Molecular typing and resistance mechanisms of carbapenem resistant Pseudomonas aeruginosa isolated from a Chinese surgical intensive care unit / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Carbapenems are an important class of drugs for the treatment of Pseudomonas aeruginosa (P. aeruginosa) infections. However, carbapenem resistance has been commonly observed in nonfermenter species of bacteria. The purpose of this study was to investigate the molecular epidemiology and carbapenem resistant mechanisms of P. aeruginosa isolated from a surgical intensive care unit (SICU) in China.</p><p><b>METHODS</b>The molecular typing was analyzed by REP-PCR. Enzyme activity was measured with a 260 nm wavelength spectrophotometer. The levels of outer membrane proteins OprD and OprN were measured by Western blotting. The levels of mexA gene transcriptional expression were measured by quantitative real-time PCR. The metallo-beta-lactamase genes IMP, VIM, SPM, GES, and GIM were amplified by PCR. DNA fragments were sequenced by an automated ABI PRISM 3700.</p><p><b>RESULTS</b>Forty-two strains resistant to carbapenems isolated from a SICU were analyzed. REP-PCR revealed 34 belonging to type A, a predominant strain in this SICU. But we did not find metallo-beta-lactamases IMP, VIM, SPM, GES, or GIM genes by PCR. With a three-dimensional extract test, we found 34 strains producing high levels of AmpC enzymes. We also observed the activity of beta-lactamases enzymes in the imipenem resistant group, which was statistically different from the sensitive group. Western blotting revealed that 23 strains showed loss of OprD, 18 strains had decreased OprD expression, and 14 strains expressed OprN. We discovered 27 strains that overexpressed mexA by quantitative real-time PCR, and the resistance rate to meropenem was statistically different between the overexpressing group and the low-expressing group. Nucleotide sequences and deduced amino acid sequence analysis revealed that eight strains carried mutations in the mexR gene operon down regulating MexAB-OprM. The nucleotide sequences of mexR genes from PA36, PA41 and PA48 were submitted to the Genebank with accession numbers of AY899299, AY899300, and AY899301.</p><p><b>CONCLUSIONS</b>There was a predominant strain in the SICU of our hospital. Imipenem resistance is mainly mediated by OprD deficiency or loss, and high activity AmpC enzymes. Overexpression of MexAB-OprM is one of the mechanisms of meropenem resistance, which are partly upregulated by mutations in the mexR gene. The expression of MexEF-OprN also plays an important role in the carbapenem resistance.</p>

Relationship between genomic types of Escherichia coli and clinical diseases / 华中科技大学学报（医学）（英德文版）

In this study, by analysis of genome structures of E. coli, the relationships between the genomic types of E. coli and the associated diseases were investigated. Samples of sputum, urine and other excretions from patients with different infective diseases were collected. And 62 E. coli strains were isolated from these samples. Intact bacterial genomic DNA was cleaved with I-CeuI, separated by pulsed field gel electrophoresis and then typed on the basis of cleavage map. The results showed that 7 I-CeuI sites were found in all the genome structures of the 62 E. coli, indicating that there were 7 rrn operons in the genomes. The size of genome ranged from 4500 kb to 5000 kb. According to the genome structures, 62 E. coli strains were divided into 30 genome types. It was concluded that genome structures of E. coli isolated from the patients with different infective diseases varied to some extent, suggesting that some genome types of E. coli were closely related to some infective diseases.

Outer Membrane Protein and ?-Lactamases in Imipenem Resistant Pseudomonas aeruginosa / 中华医院感染学杂志

OBJECTIVE To investigate the mechanisms for carbapenem resistance in clinical isolates of Pseudomonas aeruginosa from surgical intensive care unit(SICU).METHODS The minimal inhibitory concentrations(MICs) of various antibiotics were detected with agar dilution method;their ?-lactamases were extracted,types of their enzymes were identified and then their physical and chemical characteristics were studied by three dimentional extract test and isoelectric focusing(IEF) electropheresis;primers specific to IMP and VIM genes were utilized to amplify the metallo-?-lactamase genes.The levels of outer membrane protein OprD2 were measured by Western blot.RESULTS Forty one strains were resistant to imipenem from 49 strains of P.aeruginosa isolated from SICU during 3 years.Among them,34 isolates were found to produce high level of AmpC enzymes.Eight produced extended-spectrum ?-lactamases(ESBLs) at the same time.2 produced ESBLs only.No metallo-?-lactamases were detected.The activity of enzymes in the imipenem resistant group(74.32?53.42) was statistically different from the sensitive one(8.7?16.16,P