• Annals of Laboratory Medicine
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• v.38 no.6
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• pp.563-568
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• 2018

Background: Delamanid, bedaquiline, and linezolid have recently been approved for the treatment of multidrug- and extensively drug-resistant (MDR and XDR, respectively) tuberculosis (TB). To use these drugs effectively, drug susceptibility tests, including rapid molecular techniques, are required for accurate diagnosis and treatment. Furthermore, mutation analyses are needed to assess the potential for resistance. We evaluated the minimum inhibitory concentrations (MICs) of these three anti-TB drugs for Korean MDR and XDR clinical strains and mutations in genes related to resistance to these drugs. Methods: MICs were determined for delamanid, bedaquiline, and linezolid using a microdilution method. The PCR products of drug resistance-related genes from 420 clinical Mycobacterium tuberculosis strains were sequenced and aligned to those of M. tuberculosis H37Rv. Results: The overall MICs for delamanid, bedaquiline, and linezolid ranged from ${\leq}0.025$ to >1.6 mg/L, ${\leq}0.0312$ to >4 mg/L, and ${\leq}0.125$ to 1 mg/L, respectively. Numerous mutations were found in drug-susceptible and -resistant strains. We did not detect specific mutations associated with resistance to bedaquiline and linezolid. However, the Gly81Ser and Gly81Asp mutations were associated with resistance to delamanid. Conclusions: We determined the MICs of three anti-TB drugs for Korean MDR and XDR strains and identified various mutations in resistance-related genes. Further studies are needed to determine the genetic mechanisms underlying resistance to these drugs.

• Journal of Microbiology and Biotechnology
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• v.32 no.12
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• pp.1537-1546
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• 2022

Staphylococcus aureus is a cause of high mortality in humans and therefore it is necessary to prevent its transmission and reduce infections. Our goals in this research were to investigate the frequency of methicillin-resistant S. aureus (MRSA) in Taif, Saudi Arabia, and assess the relationship between the phenotypic antimicrobial sensitivity patterns and the genes responsible for resistance. In addition, we examined the antimicrobial efficiency and application of silver nanoparticles (AgNPs) against MRSA isolates. Seventy-two nasal swabs were taken from patients; MRSA was cultivated on Mannitol Salt Agar supplemented with methicillin, and 16S rRNA sequencing was conducted in addition to morphological and biochemical identification. Specific resistance genes such as ermAC, aacA-aphD, tetKM, vatABC and mecA were PCR-amplified and resistance plasmids were also investigated. The MRSA incidence was ~49 % among the 72 S. aureus isolates and all MRSA strains were resistant to oxacillin, penicillin, and cefoxitin. However, vancomycin, linezolid, teicoplanin, mupirocin, and rifampicin were effective against 100% of MRSA strains. About 61% of MRSA strains exhibited multidrug resistance and were resistant to 3-12 antimicrobial medications (MDR). Methicillin resistance gene mecA was presented in all MDR-MRSA strains. Most MDR-MRSA contained a plasmid of > 10 kb. To overcome bacterial resistance, AgNPs were applied and displayed high antimicrobial activity and synergistic effect with penicillin. Our findings may help establish programs to control bacterial spread in communities as AgNPs appeared to exert a synergistic effect with penicillin to control bacterial resistance.

• Korean Journal of Veterinary Service
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• v.46 no.1
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• pp.35-45
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• 2023

