Ambrose L Cheung

Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States

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Publications (141)647.25 Total impact

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    ABSTRACT: Staphylococcus aureus uses the two-component regulatory system, GraRS, to sense and respond to host defense peptides ( HDPs ). However, the mechanistic impact of GraS, or its extracellular sensing loop ( EL ) on HDP resistance is essentially unexplored. Null mutants in the GraS holoprotein (Δ graS ) or its EL (ΔEL) were compared for mechanisms of resistance to HDPs of relevant immune sources: neutrophil α-defensin, hNP-1, cutaneous β-defensin, hBD-2 or the platelet kinocidin congener, RP-1. Actions studied by flow cytometry included: energetics ( ENR ); membrane permeabilization ( PRM ); annexin-V binding ( ANX ); or cell death protease activation ( CDP ). Assay conditions simulated bloodstream (7.5) or phagolysosomal (5.5) pH contexts. S. aureus strains were more susceptible to HDPs at pH 7.5 versus pH 5.5, and each HDP exerted a distinct effect signature. The impacts of Δ graS and ΔEL on HDP resistance were peptide- and pH-dependent. Both mutants exhibited defects in ANX response to hNP-1 or hBD-2 at pH 7.5, but only hNP-1 at pH 5.5. Both mutants exhibited hyper- PRM , - ANX , and - CDP responses to RP-1 at both pHs, and hypo- ENR at pH 5.5. The actions correlated with Δ graS or ΔEL hypersusceptibility to hNP-1 or RP-1 (but not hBD-2) at pH 7.5, and all study HDPs at pH 5.5. An exogenous EL-mimic protected mutant strains from hNP-1 and hBD-2, but not RP-1, indicating GraS and its EL play non-redundant roles in S. aureus survival responses to specific HDPs. These findings suggest GraS mediates specific resistance countermeasures to HDPs in immune contexts that are highly relevant to S. aureus pathogenesis in humans.
    Infection and Immunity 11/2015; DOI:10.1128/IAI.01030-15 · 3.73 Impact Factor
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    ABSTRACT: Staphylococcus aureus is a major human pathogen that causes a range of infections from acute invasive to chronic and difficult-to-treat. Infection strategies associated with persisting S. aureus infections are bacterial host cell invasion and the bacterial ability to dynamically change phenotypes from the aggressive wild-type to small colony variants (SCVs), which are adapted for intracellular long-term persistence. The underlying mechanisms of the bacterial switching and adaptation mechanisms appear to be very dynamic, but are largely unknown. Here, we analyzed the role and the crosstalk of the global S. aureus regulators agr, sarA and SigB by generating single, double and triple mutants, and testing them with proteome analysis and in different in vitro and in vivo infection models. We were able to demonstrate that SigB is the crucial factor for adaptation in chronic infections. During acute infection, the bacteria require the simultaneous action of the agr and sarA loci to defend against invading immune cells by causing inflammation and cytotoxicity and to escape from phagosomes in their host cells that enable them to settle an infection at high bacterial density. To persist intracellularly the bacteria subsequently need to silence agr and sarA. Indeed agr and sarA deletion mutants expressed a much lower number of virulence factors and could persist at high numbers intracellularly. SigB plays a crucial function to promote bacterial intracellular persistence. In fact, ΔsigB-mutants did not generate SCVs and were completely cleared by the host cells within a few days. In this study we identified SigB as an essential factor that enables the bacteria to switch from the highly aggressive phenotype that settles an acute infection to a silent SCV-phenotype that allows for long-term intracellular persistence. Consequently, the SigB-operon represents a possible target to develop preventive and therapeutic strategies against chronic and therapy-refractory infections.
