Detection of antimicrobial-resistant Escherichia coli isolated from chicken eggshell swabs sold in traditional markets in Surabaya City

Abstract

Chicken eggs are widely consumed as an affordable and important source of animal protein; however, eggshell surfaces may become contaminated with pathogenic and antimicrobial-resistant bacteria, posing a potential public health risk. This study aimed to detect Escherichia coli contamination on chicken eggshell swabs collected from traditional and modern markets in Surabaya City, Indonesia, and to determine the antimicrobial susceptibility profiles of the confirmed isolates. A total of 150 eggshell swab samples were collected from five regions of Surabaya during August 2024. Isolation and identification of E. coli were performed using Buffered Peptone Water (BPW), Eosin Methylene Blue Agar (EMBA), Gram staining, IMViC biochemical tests, and Triple Sugar Iron Agar (TSIA). Antimicrobial susceptibility testing was conducted using the Kirby–Bauer disk diffusion method against aztreonam, chloramphenicol, gentamicin, tetracycline, and trimethoprim-sulfamethoxazole according to CLSI 2020 guidelines. Among the 150 samples, 17 isolates showed presumptive E. coli characteristics on EMBA, while only 8 isolates (5.33%) were biochemically confirmed as E. coli. The distribution of confirmed isolates was equal between traditional and modern markets, with 4 isolates (2.67%) from each market type. Antimicrobial susceptibility testing showed that all confirmed isolates were fully susceptible to aztreonam, chloramphenicol, and gentamicin. In contrast, resistance was highest against tetracycline (75%), followed by trimethoprim-sulfamethoxazole (37.5%). Three isolates exhibited multidrug resistance patterns. These findings indicate that chicken eggshells sold in Surabaya City may serve as reservoirs of antimicrobial-resistant E. coli, highlighting the need for improved hygienic handling practices and prudent antibiotic use in poultry production to reduce foodborne antimicrobial resistance risks.