Efficient isolation of therapeutic erythromycin-resistant Campylobacter

Purpose: Campylobacter is one of the most common causes of human bacterial gastroenteritis in the world. C. jejuni and C. coli are the species most commonly associated with the disease. During the past decades, Campylobacter has become increasingly resistant to both macrolides and fluoroquinolones. Resistance to these classes of antibiotics in Campylobacter is a serious threat to public health. Since Resistant Campylobacter spp. to fluoroquinolones have emerged in Japan, the most recommended drug is erythromycin (macrolide) when an antibiotic chemotherapy is needed for treatment of patients with Campylobacter infection. In contrast to significantly high rate of fluoroquinolone resistance, Japan has reported a low and stable rate of macrolide resistance in C. jejuni and C. coli isolated from humans. However, the Japanese Veterinary Antimicrobial Resistance Monitoring System (JVARM) has revealed a general trend of rising erythromycin resistance in Campylobacter. Our final goal is to show the correlation among erythromycin-resistant Campylobacter isolates from patients with enteritis, food-producing animals and foods (such as chicken meats) in the same geographic area in Japan. As the first step in the project, the aim of this study is to develop a selective medium for the isolation of erythromycin-resistant Campylobacter from materials. Methods & Materials: The medium contains erythromycin as the selective agent in Preston Agar with 5% defibrinated sheep blood. Seventeen Campylobacter strains with erythromycin MICs (Minimum Inhibitory Concentrations) of 0.25 to 512 μg/ml were used as erythromycin-resistant or erythromycin-susceptible reference strains to examine the selectivity of this medium in this study. MICs were determined by Etest (bioMérieux). The strains were grown on the agar plates at 37 or 42 °C under microaerobic conditions. Results: Among the reference strains, all the erythromycin-resistant Campylobacter strains grew well on the medium but the growth of the erythromycin-susceptible strains were significantly inhibited. Seventy two clinical isolates were examined and five strains were grew on the medium. Erythromycin MICs of the three of them were more than 256 μg/ml. Conclusion: The results suggested that the medium allow the successful selection of erythromycin-resistant Campylobacter strains. The medium will useful efficient isolation of erythromycin-resistant Campylobacter. (This work was supported by Grant-in-Aid for Scientific Research(C) Number 17K09160.)