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We compared 47 enterohemorrhagic Escherichia coli (EHEC) O157 isolates with 184 EHEC non-O157 isolates from Korean patients with diarrhea. In the O157 group, the strains harboring both Shiga toxin genes (stx1 and stx2) were detected with highest frequency, whereas the strains harboring only stx1 gene were most frequently detected in the non-O157 group. Eight virulence genes (eaeA, hlyA, ehx, iha, efa1, tir, toxB, and espA) were found to show a higher frequency of occurrence in the O157 group than in the non-O157 group. In addition, the symptom of bloody diarrhea was exhibited at a higher rate in the O157 group (51.1%) than in the non-O157 group (16.8%). Our findings demonstrate that EHEC O157 strains are more frequently implicated in cases of bloody diarrhea in the Korean population than EHEC non-O157 strains.

Background: Two outbreaks of gastroenteritis occurred in South Korea, affecting a middle school in the Jeollanam-do province in 2013 (Outbreak 1) and 10 schools in the Incheon province in 2014 (Outbreak 2). We investigated the outbreaks to identify the pathogen and mode of transmission., Methods: A retrospective cohort study was conducted in the Outbreak 1; and case-control studies were performed for the Outbreak 2. Samples from students, environments, and preserved food items were collected and pulsed-field gel electrophoresis (PFGE) was conducted to identify strains of pathogen., Results: We identified 167 and 1022 students who met the case definition (≥3 loose stools in any 24-h period) in the Outbreaks 1 and 2, respectively. The consumption of cabbage kimchi and young radish kimchi were significantly associated with the illness. Adjusted odds ratios of kimchi were 2.62-11.74. In the Outbreak 1, cabbage kimchi was made and consumed in the school restaurant and in the Outbreak 2, young radish kimchi was supplied by food company X and distributed to all the 10 schools in the Incheon province. Enterotoxigenic Escherichia coli (ETEC) O6 was isolated from fecal samples in 375 cases (33.9%) and from kimchi samples. PFGE patterns of the outbreak strains isolated from cases and food were indistinguishable in each outbreak., Conclusion: The suspected food vehicle in these two consecutive outbreaks was kimchi contaminated with ETEC O6. We recommend continued monitoring and stricter sanitation requirements for the food supply process in Korea, especially in relation to kimchi.

In June 2013, a diarrheal outbreak occurred among high school students in Incheon, South Korea. We investigated the outbreak to identify the pathogen and mode of transmission. A case-control study using a self-administered questionnaire was conducted by local authorities and the Korean Centers for Disease Control and Prevention. Bacterial cultures of stool samples, environmental samples, and samples of preserved food items were prepared. PCR, serotyping, and pulsed-field gel electrophoresis (PFGE) were used to identify and characterize the outbreak-related pathogen. We identified 54 cases of gastroenteritis, with symptoms including diarrhea, abdominal pain, and nausea. None of the food items served in the high school cafeteria were significantly associated with illness, although the odds ratio for kippered trotters mixed with vegetables was relatively high (odds ratio: 2.92, 95% confidence interval: 0.62-13.69). Enteroaggregative Escherichia coli (EAEC) was isolated from this item and the stool samples from 22 symptomatic students and 4 asymptomatic food handlers. The PFGE patterns of EAEC isolated from these sources were indistinguishable. This outbreak was caused by EAEC, and kippered trotters mixed with vegetables, perhaps contaminated by asymptomatic food handlers, were linked to the outbreak. This case-control study highlights the importance of safe food preparation.

To characterize the extended-spectrum beta-lactamases (ESBLs) in diarrheagenic Escherichia coli from Korea in 2008-2011, we screened seven enterotoxigenic E. coli (ETEC) and one enteroaggregative E. coli (EAEC) that produce ESBLs from a nationwide survey. All eight isolates produced CTX-M-type ESBLs, including CTX-M-12 (n = 4), CTX-M-14 (n = 2), and CTX-M-15 (n = 2). PCR-based replicon typing indicated that the blaCTX-M-12 genes of four ETEC isolates were carried on a conjugative IncF plasmid, whereas the blaCTX-M-14 of one EAEC was located on an IncK plasmid. This is the first report of the occurrence of blaCTX-M genes in clinical isolates of EAEC in Korea. The ESBL-producing isolates were shown to be different based on pulsed-field gel electrophoresis and multilocus sequence typing, whereas the four isolates with CTX-M-12 were clonally related. These observations raise an alarm for the spread of plasmid-mediated resistance to ESBL among diarrheagenic E. coli.

The aim of this study was to investigate for the first time the prevalence and types of extended-spectrum beta-lactamase (ESBL) and plasmid-mediated AmpC beta-lactamase (PABL) in Enterobacteriaceae in Korean long-term care facilities (LTCFs). ESBL rates were 45.3% (72/159) in Escherichia coli and 42.7% (50/117) in Klebsiella pneumoniae. In E. coli, CTX-M-28, the most prevalent ESBLs, was identified for the first time in Korea in 44 isolates. In K. pneumoniae, SHV-12 was found in 27 isolates (52.9% of ESBLs), among which 25 isolates also contained SHV-11. Twenty-seven isolates had SHV and CTX-M beta-lactamase simultaneously. PABL genes were detected in 39.3% (46/117) of K. pneumoniae and 3.1% (5/159) E. coli. In E. coli, DHA-1(3), CMY-2(1), and CMY-6(1) were detected, whereas in K. pneumoniae, only DHA-1 was detected. Among the PABL-producing organisms, 80.0% (E. coli) and 52.2% (K. pneumoniae) simultaneously produced ESBLs. In conclusion, LTCF residents in Korea have a very high prevalence of E. coli and K. pneumoniae producing ESBLs, PABLs, or both, and the genotypes of ESBL and PABL were identical with those found in general hospitals.