Prevalence and Antimicrobial Resistance Pattern of Salmonella Isolated from Table Eggs in Chitwan District, Nepal

Abstract

Egg-borne salmonellosis is a significant global public health concern. The rise in antimicrobial resistance in Salmonella has emerged as a worldwide challenge in recent decades. This study aimed to assess the prevalence of Salmonella in table eggs and determine the antimicrobial resistance profiles of the isolates in Chitwan District, Nepal. A total of 146 table eggs—106 from retail shops and 40 from layer farms—were collected between September and December 2022 using purposive sampling. Standard microbiological techniques including pre-enrichment, selective enrichment, culture isolation on XLD agar, and a series of biochemical tests were employed for Salmonella identification. Antimicrobial susceptibility testing (AST) was conducted using the disc diffusion method against five commonly used antibiotics: ceftriaxone, tetracycline, chloramphenicol, enrofloxacin, and ciprofloxacin. The overall prevalence of Salmonella in table eggs was 6.16%. Retail shop samples showed a higher contamination rate (7.55%) compared to those from layer farms (2.5%). Within the retail samples, Salmonella was recovered from 2.73% of egg shells, 1.36% of contents, and 1.36% of both shell and contents. Conversely, only one positive isolate (0.68%) was found in eggshells from farm-sourced samples, with no detection in contents. Statistical analysis revealed no significant difference (p > 0.05) in contamination between shell and content, or between sources. However, eggshell contamination was generally more common, indicating greater external exposure to bacterial pathogens, likely during post-farm handling. The antibiotic sensitivity test showed that all isolates (100%) were resistant to enrofloxacin, while resistance rates to ciprofloxacin, tetracycline, and chloramphenicol were 36.3%, 27.3%, and 18.2%, respectively. The lowest resistance was observed against ceftriaxone (9.1%). Notably, 18.18% of isolates exhibited multidrug resistance (MDR), defined as resistance to three or more antibiotic classes. In conclusion, this study reveals a modest but significant prevalence of Salmonella contamination in eggs, with elevated risks linked to retail-sourced eggs and external shell contamination. The documented resistance to critical antibiotics, including fluoroquinolones, adds urgency to national surveillance and stewardship programs aimed at controlling the spread of AMR pathogens from food sources to humans.