Wei-Hua Zhao

Mechanism of Synergy between Epigallocatechin Gallate and β-Lactams against Methicillin-Resistant Staphylococcus aureus

ABSTRACT Compared to MICs (more than 800 μg/ml) of (−)-epigallocatechin gallate (EGCg) against Escherchia coli, MICs of EGCg against methicillin-susceptible and methicillin-resistantStaphylococcus aureus (MSSA and MRSA) were 100 μg/ml or less. Furthermore, less than 25 μg EGCg per ml obviously reversed the high level resistance of MRSA to all types of tested β-lactams, including benzylpenicillin, oxacillin, methicillin, ampicillin, and cephalexin. EGCg also induced a supersusceptibility to β-lactams in MSSA which does not express mecA, encoding penicillin-binding protein 2′ (PBP2′). The fractional inhibitory concentration (FIC) indices of the tested β-lactams against 25 isolates of MRSA were from 0.126 to 0.625 in combination with 6.25, 12.5 or 25 μg of EGCg per ml. However, no synergism was observed between EGCg and ampicillin against E. coli. EGCg largely reduced the tolerance of MRSA and MSSA to high ionic strength and low osmotic pressure in their external atmosphere, indicating damage of the cell wall. Unlike dextran and lipopolysaccharide, peptidoglycan fromS. aureus blocked both the antibacterial activity of EGCg and the synergism between EGCg and oxacillin, suggesting a direct binding of EGCg with peptidoglycan on the cell wall. EGCg showed a synergistic effect with dl-cycloserine (an inhibitor of cell wall synthesis unrelated to PBP2′) but additive or indifferent effect with inhibitors of protein and nuclear acid synthesis. EGCg did not suppress either PBP2′ mRNA expression or PBP2′ production, as confirmed by reverse transcription-PCR and a semiquantitative PBP2′ latex agglutination assay, indicating an irrelevance between the synergy and PBP2′ production. In summary, both EGCg and β-lactams directly or indirectly attack the same site, peptidoglycan on the cell wall. EGCg synergizes the activity of β-lactams against MRSA owing to interference with the integrity of the cell wall through direct binding to peptidoglycan.

Epigallocatechin Gallate Synergistically Enhances the Activity of Carbapenems against Methicillin-Resistant Staphylococcus aureus

ABSTRACT Combinations of carbapenems and epigallocatechin gallate (EGCg; a main constituent of tea catechins) showed potent synergy against 24 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). MICs of imipenem in the presence of EGCg at 3.125, 6.25, 12.5, and 25 μg/ml, were restored to the susceptible breakpoint (≤4 μg/ml) for 8, 38, 46, and 75% of the MRSA isolates, respectively. Similar results were also observed for combinations of panipenem or meropenem and EGCg. Therefore, the combinations may be worthy of further evaluation in vivo against MRSA infection.

Inhibition of Penicillinase by Epigallocatechin Gallate Resulting in Restoration of Antibacterial Activity of Penicillin against Penicillinase-Producing Staphylococcus aureus

ABSTRACT The combination of epigallocatechin gallate (EGCg, a main constituent of tea catechins) with penicillin showed synergism against 21 clinical isolates of penicillinase-producing Staphylococcus aureus. Besides binding directly to peptidoglycan, the inhibition of penicillinase activity by EGCg is responsible for the synergism. EGCg inhibited the penicillinase activity in a dose-dependent fashion, with a 50% inhibitory concentration of 10 μg/ml.

Epidemiology and genetics of CTX-M extended-spectrum β-lactamases in Gram-negative bacteria

CTX-M enzymes, the plasmid-mediated cefotaximases, constitute a rapidly growing family of extended-spectrum β-lactamases (ESBLs) with significant clinical impact. CTX-Ms are found in at least 26 bacterial species, particularly in Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis. At least 109 members in CTX-M family are identified and can be divided into seven clusters based on their phylogeny. CTX-M-15 and CTX-M-14 are the most dominant variants. Chromosome-encoded intrinsic cefotaximases in Kluyvera spp. are proposed to be the progenitors of CTX-Ms, while ISEcp1, ISCR1 and plasmid are closely associated with their mobilization and dissemination.

Regulation of mast cell development by inflammatory factors.

Mast cells are potent effectors playing a key role in IgE-associated hypersensitivity reactions, allergic disorders, inflammation and protective immune responses. Mast cell development in vivo occurs mainly in non-hematopoietic microenvironments and increased mast cell numbers can be seen in various inflammatory diseases and pathologic conditions. SCF (also known as kit ligand or KitL) and c-kit signaling are essential for both human and murine mast cell development, while IL-3 is required for murine mast cell hyperplasia that occurs in response to various stimuli. Besides SCF and IL-3, the cytokines IL-4, IL-9, IL-10 and IL-13 are also called mast cell growth factors due to their actions synergistically promoting mast cell proliferation and differentiation in the presence of SCF or IL-3. These cytokines alone however are unable to support neither the proliferation nor survival of mast cells. Most research has focused on examining the direct effects of the above cytokines on mast cells or their precursors. However, it is difficult to explain the process of mast cell development only in terms of the above mast cell growth factors. A series of experiments in our laboratory and by others has revealed that inflammatory mediators and cytokines, as triggers or regulators, are also crucial for mast cell development. This review summarizes recent progress in our understanding of how various inflammatory factors regulate mast cell development, with particular focus on the effects of prostaglandin E (PGE), TNF-alpha, IL-6, IFN-gamma and an unknown apoptosis-inducing factor produced by IL-4-stimulated macrophages.

