Medicine and Health Sciences Commons^™

Metabolism Shapes Immune Responses To Staphylococcus Aureus., Prabhakar Arumugam, Tammy Kielian

Journal Articles: Pathology and Microbiology

BACKGROUND: Staphylococcus aureus (S. aureus) is a common cause of hospital- and community-acquired infections that can result in various clinical manifestations ranging from mild to severe disease. The bacterium utilizes different combinations of virulence factors and biofilm formation to establish a successful infection, and the emergence of methicillin- and vancomycin-resistant strains introduces additional challenges for infection management and treatment.

SUMMARY: Metabolic programming of immune cells regulates the balance of energy requirements for activation and dictates pro- versus anti-inflammatory function. Recent investigations into metabolic adaptations of leukocytes and S. aureus during infection indicate that metabolic crosstalk plays a crucial role in …

Pre-Exposure To Mrna-Lnp Inhibits Adaptive Immune Responses And Alters Innate Immune Fitness In An Inheritable Fashion, Zhen Qin, Aurélie Bouteau, Christopher Herbst, Botond Z. Igyártó

Department of Microbiology and Immunology Faculty Papers

Hundreds of millions of SARS-CoV-2 mRNA-LNP vaccine doses have already been administered to humans. However, we lack a comprehensive understanding of the immune effects of this platform. The mRNA-LNP-based SARS-CoV-2 vaccine is highly inflammatory, and its synthetic ionizable lipid component responsible for the induction of inflammation has a long in vivo half-life. Since chronic inflammation can lead to immune exhaustion and non-responsiveness, we sought to determine the effects of pre-exposure to the mRNA-LNP on adaptive immune responses and innate immune fitness. We found that pre-exposure to mRNA-LNPs or LNP alone led to long-term inhibition of the adaptive immune response, which …

Immunomodulation Of Myeloid-Derived Suppressor Cells By Particulate B-Glucan In Cancer., Sabrin Husein Albeituni

Electronic Theses and Dissertations

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells that promote tumor progression. In this study, we investigated the effect of dectin-1 stimulation by yeast-derived particulate β-glucan in MDSC function and differentiation in cancer. In vivo treatment of mice bearing lewis lung carcinoma and mammary cell carcinoma with particulate β-glucan decreased tumor weight and splenomegaly, and reduced the accumulation of polymorphonuclear-MDSC (PMN-MDSC) but not monocytic-MDSC (M-MDSC) in the spleen and tumor. In addition, particulate β-glucan differentially modulated the function of different MDSC subsets; it enhanced PMN-MDSC respiratory burst and apoptosis, and induced the differentiation of M-MDSC into …

Nonreplicating, Cyst-Defective Type Ii Toxoplasma Gondii Vaccine Strains Stimulate Protective Immunity Against Acute And Chronic Infection, Barbara Andrea Fox, David J. Bzik

Dartmouth Scholarship

Live attenuated vaccine strains, such as type I nonreplicating uracil auxotroph mutants, are highly effective in eliciting lifelong immunity to virulent acute infection by Toxoplasma gondii. However, it is currently unknown whether vaccine-elicited immunity can provide protection against acute infection and also prevent chronic infection. To address this problem, we developed nonreverting, nonreplicating, live attenuated uracil auxotroph vaccine strains in the type II Δku80 genetic background by targeting the deletion of the orotidine 5′-monophosphate decarboxylase (OMPDC) and uridine phosphorylase (UP) genes. Deletion of OMPDC induced a severe uracil auxotrophy with loss of replication, loss of …

In Vivo Cigarette Smoke Exposure Decreases Ccl20, Slpi, And Bd-1 Secretion By Human Primary Nasal Epithelial Cells, James Jukosky, Benoit J. Gosselin, Leah Foley, Tenzin Dechen, Steven Fiering, Mardi A. Crane-Godreau

