Susceptibility of β-Lactam Antibiotics and Genetic Mutation of Drug-Resistant Mycobacterium tuberculosis Isolates in Korea / 결핵및호흡기질환

Background@#Mycobacterium tuberculosis (Mtb) is resistant to the β-lactam antibiotics due to a non-classical transpeptidase in the cell wall with β-lactamase activity. A recent study showed that meropenem combined with a β-lactamase inhibitor clavulanate, was effective in MDR and XDR tuberculosis (TB). However, clavulanate can only be used in drugs containing amoxicillin in Korea. In this study, we investigated the susceptibility and genetic mutations of drug-resistant Mtb isolates to amoxicillin-clavulanate and meropenem-clavulanate to improve the diagnosis and treatment of drug-resistant TB patients. @*Methods@#The minimum inhibitory concentration (MIC) of amoxicillin-clavulanate and meropenem-clavulanate was examined by resazurin microtiter assay. We used 82 MDR and 40 XDR strains isolated in Korea and two reference laboratory strains. Mutations of drug targets blaC, blaI, ldtA, ldtB, dacB2, and crfA were analyzed by PCR and DNA sequencing. @*Results@#The MIC90 values of amoxicillin and meropenem with clavulanate in drug-resistant Mtb isolates were 64 and 16, respectively. Gene mutations related to amoxicillin/clavulanate and meropenem/clavulanate resistance could not be identified, but T448G mutation of was found in the blaC gene related to β-lactam antibiotics high susceptibility. @*Conclusion@#Our results provide clinical consideration of β-lactams in treating drug-resistant TB and potential molecular markers of amoxicillin-clavulanate and meropenem-clavulanate susceptibility.

Comparing Two Mycobacterium tuberculosis Genomes from Chinese Immigrants with Native Genomes Using Mauve Alignments / 결핵및호흡기질환

BACKGROUND: The number of immigrants with tuberculosis (TB) increases each year in South Korea. Determining the transmission dynamics based on whole genome sequencing (WGS) to cluster the strains has been challenging. METHODS: WGS, annotation refinement, and orthology assignment for the GenBank accession number acquisition were performed on two clinical isolates from Chinese immigrants. In addition, the genomes of the two isolates were compared with the genomes of Mycobacterium tuberculosis isolates, from two native Korean and five native Chinese individuals using a phylogenetic topology tree based on the Multiple Alignment of Conserved Genomic Sequence with Rearrangements (Mauve) package. RESULTS: The newly assigned accession numbers for two clinical isolates were CP020381.2 (a Korean-Chinese from Yanbian Province) and CP022014.1 (a Chinese from Shandong Province), respectively. Mauve alignment classified all nine TB isolates into a discriminative collinear set with matched regions. The phylogenetic analysis revealed a rooted phylogenetic tree grouping the nine strains into two lineages: (1) strains from Chinese individuals and (2) strains from Korean individuals. CONCLUSION: Phylogenetic trees based on the Mauve alignments were supposed to be useful in revealing the dynamics of TB transmission from immigrants in South Korea, which can provide valuable information for scaling up the TB screening policy for immigrants.

The Rate of Drug-Resistant Tuberculosis in Korean Children and Adolescents Since 2007

The incidence of drug-resistant tuberculosis (DR-TB) in pediatric populations is a critical indicator of national TB management and treatment strategies. Limited data exist regarding the rate of pediatric DR-TB. In this study, we aimed to analyze the status of DR-TB in Korean children from 2007 to 2013. We analyzed specimens submitted to the Korean Institute of Tuberculosis using Mycobacterium tuberculosis culture and drug susceptibility tests (DSTs) from January 2007 through December 2013. Specimens from patients ≤ 19 years of age were included. Among the 2,690 cases, 297 cases were excluded because of insufficient data, leaving 2,393 cases for the final analysis. In total, resistance to one or more TB drugs was 13.5%. The resistance rates of each of the drugs were as follows: isoniazid (INH) 10.2%, rifampin (RFP) 5.1%, ethambutol (EMB) 3.7%, and pyrazinamide (PZA) 3.1%. The resistance rate of multidrug-resistant TB (MDR-TB) was 4.2%, and that of extensively drug-resistant TB (XDR-TB) was 0.8%. The overall drug resistance rate demonstrated significant increase throughout the study period (P 15 years (P < 0.001). The drug resistance rate has increased throughout the study period.

