First insight into Escherichia coli virulence in South Korean quails: prevalence of stx and public health risk exposure?

Article information

Korean J Vet Res. 2026;66.e11

Publication date (electronic) : 2026 May 28

doi : https://doi.org/10.14405/kjvr.20250044

Goun Park^1,†, Sujin Park^1,†, Yeongju Yu², Jin-san Moon², JaeKyeom Kim², Sung-Il Kang², Chunghyun Kim^1,

¹Department of Animal Health and Welfare, University of Hose, Asan 31499, Korea

²Avian Disease Division, Animal and Plant Quarantine Agency, Gimcheon 39660, Korea

^*Corresponding Author: Chunghyun Kim Department of Animal Health and Welfare, University of Hoseo, 20 Hoseo-ro 79beon-gil, Baebang-eup, Asan 31499, Korea Tel: +82-41-540-9519 E-mail: juda1974@hoseo.edu

†These authors contributed equally to this work.

Received 2025 December 9; Revised 2026 March 22; Accepted 2026 April 15.

South Korea's quail farming industry has consistently expanded into large-scale operations, driven by a growing consumer market for quail eggs and diverse processed products [1]. The Japanese quail (Coturnix japonica) is raised extensively because of its high productivity, requiring less space and having a rapid four-week egg-laying cycle, ensuring high capital efficiency [2,3]. In addition, reduced production costs, stemming from the exemption from mandatory Newcastle disease vaccination, significantly enhance the competitiveness of the industry [1].

Despite the economic benefits, the South Korean quail egg industry faces significant food safety concerns [1]. In 2023, processed quail egg products were recalled due to bacterial contamination exceeding the regulatory limits by up to 285 times [4]. While quail eggs are a dietary staple, there is a notable lack of in-depth research on harmful microorganisms in these products [5]. This is particularly concerning given that pathogenic Escherichia coli is a major cause of foodborne illness in Korea. In 2023, E. coli was responsible for 46 of 359 outbreaks and affected 2,287 patients, making it the second-most-prevalent bacterial cause after Salmonella.

E. coli is categorized into 2 main groups: diarrheagenic E. coli, which affects the gastrointestinal tract, and extraintestinal pathogenic E. coli (ExPEC), which can cause infections beyond it [6–8]. Avian pathogenic E. coli (APEC), an ExPEC subtype, is a major concern in poultry [9], causing disease and economic losses through various virulence factors, including adhesins and toxins [10,11]. Key virulence-associated factors, such as fimC, iss, tsh, hlyF, and iroN, are prevalent in quail APEC strains. hlyF is also found in human ExPEC. The potential exchange of these virulence-associated factors between APEC and human ExPEC strains raises significant public health concerns, especially given interconnected food supply chains [11,12].

Since 2016, South Korea’s Poultry Disease Control Program has focused on surveying chicken and duck farms to minimize the risk of public health and economic losses from outbreaks, including proactive measures against E. coli, Salmonella spp., avian influenza, and Newcastle disease virus. By contrast, quail farms have largely been excluded, leading to a significant lack of disease information for these operations.

Despite the growing importance of quail farming in South Korea and the well-documented role of E. coli as a major poultry pathogen, no systematic investigation of E. coli infections in commercial quail farms has been conducted thus far. Quail farms have largely been excluded from the national Poultry Disease Control Program, resulting in a critical knowledge gap regarding the prevalence, pathogenic characteristics, and public health implications of E. coli in this species.

Therefore, this study investigated the prevalence and isolation of E. coli from commercial quail farms across South Korea, and characterized the O-serotypes, antimicrobial resistance profiles, and virulence-associated genes of the isolated strains. In addition, the potential public health risks posed by quail-derived E. coli were assessed, with particular emphasis on the presence of Shiga toxin-encoding genes (stx), by comparing the findings with those reported for E. coli from chickens and ducks in Korea.

Responding to a pressing need, a two-year project was launched to investigate the prevalence and characteristics of E. coli infections in quails across South Korea. This initiative, the first systematic study of its kind, analyzed the genetic characteristics of E. coli isolated from over 74 quail flocks on 17 farms between 2022 and 2023. These 17 farms were a part of the 84 quail farms nationwide that each house more than 20,000 quails.