Dartmouth Scholarship

Smokers and individuals exposed to second-hand cigarette smoke have a higher risk of developing chronic sinus and bronchial infections. This suggests that cigarette smoke (CS) has adverse effects on immune defenses against pathogens. Epithelial cells are important in airway innate immunity and are the first line of defense against infection. Airway epithelial cells not only form a physical barrier but also respond to the presence of microbes by secreting antimicrobials, cytokines, and chemokines. These molecules can lyse infectious microorganisms and/or provide signals critical to the initiation of adaptive immune responses. We examined the effects of CS on antimicrobial secretions of …

Acidosis Potentiates The Host Proinflammatory Interleukin-1Β Response To Pseudomonas Aeruginosa Infection, I. M. Torres, Y. R. Patankar, Tamer B. Shabaneh, E. Dolben, Deborah Hogan, David Leib, Brent L. Berwin

Dartmouth Scholarship

Infection by Pseudomonas aeruginosa, and bacteria in general, frequently promotes acidification of the local microenvironment, and this is reinforced by pulmonary exertion and exacerbation. However, the consequence of an acidic environment on the host inflammatory response to P. aeruginosa infection is poorly understood. Here we report that the pivotal cellular and host proinflammatory interleukin-1β (IL-1β) response, which enables host clearance of the infection but can produce collateral inflammatory damage, is increased in response to P. aeruginosa infection within an acidic environment. Synergistic mechanisms that promote increased IL-1β release in response to P. aeruginosa infection in an acidic environment are …

Intrinsic Innate Immunity Fails To Control Herpes Simplex Virus And Vesicular Stomatitis Virus Replication In Sensory Neurons And Fibroblasts, Pamela C. Rosato, David A. Leib

Dartmouth Scholarship

Herpes simplex virus 1 (HSV-1) establishes lifelong latent infections in the sensory neurons of the trigeminal ganglia (TG), wherein it retains the capacity to reactivate. The interferon (IFN)-driven antiviral response is critical for the control of HSV-1 acute replication. We therefore sought to further investigate this response in TG neurons cultured from adult mice deficient in a variety of IFN signaling components. Parallel experiments were also performed in fibroblasts isolated concurrently. We showed that HSV-1 replication was comparable in wild-type (WT) and IFN signaling-deficient neurons and fibroblasts. Unexpectedly, a similar pattern was observed for the IFN-sensitive vesicular stomatitis virus (VSV). …

Gastrointestinal Cell Mediated Immunity And The Microsporidia, Magali M. Moretto, Imtiaz A. Khan, Louis M. Weiss

Microbiology, Immunology, and Tropical Medicine Faculty Publications

No abstract provided.

Differential Effects Of Interleukin-17 Receptor Signaling On Innate And Adaptive Immunity During Central Nervous System Bacterial Infection., Debbie Vidlak, Tammy Kielian

Journal Articles: Pathology and Microbiology

Although IL-17A (commonly referred to as IL-17) has been implicated in the pathogenesis of central nervous system (CNS) autoimmune disease, its role during CNS bacterial infections remains unclear. To evaluate the broader impact of IL-17 family members in the context of CNS infection, we utilized IL-17 receptor (IL-17R) knockout (KO) mice that lack the ability to respond to IL-17, IL-17F and IL-17E (IL-25). In this article, we demonstrate that IL-17R signaling regulates bacterial clearance as well as natural killer T (NKT) cell and gamma-delta (γδ) T cell infiltrates during Staphylococcus aureus-induced brain abscess formation. Specifically, when compared with wild-type (WT) …

An Inside Job: Hacking Into Janus Kinase/Signal Transducer And Activator Of Transcription Signaling Cascades By The Intracellular Protozoan Toxoplasma Gondii, Eric Y. Denkers, David J. Bzik, Barbara A. Fox, Barbara A. Butcher

Dartmouth Scholarship

The intracellular protozoan Toxoplasma gondii is well known for its skill at invading and living within host cells. New discoveries are now also revealing the astounding ability of the parasite to inject effector proteins into the cytoplasm to seize control of the host cell. This review summarizes recent advances in our understanding of one such secretory protein called ROP16. This molecule is released from rhoptries into the host cell during invasion. The ROP16 molecule acts as a kinase, directly activating both signal transducer and activator of transcription 3 (STAT3) and STAT6 signaling pathways. In macrophages, an important and preferential target …