β-Lactamases identified in clinical isolates of Pseudomonas aeruginosa

The increased prevalence of β-lactamases in Pseudomonas aeruginosa has begun to reduce the clinical efficacy of β-lactams against the most common opportunistic pathogen. Of over 800 β-lactamases identified from Gram-negative bacilli, at least 120 β-lactamases have been detected in P. aeruginosa. IMPs and VIMs are predominantly found in P. aeruginosa and like Acinetobacter spp., P. aeruginosa is also a predominant source of OXAs, indicating that P. aeruginosa is a crucial reservoir of β-lactam resistance determinants. This review summarizes the β-lactamases identified in clinical isolates of P. aeruginosa, with a particular focus on AmpC-type β-lactamases, extended-spectrum β-lactamases, and carbapenemases.

IMP-type metallo-β-lactamases in Gram-negative bacilli: distribution, phylogeny, and association with integrons

Twenty-nine IMP-type β-lactamases (IMPs) have been identified in at least 26 species of clinically important Gram-negative bacilli from more than 24 countries/regions. Most of blaIMP genes are harbored by class 1 integrons that are usually embedded in transposons and/or plasmids, footnoting their horizontal transfer and worldwide distribution. blaIMP genes usually co-exist with other resistance genes, such as aacA, catB, and blaOXA, resulting in multi-drug resistance. Compared to other gene cassettes, 76.3% of the blaIMP gene cassettes are located adjacent to Pc promoter of the class 1 integrons, indicating that the blaIMP genes are readily expressed in most of bacterial hosts.

Acinetobacter: A potential reservoir and dispenser for β-lactamases

Innate resistance and remarkable ability to acquire additional resistance determinants underline the clinical importance of Acinetobacter. Over 210 β-lactamases belonging to 16 families have been identified in the genus, mostly in clinical isolates of A. baumannii. In this review, we update the current taxonomy of the genus Acinetobacter and summarize the β-lactamases detected in Acinetobacter spp. with an emphasis on Acinetobacter-derived cephalosporinases (ADCs) and carbapenem-hydrolysing class D β-lactamases (CHDLs). We also discuss the roles of integrons and insertion sequence (IS) elements in the expression and dissemination of such resistance determinants.

Up-regulation of IL-33 expression in various types of murine cells by IL-3 and IL-4.

The crucial roles of the novel cytokine IL-33 in allergic, inflammatory, infectious and autoimmune diseases are becoming characterized. However, the cytokines which regulate IL-33 expression and secretion are still largely unknown. In this study, IL-3 and IL-4 were found to up-regulate IL-33 mRNA expression in mouse peritoneal exudate cells by a two-color DNA microarray and further confirmed by real time PCR and ELISA. IL-3 and IL-4 synergistically promote IL-33 mRNA expression and IL-33 intracrine in the heterogeneous cell populations as peritoneal exudates cells, bone marrow cells and splenic cells. IL-3 and IL-4 also induced IL-33 introcrine in the peritoneal exudate cells from the macrophage-deficient op/op mice, suggesting that macrophage is not the only target of IL-3 and IL-4 in the heterogeneous peritoneal exudate cells. Furthermore, IL-3 and IL-4 were verified to promote the IL-33 intracrine in the homogeneous cell population as fibroblasts and mast cells. These results indicate that up-regulation of IL-33 expression by IL-3 and IL-4 is not a feature particular to a specific type of cells. Up to 100 cytokines were screened, but none of them stimulated the secretion or release of IL-33 in the culture system. In summary, we confirm for the first time that IL-3 and IL-4 are critical for IL-33 intracrine in murine cells of various types, indicating that IL-3 and IL-4 may play an important role in the constitutive expression of IL-33 in vivo.

Acquired metallo-β-lactamases and their genetic association with class 1 integrons and ISCR elements in Gram-negative bacteria.

Metallo-β-lactamases (MBLs) can hydrolyze almost all β-lactam antibiotics and are resistant to clinically available β-lactamase inhibitors. Numerous types of acquired MBLs have been identified, including IMP, VIM, NDM, SPM, GIM, SIM, DIM, KHM, TMB, FIM and AIM. IMPs and VIMs are the most frequent MBLs and disseminate in members of the family Enterobacteriaceae, Pseudomonas spp. and Acinetobacter spp. Acquired MBL genes are often embedded in integrons, and some are associated with insertion sequence (IS) elements. The class 1 integrons and IS common region (ISCR) elements are usually harbored in transposons and/or plasmids, forming so-called mobile vesicles for horizontal transfer of captured genes between bacteria. Here, we review the MBL superfamily identified in Gram-negative bacteria, with an emphasis on the phylogeny of acquired MBLs and their genetic association with class 1 integrons and IS common region elements.