Characterization of Erythromycin-Resistant Porcine Isolates of Campylobacter Coli.

Erythromycin-resistant Campylobacter organisms were isolated from swine, and their resistance to the antibiotic was characterized. One hundred fourteen Campylobacter organisms were isolated from 572 swine intestinal samples. All isolates were identified as Campylobacter coli by sequence analysis of 16S rRNA gene and polymerase chain reactions with primers specific to hippuricase gene in Campylobacter jejuni and aspartokinase gene in C. coli. Minimal inhibitory concentrations (MICs) of erythromycin were determined by using the agar dilution method, and 80 isolates were found to be resistant to erythromycin (MIC >/=4 mug/ml). Of these, 31 isolates had low-level resistance (MIC =4-16 mug/ml), and 49 isolates had high-level resistance (HLR, MIC >/=32 mug/ml). The HLR isolates carried a point mutation at position A2075 --> G in domain V of the 23S rRNA gene, whereas the low-level resistance isolates carried no mutation. These 49 HLR isolates were characterized by pulsed-field gel electrophoresis and multilocus sequence typing to study their genetic diversity. Pulsed-field gel electrophoresis identified 16 distinct types with 50% genetic similarity as the cutoff. On the other hand, 28 different sequence types (STs), including 10 new STs, were identified with multilocus sequence typing. Forty-six of 49 erythromycin HLR isolates showed crossresistance to 6 macrolide derivatives.