Development of a Standardized Susceptibility Test for Campylobacter with Quality-Control Ranges for Ciprofloxacin,Doxycycline,Erythromycin,Gentamicin,and Meropenem

Abstract

A standardized agar dilution susceptibility testing method was developed for Campylobacter that consisted of testing on Mueller–Hinton medium supplemented with 5% defibrinated sheep blood in an atmosphere of 10% CO₂, 5% O₂, and 85% N₂. Campylobacter jejuni ATCC 33560 was identified as a quality-control (QC) strain. Minimal inhibitory concentration (MIC) QC ranges were determined for two incubation time/temperature combinations: 36°C for 48 hr and 42°C for 24 hr. Quality-control ranges were determined for ciprofloxacin, doxycycline, erythromycin, gentamicin, and meropenem. For all antimicrobial agents tested at both temperatures, 95–100% of the QC MIC results fell within recommended QC ranges. Twenty-one Campylobacter clinical isolates, encompassing five species of Campylobacter (C. jejuni, C. coli, C. jejuni, subsp. doylei, C. fetus, and C. lari) were tested in conjunction with the C. jejuni QC strain. While C. jejuni and C. coli could be reliably tested under both test conditions, growth of C. jejuni subsp. doylei, C. fetus, and C. lari isolates was inconsistent when incubated at 42°C. Therefore, it is recommended that these species only be tested at 36°C.