Ming-Hsun Lee

Clinical manifestations, antibiotic susceptibility and molecular analysis of Mycobacterium kansasii isolates from a university hospital in Taiwan

OBJECTIVESnMycobacterium kansasii causes a variety of infections. Although previous reports on the prognosis of antimicrobial therapy have been mostly satisfactory, problems involving treatment failure or relapse have been encountered. The purpose of this study was to establish a relationship between the clinical treatment outcomes of M. kansasii infections and bacterial drug susceptibility, and their clonality.nnnMETHODSnA total of 37 M. kansasii clinical isolates and clinical information on 34 patients were retrospectively collected in a tertiary medical centre in Taiwan. Bacterial drug susceptibility was determined by the microdilution method. The phylogenetic relationship was analysed by PFGE analysis.nnnRESULTSnResults of PFGE typing revealed a major cluster (cluster I) and eight other divergent patterns. Two/three strains leading to treatment failure were also multidrug resistant and belonged to cluster I.nnnCONCLUSIONSnA relationship between high drug resistance and genetic relatedness of some M. kansasii strains was established. This was associated with clinical treatment failure.

Synergy of imipenem/colistin methanesulfonate combinations against imipenem-nonsusceptible multidrug-resistant Acinetobacter baumannii

BACKGROUNDnThe optimal combination ratio of imipenem to colistin methanesulfonate (CMS) against imipenem-nonsusceptible multidrug-resistant Acinetobacter baumannii (INS-MDRAB) has not been determined in previous studies. To provide an alternative therapeutic option for clinical INS-MDRAB isolates, we investigated whether clinically achievable serum concentrations of CMS in combination with imipenem enhance the in vitro activity of imipenem against the INS-MDRAB isolates.nnnMATERIALS AND METHODSnFifty-nine INS-MDRAB isolates with imipenem minimal inhibitory concentration (MIC) values of ≥8 mg/L were selected randomly from the Clinical Microbiology Laboratory at a university-affiliated medical center between July 1998 and May 2005. The in vitro activity of imipenem among these 59 clinical isolates was explored via serial two-fold dilutions containing a range of imipenem concentration from 0.125 mg/L to 256 mg/L, in combination with two fixed CMS concentrations at 0.5 mg/L and 1 mg/L. Genotype classification was performed using the pulsed-field gel electrophoresis method and infrequent-restriction-site polymerase chain reaction.nnnRESULTSnA significant reversal of imipenem resistance (i.e., MICs ≤ 4 mg/L) was observed in 34 (57.6%) isolates and 44 (74.6%) isolates with the tests of CMS concentrations at 0.5 mg/L and 1 mg/L, respectively (p = 0.041). Genotype 1 was predominant (43 isolates, 72.9%) with imipenem resistance reversal rates of 51.2% and 79.1% (p = 0.004) in the tests of CMS at 0.5 mg/L and 1 mg/L, respectively.nnnCONCLUSIONnThe synergy of imipenem/CMS against INS-MDRAB was significantly better for the CMS concentration at 1 mg/L than that at 0.5 mg/L, especially in our predominant clone. Our results provided insightful information for treating INS-MDRAB infections in clinical practice.

Development of carbapenem resistance in Pseudomonas aeruginosa is associated with OprD polymorphisms, particularly the amino acid substitution at codon 170

Objectives: Pan‐susceptible Pseudomonas aeruginosa (PSPA) clinical isolates carrying an OprD with loop 7 shortening (the group‐1A allele) were found to rapidly develop carbapenem resistance under continuous selection pressure. We further studied whether OprD polymorphisms are associated with the potential to develop carbapenem resistance. Methods: OprD amino acid sequences of 126 PSPA clinical isolates were analysed to determine their STs using P. aeruginosa strain PAO1 as the control strain. Site‐directed mutagenesis was performed in PAO1 to generate polymorphisms of interest. A disc diffusion method was used to select carbapenem‐resistant variants from the mutant strains. Expression levels of oprD were determined by quantitative RT‐PCR. MICs of carbapenems were determined by Etest. Results: Forty‐eight (38.1%) of the tested isolates carried the group‐1A allele. Another two major STs, C1 and C2, both of which harboured an F170L polymorphism, were found in 21 (16.7%) and 39 (31.0%) isolates, respectively. The PAO1 type was also found in 14 (11.1%) isolates. Under continuous selective pressure, isolates of most STs developed carbapenem resistance at different numbers of passaging events; only those belonging to the PAO1 type remained susceptible. However, PAO1 mutants carrying either the oprD group‐1A allele or the OprD‐F170L polymorphism were able to develop carbapenem resistance. Reduced oprD expression triggered by continuous imipenem challenge was found in PAO1 mutants, but not in the PAO1 WT strain. Conclusions: OprD polymorphisms, particularly the F170L substitution and the specific shortening in loop 7, appear to determine the potential for P. aeruginosa to develop carbapenem resistance.