    PLoS Pathogens 04/2015; 11(4):e1004870. DOI:10.1371/journal.ppat.1004870 · 7.56 Impact Factor
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    Mary Janice Jones · Niles P Donegan · Irina V Mikheyeva · Ambrose L Cheung ·
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    ABSTRACT: Methicillin resistant Staphylococcus aureus (MRSA) is an opportunistic pathogen found in hospital and community environments that can cause serious infections. A major barrier to genetic manipulations of clinical isolates has been the considerable difficulty in transforming these strains with foreign plasmids, such as those from E. coli, in part due to the type I and IV Restriction Modification (R-M) barriers. Here we combine a Plasmid Artificial Modification (PAM) system with DC10B E. coli cells (dcm mutants) to bypass the barriers of both type I and IV R-M of S. aureus, thus allowing E. coli plasmid DNA to be transformed directly into clinical MRSA strains MW2, N315 and LAC, representing three of the most common clonal complexes. Successful transformation of clinical S. aureus isolates with E. coli-derived plasmids should greatly increase the ability to genetically modify relevant S. aureus strains and advance our understanding of S. aureus pathogenesis.
    PLoS ONE 03/2015; 10(3):e0119487. DOI:10.1371/journal.pone.0119487 · 3.23 Impact Factor
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    ABSTRACT: In a loss of viability screen using small molecules against methicillin resistant S. aureus MRSA USA300 with sub-MIC β-lactam, we found a small molecule, designated as DNAC-1, that potentiated the effect of oxacillin (MIC of oxacillin decreased from 64 to 0.25 μg/ml). Fluorescence microscopy indicated disruption of membrane structures within 15 minutes of exposure to DNAC-1 at 2x MIC. This permeabilization was accompanied by a rapid loss of membrane potential, as monitored by the DiOC2 dye. Macromolecular analysis showed inhibition of staphylococcal cell wall synthesis by DNAC-1. Transmission electron microscopy of treated MRSA USA300 cells revealed a slightly thicker cell wall together with mesosome -like projections into the cytosol. Exposure of USA300 cells to DNAC-1 was associated with mislocalization of FtsZ accompanied by localization of PBP2 and PBP4 away from the septum as well as mild activation of the vraRS-mediated cell-wall stress response. However, DNAC-1 does not have any generalized toxicity towards mammalian host cells. DNAC-1, in combination with ceftriaxone, is also effective against an assortment of Gram negative pathogens. Using a murine subcutaneous co-injection model with 10(8) CFU of USA 300 as a challenge inoculum, DNAC-1 alone or DNAC-1 with sub-MIC oxacillin resulted in a 6-log reduction in bacterial load and decreased abscess formation as compared to the untreated control. We propose that DNAC-1, by exerting a bimodal effect on the cell membrane and the cell wall, is a viable candidate for development of combination therapy against many common bacterial pathogens. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Antimicrobial Agents and Chemotherapy 01/2015; 59(4). DOI:10.1128/AAC.04164-14 · 4.48 Impact Factor
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    ABSTRACT: The Staphylococcus aureus two-component regulatory system, GraRS, is involved in resistance to killing by distinct host defense cationic antimicrobial peptides (HD-CAPs). It is believed to regulate downstream target genes such as mprF and dltABCD to modify the S. aureus surface charge. However, the detailed mechanism(s) by which the histidine kinase, GraS, senses specific HD-CAPs is not well defined. Here, we studied a well-characterized clinical methicillin-resistant S. aureus (MRSA) strain (MW2), its isogenic graS deletion mutant (ΔgraS strain), a nonameric extracellular loop mutant (ΔEL strain), and four residue-specific ΔEL mutants (D37A, P39A, P39S, and D35G D37G D41G strains). The ΔgraS and ΔEL strains were unable to induce mprF and dltA expression and, in turn, demonstrated significantly increased susceptibilities to daptomycin, polymyxin B, and two prototypical HD-CAPs (hNP-1 and RP-1). Further, P39A, P39S, and D35G-D37G-D41G ΔEL mutations correlated with moderate increases in HD-CAP susceptibility. Reductions of mprF and dltA induction by PMB were also found in the ΔEL mutants, suggesting these residues are pivotal to appropriate activation of the GraS sensor kinase. Importantly, a synthetic exogenous soluble EL mimic of GraS protected the parental MW2 strain against hNP-1- and RP-1-mediated killing, suggesting a direct interaction of the EL with HD-CAPs in GraS activation. In vivo, the ΔgraS and ΔEL strains displayed dramatic reductions in achieved target tissue MRSA counts in an endocarditis model. Taken together, our results provide new insights into potential roles of GraS in S. aureus sensing of HD-CAPs to induce adaptive survival responses to these molecules.