Farm selection was not based on a pre-designed, stratified sampling framework. Instead, 17 farms were enrolled based on voluntary participation because obtaining prior consent from the farm owners was essential, given biosecurity considerations under Korean animal disease prevention regulations.

From these flocks, birds exhibiting clinical signs consistent with colibacillosis, including perihepatitis, arthritis, and salpingitis, were identified as suspect cases. Fourteen symptomatic quails were selected for further examination based on the presence of gross lesions indicative of localized or systemic E. coli infection. Bacterial isolation was performed from the affected tissues, and 19 E. coli isolates were recovered: 12 from the liver, 5 from the joints, and 2 from the oviduct. Where multiple isolates were recovered from a single bird, each morphologically or biochemically distinct colony was retained as an independent isolate for further characterization.

Nineteen E. coli strains were isolated from 14 symptomatic quails that exhibited the signs of systemic infection rather than intestinal colonization, with clinical manifestations and lesions such as perihepatitis, arthritis, and salpingitis. MacConkey agar and Blood Agar Plate were utilized as selective media to isolate the E. coli. Presumptive E. coli isolates were then identified using VITEK 2 Gram-Negative Identification cards (bioMérieux, USA) according to the manufacturer’s instructions.

A recent study further characterized these nineteen E. coli isolates, reflecting systemic infections in quails. The samples were collected from specific anatomical sites, including the liver (n = 12), joint (n = 5), and oviduct (n = 2). APEC O-serogrouping was performed by slide agglutination using 182 polyvalent and monovalent O-antisera (Joongkyeom, Korea). The antigens were prepared from E. coli cultured on Tryptic Soy Agar (37°C overnight), inactivated at 1.8 × 10⁹ CFU/mL (121°C/15 min), and resuspended in sterilized saline. Twenty μL of antigen and antisera were mixed on a slide, hand-tilted for 2 minutes, with agglutination indicating a positive reaction. The minimum inhibitory concentrations for 19 APEC isolates against 17 antimicrobials were determined via broth microdilution and agar dilution, following Clinical and Laboratory Standards Institute protocols [13]. The isolates were categorized as non-drug resistant, non-multidrug resistant (1–2 resistant classes), or multidrug resistant (MDR; ≥3 resistant classes) [11]. The polyvalent-positive isolates were confirmed with monovalent antisera. The polymerase chain reaction (PCR) was performed to detect 14 virulence-associated genes, yielding several important findings [11].

All prevalence data are expressed as proportions (no. of positive isolates/total isolates × 100). No formal inferential statistical tests were performed because the primary objective of this study was the descriptive characterization of E. coli isolates from quail farms. Comparisons with data from other poultry species are qualitative and based on the values in the literature.

The O-serotype distribution of E. coli isolates from quails (Table 1) was compared with common serotypes reported in chicken and duck populations in South Korea [11]. The O45 serotype was identified in the quail isolates and the APEC strains commonly reported in chickens and ducks, indicating its prevalence across various avian species [11]. Nevertheless, a distinct set of O-serotypes, including O8, O34, O130, O157, O115, O125, O178, O117, O5, O26, O116, and O164, was detected exclusively among the quail-derived isolates [11]. These specific serotypes were not explicitly highlighted as predominant in the comparative literature concerning E. coli from other poultry [11].

Table 1.

Prevalence of O-serotype and antimicrobial resistance patterns of APEC isolates from Japanese quail

Therefore, the E. coli strains colonizing or infecting quails may exhibit a unique O-serotype distribution compared to those typically reported in chickens and ducks. This observed distinction warrants further investigation to understand the host specificity and epidemiological implications of E. coli in quails. Antimicrobial susceptibility analysis of E. coli from quails (Table 1) showed high multidrug resistance (MDR), with 8/19 (42.1%) strains being resistant to 3 or more antibiotic classes. Significant resistance rates were observed for florfenicol (89.5%), ciprofloxacin (84.2%), and trimethoprim/sulfamethoxazole (84.2%). By contrast, the comparative literature on E. coli from chickens and ducks highlights general trends in MDR and fluoroquinolone resistance. Nevertheless, it lacks specific, quantitative resistance data for individual antimicrobial agents in these other poultry species. This distinction shows that the quail data provide a more detailed, quantitative understanding of the resistance profiles, in contrast to the largely qualitative reporting for other poultry in the cited work.

