Antimicrobial Resistance Pattern in Campylobacter strains Isolated from both No-Antibiotics-Ever (NAE) and Conventional Broiler Complexes: Genotypic and Phenotypic Characterization

Authors: ADHIKARI, YAGYA - Auburn University; BOURASSA, DIANNA - Auburn University; POUDEL, SABIN - Auburn University; BAILEY, MATTHEW - Auburn University; ZHANG, LI - Mississippi State University; Buhr, Richard; MACKLIN, KENNETH - Mississippi State University

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: This study reveals that antimicrobial resistance (AMR) in Campylobacter, especially strains isolated from commercial broiler operations, is both pervasive and complex in nature. By examining both genotypic and phenotypic markers, the research demonstrates that nearly half of the isolates exhibited resistance to at least one antibiotic, and a notable fraction (13%) were multi-drug resistant—all identified in conventional (antibiotic-using) broiler systems. Tetracycline resistance was particularly prevalent, underscoring the ongoing challenge posed by its widespread use in agriculture. Both Campylobacter jejuni and Campylobacter coli displayed significant resistance rates, yet the distribution of resistance did not vary significantly across different farm environments or production stages. The detection of AMR genes such as bla OXA-61 and tet (O) suggests that genetic determinants of drug resistance are well established within these populations. The study’s findings carry public health implications: the circulation of resistant Campylobacter within broiler production environments increases the risk of these bacteria contaminating poultry meat and, subsequently, the food supply. This not only threatens to prolong the duration and severity of foodborne illnesses but also highlights the potential for conventional farming practices to foster the emergence of multi-drug resistant strains, reinforcing the need for stewardship of antimicrobial use in agriculture.

Technical Abstract: Drug-resistant Campylobacter is a serious public health concern because of its increasing resistance to clinically important antimicrobials. To determine the antimicrobial resistance (AMR) pattern, the phenotypic and genotypic characteristics of Campylobacter isolated from two commercial integrated broiler complexes (No-Antibiotics-Ever (NAE) and Conventional) were studied. Genotypic analysis of AMR genes were identified using ResFinder while the phenotypic resistance test was performed using the broth microdilution method. Odds ratio and 95% confidence limits were calculated for complex types and stages of broiler production (a=0.05). The AMR genes identified were bla OXA-61 (29%), bla OXA-184 (4%), tet (O) (13%), tet (O/32/O) (12%) and aph (3’)-III (7%). The phenotypic results showed that 48% (30/63) of isolates were resistant to at least one antibiotic while 13% (8/63) of isolates were multi-drug resistant (MDR) (resistant = 3 antibiotic classes). Among 30 resistant isolates, the highest resistance was observed for tetracycline (46%) followed by clindamycin (16%), azithromycin (10%), erythromycin (8%), florfenicol (8%), nalidixic acid (2%) and meropenem (2%). In addition, 61% (13/21) of Campylobacter jejuni (C. jejuni) and 40% (17/42) of Campylobacter coli (C. coli) isolates showed resistance to at least one antimicrobial. There was no significant differences in detection of Campylobacter strain having antimicrobial resistance in the environments of different complexes and stages of broiler production (p>0.05). However, all 8 MDR strains were isolated from a conventional broiler complex. The presence of antimicrobial resistant Campylobacter in the surroundings of farms and facilities poses a significant risk of these bacteria entering into the complex and could contaminate the final meat product, potentially resulting in prolonged foodborne illness in consumers.