Antibiotic susceptibility patterns of Salmonella isolates from clinical, food, and environmental sources in Addis Ababa and surrounding towns, Ethiopia.

Abstract

The increasing prevalence of antimicrobial resistance in Salmonella poses significant challenges to public health globally, particularly in low-resource settings such as Ethiopia. This study aimed to assess the antimicrobial resistance profiles of Salmonella isolates from human, food, and environmental sources in Addis Ababa and surrounding towns, with a focus on multidrug resistance (MDR) patterns. A total of 552 samples, consisting of 386 stool samples from patients with diarrhea and 166 food (meat) and environmental samples (such as waste water, cutting board, knife, and chicken dropping), were collected from 12 health facilities and two slaughterhouses. Salmonella was isolated and screened through selective culture methods and biochemical tests. Antimicrobial sensitivity tests were done by the Kirby-Bauer disk diffusion method. Among the 61 Salmonella isolates tested, the highest resistance was observed against tetracycline (63.9%), followed by ampicillin (55.7%). Resistance to trimethoprim-sulfamethoxazole and chloramphenicol was noted in 24.6% and 19.7% of isolates, respectively. Azithromycin resistance was also sensible at 27.9%. In contrast, ciprofloxacin showed relatively low resistance at 8.2%. Multidrug resistance defined as resistance to three or more antimicrobial classes was detected in 37.7% of isolates. Notably, clinical isolates exhibited significantly higher resistance levels compared to food and environmental sources, with 40% of clinical isolates demonstrating MDR patterns. Gentamicin (3.3%), ceftriaxone (6.6%), and amoxicillin-clavulanic acid (9.8%) remained largely effective, showing low resistance rates. This is one of the few comprehensive studies from Ethiopia examining Salmonella resistance across clinical, food, and environmental samples. High antimicrobial resistance, especially to ampicillin and tetracycline, highlights the urgent need for improved surveillance, rational antibiotic use, and infection control. The presence of multidrug-re