Seok Hoon Jeong
Ann Clin Microbiol 2009 March, 12(1): 1-5. Published on 20 March 2009.
A rapid dissemination of carbapenem-resistant Acinetobacter spp. represents a significant clinical threat. Production of OXA carbapenemases and metallo-β- lactamases (MBLs) is the most important mechanism in acquiring carbapenem resistance in Acinetobacter spp. Carbapenem resistance has also ascribed to non- enzymatic mechanisms, including changes in outer membrane proteins, alterations in the affinity or expression of penicillin-binding proteins, and overexpression of efflux pumps. The most important mechanism in A. baumannii isolates from Korea is the production of OXA-23, while that in other species of Acinetobacter is the production of metallo-β-lactamases.
[in Korean]
Eun-Ha Koh, In-Suk Kim, Sunjoo Kim
Ann Clin Microbiol 2009 March, 12(1): 6-10. Published on 20 March 2009.
Background: Streptococcus pyogenes is the most common cause of bacterial pharyngitis. T antigens and emm genotypes are essential markers for an epidemiological study of S. pyogenes. Macrolide resistance of S. pyogenes is a serious obstracle to successfully treating a sore throat.
Methods: One-hundred forty-seven strains of S. pyogenes isolated from healthy school children in 2006 were subjected to T typing and emm genotyping. A disk diffusion method was applied for several antibiotics. A double disk diffusion test was performed to evaluate the phenotype distribution of macrolide resistance.
Results: Among T antigens and emm genotypes, T11 (19.7%) and emm78 (16.7%), respectively, were the most common in 2006. Both T5/27/44 (2.3%) and emm44/61 (9.1%) declined to a great extent from about 29% in 2004. The rate of resistance to antibiotics were 11.6% to erythromycin, 4.8% to clindamycin, 21.8% to tetracycline, and 7.5% to ofloxacin. M and cMLSB phenotypes were 52.9% and 41.2% respectively.
Conclusion: T typing and emm genotyping proved a dynamic change in their distribution in 2006 compared to the results of 2004. Erythromycin and clindamycin resistance remained low as in 2004, whereas ofloxacin resistance increased slightly. M and cMLSB phenotypes were equivalent in 2006, whereas cMLSB was predominant in 2004.
[in Korean]
Yun Ha Jang, Jaewoo Chung, Seungmi Baek, Sookja Park, Heungsup Sung, Mi-Na Kim
Ann Clin Microbiol 2009 March, 12(1): 11-16. Published on 20 March 2009.
Background: We evaluated multiplex PCR for species identification and toxin typing to improve the sensitivity and turnaround time of toxigenic Clostridium difficile culture (TCDC).
Methods: We performed multiplex PCR using primers targeting the species-specific gene, tpi, and the toxin genes, tcdA and tcdB. From January to March 2008, 528 stool specimens were tested with direct toxin assay (DT) using C. difficile Tox A/B II (Techlab, Blacksburg, USA) and TCDC. For 288 specimens from early study period, toxin production by C. difficile isolates of TCDC was measured by enzyme immunoassay with culture supernatants using VIDAS C. difficile Toxin A&B (CDAB; bioMérieux, Marcy-l’Etoile, France) and multiplex PCR with isolated colonies. For 240 specimens from late period, only multiplex PCR was used to test toxin production by the isolates.
Results: During the early period, 29 C. difficile were isolated and their toxin-positive rates were 65.5% by PCR and 44.8% by CDAB (P＜0.05). Among 528 stool specimens, the results of DT+/TCDC+, DT+/ TCDC-, and DT-/TCDC+ were 32 (6.1%), 33 (6.3%), and 10 (1.9%), respectively, when tested with PCR. 13.3% of total 75 positive specimens was detected only by TCDC. Of the 42 toxigenic C. difficile isolates, all were positive for tpi, 30 (71.4%) were tcdA+/tcdB+, and 12 (28.6%) were tcdA-/tcdB+.
Conclusion: TCDC using multiplex PCR for species identification and toxin typing is sensitive and rapid to be used as a routine diagnostic test.
[in Korean]
Ji Youn Sung, Sun Hoe Koo, Kye Chul Kwon, Jong Woo Park, Chi Seon Ko, So Youn Shin, Jeong Hoon Song
Ann Clin Microbiol 2009 March, 12(1): 17-23. Published on 20 March 2009.
Background: The genes of metallo-β-lactamase (MBL), a powerful carbapenemase, are carried as a part of the mobile gene cassettes inserted into integrons playing an important role in rapid dissemination of antibiotic resistance genes among bacterial isolates. In this study, we investigated carbapenemase genes and class 1 integrons integrated into the gene cassettes in imipenem-non susceptible P. aeruginosa.
Methods: From July 2006 to March 2008, 81 consecutive, non-duplicate, imipenem-non susceptible P. aeruginosa were isolated at Chungnam National University Hospital in Chungcheong province of Korea. The modified Hodge and double disk synergy tests were conducted for the screening of carbapenemase and MBL production, respectively, and PCR and DNA sequencing were performed for the detection of carbapenemase genes and class 1 integron gene cassettes. We also employed the repetitive element sequence-based (Rep)-PCR method for an epidemiologic study.
