• Tuberculosis and Respiratory Diseases
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• v.46 no.5
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• pp.618-627
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• 1999

Background : Rifampicin (RFP) is a key component of the antituberculous short-course chemotherapy. Usually the RFP resistant M.tuberculosis is also resistant to isoniazid (INH), so the RFP resistance is the marker of multi-drug resistant (MDR) tuberculosis. But unusual cases of mono-RFP-resistant tuberculosis have been recently reported with increasing frequency, especially associated with HIV infection in western countries. Therefore, we conducted a retrospective study to investigate the frequency, causes, and the clinical characteristics of mono-RFP-resistant tuberculosis in Korea. Methods : Of the bacteriologically confirmed and susceptibility-proven 699 pulmonary tuberculosis patients (921 isolates) who visited Asan Medical Center from January 1990 to August 1997, eighteen patients with INH-susceptible and RFP-resistant tuberculosis were evaluated. Previous history of tuberculosis, antituberculous drug compliances, associated systemic illness, drug susceptibility patterns, and clinical outcomes were analysed. And rpoB gene sequencing was done in 6 clinical isolates of M. tuberculosis. Results : The mean age of 18 patients was $43{\pm}14$ years, and the sex ratio is 12:6 (M : F). Sixteen (89%) patients had previous history of tuberculosis. None had diagnosed gastrointestinal disorders, and 2 HIV tests that were performed came out negative. Susceptibility tests were done repeatedly in eleven patients, and six (55%) were mono-RFP resistant repeatedly while five (45%) evolved to MDR tuberculosis. Eight (44%) patients were cured, six (33%) failed, three (17%) were lost to follow-up, and the other one is now on treatment. rpoB gene sequencing showed 5 mutations, codon 531 TCG to TIG mutation in 4 isolates and 526 CAC to TAC in 1 isolate. Conclusion : The clinical characteristics of mono-RFP resistant tuberculosis were similar to that of MDR tuberculosis in Korea where the HIV infection rate is lower than western countries. But some patients with mono-RFP-resistant tuberculous could be cured by primary drug regimens including RFP, suggesting that mono-RFP-resistant tuberculous is a different entity from MDR tuberculosis.

• Tuberculosis and Respiratory Diseases
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• v.43 no.6
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• pp.862-870
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• 1996

Background : Multidrug-resistant tuberculosis(MDR-Tb) has been increased not only in Asia but also in Western society, which may cause public health problems and reduce the efficacy of treatment of tuberculosis. In Western society HIV infection is believed to do a central role in increasing incidence of MDR tuberculosis, but MDR-Tb in Korea may be somewhat different about clinical features, underlying disorders, and prognosis. Goble et al reponed that overall treatment failure rate in MDR-Tb including resistance to isoniazid(INH) and rifampin (RFP) was 44 %. The aim of this study is to find the treatment result in Korea and the factors determining the prognosis. Methods: A retrospective study of pulmonary tuberculosis cultured M. tuberculosis from sputum or bronchial washing fluid between 1986 through 1992 was conducted in the Seoul Paik Hospital, Inje University. We reviewed clinical courses of 141 patients, who had a tuberculosis with resistance to 2 or more drugs including isoniazid(INH) and rifampin(RFP). One hundred and 4 patients of 141 patients had completed treatment and followed up for more than one year. Results: Of 104 (mean age $43.6{\pm}16.7$, M: F=63 : 41) patients with sufficient follow-up data, 73(84.6%) patients responded which is defined as negative Sputum cultures for at least 3 consecutive months. Seven patients(6.7%) had a failure in negative conversion and 9(8.7%) of the patients who initially responded relapsed. Overall treatment failure rate was 15.4%, Patients who were treated for less than 12 months had a higher relapse rate(12.3%) than 18 months(4.9%). And there was a statistically significant correlation between the relapse rate and the number of drugs to which isolates wera resistant(p<0.05). Conclusion : The treatment failure rate of MDR-Tb in Korea was lower than previous studies in western Country and the major determining factor of prognosis was the number of resistant drugs to M. tuberculosis at drug sensitivity test. For reducing the relapse rate, we recommend more than 12 months of treatment for MDR tuberculosis.

