Seung-Hak Cho

Prevalence, genetic diversity, and antibiotic susceptibility of Bacillus cereus strains isolated from rice and cereals collected in Korea.

Incidence and properties of Bacillus cereus strains naturally present in cereals were evaluated by phenotypic characterization, antibiotic susceptibility testing, and pulsed-field gel electrophoresis. Of 293 cereal samples tested, 73 (25%) contained B. cereus strains. Incidence of B. cereus isolates varied with respect to sample; they were found in 15 (37%) of 83 brown rice samples, 23 (37%) of 63 glutinous rice samples, 16 (21%) of 76 barley samples, and 19 (27%) of 71 Jobs tears samples. All B. cereus isolates from cereals were positive for diarrheal toxin genes. The isolates were susceptible to most of the antibiotics tested, but they were highly resistant to ampicillin, cefepime, oxacillin, and penicillin. Of the genes assayed by the PCR technique, a high frequency of nheA (99%) and hblDC (84%) was found in the genomic DNA of cereal-associated isolates, whereas cytK was less common (55%). From the strains carrying the hblDC genes, 93% produced enterotoxin HBL. B. cereus isolates did not have significant genetic homology. The genetic diversity and toxic potential differ among the strains isolated from cereals. These results provide important information on toxin gene profiles of cereal-associated B. cereus for population studies.

Toxin genes profiles and toxin production ability of Bacillus cereus isolated from clinical and food samples.

Bacillus cereus can cause diarrheal and emetic type of food poisoning but little study has been done on the main toxins of food poisoning caused by B. cereus in Korea. The objective of this study is to characterize the toxin gene profiles and toxin-producing ability of 120 B. cereus isolates from clinical and food samples in Korea. The detection rate of nheABC, hblCDA, entFM, and cytK enterotoxin gene among all B. cereus strains was 94.2, 90.0, 65.8, and 52.5%, respectively. The ces gene encoding emetic toxin was not detected in all strains. Bacillus cereus strains carried at least 1 of the 8 enterotoxin genes were classified into 12 groups according to the presence or absence of 8 virulence genes. The 3 major patterns, I (nheABC, hblCDA, entFM, and cytK gene), II (nheABC, hblCDA and entFM gene), and VI (nheABC and hblCDA gene), accounted for 79.2% of all strains (95 out of 120 B. cereus isolates). Non-hemolytic enterotoxin (NHE) and hemolysin BL (HBL) enterotoxins were produced by 107 and 100 strains, respectively. Our finding revealed that NHE and HBL enterotoxins encoded by nhe and hbl genes were the major toxins among B. cereus tested in this study and enterotoxic type of B. cereus was predominant in Korea.

Obesity Alters the Microbial Community Profile in Korean Adolescents

Obesity is an increasing public health concern worldwide. According to the latest Organization for Economic Co-operation and Development (OECD) report (2014), the incidence of child obesity in Korea has exceeded the OECD average. To better understand and control this condition, the present study examined the composition of the gut microbial community in normal and obese adolescents. Fecal samples were collected from 67 obese (body mass index [BMI] ≥ 30 kg/m2, or ≥ 99th BMI percentile) and 67 normal (BMI < 25 kg/m2 or < 85th BMI percentile) Korean adolescents aged 13–16 years and subjected to 16S rRNA gene sequencing. Analysis of bacterial composition according to taxonomic rank (genus, family, and phylum) revealed marked differences in the Bacteroides and Prevotella populations in normal and obese samples (p < 0.005) at the genus and family levels; however, there was no difference in the Firmicutes-to-Bacteroidetes (F/B) ratio between normal and obese adolescents samples at the phylum level (F/B normal = 0.50 ± 0.53; F/B obese = 0.56 ± 0.86; p = 0.384). Statistical analysis revealed a significant association between the compositions of several bacterial taxa and child obesity. Among these, Bacteroides and Prevotella showed the most significant association with BMI (p < 0.0001 and 0.0001, respectively). We also found that the composition of Bacteroides was negatively associated with triglycerides (TG), total cholesterol, and high-sensitive C-reactive protein (hs-crp) (p = 0.0049, 0.0023, and 0.0038, respectively) levels, whereas that of Prevotella was positively associated with TG and hs-crp levels (p = 0.0394 and 0.0150, respectively). We then applied the association rule mining algorithm to generate “rules” to identify the association between the populations of multiple bacterial taxa and obesity; these rules were able to discriminate obese from normal states. Therefore, the present study describes a systemic approach to identify the association between bacterial populations in the gut and childhood obesity.

