Hae-Sun Chung

Nosocomial Clustering of NDM-1-Producing Klebsiella pneumoniae Sequence Type 340 Strains in Four Patients at a South Korean Tertiary Care Hospital

ABSTRACT In November 2010, NDM-1-producing Klebsiella pneumoniae (NDMKP) was identified for the first time in South Korea from four patients with no history of traveling abroad who stayed for 21 to 205 days in a tertiary care hospital. All were sequence type (ST) 340 and had nearly identical XbaI pulsed-field gel electrophoresis (PFGE) patterns. The bla NDM-1-carrying plasmids were in the IncN group, with sizes ranging from 50 to 200 kb. These findings suggest that NDMKP had already been introduced into South Korea before this clustering was found.

Performance of the Vitek MS matrix-assisted laser desorption ionization time-of-flight mass spectrometry system for identification of Gram-positive cocci routinely isolated in clinical microbiology laboratories

We evaluated the performance of the Vitek MS for identification of Gram-positive cocci routinely isolated in clinical microbiology laboratories. With a total of 424 well-characterized isolates, the results of the Vitek MS were compared to those of conventional methods and 16S rRNA gene sequencing. The Vitek MS correctly identified 97.9 % of the isolates tested to species level. The Vitek MS correctly identified the species of 97.2 % of the staphylococci (95.9 % of coagulase-negative staphylococci), 97.8 % of the streptococci, and 100 % of the enterococci. For the identification of Gram-positive cocci isolates, the overall concordance rate between conventional identification and the Vitek MS was 94.5 %. The Vitek MS matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) system can be a reliable and rapid method for the identification of most relevant Gram-positive cocci. In addition, expanding the database of the Vitek MS, especially for coagulase-negative staphylococci, is needed to enhance the performance of the Vitek MS.

Antimicrobial Susceptibility of Stenotrophomonas maltophilia Isolates from Korea, and the Activity of Antimicrobial Combinations against the Isolates

The aim of this study was to determine antimicrobial susceptibility of recent clinical Stenotrophomonas maltophilia isolates from Korea, and to compare the activity levels of several combinations of antimicrobials. A total of 206 non-duplicate clinical isolates of S. maltophilia was collected in 2010 from 11 university hospitals. Antimicrobial susceptibility testing was performed using the Clinical Laboratory Standards Institute agar dilution method. In vitro activity of antimicrobial combinations was tested using the checkerboard method. The susceptibility rates to trimethoprim-sulfamethoxazole and minocycline were 96% and 99%, respectively. The susceptibility rate to levofloxacin was 64%. All of four antimicrobial combinations showed synergy against many S. maltophilia isolates. A combination of trimethoprim-sulfamethoxazole plus ticarcillin-clavulanate was most synergistic among the combinations. None of the combinations showed antagonistic activity. Therefore, some of the combinations may be more useful than individual drugs in the treatment of S. maltophilia infection. Further clinical studies are warranted to validate our in vitro test results.

The sul1 Gene in Stenotrophomonas maltophilia With High-Level Resistance to Trimethoprim/Sulfamethoxazole

Emerging resistance to trimethoprim/sulfamethoxazole (SXT) poses a serious threat to the treatment of Stenotrophomonas maltophilia infections. We determined the prevalence and molecular characteristics of acquired SXT resistance in recent clinical S. maltophilia isolates obtained from Korea. A total of 252 clinical isolates of S. maltophilia were collected from 10 university hospitals in Korea between 2009 and 2010. Antimicrobial susceptibility was determined by using the CLSI agar dilution method. The sul1, sul2, and sul3 genes, integrons, insertion sequence common region (ISCR) elements, and dfrA genes were detected using PCR. The presence of the sul1 gene and integrons was confirmed through sequence analysis. Among the 32 SXT-resistant isolates, sul1 was detected in 23 isolates (72%), all of which demonstrated high-level resistance (≥64 mg/L) to SXT. The sul1 gene (varying in size and structure) was linked to class 1 integrons in 15 of the 23 isolates (65%) harboring this gene. None of the SXT-susceptible isolates or the SXT-resistant isolates with a minimum inhibitory concentration of 4 and 8 mg/L were positive for sul1. Moreover, the sul2, sul3, and dfrA genes or the ISCR elements were not detected. The sul1 gene may play an important role in the high-level SXT resistance observed in S. maltophilia.