Crosstalk Between Gastrointestinal Epithelial Cells And Resident Microbiota Promotes Immune Homeostasis, Eric William Rogier

Theses and Dissertations--Microbiology, Immunology, and Molecular Genetics

The gastrointestinal tract houses one of the most dense and diverse communities of bacteria on the planet. The mutualistic relationship between the host and commensal microbe permits the microbe an ideal environment to grow and provides the host with increased caloric intake, maturation of the adaptive immune system, and resistance against invading pathogens. To maintain a system in which both parties benefit, the epithelium has evolved numerous strategies to ensure epithelial cells respond to microbes appropriately and that potentially hazardous commensals remain distanced from the soma proper. Breakdown of these propitiating mechanisms elicits unchecked inflammation and can lead to pathology …

Effects Of Apoptotic Cell Accumulation Caused By Mer Deficiency On Germinal Center B Cells And Helper T Cells, Tahsin N. Khan, Eric B. Wong, Ziaur S.M. Rahman

Department of Microbiology and Immunology Faculty Papers

Mer (MerTK), a member of the Tyro-3/Axl/Mer subfamily receptor tyrosine kinases, expression on phagocytes facilitates their clearance of apoptotic cells (ACs). Mer expression in germinal centers (GCs) occurs predominantly on tingible body macrophages. B and T cells do not express Mer. Mer deficiency (Mer-/-) results in the accumulation of ACs in GCs and augmented antibody-forming cell (AFC), GC and IgG2 Ab responses against T-dependent (TD) Ag. Here, we show that AC accumulation in GCs and elevated AFC, GC and IgG2 Ab responses in Mer-/- mice lasted for at least 80 days after immunization with NP-OVA. Enhanced responses and AC accumulation …

Innate And Adaptive Immunity To The Nematode Strongyloides Stercoralis In A Mouse Model., Sandra Bonne-Annee, Jessica A. Hess, David Abraham

Department of Microbiology and Immunology Faculty Papers

Mice have been used to the study the mechanisms of protective innate and adaptive immunity to larval Strongyloides stercoralis. During primary infection, neutrophils and eosinophils are attracted by parasite components and kill the larvae by release of granule products. Eosinophils also function as antigen-presenting cells for the induction of a Th2 response. B cells produce both IgM and IgG that collaborate with neutrophils to kill worms in the adaptive immune response. Vaccine studies have identified a recombinant diagnostic antigen that induced high levels of immunity to infection with S. stercoralis in mice. These studies demonstrate that there are redundancies in …

Step-Wise Loss Of Bacterial Flagellar Torsion Confers Progressive Phagocytic Evasion, Rustin R. Lovewell, Ryan M. Collins, Julie L. Acker, George A. O'Toole, Matthew J. Wargo, Brent Berwin, Craig R. Roy

Dartmouth Scholarship

Phagocytosis of bacteria by innate immune cells is a primary method of bacterial clearance during infection. However, the mechanisms by which the host cell recognizes bacteria and consequentially initiates phagocytosis are largely unclear. Previous studies of the bacterium Pseudomonas aeruginosa have indicated that bacterial flagella and flagellar motility play an important role in colonization of the host and, importantly, that loss of flagellar motility enables phagocytic evasion. Here we use molecular, cellular, and genetic methods to provide the first formal evidence that phagocytic cells recognize bacterial motility rather than flagella and initiate phagocytosis in response to this motility. We demonstrate …

Myd88 Is Pivotal For Immune Recognition Of Citrobacter Koseri And Astrocyte Activation During Cns Infection., Shuliang Liu, Tammy Kielian

Journal Articles: Pathology and Microbiology

Citrobacter koseri (C. koseri) is a Gram-negative bacterium that can cause a highly aggressive form of neonatal meningitis, which often progresses to establish multi-focal brain abscesses. The roles of Toll-like receptor 4 (TLR4) and its signaling adaptor MyD88 during CNS C. koseri infection have not yet been examined, which is important since recent evidence indicates that innate immune responses are tailored towards specific pathogen classes. Here TLR4 WT (C3H/FeJ) and TLR4 mutant (C3H/HeJ) mice as well as MyD88 KO animals were infected intracerebrally with live C. koseri, resulting in meningitis and ventriculitis with accompanying brain abscess formation. MyD88 KO mice …