Results: MBLs were detected in 13.6% (11/81) of imipenem-non susceptible P. aeruginosa. Ten isolates were found to carry blaIMP-1, whereas 1 isolate was found to carry a blaVIM-2. All of the IMP-1-producing strains harbored 4.0 kb class 1 integron containing chloramphenicol, aminoglycoside, and β-lactam- resistant genes. However, blaIMP-1 was not detected at class 1 integron. A 2.5 kb class 1 integron harboring blaVIM-2 was detected in a VIIM-2- producing strain. One identical pattern was observed in ten IMP-1 producing strains.
Conclusion: IMP-1 producing P. aeruginosa strains are currently distributed throughout Chungcheong province of Korea. In particular, all of the strains harbored class 1 integrons containing variant antibiotic resistance gene cassettes.
[in Korean]
Soon Deok Park, Young Uh, In Ho Jang, Ohgun Kwon, Kap Jun Yoon, Hyo Youl Kim
Ann Clin Microbiol 2009 March, 12(1): 24-29. Published on 20 March 2009.
Background: Accurate detection of organisms producing extended-spectrum β-lactamase (ESBL) and AmpC β-lactamase is very important for treatment of patients. However, unlike the ESBL confirmatory test, there are no guidelines for detection of organisms producing AmpC β-lactamase. We evaluated a detection method using boronic acid (BA) for ESBL and AmpC β-lactamase.
Methods: Clinical isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis showing intermediate resistance or resistance to cefoxitin (FOX) or positive for ESBL were tested. A ≥5 mm increase in zone diameter of ceftazidime/clavulanic acid/BA (CAZ/CA/BA) and/or cefotaxime/clavulanic acid/BA (CTX/CA/BA) versus CAZ/BA and/or CTX /BA was considered positive for ESBL. Likewise, a ≥5 mm increase in zone diameter of FOX/BA and/or cefotetan/BA (CTT/BA) versus FOX and/or CTT alone was considered positive for AmpC β-lactamase.
Results: Among 622 clinical isolates, ESBL positive rates by the CLSI ESBL confirmatory test or by the BA method were 18.1% or 18.4% for E. coli, 38.3% or 40.4% for K. pneumoniae, 8.7% or 8.7% for K. oxytoca, and 14.8% or 14.8% for P. mirabilis, respectively. AmpC β-lactamase positive rates using the BA method were 3.7% for E. coli, 33.3% for K. pneumoniae, 0% for K. oxytoca, and 7.4% for P. mirabilis. The detection rates of coproducing ESBL and AmpC β-lactamase were 2.4% in E. coli, 27.1% in K. pneumoniae, and 3.7% in P. mirabilis.
Conclusion: The ESBL confirmatory method using BA was found to enhance the detection of ESBLs, even when potentially masked by AmpC β-lactamase.
[in Korean]
Heungsup Sung, Jung-Oak Kang, Mi Ae Lee, Jongwook Lee, Hae Kyung Lee, Mi-Kyung Lee, Ji-Hun Lim, Mi-Na Kim, Helicobacter Study Group
Ann Clin Microbiol 2009 March, 12(1): 30-36. Published on 20 March 2009.
Background: CLSI provides a guideline only for a agar dilution method of testing clarithromycin susceptibility for Helicobacter pylori. This study was to evaluate a disk diffusion method for clarithromycin and amoxicillin.
Methods: One hundred and forty clinical isolates of H. pylori isolated from May 2005 to May 2007 were tested by the CLSI agar dilution method and a disk diffusion method using 2μg (2CLR) and 15μg (15CLR) clarithromycin disks and 2μg (2AMX) and 10μg (10AMX) amoxicillin disks. The interpretation criteria used for the disk diffusion method were established by linear regression and error rate-bounded method for disk diffusion zone of inhibition (DDZ) compared to MIC.
Results: Resistance and intermediate rates to clarithromycin were 21.4% and 1.4%, respectively. A number of isolates with MIC 0.5, 1, and 2 (μg/mL) to amoxicillin were 7, 2, and 1, respectively. For 2CLR and 15CLR, the coefficients of determination (R2) between MIC and DDZ were 0.931 and 0.923 (P＜ 0.001), respectively, and the criteria for resistance/ susceptibility were 12/28 mm for 2CLR and 23/39 mm for 15CLR. For 2AMX and 10AMX, the R2 between MIC and DDZ were 0.478 and 0.421 (P＜ 0.001), respectively, and the criteria for resistance with breakpoint of 2μg/mL were 21 mm for 2AMX and 32 mm for 10AMX. All isolates had DDZ＜60 mm with 2CLR and 2AMX, but 61.4% and 75.7% of the isolates had DDZ＜60 mm with 15CLR and 10AMX, respectively.
