• Journal of Microbiology and Biotechnology
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• v.6 no.3
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• pp.219-220
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• 1996

The pKH2 isolated from the multidrug-resistant Staphylococcus aureus SA2 is a 40.98-kb plasmid and mediates resistance to ampicillin, clindamycin, erythromycin, kanamycin, and streptomycin. The 3.4-kb HindIII fragment conferring kanamycin resistance was cloned from the pKH2 into pBluescriptII $KS^+$ and partial sequence determination of that fragment was carried out. Sequence analysis revealed that the kanamycin resistance gene which encoded aminoglycoside 3'-phosphotransferase was linked to the streptothricin resistance gene. But a nonsense mutation was found in the streptothricin resistance gene and this mutation resulted in a truncated protein of streptothricin acetyltransferase. Homology comparison with nucleotide sequence databases revealed that the 3.4-kb HindIII fragment of pKH2 had been derived not from S. aureus but from Gram-negative Campylobacter coli.

• Journal of Microbiology and Biotechnology
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• v.26 no.9
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• pp.1605-1612
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• 2016

Quinolone-resistant Salmonella strains were isolated from patient samples, and several quinolone-sensitive strains were used to analyze mutations in the quinolone resistance-determining region (QRDR) of gyrA, gyrB, parC, and parE and to screen for plasmid-mediated quinolone resistance. Among the 21 strains that showed resistance to nalidixic acid and ciprofloxacin (MIC 0.125-2.0 μg/ml), 17 strains had a mutation in QRDR codon 87 of gyrA, and 3 strains had a single mutation (Ser83 → Phe). Another cause of resistance, efflux pump regulation, was studied by examining the expression of acrB, ramA, marA, and soxS. Five strains, including Sal-KH1 and Sal-KH2, showed no increase in relative expression in an analysis using the qRT-PCR method (p < 0.05). In order to determine the genes involved in the resistance, the Sal-9 isolate that showed decreased susceptibility and did not contain a mutation in the gyrA QRDR was used to make the STM (MIC 8 μg/ml) and STH (MIC 16 μg/ml) ciprofloxacin-resistant mutants. The gyrA QRDR Asp87 → Gly mutation was identified in both the STM and STH mutants by mutation analysis. qRT-PCR analysis of the efflux transporter acrB of the AcrAB-TolC efflux system showed increased expression levels in both the STM (1.79-fold) and STH (2.0-fold) mutants. In addition, the expression of the transcriptional regulator marA was increased in both the STM (6.35-fold) and STH (21.73-fold) mutants. Moreover, the expression of soxS was increased in the STM (3.41-fold) and STH (10.05-fold) mutants (p < 0.05). Therefore, these results indicate that AcrAB-TolC efflux pump activity and the target site mutation in gyrA are involved in quinolone resistance.

• The Journal of the Korean Society for Microbiology
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• v.35 no.2
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• pp.181-190
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• 2000

To investigate resistance to lamivudine (3TC), we examined the incidence of M184V in 20 HIV-1 patients treated with 3TC for $13.1{\pm}9$ months. Fourteen of 20 patients had been exposed to zidovudine (ZDV) or didanosine (ddI) prior to 3TC therapy. Nested PCR targeting to reverse transcriptase (RT) and direct sequencing were performed for peripheral blood mononuclear cells sampled serially. There were resistance mutations to ZDV in at least 9 patients at baseline, although there was no resistance mutation to 3TC. We could detect M184V in 6 (30%) out of 20 patients. The incidence of M184V increased as the duration of therapy prolongs (13% in samples <12 months; 47% in samples ${\ge}12$ months). The frequency of mutation M184V was higher in patients with previous mutation to ZDV than in patients with wild type. Resistance mutation was not detected in 7 patients. This study shows that resistance to 3TC tends to develop rapidly in patients with baseline mutations or two drugs combination therapy than in those treated simultaneously with triple drugs. This report is the first on resistance to 3TC in Korean AIDS patients.