The Pseudomonas Aeruginosa Magnesium Transporter Mgte Inhibits Transcription Of The Type Iii Secretion System, Gregory G. Anderson, Timothy L. Yahr, Rustin R. Lovewell, George A. O'Toole

Dartmouth Scholarship

Pseudomonas aeruginosa is an opportunistic pathogen that causes life-long pneumonia in individuals with cystic fibrosis (CF). These long-term infections are maintained by bacterial biofilm formation in the CF lung. We have recently developed a model of P. aeruginosa biofilm formation on cultured CF airway epithelial cells. Using this model, we discovered that mutation of a putative magnesium transporter gene, called mgtE, led to increased cytotoxicity of P. aeruginosa toward epithelial cells. This altered toxicity appeared to be dependent upon expression of the type III secretion system (T3SS). In this study, we found that mutation of mgtE results in increased T3SS …

Salicylic Acid Diminishes Staphylococcus Aureus Capsular Polysaccharide Type 5 Expression, Lucia P. Alvarez, Maria S. Barbagelata, Mariana Gordiola, A. L. Cheung

Dartmouth Scholarship

Capsular polysaccharides (CP) of serotypes 5 (CP5) and 8 (CP8) are major Staphylococcus aureus virulence factors. Previous studies have shown that salicylic acid (SAL), the main aspirin metabolite, affects the expression of certain bacterial virulence factors. In the present study, we found that S. aureus strain Reynolds (CP5) cultured with SAL was internalized by MAC-T cells in larger numbers than strain Reynolds organisms not exposed to SAL. Furthermore, the internalization of the isogenic nonencapsulated Reynolds strain into MAC-T cells was not significantly affected by preexposure to SAL. Pretreatment of S. aureus strain Newman with SAL also enhanced internalization into MAC-T …

Role Of Pknb Kinase In Antibiotic Resistance And Virulence In Community-Acquired Methicillin-Resistant Staphylococcus Aureus Strain Usa300, S. Tamber, J. Schwartzman, A. L. Cheung

Dartmouth Scholarship

The regulation of cellular processes by eukaryote-like serine/threonine kinases is widespread in bacteria. In the last 2 years, several studies have examined the role of serine/threonine kinases in Staphylococcus aureus on cell wall metabolism, autolysis, and virulence, mostly in S. aureus laboratory isolates in the 8325-4 lineage. In this study, we showed that the pknB gene (also called stk1) of methicillin-resistant S. aureus (MRSA) strain COL and the community-acquired MRSA (CA-MRSA) strain USA300 is involved in cell wall metabolism, with the pknB mutant exhibiting enhanced sensitivity to β-lactam antibiotics but not to other classes of antibiotics, including aminoglycosides, ciprofloxacin, …

Long-Term Immunity To Lethal Acute Or Chronic Type Ii Toxoplasma Gondii Infection Is Effectively Induced In Genetically Susceptible C57bl/6 Mice By Immunization With An Attenuated Type I Vaccine Strain, Jason P. Gigley, Barbara A. Fox, David J. Bzik

Dartmouth Scholarship

C57BL/6 (B6) mice are genetically highly susceptible to chronic type II Toxoplasma gondii infections that invariably cause lethal toxoplasmic encephalitis. We examined the ability of an attenuated type I vaccine strain to elicit long-term immunity to lethal acute or chronic type II infections in susceptible B6 mice. Mice immunized with the type I cps1-1 vaccine strain were not susceptible to a lethal (100-cyst) challenge with the type II strain ME49. Immunized mice challenged with 10 ME49 cysts exhibited significant reductions in brain cyst and parasite burdens compared to naive mice, regardless of the route of challenge infection. Remarkably, cps1-1 strain-immunized …

