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Abstract: In order to characterize molecular mechanisms of first- and second-line drug resistance in Mycobacterium tuberculosis and to evaluate the use of molecular markers of resistance, we analyzed 62 multidrug-resistant, 100 extensively drug-resistant, and 30 pan-susceptible isolates from Korean tuberculosis patients. Twelve genome regions associated with drug resistance, including katG, ahpC, and inhA promoter for isoniazid (INH); embB for ethambutol (EMB), rpoB for rifampin (RIF), pncA for pyrazinamide (PZA), gyrA for fluoroquinolones; rpsL, gidB, and rrs for streptomycin; rrs and eis for kanamycin (KM); rrs and tylA for capreomycin (CAP); and rrs for amikacin (AMK) were amplified simultaneously by polymerase chain reaction, and the DNA sequences were determined. We found mutations in 140 of 160 INH-resistant isolates (87.5%), 159 of 162 RIF-resistant isolates (98.15%), 127 of 143 EMB-resistant isolates (88.8%), 108 of 123 ofloxacin-resistant isolates (87.8%), and 107 of 122 PZA-resistant isolates (87.7%); 43 of 51 STM-resistant isolates (84.3%), 15 of 17 KM-resistant isolates (88.2%), and 14 of 15 (AMK and CAP)-resistant isolates (93.3%) had mutations related to specific drug resistance. In addition, the sequence analyses of the study revealed many novel mutations involving these loci. This result suggests that mutations in the rpoB531, katGSer315Thr, and C-15T in the inhA promoter region, and gyrA94, embB306, pncA159, rpsL43, and A1401G in the rrs gene could serve as useful markers for rapid detection of resistance profile in the clinical isolates of M. tuberculosis in Korea, with potentials for the new therapeutic benefits in actual clinical practice. [Copyright &y& Elsevier]

Abstract: The present study aimed to describe the prevalence and molecular epidemiology of metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa isolates obtained from non-tertiary care hospitals and geriatric hospitals in South Korea. Of the 644 isolates, 224 were carbapenem-resistant, amongst which 41 (18.3%) were MBL-producers and the major MBL type was IMP-6 (35 isolates). IMP-6-producing isolates were multidrug-resistant and showed higher minimum inhibitory concentrations for meropenem than imipenem. All of the IMP-6-producing isolates had class 1 integrons with amplification sizes of 4.5kb/5.5kb (34 isolates) or 3.0kb (1 isolate); 4.5kb/5.5kb integrons had bla IMP-6–qac–aacA4–bla OXA-1–aadA1 (5.5kb) and aadB–cmlA–bla OXA-10–aadA1 (4.5kb). Pulsed-field gel electrophoresis (PFGE) analysis indicated that all IMP-6-producing P. aeruginosa from various geographic areas had nearly identical patterns with >85% similarity. All IMP-6-producing isolates showed high genetic similarity to those obtained from tertiary care hospitals and had the same integron type, indicating the spread of these strains to the three types of hospitals nationwide. These data show the wide spreading of clonally related IMP-6-producing P. aeruginosa (sequence type235) through tertiary, non-tertiary and geriatric hospitals in South Korea. Continuous monitoring and thorough infection control should be performed in all types of hospitals to prevent further spreading of MBL-producing P. aeruginosa. [Copyright &y& Elsevier]

Abstract: High-level mupirocin resistance results from the acquisition of a mupirocin resistance (Mupr) plasmid carrying the mupA gene. In this study, we investigated the heterogeneous location of the mupA gene as well as sequence variations in mupA restriction fragment length polymorphism (RFLP) types of high-level mupirocin-resistant (MuH) staphylococci isolated from tertiary hospitals and long-term care facilities in South Korea. RFLP patterns of the mupA gene were investigated in 14 MuH staphylococci isolates, and sequence variations of the cassette-like construction composed of the transfer gene complex (trs), an insertion sequence (IS257-like) and the mupA gene of the Mupr plasmid were also studied. Among the 14 isolates, four different EcoRI/HindIII banding patterns were observed, which were determined to be caused by sequence deletion between the mupA gene and trsLM of the trs gene complex. Four different sequence types were also identified for the trsLM–IS257-like–mupA cassette. The IS257-like sequence of all MuH staphylococci showed two base pair substitutions and one base deletion compared with the sequence of IS257. The heterogeneous location of the mupA gene was caused by sequence deletion adjacent to the IS257-like sequence of the trsLM–IS257-like–mupA cassette construction, and the IS257-like sequence was found in all MuH staphylococci. [Copyright &y& Elsevier]