Ya-Gang Chen

Plasmid-mediated KPC-2 in a Klebsiella pneumoniae isolate from China.

ABSTRACT A carbapenem-resistant isolate of Klebsiella pneumoniae producing class A carbapenemase KPC-2 was identified in Zhejiang, China. The KPC-2 gene was located on an approximately 60-kb plasmid in a genetic environment partially different from that of blaKPC-2 in the isolates from the United States and Colombia.

Evaluation of Phenotypic Tests for Detection of Metallo-β-Lactamase-Producing Pseudomonas aeruginosa Strains in China

ABSTRACT A total of 264 nonduplicate strains of imipenem (IPM)-nonsusceptible Pseudomonas aeruginosa were isolated from hospitals in 16 different regions throughout China. These 264 IPM-nonsusceptible clinical isolates of P. aeruginosa were examined by PCR, a metallo-β-lactamase (MBL) Etest, a double-disk synergy test (DDST), and a test using combined IPM disks supplemented with various amounts of EDTA. A total of 24 strains positive for MBLs were confirmed by PCR and DNA sequence analysis: 10 strains positive for the blaVIM-2 gene, 13 strains positive for the blaIMP-9 gene, and 1 strain positive for the blaIMP-1 gene. Real-time reverse transcriptase PCR (RT-PCR) was used to verify whether the isolates harboring MBL genes produced the enzyme and was considered the standard for evaluation of the methodology in this study. Of these 24 MBL-positive stains, 21 were confirmed as MBL-producing strains by real time RT-PCR for MBL expression and the other 3 had no expression of MBLs. The sensitivities, specificities, and positive and negative predictive values for the MBL Etest, the DDST, and the combined disk (CD) assay were evaluated. The best method for screening for MBL production in P. aeruginosa strains from China was the CD assay (IMP-EDTA) using 750 μg of EDTA/disk with a breakpoint of ≥6 mm. In the CD assay (IPM-EDTA) with 290 μg and 750 μg EDTA, the zone diameter increases for VIM-2-producing P. aeruginosa isolates were greater than those for IMP-9-producing P. aeruginosa isolates (P = 0.00).

Distribution of the ACME-arcA gene among meticillin-resistant Staphylococcus haemolyticus and identification of a novel ccr allotype in ACME-arcA-positive isolates.

The aim of this study was to investigate the prevalence and characteristics of ACME (arginine catabolic mobile element)-arcA-positive isolates among meticillin-resistant Staphylococcus haemolyticus (MRSH). ACME-arcA, native arcA and SCCmec elements were detected by PCR. Susceptibilities to 10 antimicrobial agents were compared between ACME-arcA-positive and -negative isolates by chi-square test. PFGE was used to investigate the clonal relatedness of ACME-arcA-positive isolates. The phylogenetic relationships of ACME-arcA and native arcA were analysed using the neighbour-joining methods of mega software. A total of 42 (47.7 %) of 88 isolates distributed in 13 PFGE types were positive for the ACME-arcA gene. There were no significant differences in antimicrobial susceptibility between ACME-arcA-positive and -negative isolates. A novel ccr allotype (ccrAB(SHP)) was identified in ACME-arcA-positive isolates. Among 42 ACME-arcA-positive isolates: 8 isolates harboured SCCmec V, 8 isolates harboured class C1 mec complex and ccrAB(SHP); 22 isolates harbouring class C1 mec complex and 4 isolates harbouring class C2 mec complex were negative for all known ccr allotypes. The ACME-arcA-positive isolates were first found in MRSH with high prevalence and clonal diversity, which suggests a mobility of ACME within MRSH. The results from this study revealed that MRSH is likely to be one of the potential reservoirs of ACME for Staphylococcus aureus.

Thymosin α1- and Ulinastatin-Based Immunomodulatory Strategy for Sepsis Arising from Intra-Abdominal Infection Due to Carbapenem-Resistant Bacteria