Flagellum-Mediated Biofilm Defense Mechanisms Of Pseudomonas Aeruginosa Against Host-Derived Lactoferrin, Jeff G. Leid, Mathias Kerr, Candice Selgado, Chelsa Johnson, Gabriel Moreno, Alyssa Smith, Mark E. Shirtliff, Georg A. O'Toole, Emily K. Cope

Dartmouth Scholarship

Chronic infection with the gram-negative organism Pseudomonas aeruginosa is a leading cause of morbidity and mortality in human patients, despite high doses of antibiotics used to treat the various diseases this organism causes. These infections are chronic because P. aeruginosa readily forms biofilms, which are inherently resistant to antibiotics as well as the host's immune system. Our laboratory has been investigating specific mutations in P. aeruginosa that regulate biofilm bacterial susceptibility to the host. To continue our investigation of the role of genetics in bacterial biofilm host resistance, we examined P. aeruginosa biofilms that lack the flgK gene. This mutant …

Genetic Evidence For An Alternative Citrate-Dependent Biofilm Formation Pathway In Staphylococcus Aureus That Is Dependent On Fibronectin Binding Proteins And The Grars Two-Component Regulatory System, Robert M. Q. Shanks, Michael A. Meehl, Kimberly M. Brothers, Raquel M. Martinez, Niles P. Donegan, Martha L. Graber, Ambrose L. Cheung, George A. O'Toole

Dartmouth Scholarship

We reported previously that low concentrations of sodium citrate strongly promote biofilm formation by Staphylococcus aureus laboratory strains and clinical isolates. Here, we show that citrate promotes biofilm formation via stimulating both cell-to-surface and cell-to-cell interactions. Citrate-stimulated biofilm formation is independent of the ica locus, and in fact, citrate represses polysaccharide adhesin production. We show that fibronectin binding proteins FnbA and FnbB and the global regulator SarA, which positively regulates fnbA and fnbB gene expression, are required for citrate's positive effects on biofilm formation, and citrate also stimulates fnbA and fnbB gene expression. Biofilm formation is also stimulated by several …

Signaling Through Galphai2 Protein Is Required For Recruitment Of Neutrophils For Antibody-Mediated Elimination Of Larval Strongyloides Stercoralis In Mice., Udaikumar M. Padigel, Louis Stein, Kevin Redding, James J. Lee, Thomas J. Nolan, Gerhard A. Schad, Lutz Birnbaumer, David Abraham

Department of Microbiology and Immunology Faculty Papers

The heterotrimeric guanine nucleotide-binding protein Galphai2 is involved in regulation of immune responses against microbial and nonmicrobial stimuli. Galphai2-/- mice have a selectively impaired IgM response consistent with a disorder in B cell development yet have augmented T cell effector function associated with increased production of IFN-gamma and IL-4. The goal of the present study was to determine if a deficiency in the Galphai2 protein in mice would affect the protective immune response against Strongyloides stercoralis, which is IL-4-, IL-5-, and IgM-dependent. Galphai2-/- and wild-type mice were immunized and challenged with S. stercoralis larvae and analyzed for protective immune responses …

Transcutaneous Immunization With Toxin-Coregulated Pilin A Induces Protective Immunity Against Vibrio Cholerae O1 El Tor Challenge In Mice, Julianne E. Rollenhagen, Anuj Kalsy, Francisca Cerda, Manohar John

Dartmouth Scholarship

Toxin-coregulated pilin A (TcpA) is the main structural subunit of a type IV bundle-forming pilus of Vibrio cholerae, the cause of cholera. Toxin-coregulated pilus is involved in formation of microcolonies of V. cholerae at the intestinal surface, and strains of V. cholerae deficient in TcpA are attenuated and unable to colonize intestinal surfaces. Anti-TcpA immunity is common in humans recovering from cholera in Bangladesh, and immunization against TcpA is protective in murine V. cholerae models. To evaluate whether transcutaneously applied TcpA is immunogenic, we transcutaneously immunized mice with 100 mug of TcpA or TcpA with an immunoadjuvant (cholera toxin [CT], …