Subcutaneous Phaeohyphomycosis Caused by Phaeoacremonium Species in a Kidney Transplant Patient: The First Case in Korea

Phaeohyphomycosis is a subcutaneous infection caused by dark pigmented fungi, including fungi of the species Phaeoacremonium, Alternaria, Exophiala, and Pyrenochaeta. In August 2005, a 54-yr-old man who had received a renal transplant 5 yr ago was admitted to our hospital with a subcutaneous mass on the third finger of the right hand; the mass had been present for several months. He had been receiving immunosuppressive agents for several years. He underwent excision of the mass, which was followed by aspiration of the wound for bacterial and fungal cultures. Many fungal hyphae were observed on the histology slide treated with periodic acid-Schiff stain. A few white waxy colonies with a woolly texture grew on the Sabouraud dextrose agar at 30℃ and changed to dark brown in color. Nucleotide sequencing of internal transcribed spacer regions revealed 100% homology to the Phaeoacremonium aleophilum anamorph and Togninia minima teleomorph (514 bp/514 bp). The patient completely recovered after wide surgical excision. Here, we report the first case of phaeohyphomycosis caused by Phaeoacremonium species in a kidney transplant patient in Korea.

Different antimicrobial susceptibility testing methods to detect ertapenem resistance in enterobacteriaceae: VITEK2, MicroScan, Etest, disk diffusion, and broth microdilution

We investigated different antimicrobial susceptibility testing methods to detect ertapenem resistance in Enterobacteriaceae. A total of 72 Enterobacteriaceae isolates were collected from a clinical microbiology laboratory of a tertiary university hospital, all of which were detected ertapenem resistance by the VITEK2 system. Bacterial identification and antimicrobial susceptibility were determined using the VITEK2. Ertapenem susceptibility test was performed using the MicroScan, Etest and a disk diffusion test. Ertapenem MICs were confirmed using the broth microdilution (BMD). Sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively) of each method for the detection of ertapenem resistance were calculated. Carbapenemases and AmpC β-lactamase were screened using phenotypic methods. Among the 72 isolates, 20 isolates (27.8%) were resistant to ertapenem. Etest showed high sensitivity and specificity (85.0% and 88.5%, respectively) and excellent concordance with BMD. The disk diffusion test had the lowest sensitivity of 50.0%. The VITEK2 showed the lowest essential and categorical agreement (30.5% and 27.8%, respectively). The MicroScan showed relatively good agreement with BMD compared to the VITEK2. Most category disagreements were minor errors. There were 3 very major errors in both the MicroScan and disk diffusion test. Only 1 isolate was positive for carbapenemase screening test and all of the isolates were positive for AmpC screening test. In conclusion, the detection of ertapenem resistance in Enterobacteriaceae has limitations using routine testing such as an automated system or disk diffusion. Confirmation of results by an additional MIC test is recommended for accurate resistance results of ertapenem.

Characterization of the Multidrug-Resistant Acinetobacter species Causing a Nosocomial Outbreak at Intensive Care Units in a Korean Teaching Hospital: Suggesting the Correlations with the Clinical and Environmental Samples, Including Respiratory Tract-related Instruments

Background: Acinetobacter spp. is an important nosocomial pathogen for which increasing resistance to multiple antimicrobial agents has been observed. Prevalence of multidrug-resistant (MDR) Acinetobacter spp. in the intensive care unit (ICU) at a teaching hospital in Korea started to increase in 2008. The aim of this study was to determine the source of pathogen spread and to characterize the emerging strains at an early stage of outbreak. Methods: Samples from respiratory instruments and fomites in the ICUs, as well as from the healthcare workers, were cultured to identify the sources of MDR Acinetobacter spp. Antimicrobial susceptibility was determined by the CLSI disk diffusion method. Pulsed field gel electrophoresis (PFGE) was performed for clinical and environmental isolates in order to determine clonality. Carbapenemase genes were detected by multiplex PCR. Infection control measures including peer-monitoring of hand washing, environmental cleaning and standard precautions were enforced. Results: Among the samples from the ICU tools (105) and healthcare worker’s hands (44), 31 (30%) and 2 (5%) respective samples yielded MDR Acinetobacter spp. Among the environmental samples, 90% were from respiratory-related equipment. The majority of clinical and environmental MDR Acinetobacter spp. (44/55) belonged to the pulsotype A. baumannii and carried both blaOXA-51-like and blaOXA-23-like genes. Even though infection-control measures were enforced, prevalence of MDR Acinetobacter spp. continues to increase. Conclusion: An outbreak of MDR Acinetobacter spp. in a Korean hospital was caused by A. baumannii carrying the blaOXA-23-gene and was correlated with contaminated respiratory-related instruments in the ICUs. More intensive measures for nosocomial infection control are needed for successful prevention of Acinetobacter spread in hospitals. (Ann Clin Microbiol 2014;17:29-34)