OBJECTIVE The aim of this study was to evaluate the potential efficacy of therapy with thymosin alpha(1) and ulinastatin for patients with sepsis due to carbapenem-resistant bacteria. DESIGN Prospective, randomized, parallel controlled clinical study. METHODS A total of 120 patients received a diagnosis of sepsis caused by infection with carbapenem-resistant bacteria and satisfied the study enrollment criteria. Sixty patients received carbapenems combined with thymosin alpha(1) and ulinastatin (the CTU group), and the other 60 patients were treated with carbapenems and placebo (the CP group). For both groups, flow cytometry was used to enumerate lymphocyte subsets, and ELISA was used to determine cytokine concentrations. RESULTS When the 2 groups were compared, the CTU group exhibited a better performance with respect to organ failure scores such as the Acute Physiology and Chronic Health Evaluation II score, the Multiple Organ Failure Score, and the Glasgow Coma Scale. The CTU group also showed significant improvements in CD4(+)CD8(+) count after initiation of treatment. In addition, compared with the CP group, in the CTU group the balance between proinflammatory mediators (such as tumor necrosis factor-alpha, interleukin [IL]-1beta, IL-6, and IL-8) and anti-inflammatory cytokines (including IL-4 and IL-10) was better modulated, and the cumulative survival rate of the CTU group exceeded that of the CP group by 17.8% at day 28, 25.9% at day 60, and 27.4% at day 90. CONCLUSION Immunomodulatory therapy that combines thymosin alpha(1) and ulinastatin appears to improve the survival rate for patients infected with carbapenem-resistant bacteria. The number of patients in this study was relatively small, and although the same number of patients was initially enrolled in each study group, the groups were not the same size at the end of the study. Therefore, a larger clinical trial should be conducted to validate this conclusion. TRIAL REGISTRATION The trial was registered with the Chinese State Food and Drug Administration (Peking Science and Technology Development Plan, 2002[641]), (registration number 2007Y0211).

Triclosan resistance in clinical isolates of Acinetobacter baumannii

The susceptibility to triclosan of 732 clinical Acinetobacter baumannii isolates obtained from 25 hospitals in 16 cities in China from December 2004 to December 2005 was screened by using an agar dilution method. Triclosan MICs ranged between 0.015 and 16 mg l(-1), and the MIC(90) was 0.5 mg l(-1), lower than the actual in-use concentration of triclosan. Twenty triclosan-resistant isolates (MICs >or=1 mg l(-1)) were characterized by antibiotic susceptibility, clonal relatedness, fabI mutation, fabI expression, and efflux pump phenotype and expression to elucidate the resistance mechanism of A. baumannii to triclosan. The resistance rates of triclosan-resistant isolates to imipenem, levofloxacin, amikacin and tetracycline were higher than those of triclosan-sensitive isolates. Triclosan resistance was artificially classified as low level (MICs 1-2 mg l(-1)) or high level (MICs >or=4 mg l(-1)). High-level triclosan resistance could be explained by a Gly95Ser mutation of FabI, whilst wild-type fabI was observed to be overexpressed in low-level resistant isolates. Active efflux did not appear to be a major reason for acquired triclosan resistance, but acquisition of resistance appeared to be dependent on a background of intrinsic triclosan efflux.

In vivo development of carbapenem resistance in clinical isolates of Enterobacter aerogenes producing multiple β-lactamases

Four clinical strains of extended-spectrum beta-lactamase- and AmpC-producing Enterobacter aerogenes were isolated successively from a liver transplantation patient. Isolates C(1) and C(2) were isolated prior to carbapenem therapy, whilst isolates C(3) and C(4) were recovered after 40 days of carbapenem therapy. The homology of these strains was analysed by pulsed-field gel electrophoresis (PFGE). beta-Lactamases were analysed by isoelectric focusing, polymerase chain reaction (PCR) and sequencing. Outer membrane proteins were analysed by PCR, sequencing, sodium dodecyl sulphate-polyacrylamide gel electrophoresis and Western blot. Disruption of OmpE36 in C(1) in vitro was also performed by homologous gene recombination. The isolates demonstrated an indistinguishable PFGE pattern. Molecular characterisation revealed that, in addition to the pre-existing multiple beta-lactamases (DHA-1, TEM-1, SHV-5, CTX-M-3 and CTX-M-14) found in C(1) and C(2), isolates C(3) and C(4) failed to express OmpE36 owing to insertional inactivation by an IS903-like insertion sequence. Other resistance mechanisms, such as production of carbapenem-hydrolysing enzymes or expression of chromosomal efflux, were apparently not involved. Completely replacing OmpE36 by the kanamycin resistance gene (kan) resulted in a significant increase in carbapenem minimum inhibitory concentrations of an ompE36 mutant. Thus, C(3) and C(4) were apparently derived from the previously imipenem-susceptible isolates C(1) and C(2). Following carbapenem exposure, depletion of OmpE36 expression resulted in the collateral effect of carbapenem resistance.

Heteroresistance to Teicoplanin in Enterococcus faecium Harboring the vanA Gene

Hospital-acquired infections caused by vancomycin-resistant enterococci (VRE) are increasing. The resistance of VRE to multiple antibiotics makes them clinically challenging. There are at least six phenotypes of VRE, including VanA, VanB, VanC, VanD, VanE, and VanG ([2][1], [8][2]). These phenotypes