Biomedical subjects

Wenming Zhu

Publications and source records attributed to Wenming Zhu.

4 recordsLinked to original sources

PubMed2006

High-level vancomycin-resistant Staphylococcus aureus isolates associated with a polymicrobial biofilm.

Glycopeptides such as vancomycin are the treatment of choice for infections due to methicillin-resistant Staphylococcus aureus. This study describes the identification of high-level vancomycin-resistant S. aureus (VRSA) isolates in a polymicrobial biofilm within an indwelling nephrostomy tube in a patient in New York. S. aureus, Enterococcus faecalis, Enterococcus faecium, Micrococcus species, Morganella morganii, and Pseudomonas aeruginosa were isolated from the biofilm. For VRSA isolates, vancomycin MICs ranged from 32 to >128 microg/ml. VRSA isolates were also resistant to aminoglycosides, fluoroquinolones, macrolides, penicillin, and tetracycline but remained susceptible to chloramphenicol, linezolid, rifampin, and trimethoprim-sulfamethoxazole. The vanA gene was localized to a plasmid of approximately 100 kb in VRSA and E. faecium isolates from the biofilm. Plasmid analysis revealed that the VRSA isolate acquired the 100-kb E. faecium plasmid, which was then maintained without integration into the MRSA plasmid. The tetracycline resistance genes tet(U) and tet(S), not previously detected in S. aureus isolates, were identified in the VRSA isolates. Additional resistance elements in the VRSA isolate included a multiresistance gene cluster, ermB-aadE-sat4-aphA-3, msrA (macrolide efflux), and the bifunctional aminoglycoside resistance gene aac(6')-aph(2")-Ia. Multiple combinations of resistance genes among the various isolates of staphylococci and enterococci, including vanA, tet(S), and tet(U), illustrate the dynamic nature of gene acquisition and loss within and between bacterial species throughout the course of infection. The potential for interspecies transfer of antimicrobial resistance genes, including resistance to vancomycin, may be enhanced by the microenvironment of a biofilm.

Acetamides↗

PubMed2005

Correlation of penicillin Binding protein 2a detection with oxacillin resistance in Staphylococcus aureus and discovery of a novel penicillin binding protein 2a mutation.

We compared a rapid slide latex agglutination test (LAT; Oxoid, Basingstoke, United Kingdom) that detects penicillin binding protein 2a (PBP2a) with MicroScan conventional panels (Dade Behring, West Sacramento, CA) for detection of oxacillin resistance in Staphylococcus aureus. The PBP2a LAT demonstrated 99% agreement with MicroScan oxacillin MIC results for 388 isolates of S. aureus. All 249 oxacillin-resistant isolates gave strong positive reactions in the LAT (100% sensitivity). Three of the 139 oxacillin-susceptible isolates were also strongly positive and one was weakly positive in the LAT (97.1% specificity). The three oxacillin-susceptible isolates with strongly positive reactions were further characterized. The mecA gene was detected in all three by PCR; one isolate was determined to be resistant to oxacillin by reference broth microdilution testing (MIC, 8 microg/ml), one isolate was inducibly resistant to oxacillin (MIC of 16 microg/ml after overnight induction), and one isolate remained susceptible regardless of the method used for testing. Sequence analysis of a 2.1-kb gene fragment of the mecA gene from the susceptible isolate revealed a one-base substitution at nucleotide position 1449 which results in a Met-to-Ile change for amino acid residue 483. This amino acid substitution has not been previously reported and may be associated with a change in the function of PBP2a resulting in oxacillin susceptibility. An additional 487 isolates were tested in parallel with the both the LAT and MicroScan panels using criteria in which only strong (3 to 4+) or repeatedly weak (1 to 2+) LAT reactions were considered positive, and the results showed 99.4% agreement. The PBP2a LAT provided rapid and reliable detection of oxacillin resistance and proved a useful adjunct to the phenotypic method. Both methods provided reliable detection of oxacillin-resistant S. aureus and facilitated the discovery of a novel, functionally impaired form of PBP2a.

Anti-Bacterial Agents↗

PubMed2004

Participation of fad and mbt genes in synthesis of mycobactin in Mycobacterium smegmatis.

Colonies of Mycobacterium smegmatis LR222 on iron-limiting (0.1 micro M Fe) minimal medium agar fluoresce under UV light due to the accumulation in the cells of the deferri form of the siderophore mycobactin. Two mutants with little or no fluorescence, designated LUN8 and LUN9, were isolated by screening colonies of transposon (Tn611)-mutagenized M. smegmatis. Ferrimycobactin prepared from iron-restricted cells of the wild type had an R(f) of 0.62 on high-performance thin-layer chromatography (HPTLC) and a characteristic visible absorption spectrum with a peak near 450 nm. Similar extracts from LUN8 cells contained a small amount of ferrimycobactin with an R(f) of 0.58 on HPTLC and an absorption spectrum with the peak shifted to a wavelength lower than that of the wild-type ferrimycobactin. Nuclear magnetic resonance spectroscopy studies suggested that the LUN8 mycobactin may have an altered fatty acid side chain. Mutant strain LUN9 produced no detectable mycobactin. Neither mutant strain produced measurable amounts of excreted mycobactin, although both excreted exochelin (the mycobacterial peptido-hydroxamate siderophore), and both mutants were more sensitive than the wild-type strain to growth inhibition by the iron chelator ethylenediamine-di(o-hydroxyphenylacetic acid). The transposon insertion sites were identified, and sequence analyses of the cloned flanking chromosome regions showed that the mutated gene in LUN9 was an orthologue of the Mycobacterium tuberculosis mycobactin biosynthetic gene mbtE. The mutated gene in LUN8 had homology with M. tuberculosis fadD33 (Rv1345), a gene that may encode an acyl-coenzyme A synthase and which previously was not known to participate in synthesis of mycobactin.

Cloning, Molecular↗

PubMed2003

Resuscitation factors from mycobacteria: homologs of Micrococcus luteus proteins.

SETTING: Resuscitation promoting factors (Rpfs) are proteins, originally identified in Micrococcus luteus, that promote recovery of bacteria from a viable but non-replicating phase (e.g., stationary phase or latency) to a replicating phase. Purified M. luteus Rpf can stimulate growth and increase recovery of M. luteus bacteria as well as Mycobacterium tuberculosis bacteria from prolonged stationary cultures. OBJECTIVE: To clone and characterize Rpfs from mycobacteria. DESIGN: We cloned one M. avium subsp. paratuberculosis rpf gene and one M. tuberculosis rpf gene into the pET19b or pET21a vector for expression in Escherichia coli. The His-tag recombinant proteins were purified and characterized. RESULTS: When the purified recombinant proteins were added to Sauton medium (a relatively minimal medium) at 100-500 pM, lag phase for mycobacteria from non-replicating cultures was shortened and there was a 10- to 100-fold increase in colony-forming units compared with control samples. In most probable number assays, the mycobacterial Rpfs increased recovery of mycobacteria from late stationary culture by about 10-fold. The Rpfs also promoted recovery of extensively washed Mycobacterium smegmatis bacteria inoculated into Sauton medium. Rpfs had only minor effects on growth of M. tuberculosis in BACTEC 12B broth, a rich medium. CONCLUSION: The mycobacterial Rpfs demonstrate resuscitation activities similar to those of the M. luteus Rpf.

Amino Acid Sequence↗