Comparative evaluation of two matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) systems, Vitek MS and Microflex LT, for the identification of Gram-positive cocci routinely isolated in clinical microbiology laboratories.

We evaluated the performance of two MALDI-TOF MS systems for the identification of clinically important Gram-positive cocci. Vitek MS and Microflex LT correctly identified 97.2% and 94.7%, respectively. Both systems offer reliable and rapid identification of clinically important Gram-positive cocci isolated in clinical laboratories, including staphylococci, streptococci, and enterococci. Expanding the databases, especially of coagulase-negative staphylococci and viridans streptococci, would enhance performance.

Clonal Change of blaSIM-1-Carrying Acinetobacter spp. from 2003 to 2008 in the Hospital Where It Was Initially Discovered

SIM-1 metallo-β-lactamase was first discovered from carbapenem-resistant Acinetobacter spp. isolated in a Korean University Hospital in 2003, and was recently reported to have been discovered in A. baylyi isolated in nearby China. The aims of this study were to reveal clonal changes in bla(SIM-1)-harboring Acinetobacter isolates collected from 2003 to 2008 in the same Korean hospital, where they were first discovered to gain further insight into the relation between bla(SIM-1)-harboring plasmids and Acinetobacter spp. Among 1,761 nonduplicated imipenem-resistant Acinetobacter spp. isolates, 29 isolates were identified as bla(SIM-1) carriers. They were categorized into nine types according to pulsed-field gel electrophoresis findings. While most bla(SIM-1)-carrying isolates from 2003 to 2005 belonged to A. pittii, those from 2006 to 2007 were mostly isolates of A. nosocomialis. Most of the bla(SIM-1) genes were carried on ca. 280-kb plasmids and were only discovered in non-baumannii Acinetobacter spp. Integrons carrying the bla(SIM-1) gene were identical in structure in all species. These findings suggest that the plasmids were transferable, but not promiscuous. Further surveillance should be continued to detect and control further spread of the bla(SIM-1) gene, as the appearance of the bla(SIM-1) gene in different Acinetobacter spp. in different countries has already begun.

Evaluation of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Identification of Aerobic Bacteria in a Clinical Microbiology Laboratory

Background: Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been used for the identification of bacteria worldwide. To our knowledge, the evaluation of MALDI-TOF MS for the identification of bacteria in Korea has not been studied. In this paper we compared the identification results of aerobic bacteria using MALDI-TOF MS to those results using conventional biochemical methods. Methods: We evaluated the performance of a MALDITOF MS system (Bruker Daltonics, Leipzig, Germany) on consecutive aerobic isolates collected from January to February of 2011 which were identified using conventional methods (biochemical testing and commercial identification kits). Either directly smearing onto the target plate or protein extraction methods were additionally used if no reliable or discordant results were obtained. Results: Among 523 isolates tested, 506 (97%) isolates had valid scores (≥2.0), 11 (2%) isolates gave intermediate scores (1.7≤ score <2.0), and 6 (1%) isolates yielded no reliable identification (score <1.7). Of the 506 valid results (score ≥2.0) by MALDI-TOF MS, the identification matched at the species level in 486 (96%) isloates, matched at the genus level in 17 (3%) isloates, and was discordant at the genus and species levels in 3 (1%) isloates. Conclusion: The overall matching rate at the species level of MALDI-TOF MS was very high. When MALDI-TOF MS did not yield reliable results by direct smear, additional direct smears or protein extraction methods could be used to obtain better results. Our results showed that MALDI-TOF MS is a very useful method for the identification of aerobic bacteria isolated in clinical microbiology laboratories. (Korean J Clin Microbiol 2012;15:60-66)