| Overuse of antimicrobials in food animals has contributed to the emergence and development of antimicrobial resistance in human pathogens, which can compromise our ability to treat infectious diseases. An effective surveillance program for monitoring antimicrobial resistance and a better understanding of mechanisms of antimicrobial resistance will provide important information for developing rational strategies to prevent and control this public health problem. Campylobacter, a leading cause of bacterial gastroenteritis in the United States and many other countries, has acquired resistance to antimicrobials commonly used for treatment. The objectives of this study were to characterize Campylobacter isolated from retail raw meats in the greater Washington DC area, to determine their antimicrobial susceptibilities, and to identify novel resistance determinants. In the first study, pulsed-field gel electrophoresis (PFGE) and automated ribotyping were conducted to analyze the DNA fingerprints of 120 Campylobacter isolates, which generated 44 PFGE patterns and 22 RiboGroups. PFGE had a higher discriminatory power than ribotyping, and the two methods were complementary in typing Campylobacter. The second study compared Etest and agar dilution for susceptibility testing of 135 Campylobacter isolates. The overall agreement of minimum inhibitory concentrations determined using Etest and agar dilution was 61.9%, ranging from 21.4% for nalidixic acid to 92.6% for gentamicin. The third study examined antimicrobial resistance of Campylobacter, and investigated genetic mechanisms of resistance to ciprofloxacin and erythromycin, the drugs of choice for treating Campylobacter infection. The most common resistance among the Campylobacter isolates was to tetracycline (81.8%). Resistance rates to erythromycin and ciprofloxacin were 54.7% and 34.6% respectively. Campylobacter coli exhibited significantly higher resistant rates to erythromycin and ciprofloxacin than Campylobacter jejuni, and isolates from turkey showed significantly higher resistant rates than isolates from chicken. DNA sequencing analysis identified 5 novel point mutations in the gyrA gene among ciprofloxacin-resistant C. jejuni. In summary, we demonstrated that Campylobacter isolated from retail meats in the Washington DC area were diverse. Many Campylobacter isolates were resistant to antimicrobials of clinical importance. Point mutations in gyrA and 23S rRNA were associated with resistance to ciprofloxacin and erythromycin, respectively. |