    Infection and Immunity 10/2014; 82(12). DOI:10.1128/IAI.02480-14 · 3.73 Impact Factor
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    Niles P Donegan · Jonathan S Marvin · Ambrose L Cheung ·
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    ABSTRACT: Staphylococcus aureus responds to changing extracellular environments in part by adjusting its proteome through alterations of transcriptional priorities and selective degradation of the preexisting pool of proteins. In Bacillus subtilis, the proteolytic adaptor protein MecA has been shown to play a role in assisting with the proteolytic degradation of proteins involved in competence and the oxidative stress response. However, the targets of TrfA, the MecA homolog in S. aureus, have not been well characterized. In this work, we investigated how TrfA assists chaperones and proteases to regulate the proteolysis of several classes of proteins in S. aureus. By fusing the last 3 amino acids of the SsrA degradation tag to Venus, a rapidly folding yellow fluorescent protein, we obtained both fluorescence-based and Western blot assay-based evidence that TrfA and ClpCP are the adaptor and protease, respectively, responsible for the degradation of the SsrA-tagged protein in S. aureus. Notably, the impact of TrfA on degradation was most prominent during late log phase and early stationary phase, due in part to a combination of transcriptional regulation and proteolytic degradation of TrfA by ClpCP. We also characterized the temporal transcriptional regulation governing TrfA activity, wherein Spx, a redox-sensitive transcriptional regulator degraded by ClpXP, activates trfA transcription while repressing its own promoter. Finally, the scope of TrfA-mediated proteolysis was expanded by identifying TrfA as the adaptor that works with ClpCP to degrade antitoxins in S. aureus. Together, these results indicate that the adaptor TrfA adds temporal nuance to protein degradation by ClpCP in S. aureus.
    Journal of Bacteriology 09/2014; 196(23). DOI:10.1128/JB.02222-14 · 2.81 Impact Factor
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    Samin Kim · Dindo Reyes · Marie Beaume · Patrice Francois · Ambrose Cheung ·
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    ABSTRACT: High-throughput RNA sequencing technology has found the 5′ untranslated region of sarA to contain two putative small RNAs (sRNAs), designated teg49 and teg48. Northern blot analysis disclosed that teg49 and teg48 were detectable within the P3-P1 and P1 sarA promoter regions, respectively. Focusing on teg49, we found that this sRNA, consisting of 196 nucleotides, is transcribed in the same direction as the sarA P3 transcript. The expression of both P3 and teg49 transcripts is dependent on sigB and cshA, which encodes a DEAD box RNA helicase. Within the sRNA teg49, there are two putative hairpin-loop structures, HP1 and HP2. Transversion mutation of the HP1 loop produced a smaller amount of sarA P3 and P2 transcripts and SarA protein than the corresponding HP1 stem and the HP2 stem and loop mutations, leading to lower RNAII transcription and derepression of aur transcription. The HP1 loop mutant also exhibited less biofilm formation than the parental and complemented strains. Complementation with shuttle plasmid pEPSA5 carrying teg49 was able to reestablish sarA P3 and P2 transcription and augment RNAII expression in the HP1 loop mutant. We thus conclude that teg49, embedded within the extended promoter regions of sarA, is modulated by sigB and cshA and plays an important trans-acting role in modulating the transcription and ensuing expression of sarA.
