| Seong-Han Kim | 7 Articles |
<b>Objectives</b><br/>
A fast and accurate diagnosis is necessary to control and eliminate tuberculosis (TB). In Korea, TB continues to be a serious public health problem. In this study, diagnostic tests on clinical samples from patients suspected to have TB were performed and the sensitivity and specificity of the various techniques were compared. The main objective of the study was to compare various diagnostic tests and evaluate their sensitivity and specificity for detecting tuberculosis.<br/><b>Methods</b><br/>
From January 2013 to December 2013, 170,240 clinical samples from patients suspected to have TB were tested with smear microscopy, acid-fast bacilli culture, and real-time polymerase chain reaction (PCR). The test results were compared and data were analyzed.<br/><b>Results</b><br/>
A total of 8216 cultures tested positive for TB (positive detection rate, 4.8%). The contamination rate in the culture was 0.6% and the isolation rate of nontuberculous mycobacteria was 1.0%. The sensitivity and specificity of smear microscopy were 56.8% and 99.6%, respectively. The concordance rate between the solid and liquid cultures was 92.8%. <i>Mycobacterium</i> isolates were not detected in 0.4% of the cases in the liquid culture, whereas no <i>Mycobacterium</i> isolates were detected in 6.8% of the cases in the solid culture. The sensitivity and specificity of real-time PCR for the solid culture were 97.2% and 72.4%, respectively, whereas the corresponding data for the liquid culture were 93.5% and 97.2%.<br/><b>Conclusion</b><br/>
The study results can be used to improve existing TB diagnosis procedure as well as for comparing the effectiveness of the assay tests used for detecting <i>Mycobacterium tuberculosis</i> isolates.
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<b>Objectives</b><br/>
Our previous longitudinal multicenter-based carriage study showed that the average carriage rate of <i>Streptococcus pneumoniae</i> was 16.8% in 582 healthy children attending kindergarten or elementary school in Seoul, Korea. We assessed serotype-specific prevalence and antimicrobial resistance among colonizing pneumococcal isolates from young children in the era of low use of the seven-valent pneumococcal conjugate vaccine (PCV7).<br/><b>Methods</b><br/>
Serotypes were determined by an agglutination test with specific antisera or by a multiplex polymerase chain reaction (PCR) assay. An antimicrobial susceptibility test was performed with broth microdilution in Korean 96-well panels from Dade-MicroScan (Sacramento, CA, USA).<br/><b>Results</b><br/>
Pneumococcal colonization patterns were dynamic and longterm persistent carriage was rare, which indicated a sequential turnover of pneumococcal strains. Of the 369 pneumococci (except for 23 killed isolates), 129 (34.9%) isolates were PCV7 vaccine serotypes (VTs); 213 (57.8%) isolates were nonvaccine serotypes (NVTs); and the remaining 27 (7.2%) isolates were nontypable (NT). The highest rates of multidrug resistance (MDR) were observed in VTs (86.0%; 111/129 isolates) and NVTs (70.0%; 149/213 isolates).<br/><b>Conclusion</b><br/>
This study overall showed the frequent carriage of VTs and NVTs with MDR in healthy children attending kindergarten or elementary school. Efforts should be directed toward reducing the extensive prescription of antibiotics and using new broader vaccines to reduce the expansion of MDR strains of NVTs in our community.
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<b>Objectives</b><br/>
We aimed at evaluating the virulence of atypical <i>Shigella flexneri</i> II:(3)4,7(8) by DNA microarray and invasion assay.<br/><b>Methods</b><br/>
We used a customized <i>S. flexneri</i> DNA microarray to analyze an atypical <i>S. flexneri</i> II:(3)4,7(8) gene expression profile and compared it with that of the <i>S. flexneri</i> 2b strain.<br/><b>Results</b><br/>
Approximately one-quarter of the atypical <i>S. flexneri</i> II:(3)4,7(8) strain genes showed significantly altered expression profiles; 344 genes were more than two-fold upregulated, and 442 genes were more than 0.5-fold downregulated. The upregulated genes were divided into the category of 21 clusters of orthologous groups (COGs), and the “not in COGs” category included 170 genes. This category had virulence plasmid genes, including the <i>ipa-mxi-spa</i> genes required for invasion of colorectal epithelium (type III secretion system). Quantitative reverse-transcription polymerase chain reaction results also showed the same pattern in two more atypical <i>S. flexneri</i> II:(3)4,7(8) strains. Atypical <i>S. flexneri</i> II:(3)4,7(8) showed four times increased invasion activity in Caco-2 cells than that of typical strains.<br/><b>Conclusion</b><br/>
Our results provide the intracellularly regulated genes that may be important for adaptation and growth strategies of this atypical <i>S. flexneri</i>.
