Purpose: The purpose of this study was to compare the susceptibility of C. jejuni and C. coli to five macrolides and 235 other potentially inhibitory compounds at 37 and 42°C, two commonly used incubation temperatures representing the body temperatures of humans and chickens, respectively.
Methods: C. jejuni 11168 and C. coli 49941 were subjected to phenotype microarray (PM) analysis using an Omnilog machine (Biolog). Briefly, cells in a defined medium containing a redox dye were inoculated into 96-well plates to test for chemical and antibiotic resistances including antimetabolites, respiratory inhibitors, membrane active agents, and toxic metals, at different concentrations. Cells were grown, harvested, inoculated into PM plates, incubated, and tested under microaerobic conditions (5% O2, 10% CO2, 85% N2). Duplicate series of PM plates were analyzed for each organism at 37 and 42°C. Programming languages perl and R were used to build a data analysis pipeline to statistically analyze and graphically summarize the PM data in a high-throughput fashion.
Results: Our data analysis pipeline rapidly identified significant differences (P < 0.005) in susceptibility at 37 versus 42°C for a number of compounds including: sodium dichromate, lincomycin, m-cresol, and plumbagin. Significant effects of temperature on macrolide susceptibility were observed with increased inhibition at the higher incubation temperature.
Significance: The differential response of C. jejuni 11168 and C. coli 49941 to inhibitory compounds demonstrates the importance of considering temperature when developing selective media and isolation protocols and in reporting antibiotic susceptibilities. Differences in macrolide susceptibility were especially interesting as growth inhibition was significantly decreased at normal human body temperature.