    Infection and Immunity 08/2014; 82(10). DOI:10.1128/IAI.02002-14 · 3.73 Impact Factor
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    ABSTRACT: Bacterial signaling systems are prime drug targets for combating the global health threat of antibiotic resistant bacterial infections including those caused by Staphylococcus aureus. S. aureus is the primary cause of acute bacterial skin and soft tissue infections (SSTIs) and the quorum sensing operon agr is causally associated with these. Whether efficacious chemical inhibitors of agr signaling can be developed that promote host defense against SSTIs while sparing the normal microbiota of the skin is unknown. In a high throughput screen, we identified a small molecule inhibitor (SMI), savirin (S. aureus virulence inhibitor) that disrupted agr-mediated quorum sensing in this pathogen but not in the important skin commensal Staphylococcus epidermidis. Mechanistic studies employing electrophoretic mobility shift assays and a novel AgrA activation reporter strain revealed the transcriptional regulator AgrA as the target of inhibition within the pathogen, preventing virulence gene upregulation. Consistent with its minimal impact on exponential phase growth, including skin microbiota members, savirin did not provoke stress responses or membrane dysfunction induced by conventional antibiotics as determined by transcriptional profiling and membrane potential and integrity studies. Importantly, savirin was efficacious in two murine skin infection models, abating tissue injury and selectively promoting clearance of agr+ but not Δagr bacteria when administered at the time of infection or delayed until maximal abscess development. The mechanism of enhanced host defense involved in part enhanced intracellular killing of agr+ but not Δagr in macrophages and by low pH. Notably, resistance or tolerance to savirin inhibition of agr was not observed after multiple passages either in vivo or in vitro where under the same conditions resistance to growth inhibition was induced after passage with conventional antibiotics. Therefore, chemical inhibitors can selectively target AgrA in S. aureus to promote host defense while sparing agr signaling in S. epidermidis and limiting resistance development.
    PLoS Pathogens 06/2014; 10(6):e1004174. DOI:10.1371/journal.ppat.1004174 · 7.56 Impact Factor
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    ABSTRACT: The Staphylococcus aureus genome contains three toxin–antitoxin modules, including one mazEF module, SamazEF. Using an on-column separation protocol we are able to obtain large amounts of wild-type SaMazF toxin. The protein is well-folded and highly resistant against thermal unfolding but aggregates at elevated temperatures. Crystallographic and nuclear magnetic resonance (NMR) solution studies show a well-defined dimer. Differences in structure and dynamics between the X-ray and NMR structural ensembles are found in three loop regions, two of which undergo motions that are of functional relevance. The same segments also show functionally relevant dynamics in the distantly related CcdB family despite divergence of function. NMR chemical shift mapping and analysis of residue conservation in the MazF family suggests a conserved mode for the inhibition of MazF by MazE.
    Nucleic Acids Research 04/2014; 42(10). DOI:10.1093/nar/gku266 · 9.11 Impact Factor
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    ABSTRACT: Background. Staphylococcus aureus is the most common cause of endovascular infections. The staphylococcal accessory regulator A locus (sarA) is a major virulence determinant that may potentially impact methicillin-resistant S. aureus (MRSA) persistence in such infections via its influence on biofilm formation. Methods. Two healthcare-associated MRSA isolates from patients with persistent bacteremia and 2 prototypical community-acquired MRSA strains, as well as their respective isogenic sarA mutants, were studied for in vitro biofilm formation, fibronectin-binding capacity, autolysis, and protease and nuclease activities. These assays were done in the presence or absence of sub–minimum inhibitory concentrations (MICs) of vancomycin. In addition, these strain pairs were compared for intrinsic virulence and responses to vancomycin therapy in experimental infective endocarditis, a prototypical biofilm model. Results. All sarA mutants displayed significantly reduced biofilm formation and binding to fibronectin but increased protease production in vitro, compared with their respective parental strains. Interestingly, exposure to sub-MICs of vancomycin significantly promoted biofilm formation and fibronectin-binding in parental strains but not in sarA mutants. In addition, all sarA mutants became exquisitely susceptible to vancomycin therapy, compared with their respective parental strains, in the infective endocarditis model. Conclusions. These observations suggest that sarA activation is important in persistent MRSA endovascular infection, potentially in the setting of biofilm formation.
