| Campylobacter is the most common foodborne bacterial agent causing human gastroenteritis. Erythromycin resistance in Campylobacter coli from meat animals is frequently encountered and is associated with a point mutation (A2075G) in the 23S rRNA gene. In this study we investigated transformation-mediated acquisition of erythromycin resistance by C. coli, with genomic DNA from erythromycin-resistant C. coli used as donor. Overall, transformation to erythromycin resistance was significantly more frequent in C. coli from turkeys (10 -4 to 10-6) than from swine (10-7 or less) (P < 0.01). Most transformants harbored the point mutation, A2075G in the 23S rRNA gene with high MIC (>256mug/ml), as did the donor strains. In contrast, spontaneous mutants had lower MIC (32--64mug/ml) and lacked the A2075G mutation. Temperature profoundly affected frequency of transformation to erythromycin resistance, but not to nalidixic acid resistance, with significantly higher frequency at 42°C than at 25°C. No significant difference in transformation frequency was detected between microaerobic (5--10% CO 2) and aerobic conditions. Increasing incubation time from 3--4h to 15--17h significantly increased transformation frequency to erythromycin resistance (P < 0.05). Lower transformation frequency of C. jejuni to erythromycin resistance than of C. coli using erythromycin-resistant C. coli as donor suggests that erythromycin resistance in C. coli may not be disseminated in C. jejuni as frequently as in C. coli. When grown separately at 42°C, an erythromycin-resistant transformant of C. coli 961 had a similar growth rate as its erythromycin-sensitive parental strain, whereas an erythromycin-resistant transformant of C. jejuni SC49 had a significantly longer generation time compared to its parental strain. In competitive growth studies, however, the C. coli transformant was at competitive disadvantage compared to its parental strain in stationary phase, whereas the C. jejuni transformant was at advantage. In conclusion, natural transformation has the potential to contribute to dissemination of high-level erythromycin resistance among C. coli colonizing meat animals and ecological attributes such as temperature may play an important role and exert differential impact on the potential of the organism to acquire antimicrobial resistance determinants via natural transformation. |