• Tuberculosis and Respiratory Diseases
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• v.45 no.4
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• pp.714-722
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• 1998

Background: Rifampicin (RFP) is a key component of the antituberculous short-course chemotherapy and the RFP resistance is a marker of multi-drug resistant (MDR) tuberculosis. RPoB gene encodes the $\beta$-subunit of RNA polymerase of M. tuberculosis which is the target of RFP. And the mutations of rpoB gene have been found in about 96% of rifampicin resistant clinical isolates of M. tuberculosis. So in order to find a rapid and clinically useful diagnostic method in identifying the RFP resistance, we compared the PCR -line probe method with PCR-SSCP for the detection of the rpoB gene mutation in cultured M. tuberculosis. Methods: 45 clinical isolates were collected from patients who visited Sung Kyun Kwan University Hospital. The RFP susceptibility test was referred to the referral laboratory of the Korean Tuberculosis Institute. 33 were rifampicin resistant and 12 were rifampicin susceptible. The susceptibility results were compared with the results of the PCR-BSCP and PCR-line probe method. Results: We could find rpoB mutations in 27/33(81.8%) RFP-resistant strains by PCR-line probe method, and in 23/33 (69.7%) by PCR-SSCP and there was no significant difference between two methods. There was no mutation in rifampicinn susceptible strains by both methods. Conclusion: PCR-line probe method would be a rapid, sensitive and specific method for the detection of rifampicin resistant Mycobacterium tuberculosis.

• Tuberculosis and Respiratory Diseases
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• v.43 no.6
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• pp.842-851
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• 1996

Background : Rifampicin(RFP) is a key component of the antituberculous shon-course chemotherapy and the RFP-resistance is a marker of multi-drug resistant(MDR) M. tuberculosis. rpoB gene encodes the ${\beta}$-subunit of RNA polymerase of M. tuberculosis which is the target of RFP. Recent reports show that rpoB gene mutations are the cause of RFP resistance of M. tuberculosis and the main mechanism of rpoB gene mutation is point mutation. And PCR-SSCP is a rapid and easy method for detecting point mutations. So we performed PCR-SSCP of rpoB gene of M. tuberculosis and compared the result with traditional RFP sensitivity test. Method : The 27 RFP sensitive M. tuberculosis culture isolates and 25 RFP resistant isolates were evaluated. The RFP sensitivity test was done at the Korean Tuberculosis istitute. The DNA was extracted by bead beater method and was amplified with primers TR-8 and TR-9 in a 20ul PCR reaction containing 0.1ul(luCi) [${\alpha}-^{32}P$] - dCTP. After amplification, SSCP was done using non-denaturaring polyacrylamide gel electrophoresis. Then direct sequencing was done in cases of different eletrophoretic mobility compared with that of H37Rv. In 19 cases, we compared PCR-SSCP results with patient's clinical course and the results of traditional RFP sensitivity test. Results : 1) All 27 RFP sensitive M. tuberculosis isolates showed the same electrophoretic mobility compared with that of H37Rv. And all 25 RFP resistant M. tuberculosis isolates showed different electrophoretic mobility. 2) The mechanism of rpoB gene mutation of M. tuberculosis is mainly point mutation. 3) The PCR-SSCP results correlate well with traditional RFP sensitivity and patient's clinical response to antituberculous treatment. Conclusion: The PCR-SSCP of rpoB gene is a very sensitive and rapid mehod in detecting RFP- resistant M. tuberculosis.

• Pediatric Infection and Vaccine
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• v.26 no.3
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• pp.148-160
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• 2019

Purpose: This study aimed to investigate the molecular epidemiology of a methicillin-resistant Staphylococcus aureus (MRSA) outbreak at a newborn nursery and neonatal intensive care unit (NICU). Methods: During the outbreak, from August to September 2017, MRSA isolates collected from neonates and medical staff underwent genotyping and screened for virulence factors. Antibiotic susceptibilities were tested. Results: During the study period, 41 neonates were admitted at the nursery (n=27) and NICU (n=14). Of these, 7 had MRSA infections (skin infection [n=6] and sepsis [n=1]) and 4 were colonized with MRSA. Associated medical staff (n=32) were screened; three were nasal MRSA carriers. Staphylococcal chromosomal cassette mec (SCCmec) type II, sequence type (ST) 89, spa type t375 was found to be the skin infection outbreak causing strain, with multi-drug resistance including low-level mupirocin resistance. SCCmec type IVa, ST 72, and a novel spa type designated t17879, was the cause of MRSA sepsis. Many different types of MRSA were colonized on the neonates; however, SCCmec type IVa, ST 72, spa type t664 was colonized in both neonates and a NICU nurse. All MRSA isolates from colonized infants were positive for the Panton-Valentine leukocidin (PVL) toxin gene. Conclusions: The strain causing an outbreak of skin infections had multi-drug resistance. Also, MRSA colonized in the neonates were found to carry the PVL toxin gene. Because different strains are present during an outbreak, molecular epidemiologic studies are important to identify the outbreak strain and colonized strains which aid in effective control and prevention of future MRSA outbreaks.