Asymptomatic healthy slaughterhouse workers in South Korea carrying Shiga toxin-producing Escherichia coli

A total of 1602 stool samples from healthy employees in a slaughter company were screened by PCR for Shiga toxin (Stx)-producing Escherichia coli (STEC). The PCR product of Stx-encoding genes was detected in 90 (5.6%) of 1602 stool samples. Among the 90 stx-positive workers, the Residual Products Handlers and Slaughterers had rates of 8.0% and 6.0%--higher than Inspectors, Grading Testers and Livestock Hygiene Controllers at 3.3%, 2.0% and 3.5%, respectively. Forty-nine (54.4%) were shown to have stx2; 25 (27.7%) carried stx1 and 16 (17.7%) had both stx1 and 2. Distribution of the stx PCR-positive workers by age revealed an increase in STEC infection with age (P<0.05). Phenotypic and genotypic traits of nine STEC strains isolated from eight slaughter plant workers were characterized. A variety of serotypes, five O serogroups (O8, O54, O59, O103 and O153) and two H serogroups (H7 and H32) were found, but none of the strains belonged to the serogroup O157. Eight Vero cell cytotoxicity assay-positive strains were isolated from the workers and these workers were asymptomatic and healthy. The results of the study show that slaughter plant workers are at high risk of STEC infection.

Molecular Characterization of Enterotoxigenic Escherichia coli Strains Isolated from Diarrheal Patients in Korea during 2003–2011

Enterotoxigenic Escherichia coli (ETEC) is one of the major causes of infectious diarrhea in developing countries. In order to characterize the molecular features of human ETEC isolates from Korea, we investigated the profiles of enterotoxin and colonization factor (CF) genes by polymerase chain reaction (PCR) and performed multilocus sequence typing (MLST) with a total of 291 ETEC strains. The specimens comprised 258 domestic strains isolated from patients who had diarrhea and were from widely separated geographic regions in Korea and 33 inflow strains isolated from travelers visiting other Asian countries. Heat-stable toxin (STh)-possessing ETEC strains were more frequent than heat-labile toxin (LT)-possessing ETEC strains in the domestic isolates, while the detection rates of both enterotoxin genes were similar in the inflow isolates. The profile of CF genes of domestic isolates was similar to that of inflow isolates and the major CF types of the strains were CS3-CS21-CS1/PCF071 and CS2-CS3-CS21. Most of these 2 CF types were detected in ETEC strains that possess both lt and sth genes. The major MLSTST types of domestic isolates were ST171 and ST955. Moreover, the 2 major CF types were usually found concomitantly with the 2 major MLST STs, ST171 and ST955. In conclusion, our genotyping results may provide useful information for guiding the development of geographically specific vaccines against human ETEC isolates.

Comparison of Antimicrobial Resistance in Escherichia coli Strains Isolated From Healthy Poultry and Swine Farm Workers Using Antibiotics in Korea

Objectives The aim of this study is to compare the antibiotic resistance of Escherichia coli isolates from faecal samples of workers who often use antibiotics. Methods A total of 163E coli strains isolated from faecal samples of livestock workers (poultry and swine farm workers) and restaurant workers in the same regions as a control group were analyzed by agar disc diffusion to determine their susceptibility patterns to 16 antimicrobial agents. Results Most of the tested isolates showed high antimicrobial resistance to ampicillin and tetracycline. The isolates showed higher resistance to cephalothin than other antibiotics among the cephems. Among the aminoglycosides, the resistance to gentamicin and tobramycin occurred at higher frequencies compared with resistance to amikacin and netilmicin. Our data indicated that faecal E coli isolates of livestock workers showed higher antibiotic resistances than nonlivestock workers (restaurant workers), especially cephalothin, gentamicin, and tobramycin (p < 0.05). Moreover, the rates of the livestock workers in the association of multidrug resistance were also higher than the rates of the restaurant workers. Conclusion This study implies that usage of antibiotics may contribute to the prevalence of antibiotic resistance in commensal E coli strains of humans.

