Submitted to: Microbial Drug Resistance
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2003
Publication Date: 6/20/2004
Citation: McDermott, P.F., Bodeis, S.M., Hanson, R.A., Aarestrup, F.M., Brown, S., Traczewski, M., Cray, P.J., Wallace, F.M., Critchley, I.A., Thornsberry, C. 2004. Development of a standardized susceptibility test for Campylobacter with quality control ranges for ciprofloxacin, doxycycline, erythromycin, gentamicin, and meropenem. Microbial Drug Resistance. 10(2):124-131. Interpretive Summary: Misuse of antimicrobials in both humans and animals can lead to the development of resistant bacteria including those that cause food borne illness. Campylobacter are food borne bacteria that not only cause illness in humans, but can also readily develop resistance to antimicrobials. In order to determine if bacteria are resistant to a particular antimicrobial, standardized testing methods must be established. In accordance with the National Committee for Clinical Laboratory Standards (NCCLS) guidelines, we established an antimicrobial susceptibility test for Campylobacter using the agar dilution method. Seven different laboratories evaluated the agar dilution test using one control Campylobacter and 21 different Campylobacter isolates recovered from ill people. Incubation temperatures and times were varied to determine optimal test conditions. Most laboratories reported similar results when using the control Campylobacter. However, when the 21 Campylobacter were tested, results were more variable both within and between laboratories. Additionally, we determined that optimal testing conditions were 36oC for 48 hours. These data are important for other scientists and medical clinicians as this testing method for Campylobacter will provide more reliable data and serve as a reference when developing other testing methods for measuring resistance to antimicrobials in other bacteria.
Technical Abstract: An in vitro standardized susceptibility testing method for Campylobacter was established following the National Committee for Clinical Laboratory Standards (NCCLS) guidelines outlined in document M23-A2. The agar dilution method consists of testing on Mueller-Hinton medium supplemented with 5% defibrinated sheep blood. Campylobacter jejuni ATCC 33560 was identified as a quality control (QC) strain. Minimal inhibitory concentration (MIC) results were determined after incubation in a defined microaerophilic environment at 36°C for 48 hr and 42°C for 24 hr. Quality control ranges using both incubation conditions were determined for ciprofloxacin, doxycycline, erythromycin, gentamicin, and meropenem. The QC results generated were within a three to four dilution range for seven of the participating laboratories using both incubation temperatures. 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 were also tested in conjunction with the QC strain to evaluate the testing method for use with a range of Campylobacter species (C. jejuni, C. coli, C. jejuni, subsp. doylei, C. fetus and C. lari). There was less inter- and intra-laboratory reproducibility among the clinical isolates when compared to the QC strain. While C. jejuni and C. coli could be reliably tested under both test conditions, several isolates of C. jejuni subsp. doylei, C. fetus and C. lari failed to grow when incubated at 42°C. For this reason, it is recommended that these species only be tested at 36oC. The availability of a standardized testing method for Campylobacter will provide more reliable MIC data, and serve as a reference for investingating other in vitro testing methods for measuring antimicrobial susceptibility in this important pathogen.