    The Journal of Infectious Diseases 01/2014; 209(8). DOI:10.1093/infdis/jiu007 · 6.00 Impact Factor
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    ABSTRACT: In Staphylococcus aureus, the low-molecular-weight thiol called bacillithiol (BSH), together with cognate S-transferases, is believed to be the counterpart to the glutathione system of other organisms. To explore the physiological role of BSH in S. aureus, we constructed mutants with the deletion of bshA (sa1291), which encodes the glycosyltransferase that catalyzes the first step of BSH biosynthesis, and fosB (sa2124), which encodes a BSH-S-transferase that confers fosfomycin resistance, in several S. aureus strains, including clinical isolates. Mutation of fosB or bshA caused a 16- to 60-fold reduction in fosfomycin resistance in these S. aureus strains. High-pressure liquid chromatography analysis, which quantified thiol extracts, revealed some variability in the amounts of BSH present across S. aureus strains. Deletion of fosB led to a decrease in BSH levels. The fosB and bshA mutants of strain COL and a USA300 isolate, upon further characterization, were found to be sensitive to H2O2 and exhibited decreased NADPH levels compared with those in the isogenic parents. Microarray analyses of COL and the isogenic bshA mutant revealed increased expression of genes involved in staphyloxanthin synthesis in the bshA mutant relative to that in COL under thiol stress conditions. However, the bshA mutant of COL demonstrated decreased survival compared to that of the parent in human whole-blood survival assays; likewise, the naturally BSH-deficient strain SH1000 survived less well than its BSH-producing isogenic counterpart. Thus, the survival of S. aureus under oxidative stress is facilitated by BSH, possibly via a FosB-mediated mechanism, independently of its capability to produce staphyloxanthin.
    Infection and immunity 10/2013; 82(1). DOI:10.1128/IAI.01074-13 · 3.73 Impact Factor
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    ABSTRACT: Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) frequently causes skin and soft-tissue infections, including impetigo, cellulitis, folliculitis, and infected wounds and ulcers. Uncomplicated CA-MRSA skin infections are typically managed in an outpatient setting with oral and topical antibiotics and/or incision and drainage whereas complicated skin infections often require hospitalization, intravenous antibiotics, and sometimes surgery. The aim of this study was to develop a mouse model of CA-MRSA wound infection to compare the efficacy of commonly used systemic and topical antibiotics. A bioluminescent USA300 CA-MRSA strain was inoculated into full-thickness scalpel wounds on the backs of mice and digital photography/image analysis and in vivo bioluminescence imaging were used to measure wound healing and the bacterial burden. Subcutaneous vancomycin, daptomycin and linezolid similarly reduced the lesion sizes and bacterial burden. Oral linezolid, clindamycin and doxycycline all decreased the lesion sizes and bacterial burden. Oral trimethoprim/sulfamethoxazole decreased the bacterial burden but did not decrease the lesion size. Topical mupirocin and retapamulin ointments both reduced the bacterial burden. However, the petrolatum vehicle ointment for retapamulin, but not the polyethylene glycol vehicle ointment for mupirocin, promoted wound healing and initially increased the bacterial burden. Finally, in type 2 diabetic mice, subcutaneous linezolid and daptomycin had the most rapid therapeutic effect compared with vancomycin. Taken together, this mouse model of CA-MRSA wound infection, which utilizes in vivo bioluminescence imaging to monitor the bacterial burden, represents an alternative method to evaluate the preclinical in vivo efficacy of systemic and topical antimicrobial agents.
