Campylobacter is a leading foodborne bacterial pathogen, which causes gastroenteritis in humans. This pathogenic organism is increasingly resistant to antibiotics, especially fluoroquinolones and macrolides, which are the most frequently used antimicrobials for the treatment of campylobacteriosis when clinical therapy is warranted. As a zoonotic pathogen, Campylobacter has a broad animal reservoir and infects humans via contaminated food, water or milk. Antibiotic usage in both animal agriculture and human medicine, can influence the development of antibiotic-resistant Campylobacter. This review will describe the trend in fluoroquinolone and macrolide resistance in Campylobacter, summarize the mechanisms underlying the resistance to various antibiotics and discuss the unique features associated with the emergence, transmission and persistence of antibioticresistant Campylobacter. Special attention will be given to recent findings and emphasis will be placed on Campylobacter resistance to fluoroquinolones and macrolides. A future perspective on antibiotic resistance and potential approaches for the control of antibiotic-resistant Campylobacter, will also be discussed.

Intestinal tracts of broilers and turkeys from 10 conventional broiler farms and 10 conventional turkey farms, where antimicrobials were routinely used, and from 5 organic broiler farms and 5 organic turkey farms, where antimicrobials had never been used, were collected and cultured for Campylobacter species. A total of 694 Campylobacter isolates from the conventional and organic poultry operations were tested for antimicrobial resistance to nine antimicrobial agents by the agar dilution method. Although Campylobacter species were highly prevalent in both the conventional and organic poultry operations, the antimicrobial resistance rates were significantly different between the organic operations and the conventional operations. Less than 2% of Campylobacter strains isolated from organically raised poultry were resistant to fluoroquinolones, while 46% and 67% of Campylobacter isolates from conventionally raised broilers and conventionally raised turkeys, respectively, were resistant to these antimicrobials. In addition, a high frequency of resistance to erythromycin (80%), clindamycin (64%), kanamycin (76%), and ampicillin (31%) was observed among Campylobacter isolates from conventionally raised turkeys. None of the Campylobacter isolates obtained in this study was resistant to gentamicin, while a large number of the isolates from both conventional and organic poultry operations were resistant to tetracycline. Multidrug resistance was observed mainly among Campylobacter strains isolated from the conventional turkey operation (81%). Findings from this study clearly indicate the influence of conventional and organic poultry production practices on antimicrobial resistance of Campylobacter on poultry farms.

The correlation and the level of agreement between the standardized agar dilution and the agar disk diffusion methods for antimicrobial susceptibility testing of Campylobacter were investigated. A high-level agreement between the two methods was evident for aminoglycosides and fluoroquinolones, while a low-level agreement was observed for other antibiotics.

Campylobacter jejuni is a major zoonotic pathogen transmitted to humans via the food chain and is prevalent in chickens, a natural reservoir for this pathogenic organism. Due to the importance of macrolide antibiotics in clinical therapy of human campylobacteriosis, development of macrolide resistance in Campylobacter has become a concern for public health. To facilitate the control of macrolide-resistant Campylobacter, it is necessary to understand if macrolide resistance affects the fitness and transmission of Campylobacter in its natural host. In this study we conducted pairwise competitions and comingling experiments in chickens using clonally related and isogenic C. jejuni strains, which are either susceptible or resistant to erythromycin (Ery). In every competition pair, Ery-resistant (Ery r ) Campylobacter was consistently outcompeted by the Ery-susceptible (Ery s ) strain. In the comingling experiments, Ery r Campylobacter failed to transmit to chickens precolonized by Ery s Campylobacter, while isogenic Ery s Campylobacter was able to transmit to and establish dominance in chickens precolonized by Ery r Campylobacter. The fitness disadvantage was linked to the resistance-conferring mutations in the 23S rRNA. These findings clearly indicate that acquisition of macrolide resistance impairs the fitness and transmission of Campylobacter in chickens, suggesting that the prevalence of macrolide-resistant C. jejuni will likely decrease in the absence of antibiotic selection pressure.