An Outbreak of Foodborne Illness Caused by Enteroaggregative Escherichia coli in a High School in South Korea

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.

Prevalence, Genetic Diversity, and Antibiotic Resistance of Bacillus cereus Isolated from Korean Fermented Soybean Products

Bacillus cereus contamination is a major food safety problem for Korean fermented soybean products, but few studies have assessed its potential to cause foodborne illness. The objectives of this study were to investigate the prevalence and characteristics of B. cereus isolated from Korean fermented soybean products. B. cereus was detected in 110 of 162 (67.9%) samples. The highest B. cereus frequency was observed in deonjang (68 of 93 samples, 73.1%) and cheonggukjang (18 of 25, 72.0%); however, nonhemolytic enterotoxin was detected only in 22 of 162 samples (13.6%). Although the tested B. cereus isolates showed diverse pulsotypes according to repetitive sequence-PCR banding patterns, they displayed similar antibiotic sensitivity spectra. The low frequency of enterotoxin detection suggests that the potential risk of B. cereus foodborne illness associated with Korean fermented soybean products is lower than generally presumed. However, considering the prevalence of B. cereus and the high content of fermented soybean products in the Korean diet, it is necessary to constantly monitor the level of contamination with B. cereus and its toxins in such Korean food products.

Effects of Onion Extracts on Growth Performance, Carcass Characteristics and Blood Profiles of White Mini Broilers

This experiment was carried out to investigate effects of onion extract on growth performance, meat quality and blood profiles of White mini broilers. Total of 600 one-d-old male White mini broiler chicks were divided into four groups and fed control diets (non-medicated commercial diet or antibiotics medicated) or experimental diets (non-medicated diets containing 0.3% or 0.5% onion extract) for 5 wks. The final body weight (BW) and weight gain of the group fed non-medicated control diet were lower than those of medicated control group (p<0.01). The chicks fed diet with 0.3% or 0.5% onion extract showed a similar BW to that of medicated control group. The relative weight of various organs, such as liver, spleen, bursa of Fabricius, abdominal fat, and the activities of serum enzymes were not affected by dietary treatments. There were no significant differences in meat color among groups. Whereas, groups fed diets containing onion extract had slightly lower cooking loss and higher shear force value, but not significantly. The concentrations of serum free cholesterol and triacylglycerol in groups fed diet containing onion extract were significantly decreased compared with those of controls (p<0.01). In conclusion, the onion extracts exerted a growth-promoting effect when added in White mini broiler diets, reflecting potential alternative substances to replace antibiotics.

Prevalence of Antibiotic Resistance in Escherichia coli Fecal Isolates From Healthy Persons and Patients With Diarrhea

Objectives This study aimed to investigate the prevalence of antibiotic resistance in fecal Escherichia coli isolates from healthy persons and patients with diarrhea. Methods E. coli isolates (n = 428) were obtained from fecal samples of apparently healthy volunteers and hospitalized patients with diarrhea. Susceptibility patterns of isolates to 16 antimicrobial agents were determined by agar disc diffusion. Results Most E. coli isolates exhibited less than 10% resistance against imipenem, cefotetan, aztreonam, cefepime, cefoxitin, amikacin and netilamicin, although greater than 65% were resistant to ampicillin and tetracycline. No significant difference in resistance rates for all tested antibiotics was found between isolates from the healthy-and diarrheal-patient groups, including for multi-drug resistance (p = 0.22). The highest number of resistant antibiotics was 12 antibiotics. No significant differences in antibiotic resistance were found among the sex and age strata for isolates from healthy individuals. However, antibiotic resistance rates to cefoxitin, cefotaxime, amikacin, and netilamicin were significantly higher in the isolates of men than those of women (p < 0.05) in isolates from patients with diarrhea. Furthermore, isolates from patients with diarrhea older than 40-years of age showed higher resistance to cefepime and aztreonam (p < 0.05). Conclusion High resistance to the antibiotics most frequently prescribed for diarrhea was found in isolates from patients with diarrhea and apparently healthy individuals without any significant difference.