    Antimicrobial Agents and Chemotherapy 12/2012; 57(2). DOI:10.1128/AAC.01003-12 · 4.48 Impact Factor
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    ABSTRACT: Author Summary Invasive infections caused by the human pathogen Staphylococcus aureus result in more deaths annually than infections caused by any other single infectious agent in the United States. Although neutrophil recruitment and abscess formation is crucial for effective host defense against this pathogen, how neutrophils sense and mount an inflammatory response are not completely clear. Using gene expression analysis and in vivo bioluminescence and fluorescence imaging, we found that neutrophil recruitment during a S. aureus cutaneous infection is functionally and temporally linked to IL-1β/IL-1R activation. Surprisingly, neutrophils themselves were determined to be the most abundant cell type that produced IL-1β during infection. Further, neutrophil-derived IL-1β, in the absence of other cellular sources of IL-1β, was sufficient for neutrophil recruitment, abscess formation, and bacterial clearance. Finally, mouse neutrophils produced IL-1β in direct response to live S. aureus in vitro. These findings expand our understanding of the acute neutrophil response to infection in which early recruited neutrophils serve as a source of IL-1β that is essential for amplifying and sustaining the neutrophilic response to promote abscess formation and bacterial clearance. Therapies aimed at promoting IL-1β production by neutrophils may be an effective immunotherapeutic strategy to control S. aureus infections.
    PLoS Pathogens 11/2012; 8(11):e1003047. DOI:10.1371/journal.ppat.1003047 · 7.56 Impact Factor
  • Ambrose Cheung · Bertrand Duclos ·

    The Journal of Infectious Diseases 04/2012; 205(11):1625-7. DOI:10.1093/infdis/jis255 · 6.00 Impact Factor
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    ABSTRACT: Whole-genome sequence comparison of Staphylococcus aureus strain RN4220ΔmutS, a variant of strain RN4220 carrying an insertion in the mutS gene, and its parent strain S. aureus NCTC 8325 identified variations in the nucleic acid sequence between both strains. Some of these changes concerned proteins which are part of the ribosome (RpmF, RpsB), process ribosomal RNA (RimM), are involved in cell wall biosynthesis (EzrA, MurA), or possess chaperone functions (GroEL) and therefore might compromise the fitness of the affected strain. Resequencing of these genes in S. aureus NCTC 8325 revealed that the sequence variations represent errors in the original S. aureus NCTC 8325 genome sequence and do not constitute mutations in S. aureus RN4220 or RN4220ΔmutS. In correlation with these results, growth experiments showed that the fitness of S. aureus RN4220 is comparable to that of S. aureus NCTC 8325.
    International journal of medical microbiology: IJMM 03/2012; 302(2):84-7. DOI:10.1016/j.ijmm.2012.01.002 · 3.61 Impact Factor
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    ABSTRACT: Post-arthroplasty infections are a devastating problem in orthopaedic surgery. While acute infections can be treated with a single stage washout and liner exchange, chronic infections lead to multiple reoperations, prolonged antibiotic courses, extended disability, and worse clinical outcomes. Unlike previous mouse models that studied an acute infection, this work aimed to develop a model of a chronic post-arthroplasty infection. To achieve this, a stainless steel implant in the knee joints of mice was inoculated with a bioluminescent Staphylococcus aureus strain (1 × 10(2) -1 × 10(4) colony forming units, CFUs) and in vivo imaging was used to monitor the bacterial burden for 42 days. Four different S. aureus strains were compared in which the bioluminescent construct was integrated in an antibiotic selection plasmid (ALC2906), the bacterial chromosome (Xen29 and Xen40), or a stable plasmid (Xen36). ALC2906 had increased bioluminescent signals through day 10, after which the signals became undetectable. In contrast, Xen29, Xen40, and Xen36 had increased bioluminescent signals through 42 days with the highest signals observed with Xen36. ALC2906, Xen29, and Xen40 induced significantly more inflammation than Xen36 as measured by in vivo enhanced green fluorescence protein (EGFP)-neutrophil flourescence of LysEGFP mice. All four strains induced comparable biofilm formation as determined by variable-pressure scanning electron microscopy. Using a titanium implant, Xen36 had higher in vivo bioluminescence signals than Xen40 but had similar biofilm formation and adherent bacteria. In conclusion, Xen29, Xen40, and especially Xen36, which had stable bioluminescent constructs, are feasible for long-term in vivo monitoring of bacterial burden and biofilm formation to study chronic post-arthroplasty infections and potential antimicrobial interventions.
