Prevalence, virulence profiling, and latent antimicrobial resistance determinants of Escherichia coli O157:H7 in imported Australian beef cattle during quarantine in Indonesia.

Abstract

Background and aim: Escherichia coli O157:H7 is an important zoonotic foodborne pathogen associated with severe gastrointestinal disease in humans and is increasingly recognized as a reservoir of antimicrobial resistance (AMR) determinants in food-producing animals. Imported beef cattle may contribute to the transboundary dissemination of pathogenic and antimicrobial-resistant bacteria during international livestock trade. This study aimed to determine the prevalence, virulence profiles, phenotypic antimicrobial susceptibility, and AMR genes of E. coli O157:H7 isolated from imported Australian beef cattle during quarantine in Indonesia.

Materials and methods: A cross-sectional study was conducted from March to November 2025 using 680 samples collected from imported beef cattle at five quarantine facilities in West Java and Banten, Indonesia. Samples included 650 rectal fecal specimens and 30 environmental samples. Isolation and identification of E. coli O157:H7 were performed using selective culture, biochemical characterization, and multiplex polymerase chain reaction targeting rfbO157, fliCH7, stx1, and stx2. Antimicrobial susceptibility testing was conducted using the Kirby-Bauer disk diffusion method. Detection of AMR genes (tetA, strA, sul2, qnrS, and bla _TEM) was performed by polymerase chain reaction.

Results: Of the 680 samples examined, 16 (2.35%) were confirmed as E. coli O157:H7, all originating from fecal samples. Among these isolates, 11 (68.75%) carried stx1 and/or stx2 genes and were classified as Shiga toxin-producing E. coli, whereas 5 (31.25%) were non-Shiga toxin-producing E. coli isolates. Antimicrobial susceptibility testing showed that most isolates remained susceptible to the tested antimicrobials. Resistance was highest to tetracycline (31.25%), followed by ampicillin (6.25%). No resistance was observed to streptomycin, trimethoprim-sulfamethoxazole, or enrofloxacin. Molecular analysis revealed the presence of AMR genes, including tetA (43.75%), strA (37.5%), sul2 (18.75%), qnrS (18.75%), and bla _TEM (12.5%). Several isolates carried multiple resistance genes despite showing phenotypic susceptibility.

Conclusion: Imported beef cattle during quarantine in Indonesia carried E. coli O157:H7 harboring virulence-associated Shiga toxin genes and latent AMR determinants. The presence of resistance genes in phenotypically susceptible isolates highlights the importance of integrating molecular surveillance with routine phenotypic testing to strengthen AMR monitoring and biosecurity measures within international live animal trade systems.