Pathogenic Escherichia coli is the cause of a wide range of diseases in pigs, including diarrhea, edema disease, and septicemia. Diarrhea caused E. coli may result in significant economic losses, making pathogenic E. coli an important pathogen for the swine industry. This study investigated the prevalence of virulence factor genes, antimicrobial resistance phenotypes, and resistance genes in E. coli isolated from feces of piglets in Korea between 2017 and 2020. As a result, 119 pathogenic E. coli isolates were obtained from 601 fecal samples. The F4 adhesin gene and the STb enterotoxin gene were commonly present in E. coli isolated from diarrhea samples. The dominant virulotypes of isolates from diarrhea samples were STb, Stx2e, and F4:LT:STb. More than 80% of the screened isolates were resistant to ampicillin, sulfisoxazole, chloramphenicol, or tetracycline. To confirm the resistance mechanisms for β-lactam or quinolone, we investigated the genotypic factors of resistance. Each of the ceftiofur-resistant E. coli produced an extended-spectrum β-lactamase encoded by bla_CTX-M-14, bla_CTX-M-27, and bla_CTX-M-55. And all ciprofloxacin-resistant E. coli harbored mutations in quinoloneresistance-determining-regions. In addition, some of the ciprofloxacin-resistant E. coli contained the plasmid-mediated-quinolone-resistance genes such as qepA, qnrB1, or qnrD. This study has confirmed that the F4 fimbria and the STb enterotoxin are the most predominant in pathogenic E. coli isolated from piglets with diarrhea in Korea and there is a great need for responsible and prudent use of antimicrobials to treat colibacillosis.

• Proceedings of the Zoological Society Korea Conference
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• 1995.10b
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• pp.171.1-171
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• 1995

• Proceedings of the Microbiological Society of Korea Conference
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• 1998.04a
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• pp.58.1-58.1
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• 1998

• Journal of Digital Convergence
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• v.13 no.12
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• pp.313-318
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• 2015

We investigated the prevalence of extended spectrum ${\beta}$-lactamase (ESBL) genes and 16S rRNA methyltransferase genes to study antimicrobial resistance mechanisms of Enterobacter cloacae strains isolated from a university hospital in the Chungcheong province of Korea. Eight of the bacteria strains involved in this study contained CTX-M-15 type ESBL. Among 8 strains harboring the ESBL gene, 3 strains also harbored armA gene. The three isolates showed resistance to antimicrobial agents belonged to third cephalosporin, aminoglycoside, and fluoroquinolones. Furthermore, interspecies plasmid transfer of the antimicrobial resistant genes may induced horizontal spreading of the genes and emergence of multidrug resistant bacteria. Therefore, surveillance for existence of antimicrobial resistance determinants is important to prevent distribution of antimicrobial resistant strains.

• The Plant Pathology Journal
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• v.27 no.4
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• pp.324-332
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• 2011

Soil-borne barley yellow mosaic disease caused by Barley yellow mosaic virus (BaYMV) or Barley mild mosaic virus (BaMMV) gives a serious threat to the winter barley cultivated in the southern regions in Korea. It is important to develop resistant varieties for stable and high-yield production. The objectives of this study were to evaluate 22 genotypes of exotic barley germplasms carrying the resistance genes rym1 through rym12, with the exception of rym10, and to determine the genes that confer resistance to BaYMV or BaMMV in Korea. Using the traditional visual scoring of symptoms at 4 locations over 3 years, average disease rate values differed (P < 0.001) among the genotypes. ELISA test revealed the presence of both BaYMV and BaMMV in all of the field sites but Jinju and significantly different rates of infection among genotypes and years. Barley genotypes differed in how virus quantities and pathogen-induced symptoms were correlated, especially in response to BaYMV. Disease incidence was affected by the climatic conditions present during the early growing stage before overwintering. A Chinese landrace, 'Mokusekko 3', carrying rym1 and rym5 was comparatively resistant at all locations studied. The barley genotypes carrying either rym6 or rym9 were susceptible to the viral strains. The genotypes carrying rym5 were resistant in Jinju and Milyang but susceptible in Iksan and Naju. The resistance genes rym2 and rym3 were effective in local strains and would be potent contributors to disease resistance.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.1
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• pp.59-68
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• 2016