Regarding toxin production, the stx1A gene, which encodes Shiga toxin 1, was detected by PCR in the isolates from all analyzed tissue types (liver, bone, and oviduct), a finding not previously reported in chicken and duck populations in South Korea (Table 2) [11]. The observed rates were significantly higher than the reported prevalence of stx in E. coli isolates from pigs in Korea (4.6%), but a formal statistical comparison was not performed because of the differences in study design and sample populations [12], indicating that a more rigorous public health approach regarding poultry is warranted. Given the continuous increase in Shiga toxin-producing E. coli (STEC)-associated infections in South Korea, a previous study investigated the presence of stx genes in patients presenting with diarrhea [14]. This pattern suggests that the potential for severe pathogenic effects may be heightened in quails. The hlyF gene was detected in 41.7% and 40.0% of liver isolates and bone samples, respectively. Other toxin genes, such as lt and st, were absent in all samples, whereas vat showed a high prevalence of 78.9% (15/19) across all tissue types, and stx2A was detected in a single bone isolate (5.3%).

Table 2.

Prevalence of virulence-associated genes in avian species for Escherichia coli across different tissues from poultry farms in Korea

Regarding the adhesin genes in E. coli isolated from quails, the fimC gene was highly prevalent in liver samples (83.3%), consistent with previous findings in Korean chickens and ducks [11].

Among iron acquisition genes, iroN was the most prevalent at 73.7%, comparable to chickens but significantly higher than in ducks, underscoring the importance of iron for E. coli survival [11].

Regarding protectins and serum resistance, the iss gene was found with high prevalence: 58.3%, 60.0%, and 0% in liver, bone, and oviduct samples, respectively, underscoring its critical role in APEC pathogenicity.

These findings highlight the varying prevalence of genes related to adhesins, iron acquisition, toxins, and protectins across different quail tissues [15]. The detection of virulence-associated genes, including stx1A, along with specific adhesins and protectins, suggests that quails may harbor E. coli strains carrying genes with pathogenic potential, warranting further investigation.

Although stx1 is primarily recognized for its role in human hemorrhagic colitis and Hemolytic Uremic Syndrome, its direct involvement as a primary virulence factor in avian colibacillosis in quails is less clear. APEC typically relies on diverse virulence factors like adhesins, iron acquisition systems, hemolysins, and capsules to cause systemic infections, such as perihepatitis and arthritis, rather than stx1. Stx genes, including stx1, have been found in E. coli isolated from birds, such as quails and squabs [16], suggesting they might serve as reservoirs and raising public health concerns. Hence, their specific contribution to avian disease pathology, distinct from its human impact, warrants further investigation. Stx1-positive E. coli may have originated from commensal E. coli within the quail gut that carry stx genes asymptomatically and become pathogenic under stress, or it may have originated from external contamination sources. These sources include the breeding environment (feed, water, and litter), wild birds, other animals (e.g., ruminants, which are STEC reservoirs), or human handlers. Both scenarios are plausible considering that stx1-positive E. coli caused systemic infections in this context, and further genetic characterization and epidemiological analysis would be crucial for determining the exact source.

This study had several limitations that should be considered when interpreting the findings. First, the total number of isolates (n = 19) recovered from 14 symptomatic quails was relatively small, limiting the generalizability of the prevalence estimates. Second, the 17 farms enrolled represent a subset of the 84 large-scale quail farms in South Korea, and farm selection was based on voluntary participation rather than a stratified sampling design, which may limit geographic and demographic representativeness. Finally, toxin expression was not assessed at the protein level. The detection of stx1A by PCR indicates the presence of the encoding gene but does not confirm active Shiga toxin production or pathogenic potential under field conditions.

The potential of APEC to harbor virulence factors linked to human ExPEC, especially the unique presence of the stx gene and O-serotype in quails compared to chickens and ducks, highlights a potential public health concern that warrants further investigation. Therefore, continuous monitoring at the quail production level and comprehensive research, including larger sample sizes, full virulence profiling, and longitudinal studies, are needed to understand and mitigate the potential public health threats posed by E. coli in quail eggs.