Molecular epidemiology of sequence type 33 of Shiga toxin-producing Escherichia coli O91:H14 isolates from human patients and retail meats in Korea

Sequence type (ST) 33 of Shiga toxin-producing Escherichia coli (STEC) strain O91:H14 has been proposed as a potential domestic clone of STEC in Korea because of its high prevalence among human patients with mild diarrhea or asymptomatic carriers. Herein, the clonal diversity of 17 STEC O91:H14 isolates of ST33 during 2003 to 2014 was analyzed by pulsed-field gel electrophoresis, including 14 isolates from human patients and 3 from retail meats. Their virulence characteristics, acid resistance, and antimicrobial susceptibility were also determined. Our results showed that all isolates were clustered mainly into three different pulsotypes and were likely low pathogenic without antimicrobial resistance.

Molecular Typing and Resistance Profiles of Vancomycin-Intermediate Staphylococcus aureus in Korea: Results from a National Surveillance Study, 2007-2013 / 대한임상미생물학회지

BACKGROUND: To investigate the national molecular epidemiology and resistance profiles of vancomycin-intermediate Staphylococcus aureus (VISA), we analyzed the characteristics of methicillin-resistant Staphylococcus aureus (MRSA) collected from clinical samples at tertiary or general hospitals participating in a nationwide surveillance program for VISA and vancomycin-resistant Staphylococcus aureus (VRSA) in Korea during an 12-week period in each year from 2007 to 2013. METHODS: VISA was defined by agar dilution, broth dilution and E-test methods with vancomycin minimum inhibitory concentrations of >2 μg/mL. All VISA isolates were characterized by multilocus sequence typing, staphylococcal cassette chromosome mec typing, spa typing, accessory gene regulator typing, Diversilab analysis, and antibiogram analysis. RESULTS: Of 109,345 MRSA isolates, 87,354 were screened and 426 isolates were identified as positive on brain heart infusion agar containing 4 μg/mL vancomycin (BHI-V4). Of 426 isolates, 76 isolates were identified as VISA. No VRSA isolates were detected among the isolates. Overall, a total of 6 genotypes were identified among VISA strains and the predominant clones were ST5-II-t2460, ST72-IV-t324, and ST239-III-t037 (44.7%, 15.8%, and 10.5%, respectively). Of note, ST72-IV-t324 clones are known to be a typical community-associated MRSA. ST239-III-t037 strains were more resistant to trimethoprim-sulfamethoxazole than any other type of strain. ST72-IV-t324 strains were susceptible to all of the antimicrobial agents tested except erythromycin and daptomycin. All of the VISA isolates were susceptible to linezolid and quinupristin-dalfopristin. CONCLUSION: Although VRSA is still rare, continuous monitoring of VRSA occurrence is needed, as well as VISA prevalence, epidemic clonal shift, and antimicrobial resistance.

Recent Trends of Antigenic Variation in Bordetella pertussis Isolates in Korea

Pertussis is a representative vaccine-preventable disease. However, there have been recent outbreaks in countries where even higher vaccination against the disease. One reason is the emergence of antigenic variants, which are different to vaccine type. In Korea, reported cases have rapidly increased since 2009. Therefore, we analyzed genotype of strains isolated in 2011-2012 by multilocus sequence typing method. As expected, the genotype profiles of tested genes dramatically changed. The major sequence type changed from ST1 to ST2, and new sequence type (ST8) appeared. In the minimum spanning tree, recent isolates belonging to the ACC-I-ST3 subgroup were detected that were composed of ST2, ST3, and ST6. In particular, the ST2 frequency increased to 81%. The novel ST8 was linked to the increased frequency of ST2. In addition, toxic strains carrying the ptxP3 promoter type were confirmed. This ptxP3 type emerged from 2009 and its frequency had increased to 100% in 2012. Based on these results, it can be inferred that the genotypic changes in the currently circulating strains are strongly associated with the recent increasing of pertussis in Korea. Therefore, the surveillance system should be strengthened, and genetic characterization of the isolates should be expanded to the whole genome sequence level.