BCG vaccine in Korea

The anti-tuberculosis Bacille de Calmette et Guerin (BCG) vaccine was developed between 1905 and 1921 at Pasteur Institutes of Lille in France, and was adopted by many countries. BCG strains comprise natural mutants of major virulence factors of Mycobacterium tuberculosis and that BCG sub-strains differ markedly in virulence levels. The tuberculosis became endemic in Korea after the Korean War (1950s). The BCG strain, which was donated by Pasteur Institutes, was brought to Korea in 1955, and the first domestic BCG vaccine was produced by the National Defense Research Institute (NDRI), current Korea Centers for Disease Control and Prevention (KCDC), in 1960. Since 1987, BCG manufacture work was handed over to the Korean Institute of Tuberculosis (KIT), the freeze-dried BCG vaccine was manufactured at a scale required to meet the whole amount of domestic consumption. However, since 2006, the manufacture of BCG vaccine suspended and the whole amount of BCG was imported at this point of time. Now KIT is planning to re-produce the BCG vaccine in Korea under the supervision of KCDC, this will be render great role to National Tuberculosis Control Program (NTP) and provide initiating step for developing new tuberculosis vaccines in Korea.

Exploitation of Culture Medium for Mycobacterium tuberculosis

The culture media for Mycobacterium tuberculosis (MTB) were contrived from both egg-based and agar based ingredients. In 1903, Dorset introduced the first egg-based medium. It was followed by the invention of Lowenstein-Jensen and Ogawa media that contain whole eggs as nutrient and malachite green to inhibit the growth of contaminants. These media have been used worldwide for their usefulness and inexpensiveness. However they have a fundamental disadvantage that the cultivation time for mycobacterial growth takes more than 4 weeks. In 1947, Dubos introduced the first agar medium and followed by the invention of the 7H10 by Middlebrook and Cohn. A powder base of these media contains agar, combination of seven salts, L-glutamic acid, pyridoxine, biotin, and malachite green. This requires the addition of the oleic acid, albumin, dextrose, and catalase (OADC) growth supplement. BACTEC MGIT960 has recently been introduced for rapid cultivation of MTB, which is fully automated liquid culture system with modified 7H9 broth. Agar-based medium developed by Middlebrook has a number of advantages over egg-based medium. One of them is transparency, which enables earlier detection of growing colonies. The major disadvantages of agar media are the high cost of OADC and the need for a CO2 incubator. In conclusion, there is a need for a new agar medium, which can be produced at a lower cost and earlier growth detection. In this review, we introduced the growth promoting factors which can be used as an alternative new growth supplement, cAMP and resuscitation-promoting factor (Rpf). These factors may abrogate a lag in adaption of the bacilli in culture media.

Evaluation of the Selected 12-locus MIRU for Genotyping Beijing Family Mycobacterium tuberculosis in Korea / 결핵및호흡기질환

BACKGROUND: Mycobacterial Interspersed Repetitive Units (MIRUs) that are located mainly in intergenic regions dispersed throughout the Mycobacterium tuberculosis genome. The selected MIRU loci, which were composed of a 12-locus set, demonstrated a high power for discrimination of Mycobacterium tuberculosis isolates collected from Kangwon province of Korea. To evaluate its ability to discriminate the M. tuberculosis strains, 45 clinical isolates were genotyped using the methods IS6110 RFLP and MIRU. METHODS: All the samples were collected during the period from January 2007 to December 2007 from TB patients, who were residents and registered to a public health center of Kangwon Province in Korea. A total of 45 DNAs were extracted from clinical isolated mycobacterial strains and genotyped using IS6110 RFLP, the MIRU method. RESULTS: We compared the 12-MIRU with IS6110 RFLP in the 45 samples, the 12-locus version offered less discriminatory power (Hunter-Gaston discriminatory index [HGDI]: 0.959 vs 0.998; 57.78% of clustered cases vs 8.89%). CONCLUSION: This 12-locus MIRU can be useful when additional combinations of other loci for genotyping M. tuberculosis in Korea where the Beijing family strains are dominant.