Antimicrobial susceptibilities of Campylobacter fetus: report from a reference laboratory

Campylobacter fetus is known to cause human disease, particularly in elderly and immunocompromised hosts. There are limited published data for antimicrobial susceptibility patterns with this organism, and no interpretive criteria are available. We reviewed antimicrobial susceptibilities of C. fetus isolates tested at a tertiary care center and reference laboratory over an 11-year period. C. fetus isolates from patients treated at Mayo Clinic and those sent as referrals for identification and susceptibility were included. Antimicrobial susceptibility testing was performed using agar dilution for ciprofloxacin, doxycycline, erythromycin, gentamicin, meropenem, and tetracycline. Geographic distribution, culture source, organism minimal inhibitory concentration (MIC) distributions, and MIC₅₀ and MIC₉₀ were examined. Excluding duplicates, 105 unique isolates were identified from 110 positive cultures. Blood cultures represented the most common source, followed by body fluids, skin and soft tissue, and central nervous system. Gentamicin and meropenem had favorable MIC₅₀ and MIC₉₀ of 1 µg/mL. Ciprofloxacin demonstrated an MIC₅₀ of 1 µg/mL; however, the MIC₉₀ was >2 µg/mL. Erythromycin demonstrated MIC₅₀ and MIC₉₀ of 2 µg/mL. Tetracycline and doxycycline were tested on a limited number of isolates and showed a wide range of MICs. Gentamicin and meropenem demonstrated favorable MICs in C. fetus isolates. These may represent therapeutic options for consideration in serious C. fetus infections, pending susceptibility results. Ciprofloxacin, which showed variable results, may be more appropriate for use only after susceptibility testing. C. fetus interpretive criteria are needed to aid clinicians in selection of both empiric and definitive therapies.

Our findings contribute to the scant literature on Campylobacter fetus antimicrobial susceptibility test results. We used a reference test method of agar dilution and provide MICs for a large number of organisms and antimicrobial agents.