For comparison of tetracycline-resistant ($Tc^R$) genes, we obtained 21 and 14 $Tc^R$ Staphylococcus spp. from marine environment and human patient, respectively. Although all isolates from human were identified as Staphylococcus aureus, higher proportion of $Tc^R$ isolates (12 out of 14) from human were utilizing tet(M) gene compared to that of $Tc^R$ isolates (6 out of 21) from marine environment. Additionally, collaborated utilization of tet(M) and erm(A) in $Tc^R-Em^R$ S. aureus in human patient, but not in $Tc^R$ Staphylococcus spp. isolates from marine environment was also characterized. Based on the nucleotide sequence of transposon related to $Tc^R$ gene, we confirmed the origin of tet(M) gene in $Tc^R$ Staphylococci isolated from marine environments and human are derived from Tn916/1545-like and Tn5801 transposon, respectively. It is the first report showing the presence of Tn5801 in all $Tc^R$ S. aureus carrying tet(M) in human patient. Alignment of the fully sequenced tet(M) from marine environmental isolates was also agreed with the determined transposons by showing the genomic mosaic structure composed with three genomic parts from Tn916/1545 and unknown transposons. Genetic characteristics of these tet(M) in environmental isolates were similar to each other but different from those in isolates from human showing only tet(M) from Tn916/5801 type. It may imply the presence of less dramatic communication of antibiotic resistant genes between Staphylococci isolated from marine environment and human.

• Journal of Microbiology and Biotechnology
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• v.26 no.2
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• pp.394-401
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• 2016

Recently, the clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR/Cas9) system, a genome editing technology, was shown to be versatile in treating several antibiotic-resistant bacteria. In the present study, we applied the CRISPR/Cas9 technology to kill extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli. ESBL bacteria are mostly multidrug resistant (MDR), and have plasmid-mediated antibiotic resistance genes that can be easily transferred to other members of the bacterial community by horizontal gene transfer. To restore sensitivity to antibiotics in these bacteria, we searched for a CRISPR/Cas9 target sequence that was conserved among >1,000 ESBL mutants. There was only one target sequence for each TEM- and SHV-type ESBL, with each of these sequences found in ~200 ESBL strains of each type. Furthermore, we showed that these target sequences can be exploited to re-sensitize MDR cells in which resistance is mediated by genes that are not the target of the CRISPR/Cas9 system, but by genes that are present on the same plasmid as target genes. We believe our Re-Sensitization to Antibiotics from Resistance (ReSAFR) technology, which enhances the practical value of the CRISPR/Cas9 system, will be an effective method of treatment against plasmid-carrying MDR bacteria.

• Food Science of Animal Resources
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• v.42 no.2
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• pp.225-239
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• 2022

As commensal colonizers in livestock, there has been little attention on staphylococci, especially non-aureus staphylococci (NAS), contaminating meat production chain. To assess prevalence of staphylococci in retail pork and slaughterhouse carcass samples in Korea, we collected 578 samples from Korean slaughterhouses (n=311) and retail markets (n=267) for isolation of staphylococci and determined antimicrobial resistance phenotypes in all the isolates. The presence of and prevalence of fusB-family genes (fusB, fusC, fusD, and fusF) and mutations in fusA genes were examined in fusidic acid resistant isolates. A total of 47 staphylococcal isolates of 4 different species (Staphylococcus aureus, n=4; S. hyicus, n=1; S. epidermidis, n=10; Mammaliicoccus sciuri, n=32) were isolated. Fusidic acid resistance were confirmed in 9/10 S. epidermidis and all of the 32 M. sciuri (previously S. sciuri) isolates. Acquired fusidic acid resistance genes were detected in all the resistant strains; fusB and fusC in S. epidermidis and fusB/C in M. sciuri. Multi-locus sequence type analysis revealed that ST63 (n=10, 31%) and ST30 (n=8, 25%) genotypes were most prevalent among fusidic acid resistant M. sciuri isolates. In conclusion, the high prevalence of fusB-family genes in S. epidermidis and M. sciuri strains isolated from pork indicated that NAS might act as a reservoir for fusidic acid resistance gene transmissions in pork production chains.