C-reactive protein levels can predict positive 18F-FDG PET/CT findings that lead to management changes in patients with bacteremia

BACKGROUND/PURPOSEnBacteremia portends high rates of morbidity and mortality. Although 18F-fluorodeoxyglucose positron emission tomography and computed tomography (18F-FDG PET/CT) imaging has clinical value in assessing fever of unknown origin, its usefulness in bacteremia has not been entirely elucidated. We therefore designed the current single-center retrospective study to investigate 1) the clinical value of 18F-FDG PET/CT imaging in assessing bacteremia and 2) the association between laboratory data and imaging findings.nnnMETHODSnWe examined 102 patients with bacteremia who had undergone 18F-FDG PET/CT imaging. The patients clinical and laboratory data were reviewed and analyzed in relation to 18F-FDG PET/CT findings. Patients showing positive results underwent quantitative measurements of 18F-FDG uptake.nnnRESULTSnPositive 18F-FDG PET/CT findings were identified in 74 (72.5%) patients, and 40 (54.1%) underwent modified treatment or management because of the imaging results (pxa0=xa00.003). Positive 18F-FDG PET/CT findings were significantly associated with higher white blood cell (WBC) counts and C-reactive protein (CRP) levels (pxa0=xa00.012 andxa0<xa00.001, respectively). Notably, CRP levels accurately predicted (area under curvexa0=xa00.752; pxa0<xa00.001) positive 18F-FDG PET/CT findings (optimal cut-off point: 54.025xa0mg/L).nnnCONCLUSIONnA majority (54.1%, nxa0=xa040) of the patients with positive 18F-FDG PET/CT results underwent treatment modifications; they accounted for most cases (87%) of management changes in our cohort. Leukocytosis and increased CRP levels are significantly associated with positive 18F-FDG PET/CT findings in patients with bacteremia. CRP levels >54.025xa0mg/L were accurate predictors of positive 18F-FDG PET/CT results.

Vancomycin-resistant Enterococcus faecium at a university hospital in Taiwan, 2002–2015: Fluctuation of genetic populations and emergence of a new structure type of the Tn1546-like element

BACKGROUND/PURPOSESnVancomycin resistance increased significantly to 31.3% among Enterococcus faecium in 2006 and remained high thereafter at a university hospital in Taiwan. A longitudinal study was retrospectively conducted to characterize these vancomycin-resistant E. faecium (VRE-fm).nnnMETHODSnA total of 378 non-repetitive VRE-fm blood isolates collected during 2002-2015 were studied. Multilocus sequence typing, pulsed-field gel electrophoresis, analysis of van genes and the Tn1546 structure, and conjugation experiments were performed.nnnRESULTSnThe majority (78.0%) of the isolates were associated with hospital-acquired infections. Molecular typing revealed nine major pulsotypes and five predominant sequence types (STs): ST17 (33.9%), ST78 (18.3%), ST414 (14.6%), ST18 (10.6%), and ST203 (7.4%). Fluctuation of these prevailing STs among the study years in association with some major pulsotypes was noted. All isolates carried vanA genes, except that in four isolates vanB genes were found. Among the vanA-carrying Tn1546-like elements, one predominant structure type (Type I, 55.9%) was noted throughout the study years. Since 2009, another predominant structure type (Type II, 40.1%) has emerged firstly in ST414 and gradually spread to other 11 STs in subsequent years. Isolates carrying these Type II Tn1546-like elements have become the most predominant population since 2014, majorly found in ST78 and ST17. Preliminary experiments indicated that plasmids carrying the Type II Tn1546-like elements demonstrated ten-fold higher efficiency than those carrying the Type I Tn1546-like elements.nnnCONCLUSIONnDissemination of some major STs and horizontal transfer of plasmids carrying two major structure types of Tn1546-like elements may have together contributed to the increase of VRE-fm infection.