Conclusion: Excellent correlation and agreement between MIC and DDZ were found for clarithromycin and amoxicillin. With 2μg disks, the susceptibility breakpoints were 28 mm or less; thus, two disks could be tested in one plate.
[in Korean]
Hae-Sun Chung, Chang-Seok Ki, Jang Ho Lee, Nam Yong Lee
Ann Clin Microbiol 2009 March, 12(1): 37-42. Published on 20 March 2009.
Background: We evaluated BacT/ALERT 3D liquid culture system (bioMerieux, USA) and PCR-restriction fragment length polymorphism (RFLP) for recovery and direct identification of mycobacteria, and the results were compared with a conventional culture system using an egg-based solid medium.
Methods: A total of 3,037 bronchial specimens (2,309 bronchial washing fluids and 728 bronchoalveolar lavages) were collected. Decontaminated specimens were inoculated to both BacT/ALERT MP liquid media and Ogawa solid media (3%, Shinyang, Korea). Recovery rate and detection time were compared between the two systems. Liquid media from positive cultures were centrifuged and the pellets were tested for direct identification of mycobacteria by PCR-RFLP using Myco-ID (M&D Inc., Korea).
Results: A total of 518 isolates, including 215 M. tuberculosis (MTB) and 303 non-tuberculosis mycobacteria (NTM), were recovered. The liquid media detected 492 isolates (16.2%), including 195 MTB and 297 NTM), whereas the solid media detected 416 isolates (13.7%), including 187 MTB and 229 NTM (P＜0.001); 102 isolates (28 MTB and 74 NTM) were recovered only by the liquid media, while 26 (20 MTB and 6 NTM) isolates were recovered only by the solid media. The mean time to detection was 18.1 days by the liquid media and 29.3 days by the solid media (P＜0.001). The overall time to species identification from inoculation was 21.8 days. Direct PCR-RFLP from the liquid media identified 39.1% of MTB, 6.3% of M. avium, 19.05 of M. abscessus, and 12.6% of M. intracellulare respectively.
Conclusion: Combined use of a liquid culture system and PCR-RFLP improved the recovery rate and shortened the detection time. However, solid media is still necessary to maximize the diagnostic efficiency.
[in Korean]
Yong-Kyun Kim, Jae-Seok Kim, Hyoung-Sun Lee, Hyun-Sook Koo, Han-Sung Kim, Wonkeun Song, Ji Young Park, Hae-Ran Lee, Hyoun Chan Cho, Kyu Man Lee
Ann Clin Microbiol 2009 March, 12(1): 43-47. Published on 20 March 2009.
Background: Doctors’ white coats and neckties can become contaminated with potentially pathogenic bacteria and have a possibility of causing cross infections. Our objective was to determine the level of bacterial contamination and detect methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and Clostridium difficile present on the white coats and neckties of residents.
Methods: We sampled 28 long-sleeved white coats and 14 neckties worn by residents. The tested sites for white coats were the cuffs and lower front surfaces, and for neckties, the lower surfaces. Impressions of these sites were taken with the plates containing blood agar (BAP), mannitol salt agar supplemented with oxacillin (6μg/mL), enterococcus screening agar supplemented with vancomycin (6μg/mL) and phenyl ethanol agar. The colonies grown on each plate were Gram stained and identified by standard microbiological methods.
Results: Of the 28 white coats, 7 (25.0%) carried MRSA, and of the 14 neckties, 1 (7.1%) carried MRSA. The majority of white coats (96.4%) and all neckties (100.0%) carried methicillin-resistant coagulase negative staphylococci (MRCNS). None of the white coats and neckties carried VRE or C. difficile.
Conclusion: Our results showed that white coats and neckties worn by residents were contaminated with MRSA and MRCNS. The preventive measures for clothing-borne cross contamination should be considered, especially when performing invasive procedures or having close contact with patients.
[in Korean]
Jong Hyun Kim, Eun Gyoung Lim, Hyun Chul Jang, Ju Young Park, Sun Jin Lee, Mi Sun Park, Gil Bae Choi, Bok Kwon Lee
Ann Clin Microbiol 2009 March, 12(1): 48-52. Published on 20 March 2009.
Bacillus cereus causes two types of gastrointestinal diseases: emesis and diarrhea. It produces one emetic toxin and nine different enterotoxins. In March 2008, eight of a family became sick after eating slices of raw fish. We isolated emetic toxin producing B. cereus from the stools of 6 patients and 2 subclincal humans. In this study, the presence of enterotoxin genes, such as those of haemolysin BL (Hbl), nonhemolytic enterotoxin (Nhe), B. cereus enterotoxin T (BceT), enterotoxin FM (EntFM), cytotoxin K (cytK) and cereulide were assayed by polymerase chain reaction (PCR) methods. Their enterotoxin activities were assayed using the BCET- RPLA, Tecra ELISA kit and Hep-2 vacuole activity. Bacterial isolates were subtyped by pulsed-field gel electrophoresis (PFGE). This study demonstrates the emetic toxin-producing stains of B. cereus in clinical specimens, for the first time in the Republic of Korea.
[in Korean]
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