The Clinical Features of Pertussis in Infancy / 소아감염

PURPOSE: Pertussis was very common in the past, but reported cases have dramatically decreased. The improvement of vaccination programs and unreadiness of laboratory confirmation seems to have developed this situation. This study investigated the frequency of pertussis among infants with a paroxysmal cough and compared the clinical characteristics between infants with and without pertussis. METHODS: Between June and November 2006, 27 infants admitted to the hospital that were 15-90 days old with a history of a cough for more than seven days were enrolled. The cough was described as: paroxysmal, whooping, and post-tussive vomiting. PCR and cultures for Bordetella pertussis with nasopharyngeal aspirates were obtained. The patients were divided into two groups: (1) the pertussis group that had positive results by PCR or culture; (2) the control group that had negative results by PCR and culture. Clinical and laboratory characteristics were compared between the two groups. RESULTS: Among the 27 cases, five (18.5%) were finally diagnosed with pertussis. Only one out of the five pertussis cases was initially diagnosed with a pertussis-like syndrome on admission. Compared to the group without pertussis, the pertussis group had a significantly higher frequency of: no fever (P=0.043), a paroxysmal cough (P=0.040), cyanosis (P=0.001), non-immunized status for DTaP (P=0.047), normal auscultation (P=0.028), normal chest X-ray findings (P=0.027), high absolute lymphocyte count (P=0.039), and low CRP (P=0.046). The patients with the diagnosis of pertussis had a significantly longer duration of coughing (27.2+/-10.6 vs. 12.6+/-5.6 days, P=0.039). CONCLUSION: Pertussis should be suspected in any infant with typical symptoms of pertussis in addition to: a persistent cough without fever, accompanied by paroxysms or cyanosis prior to the age of DTaP immunization. Active laboratory confirmation should be carried out to confirm more cases with pertussis.

Discriminative PCR of Bordetella pertussis from closely related Bordetella species using 16S rDNA Gene / 감염과화학요법

BACKGROUND: Polymerase-chain reaction (PCR) detection is useful to diagnosis of pertussis at initial stage because the growth rate of Bordetella pertussis (B. pertussis) is relatively slow. Currently, the primer set for the insertion sequence IS481 (BP primer) is used widely for PCR detection of B. pertussis. However, the cross-reactivity of BP primer set with Bordetella holmesii (B. holmesii) was reported recently. Therefore, discrimination of B. pertussis and B. holmesii is needed in PCR step. For this reason, we developed new primer sets based on 16S rDNA sequence for diagnostic use and estimated the efficiency of these new primer sets. MATERIALS AND METHODS: The specific PCR primers were designed from the aligned sequence matrix of 16S rDNA genes of various Bordetella species. The specificity of designed primers were estimated using clinically important 4 Bordetella species, B. pertussis, B. holmesii, Bordetella parapertussis (B. parapertussis) and Bordetella bronchiseptica (B. bronchiseptica). The sensitivity to B. pertussis of designed primers was also estimated and compared with BP primer set. RESULTS: As the results, the developed new primer set successfully distinguished B. pertussis and other Bordetella species containing B. holmesii. In the sensitivity assay, the detectable limits of 16S-F2/16S-R1 primer set for B. pertussis were revealed as 5 pg of genomic DNA and 105 cells/mL of cell suspension. In addition to these, identical results between BP with primer and new primer were obtained in clinical samples. CONCLUSION: In this study, the specific primer set for B. pertussis was developed based on 16S rDNA sequence and this primer set did not show cross-reactivity to B. holmesii. In addition to these, the applicability of this primer set to the clinical specimens was also confirmed.