    Journal of Orthopaedic Research 03/2012; 30(3):335-40. DOI:10.1002/jor.21519 · 2.99 Impact Factor
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    ABSTRACT: The two-component regulatory system, GraRS, appears to be involved in staphylococcal responses to cationic antimicrobial peptides (CAPs). However, the mechanism(s) by which GraRS is induced, regulated, and modulated remain undefined. In this study, we used two well-characterized MRSA strains (Mu50 and COL) and their respective mutants of graR and vraG (encoding the ABC transporter-dependent efflux pump immediately downstream of graRS), and show that (i) the expression of two key determinants of net positive surface charge (mprF and dlt) is dependent on the cotranscription of both graR and vraG, (ii) reduced expression of mprF and dlt in graR mutants was phenotypically associated with reduced surface-positive charge, (iii) this net reduction in surface-positive charge in graR and vraG mutants, in turn, correlated with enhanced killing by a range of CAPs of diverse structure and origin, including those from mammalian platelets (tPMPs) and neutrophils (hNP-1) and from bacteria (polymyxin B), and (iv) the synthesis and translocation of membrane lysyl-phosphatidylglycerol (an mprF-dependent function) was substantially lower in graR and vraG mutants than in parental strains. Importantly, the inducibility of mprF and dlt transcription via the graRS-vraFG pathway was selective, with induction by sublethal exposure to the CAPs, RP-1 (platelets), and polymyxin B, but not by other cationic molecules (hNP-1, vancomycin, gentamicin, or calcium-daptomycin). Although graR regulates expression of vraG, the expression of graR was codependent on an intact downstream vraG locus. Collectively, these data support an important role of the graRS and vraFG loci in the sensing of and response to specific CAPs involved in innate host defenses.
    Infection and immunity 01/2012; 80(1):74-81. DOI:10.1128/IAI.05669-11 · 3.73 Impact Factor
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    Guido Memmi · Dhanalakshmi R Nair · Ambrose Cheung ·
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    ABSTRACT: Autolysis plays an essential role in bacterial cell division and lysis with β-lactam antibiotics. Accordingly, the expression of autolysins is tightly regulated by several endogenous regulators, including ArlRS, a two component regulatory system that has been shown to negatively regulate autolysis in methicillin-sensitive Staphylococcus aureus (MSSA) strains. In this study, we found that inactivation of arlRS does not play a role in autolysis of methicillin-resistant S. aureus (MRSA) strains, such as community-acquired (CA)-MRSA strains USA300 and MW2 or the hospital-acquired (HA)-MRSA strain COL. This contrasts with MSSA strains, including Newman, SH1000, RN6390, and 8325-4, where autolysis is affected by ArlRS. We further demonstrated that the striking difference in the roles of arlRS between MSSA and MRSA strains is not due to the methicillin resistance determinant mecA. Among known autolysins and their regulators, we found that arlRS represses lytN, while no effect was seen on atl, lytM, and lytH expression in both CA- and HA-MRSA strains. Transcriptional-fusion assays showed that the agr transcripts, RNAII and RNAIII, were significantly more downregulated in the arlRS mutant of MW2 than the MSSA strain Newman. Importantly, provision of agr RNAIII in trans to the MW2 arlRS mutant via a multicopy plasmid induced autolysis in this MRSA strain. Also, the autolytic phenotype in the arlRS mutant of MSSA strain Newman could be rescued by a mutation in either atl or lytM. Together, these data showed that ArlRS impacts autolysis differently in MSSA and MRSA strains.
