| Campylobacter spp. particularly C. jejuni has been recognized as one of the most important causes of foodborne bacterial diarrhea in humans worldwide. Since poultry are considered the major reservoir of this foodborne pathogen, the prevalence along with the antimicrobial resistance of Campylobacter spp. in conventional and organic poultry operations is a matter of concern. However, relatively little information on the impact of different food animal production practices on the prevalence of antibiotic-resistant Campylobacter is available. Hence, a farm-based study was conducted to determine the prevalence and the antimicrobial resistance rates of Campylobacter isolates from both conventionally-raised and organically-raised poultry. Although Campylobacter was highly prevalent in both organic and conventional production systems, the antibiotic resistance rates were significantly higher in conventional operations than in organic operations. These findings clearly indicate the influence of different production practices on the antibiotic resistance rates of Campylobacter spp. on poultry farms, which is likely due to the result of antimicrobial usage in conventional poultry production. However, antimicrobial usage alone may not solely be responsible for the increased antibiotic resistance in Campylobacter isolates because even in the absence of antibiotic exposure, a high level of tetracycline resistance was also observed in Campylobacter isolates from organic poultry farms. Since antibiotics including tetracycline have never been used on these organic poultry farms, a high prevalence of tetracycline resistance observed among Campylobacter isolates from this operation type is interesting. Hence, another part of this study was conducted to investigate the epidemiology of tetracycline resistance of thermophilic Campylobacter on organic poultry farms. The results showed the changes of tetracycline resistance rates in Campylobacter isolates during the production cycle of one organic broiler flock with 0%, 100%, and 33.33% of tetracycline resistance rates detected at week 3, 6, and 10 of the production period, respectively. Although no tetracycline-resistant Campylobacter strains were isolated from unexposed environmental samples collected from these organic poultry farms except for one organic broiler farm, some of these samples were positive for tetracycline resistance gene [tet(O) gene]. In addition, the agreement between the disk diffusion method and the agar dilution method in identification of antimicrobial resistance of thermophilic Campylobacter was also investigated. The results indicated that the disk diffusion method can be used as a reliable alternative method for susceptibility testing of Campylobacter species to fluoroquinolone and aminoglycoside antibiotics; however, until the standard resistance breakpoints specific for Campylobacter is established and validated, the agar dilution method should be used to determine antimicrobial resistance of Campylobacter to other classes of antibiotics. Together, this study reveals the complex nature in the spread of antibiotic resistance and further highlights the need for prudent measures to prevent the occurrence and transmission of antibiotic-resistant Campylobacter in the poultry reservoir. |