• Journal of Microbiology and Biotechnology
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• v.23 no.8
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• pp.1154-1158
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• 2013

Ganciclovir resistance of human cytomegalovirus is associated with mutations in the viral UL97 gene and poses severe problems for immunocompromised patients. In this study, PCR-based restriction fragment length polymorphism and sequencing analyses detected the UL97 D605E mutation in all five clinical isolates from patients with ganciclovir-resistant human cytomegalovirus infection during prolonged ganciclovir therapy, whereas the M460V mutation was only present in 1 of 5 isolates. On the other hand, the detection rates of the D605E mutation in the stored available DNA samples from the donor and allogeneic stem cell transplantation recipients were 66.7% and 93.7%, respectively, suggesting that the presence of D605E mutation was not associated with the ganciclovir exposure. Although the D605E mutation may not be related to ganciclovir resistance, we suggest that this mutation could be an important molecular marker of human cytomegalovirus evolution in East Asian countries. Moreover, the restriction fragment length polymorphism method using the restriction enzyme HaeIII, which is generally used to detect the UL97 A591V mutation, could also detect the D605E mutation and may therefore be a useful tool for future research on the investigation of UL97 gene mutations.

• Journal of Microbiology
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• v.35 no.3
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• pp.177-180
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• 1997

The purpose of this study was to evaluate the efficiency of Line Probe Assay (LiPA) in detecting the rpoB gene mutation of clinically isolated Mycobacterium tuberculosis (MTB) and to compare the level of resistance to the various rifamycins with their mutation sites. The mutation in the rpoB gene was found in 84 (97.6%) out of 86 rifampicin (RMP) resistant strains as determined by LiPA. No mutation was observed in 2 RMP resistant strains and in any of 38 RMP susceptible strains tested. Only one of 3 strains with .DELTA.5/R5, one of 2 strains with .DELTA.3, and one of 3 strains with .DELTA.2/R2 LiPA profile showed a slightly lower level of resistance to the rifapentine than the other strains. Although we could not find correlations between mutation sites in the rpoB gene and the level of susceptibility to the various rifamycins, the LiPA is recommended as a fast screening tool for detection of RMP resistant MTB.

• Genomics & Informatics
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• v.12 no.4
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• pp.276-282
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• 2014

The disease tuberculosis, caused by Mycobacterium tuberculosis (MTB), remains a major cause of morbidity and mortality in developing countries. The evolution of drug-resistant tuberculosis causes a foremost threat to global health. Most drug-resistant MTB clinical strains are showing resistance to isoniazid and rifampicin (RIF), the frontline anti-tuberculosis drugs. Mutation in rpoB, the beta subunit of DNA-directed RNA polymerase of MTB, is reported to be a major cause of RIF resistance. Amongst mutations in the well-defined 81-base-pair central region of the rpoB gene, mutation at codon 450 (S450L) and 445 (H445Y) is mainly associated with RIF resistance. In this study, we modeled two resistant mutants of rpoB (S450L and H445Y) using Modeller9v10 and performed a docking analysis with RIF using AutoDock4.2 and compared the docking results of these mutants with the wild-type rpoB. The docking results revealed that RIF more effectively inhibited the wild-type rpoB with low binding energy than rpoB mutants. The rpoB mutants interacted with RIF with positive binding energy, revealing the incapableness of RIF inhibition and thus showing resistance. Subsequently, this was verified by molecular dynamics simulations. This in silico evidence may help us understand RIF resistance in rpoB mutant strains.

• Tuberculosis and Respiratory Diseases
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• v.80 no.3
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• pp.270-276
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• 2017