• Tuberculosis and Respiratory Diseases
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• v.45 no.6
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• pp.1178-1187
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• 1998

Background : Recently the incidence of tuberculosis is increasing in many countries and control of the disease is further threatened by the emergence of multi-drug resistant tuberculosis. So rapid detection of drug resistance is very important. Pyrazinamide (PZA) is a first-line chemotherapeutic agent for tuberculosis. Now in Korea, we perform PZase activity test instead of actual pyrazinamide susceptibility test for the detection of PZA resistant M. tuberculosis. Recently the pncA gene, encoding the PZase of M. tuberculosis, was completely sequenced. And it was reported that the mutation of pncA gene would be associated with PZA resistance of M. tuberculosis. Therefore we performed this study to evaluate the possibility for the rapid detection of PZA resistant M. tuberculosis using PCR-SSCP of pncA gene. Method : 44 cultured clinical isolates of M. tuberculosis, BCG Tokyo strain. BCG French strain, and one M. bovis isolate were studied. We used H37Rv as the reference strain, The PZase activity test was done at the reference laboratory of Korean Tuberculosis Institute. DNA was extracted by bead-beater method and 561 bp fragment including pncA gene was amplified by PCR. The PCR product were digested by BstB I enzyme. SSCP was done using MDE gel. Of the 44 strains of M. tuberculosis, 22 strains were PZase-positive and other 22 strains were PZase negative. Results : Of the 22 PZase positive strains, 18 strains(82%) showed the same mobility compared with that of H37Rv and 4(18%) showed different mobility. Of the 22 PZase-negative strains, 19(86%) strains showed the same mobility pattern compared with that of H37Rv and 3(14%) showed different mobility. Naturally PZA-resistant BeG-French strain, BCG-Tokyo strain, and one M. bovis isolate showed the same band pattern each other, but their mobility were different from that of H37Rv. The results of PZase activity test and PCR-SSCP of pncA of M. tuberculosis were statistically significantly correlated each other (p<0.01). Conclusion : The PCR-SSCP after BstB I restriction of pncA gene of M. tuberculosis may be a useful method for the rapid detection of PZA-resistant M. tuberculosis.

• Pediatric Infection and Vaccine
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• v.10 no.2
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• pp.159-166
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• 2003

Purpose : Streptococcus pneumoniae is part of the normal flora but is also responsible for causing many invasive diseases such as pneumonia, meningitis, and sepsis in addition to noninvasive diseases such as otitis in children. Multi-drug resistant strains has raised a lot of concern worldwide and thus the importance of prevention has been emphasized. We have analyzed the current serotypes and antibiotic sensitivity of each serotype as a baseline study to estimate the efficacy of the pneumococcal vaccine in Korean children. Methods : One hundred sixteen cases of pneumococcus cultured at Yonsei Medical Center from September 2001 to January 2003 were analyzed. The serotyping was done with the Quellung reaction and penicillin resistance was tested using the oxacillin disc diffusion method. Results : Pneumococcus were cultured from the sputum in 76 cases(65.5%), from the blood in 13 cases(11.2%), from the ear discharge in 12 cases(10.3%), from the throat in 7 cases(6.0%), from the nasal cavity in 2 cases(1.7%), and one case(0.9%) each from the cerebrospinal fluid, eye discharge, peritoneal fluid, post-operational wound, brain abscess, and catheter tip. Serotyping was possible with 98 cases and the following serotypes were found; 15 cases of type 19F(15.3%), 11 cases of 19A(11.2%), 8 cases of 11A(8.2%), 7 cases each of 6A, 14 and 3(7.1%), 6 cases each of 35, 6B and 23F(6.1%). Eighty two cases(70.7%) out of 116 cases were penicillin resistant and serotypes 19F, 19A, 11A, 23F, 6A, 9V constituted the majority, 48 cases(59.8%). These serotypes showed resistance to cotrimoxazole (74.4%), tetracycline(69.5%), and erythromycin(90.3%) as well. In the 22 cases cultured from children, 19A and 19F were found in 25.0%, 6A, 6B, and 23F in 10.0%, 11A, 14, 19, and 29 in 5.0%. Fifty percent(10/20) of the clinical isolates were represented in the current 7-valent pneumococcal protein conjugate vaccine, and 85%(17/20) when the cross-reacting serotypes were included. Penicillin resistance was found in 86.4%(19/22). Conclusion : The percentage of serotypes included in the 7 valent pneumococcal protein conjugate vaccine found in our study was 40.8% which was less than other prior studies. In anticipation of a change of pneumococcal serotypes, a nationwide multicenter study is needed before the initiation of pneumococcal vaccines in Korea.