Discriminative PCR of Bordetella pertussis from closely related Bordetella species using 16S rDNA Gene / 감염과화학요법

BACKGROUND: Polymerase-chain reaction (PCR) detection is useful to diagnosis of pertussis at initial stage because the growth rate of Bordetella pertussis (B. pertussis) is relatively slow. Currently, the primer set for the insertion sequence IS481 (BP primer) is used widely for PCR detection of B. pertussis. However, the cross-reactivity of BP primer set with Bordetella holmesii (B. holmesii) was reported recently. Therefore, discrimination of B. pertussis and B. holmesii is needed in PCR step. For this reason, we developed new primer sets based on 16S rDNA sequence for diagnostic use and estimated the efficiency of these new primer sets. MATERIALS AND METHODS: The specific PCR primers were designed from the aligned sequence matrix of 16S rDNA genes of various Bordetella species. The specificity of designed primers were estimated using clinically important 4 Bordetella species, B. pertussis, B. holmesii, Bordetella parapertussis (B. parapertussis) and Bordetella bronchiseptica (B. bronchiseptica). The sensitivity to B. pertussis of designed primers was also estimated and compared with BP primer set. RESULTS: As the results, the developed new primer set successfully distinguished B. pertussis and other Bordetella species containing B. holmesii. In the sensitivity assay, the detectable limits of 16S-F2/16S-R1 primer set for B. pertussis were revealed as 5 pg of genomic DNA and 105 cells/mL of cell suspension. In addition to these, identical results between BP with primer and new primer were obtained in clinical samples. CONCLUSION: In this study, the specific primer set for B. pertussis was developed based on 16S rDNA sequence and this primer set did not show cross-reactivity to B. holmesii. In addition to these, the applicability of this primer set to the clinical specimens was also confirmed.

Genetic Diversity among Virulent Mega Plasmids pXO1 and pXO2 of Bacillus anthracis Isolated in Korea

We compared genetic variations in virulence mega plasmids pXO1 and pXO2 of twenty-seven Bacillus anthracis strains from Korean patients and environmental samples together with those of Bacillus anthracis Sterne, Pasteur and A2012 standard strains. Genetic variations were analyzed in twenty-three variable regions (ten and thirteen variablenumber tandem repeats and insertion/deletions in pXO1 and pXO2, respectively). The pXO1 plasmids were classified into 7 groups and pXO2 plasmids to 12 groups. Discrete phylogenic lineages could be differentiated between environmental and clinical strains by UPGMA (unweighted pair group method with average) method. In addition, clinical strains showed more variations than environmental isolates. The pXO2 plasmid appeared genetically more unstable than pXO1. A general plasmid genotype could be suggested for Korean soil isolates since they mostly clustered into a representative group.

Epidemiological Characteristics of Salmonella Strains Isolated recently in Korea

No abstract available.

Serogroup and Verocytotoxin Productivity of Escherichia coli Isolated from Diarrheal Patients in Korea / 감염

BACKGROUND: Since 1982, many countries has reported outbreaks or sporadic cases caused by enterohaemorrhagic Escherichia coli (EHEC) serogroup strains, mainly E. coli O157:H7 type strain. However, systemic investigation about EHEC agents, including E. coli O157:H7, have not been done in Korea. Therefore, we investigated serogroup and verotoxin productivity of E. coli strains isolated from diarrheal patients and estimated risk of human infection in comparison with the EHEC strains isolated from cow, pig, and food material in Korea. METHODS: Diarrheal patient stool samples were collected and E. coli strains were isolated, according to biochemical characteristics. In order to isolate E. coli O157:H7, D-Sorbitol negative E. coli strains were selected. Serogrouping of the E. coli isolates was done by agglutination test. Verocytotoxin productivity was investigated by polymerase chain reaction (PCR) and reversed passive latex agglutination (RPLA). Human infection risk was estimated in comparison with EHEC strains isolated from cow, pig and food materials in Korea. RESULTS: Twenty-five E. coli strains were isolated from the diarrheal patients who were suspected to be infected with EHEC. However, none of these E. coli strains produced verocytotoxin. Out of 25 E. coli isolates, 16 serogroups of E. coli O1, O6, O8, O15, O20, O25, O26, O28, O29, O44, O86a, O119, O126, O128, O152 and 157:H- were found. In each of the E. coli O157:H- and O25 serogrorps 3 strains were found. CONCLUSION: None of 25 E. coli isolated from diarrheal patients who were suspected of EHEC infection produced verocytotoxin producing E. coli have been reported recently in Korea.