Background: A disputed rpoB mutation is a specific type of rpoB mutation that can cause low-level resistances to rifampin (RIF). Here, we aimed to assess the frequency and types of disputed rpoB mutations in Mycobacterium tuberculosis isolates from South Korea. Methods: Between August 2009 and December 2015, 130 patients exhibited RIF resistance on the MTBDRplus assay at Asan Medical Center. Among these cases, we identified the strains with disputed rpoB mutation by rpoB sequencing analysis, as well as among the M. tuberculosis strains from the International Tuberculosis Research Center (ITRC). Results: Among our cases, disputed rpoB mutations led to RIF resistance in at least 6.9% (9/130) of the strains that also exhibited RIF resistance on the MTBDRplus assay. Moreover, at the ITRC, sequencing of the rpoB gene of 170 strains with the rpoB mutation indicated that 23 strains (13.5%) had the disputed mutations. By combining the findings from the 32 strains from our center and the ITRC, we identified the type of disputed rpoB mutation as follows: CTG511CCG (L511P, n=8), GAC516TAC (D516Y, n=8), CTG533CCG (L533P, n=8), CAC526CTC (H526L, n=4), CAC526AAC (H526N, n=3), and ATG515GTG (M515V, n=1). Conclusion: Disputed rpoB mutations do not seem to be rare among the strains exhibiting RIF resistance in South Korea.

• Journal of Microbiology and Biotechnology
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• v.23 no.9
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• pp.1293-1303
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• 2013

Antibiotic resistance of soilborne Acinetobacter species has been poorly explored. In this study, norfloxacin resistance of a soil bacterium, Acinetobacter oleivorans DR1, was investigated. The frequencies of mutant appearance of all tested non-pathogenic Acinetobacter strains were lower than those of pathogenic strains under minimum inhibitory concentration (MIC). When the quinolone-resistance-determining region of the gyrA gene was examined, only one mutant (His78Asn) out of 10 resistant variants had a mutation. Whole transcriptome analysis using a RNA-Seq demonstrated that genes involved in SOS response and DNA repair were significantly up-regulated by norfloxacin. Determining the MICs of survival cells after norfloxacin treatment confirmed some of those cells were indeed persister cells. Ten colonies, randomly selected from among those that survived in the presence of norfloxacin, did not exhibit increased MIC. Thus, both the low mutation frequency of the target gene and SOS response under norfloxacin suggested that persister formation might contribute to the resistance of DR1 against norfloxacin. The persister frequency increased without a change in MIC when stationary phase cells, low growth rates conditions, and growth-deficient dnaJ mutant were used. Taken together, our comprehensive approach, which included mutational analysis of the target gene, persister formation assays, and RNA sequencing, indicated that DR1 survival when exposed to norfloxacin is related not only to target gene mutation but also to persister formation, possibly through up-regulation of the SOS response and DNA repair genes.

• Research in Plant Disease
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• v.26 no.1
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• pp.1-7
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• 2020

The succinate dehydrogenase inhibitor (SDHI) is a class of fungicides, which is widely and rapidly used to manage fungal pathogens in the agriculture field. Currently, fungicide resistance to SDHIs has been developed in many different plant pathogenic fungi, causing diseases on crops, fruits, vegetables, and turf. Understanding the molecular mechanisms of fungicide resistance is important for effective prevention and resistance management strategies. Two different mechanisms have currently been known in SDHI resistance. The SDHI target genes, SdhB, SdhC, and SdhD, mutation(s) confer resistance to SDHIs. In addition, overexpression of ABC transporters is involved in reduced sensitivity to SDHI fungicides. In this review, the current status of SDHI resistance mechanisms in phytopathogenic fungi is discussed.

• Journal of Interdisciplinary Genomics
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• v.5 no.2
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• pp.32-34
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• 2023

Resistance to thyroid hormone syndrome (RTH) is a genetic disease caused by the mutation of either the thyroid hormone receptor-β (THRB) gene or the thyroid hormone receptor-α (THRA) gene. RTH caused by THRB mutations (RTH-β) is characterized by the target tissue's response to thyroid hormone, high levels of triiodothyronine and/or thyroxine, and inappropriate secretion of thyroid-stimulating hormone (TSH). THRA mutation is characterized by hypothyroidism that affects gastrointestinal, neurological, skeletal, and myocardial functions. Most patients do not require treatment, and some patients may benefit from medication therapy. These syndromes are characterized by decreased tissue sensitivity to thyroid hormones, generating various clinical manifestations. Thus, clinical changes of resistance to thyroid hormones must be recognized and differentiated, and an approach to the practice of personalized medicine through an interdisciplinary approach is needed.