Antibiotic resistance profile of Citrobacter spp. isolated from rectal swabs of sheep in Ngrayung Village, Plumpang District, Tuban Regency

Abstract

Antimicrobial resistance (AMR) has become a major global concern in both human and veterinary medicine, particularly due to the increasing emergence of resistant enteric bacteria in food-producing animals. This study aimed to isolate and identify Citrobacter spp. from rectal swabs of sheep and to determine their antibiotic resistance profile in Ngrayung Village, Plumpang District, Tuban Regency. A total of 150 rectal swab samples were collected from sheep and processed using standard bacteriological methods. Isolation was performed on MacConkey Agar, followed by Gram staining and biochemical confirmation using IMViC and Triple Sugar Iron Agar tests. Antimicrobial susceptibility testing was conducted using the Kirby–Bauer disk diffusion method on Mueller–Hinton Agar according to CLSI guidelines against five antibiotics: erythromycin, tetracycline, ampicillin, cefoxitin, and aztreonam. Out of 150 samples, 40 isolates (26.7%) showed presumptive colony morphology consistent with Citrobacter spp., while 6 isolates (4.0%) were biochemically confirmed. The confirmed isolates demonstrated Gram-negative rod morphology and variable biochemical characteristics. Antimicrobial susceptibility testing revealed that all isolates (100%) were resistant to erythromycin, while resistance to ampicillin and cefoxitin was observed in 66.7% and 33.3% of isolates, respectively. Lower resistance rates were detected for tetracycline and aztreonam (16.7% each). Furthermore, 2 isolates (33.3%) were classified as multidrug-resistant (MDR), including one isolate resistant to all tested antibiotics. These findings indicate that sheep may serve as reservoirs of antimicrobial-resistant Citrobacter spp., posing potential risks for animal health, environmental contamination, and zoonotic transmission. Routine AMR surveillance, prudent antibiotic use, and improved farm biosecurity are therefore essential to support antimicrobial stewardship within a One Health framework.