<b>Objectives</b><br/>
Enteroaggregative <i>Escherichia coli</i> (EAEC) was recently reported as a major diarrheagenic pathogen in infant and adult travelers, both in developing and developed countries. EAEC strains are known to be highly resistant to antibiotics including quinolones. Therefore in this study we have determined the various mechanisms of quinolone resistance in EAEC strains isolated in Korea.<br/><b>Methods</b><br/>
For 26 EAEC strains highly resistant to fluoroquinolone, minimal inhibitory concentrations for fluoroquinolones were determined, mutations in the quinolone target genes were identified by PCR and sequencing, the presence of transferable quinolone resistance mechanism were identified by PCR, and the contribution of the efflux pump was determined by synergy tests using a proton pump inhibitor. The expression levels of efflux pump-related genes were identified by relative quantification using real-time PCR.<br/><b>Results</b><br/>
Apart from two, all tested isolates had common mutations on GyrA (Ser83Leu and Ser87Gly) and ParC (Ser80Gln). Isolates EACR24 and EACR39 had mutations that have not been reported previously: Ala81Pro in ParC and Arg157Gly in GyrA, respectively. Increased susceptibility of all the tested isolates to ciprofloxacin and norfloxacin in the presence of the pump inhibitor implies that efflux pumps contributed to the resistance against fluoroquinolones. Expression of the efflux pump-related genes, <i>tolC</i>, <i>mdfA</i>, and <i>ydhE</i>, were induced in isolates EACR 07, EACR 29, and EACR 33 in the presence of ciprofloxacin.<br/><b>Conclusion</b><br/>
These results indicate that quinolone resistance of EAEC strains mainly results from the combination of mutations in the target enzyme and an increased expression of efflux pump-related genes. The mutations Ala81Pro in ParC and Arg157Gly in GyrA have not been reported previously the exact influence of these mutations should be investigated further.
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In this study, we measured the drug resistance conferred by <i>mdfA</i> mutations in two <i>Shigella flexneri</i> strains. A mutant in <i>mdfA</i> genes was constructed by polymerase chain reaction–based, one-step inactivation of chromosomal genes. The antimicrobial susceptibility of parent and mutant strains to fluoroquinolones was determined by minimal inhibitory concentration (MICs). The <i>△mdfA</i> mutants were somewhat more susceptible to fluoroquinolones than the parent strains. The low level changes in MICs of the <i>△mdfA</i> mutants suggest that <i>mdfA</i> contributed the fluoroquinolone resistance in <i>S flexneri</i>. This finding found that the increased expression level of an MdfA efflux pump mediated fluoroquinolone resistance, but it is not likely a major effecter of higher resistance levels.
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<b>Objectives</b><br/>
This study aimed to investigate the prevalence of antibiotic resistance in fecal <i>Escherichia coli</i> isolates from healthy persons and patients with diarrhea.<br/><b>Methods</b><br/>
<i>E. coli</i> isolates (<i>n</i> = 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.<br/><b>Results</b><br/>
Most <i>E. coli</i> 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 (<i>p</i> = 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 (<i>p</i> < 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 (<i>p</i> < 0.05).<br/><b>Conclusion</b><br/>
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.
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<b>Objectives</b><br/>
To characterise the genetic and serological diversity of pathogenic <i>Escherichia coli</i>, we tested 111 <i>E coli</i> strains isolated from diarrhoeal patients in Korea between 2003 and 2006.<br/><b>Methods</b><br/>
The isolates were tested through polymerase chain reaction (PCR) and slide agglutination method for the detection of virulence genes and serotypes, respectively. To compare the expression of Shiga toxin (<i>stx</i>)-1 and <i>stx2</i> genes, real-time quantitative reverse-transcriptase PCR and rapid exprssion assay, reversed-passive latex agglutination, were performed.<br/><b>Results</b><br/>
Forty-nine Shiga toxin-producing <i>E coli</i> (STEC) strains and 62 non-STEC strains, including 20 enteropathogenic <i>E coli</i>, 20 enterotoxigenic <i>E coli</i>, 20 enteroaggregative <i>E coli</i>, and 2 enteroinvasive <i>E coli</i> were randomly chosen from the strains isolated from diarrhoeal patients in Korea between 2003 and 2006. PCR analysis indicated that locus of enterocyte effacement pathogenicity island, that is, <i>eae</i>A, <i>esp</i>ADB, and <i>tir</i> genes were present in STEC, enteropathogenic <i>E coli</i>, and enteroinvasive <i>E coli</i>. Quorum sensing-related gene <i>lux</i>S was detected in most of pathogenic <i>E coli</i> strains. Major serotypes of the STEC strains were O157 (26%) and O26 (20%), whereas the non-STEC strains possessed various serotypes. Especially, all the strains with serotype O157 carried <i>stx</i>2 and the tested virulence factors. Of the STEC strains, the data of real-time quantitative reverse-transcriptase PCR and reversed-passive latex agglutination tests showed that messenger RNA- and protein expression of <i>stx</i>2 gene were higher than those of <i>stx</i>1 gene.<br/><b>Conclusion</b><br/>
Our results provide the epidemiological information regarding the trend of STEC and non-STEC infections in the general population and show the fundamental data in association of serotypes with virulence genes in diarrhoeagenic <i>E coli</i> strains from Korea.
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