, rifamycin, and ofloxacin.
- Clindamycin, rifamycin, and cefotaxime demonstrated the highest activity.
- Discrepancies were noted for gentamicin and metronidazole susceptibility between methods.
- Resistance was observed against most other aminoglycosides, fosfomycin, polymyxin, and trimethoprim.
- Complete susceptibility was found for piperacillin, cefoxitin, imipenem, and fusidic acid.
Conclusions:
- Capnocytophaga and DF-2 exhibit susceptibility to a defined set of antibiotics, highlighting key treatment options.
- Agar diffusion testing, with adjusted breakpoints, is a viable and accurate method for routine susceptibility testing of these bacteria.