    Journal of bacteriology 12/2011; 194(4):759-67. DOI:10.1128/JB.06261-11 · 2.81 Impact Factor
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    ABSTRACT: MazF proteins are ribonucleases that cleave mRNA with high sequence-specificity as part of bacterial stress response and that are neutralized by the action of the corresponding antitoxin MazE. Prolonged activation of the toxin MazF leads to cell death. Several mazEF modules from gram-negative bacteria have been characterized in terms of catalytic activity, auto-regulation mechanism and structure, but less is known about their distant relatives found in gram-positive organisms. Currently, no solution NMR structure is available for any wild-type MazF toxin. Here we report the (1)H, (15)N and (13)C backbone and side-chain chemical shift assignments of this toxin from the pathogen bacterium Staphylococcus aureus. The BMRB accession number is 17288.
    Biomolecular NMR Assignments 10/2011; 5(2):157-60. DOI:10.1007/s12104-010-9290-1 · 0.76 Impact Factor
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    ABSTRACT: The agr locus of Staphylococcus aureus is composed of two divergent transcripts (RNAII and RNAIII) driven by the P2 and P3 promoters. The P2-P3 intergenic region comprises the SarA/SarR binding sites and the four AgrA boxes to which AgrA binds. We reported here the role of AgrA, SarA, and SarR on agr P2 and P3 transcription. Using real-time reverse transcription (RT)-PCR and promoter fusion studies with selected single, double, triple, and complemented mutants, we showed that AgrA is indispensable to agr P2 and P3 transcription, whereas SarA activates and SarR represses P2 transcription. In vitro runoff transcription assays revealed that AgrA alone promoted transcription from the agr P2 promoter, with SarA enhancing it and SarR inhibiting agr P2 transcription in the presence of AgrA or with SarA and AgrA. Electrophoretic mobility shift assay (EMSA) analysis disclosed that SarR binds more avidly to the agr promoter than SarA and displaces SarA from the agr promoter. Additionally, SarA and AgrA bend the agr P2 promoter, whereas SarR does not. Collectively, these data indicated that AgrA activates agr P2 and P3 promoters while SarA activates the P2 promoter, presumably via bending of promoter DNA to bring together AgrA dimers to facilitate engagement of RNA polymerase (RNAP) to initiate transcription.
    Journal of bacteriology 09/2011; 193(21):6020-31. DOI:10.1128/JB.05436-11 · 2.81 Impact Factor

Publication Stats

8k Citations
647.25 Total Impact Points


  • 2001-2015
    • Geisel School of Medicine at Dartmouth
      • Department of Microbiology and Immunology
      Hanover, New Hampshire, United States
    • Saratov State Medical University
      Saratow, Saratov, Russia
  • 2011
    • University of Geneva
      • Division of Infectious Diseases
      Genève, Geneva, Switzerland
  • 2010
    • Cornell University
      Ithaca, New York, United States
  • 2007-2010
    • Dartmouth–Hitchcock Medical Center
      Lebanon, New Hampshire, United States
    • University of Tuebingen
      • Institute of Medical Microbiology and Hygiene
      Tübingen, Baden-Wuerttemberg, Germany
    • University of Arkansas for Medical Sciences
      • Department of Microbiology and Immunology
      Little Rock, Arkansas, United States
  • 2003-2010
    • University of California, Los Angeles
      • • Division of Dermatology
      • • Division of Infectious Diseases
      Los Angeles, CA, United States
    • Utrecht University
      • Division of Microbiology
      Utrecht, Utrecht, Netherlands
  • 2006-2008
    • University of South Dakota
      • Division of Basic Biomedical Sciences
      Vermillion, South Dakota, United States
  • 2004-2006
    • Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center
      • Department of Medicine
      Torrance, California, United States
  • 2005
    • University CEU Cardenal Herrera
      Valenza, Valencia, Spain
  • 1988-2000
    • The Rockefeller University
      • Laboratory of Bacterial Pathogenesis and Immunology
      New York City, New York, United States
  • 1988-1995
    • Harbor-UCLA Medical Center
      • Department of Pediatrics
      Torrance, California, United States