Prophylaxis And Therapy Of Inhalational Anthrax By A Novel Monoclonal Antibody To Protective Antigen That Mimics Vaccine-Induced Immunity, Laura Vitale, Diann Blanset, Israel Lowy, Thomas O'Neill, Joel Goldstein, Stephen F. Little, Gerard P. Andrews, Gary Dorough, Ronald K. Taylor, Tibor Keler

Dartmouth Scholarship

The neutralizing antibody response to the protective antigen (PA) component of anthrax toxin elicited by approved anthrax vaccines is an accepted correlate for vaccine-mediated protection against anthrax. We reasoned that a human anti-PA monoclonal antibody (MAb) selected on the basis of superior toxin neutralization activity might provide potent protection against anthrax. The fully human MAb (also referred to as MDX-1303 or Valortim) was chosen from a large panel of anti-PA human MAbs generated using transgenic mice immunized with recombinant PA solely on the basis of in vitro anthrax toxin neutralization. This MAb was effective in prophylactic and postsymptomatic treatment of …

Staphylococcus Aureus Escapes More Efficiently From The Phagosome Of A Cystic Fibrosis Bronchial Epithelial Cell Line Than From Its Normal Counterpart, Todd M. Jarry, Ambrose L. Cheung

Dartmouth Scholarship

Staphylococcus aureus is frequently the initial bacterium isolated from young cystic fibrosis (CF) patients, and yet its role in CF disease progression has not been determined. Recent data from our lab demonstrates that S. aureus can invade and replicate within the CF tracheal epithelial cell line (CFT-1). Here we describe the finding that the fate of internalized S. aureus in CFT-1 cells differs from its complemented counterpart (LCFSN). S. aureus strain RN6390 was able to replicate within the mutant CFT-1 cells after invasion but not in the complemented LCFSN cells. At 1 h postinvasion, S. aureus containing vesicles within both …

Experimental Ocular Toxoplasmosis In Genetically Susceptible And Resistant Mice, Fangli Lu, Shiguang Huang, Mark S. Hu, Lloyd H. Kasper

Dartmouth Scholarship

Genetic factors determining the pathogenesis and course of ocular toxoplasmosis are poorly understood. In this study, we explored the development of experimental ocular pathogenesis in genetically dissimilar mice infected with either the RH strain, the PLK strain, or the immunodominant surface antigen 1 (SAG1 [P30])-deficient mutant of the RH strain of Toxoplasma gondii. At 11 days postinfection, ocular infection of C57BL/6 mice with all of the strains of parasites resulted in severe inflammatory lesions and high numbers of parasites in eye tissue; less severe ocular lesions at earlier histopathology and prolonged survival were observed in this mouse strain infected …

Heparin Stimulates Staphylococcus Aureus Biofilm Formation, Robert M. Q. Shanks, Niles P. Donegan, Martha L. Graber, Sarah E. Buckingham, Michael Zegans, Ambrose Cheung, George A. O'Toole

Dartmouth Scholarship

Heparin, known for its anticoagulant activity, is commonly used in catheter locks. Staphylococcus aureus, a versatile human and animal pathogen, is commonly associated with catheter-related bloodstream infections and has evolved a number of mechanisms through which it adheres to biotic and abiotic surfaces. We demonstrate that heparin increased biofilm formation by several S. aureus strains. Surface coverage and the kinetics of biofilm formation were stimulated, but primary attachment to the surface was not affected. Heparin increased S. aureus cell-cell interactions in a protein synthesis-dependent manner. The addition of heparin rescued biofilm formation of hla, ica, and sarA …

Role Of The Distal Sara Promoters In Sara Expression In Staphylococcus Aureus, Ambrose L. Cheung, Adhar C. Manna

Dartmouth Scholarship

The global regulatory locus sarA comprises a 375-bp open reading frame that is driven by three promoters, the proximal P1 and distal P3 and P2 promoters. We mutated the weaker P3 and P2 promoters to ascertain the effect of the change on SarA protein and target gene expression. Our results indicated that the solely active P1 promoter led to a lower SarA protein level, which has an effect on agr transcription and subsequently had corresponding effects on hla, sspA, and spa transcription, probably in both agr-independent and agr-dependent manners.

Thymidine-Dependent Staphylococcus Aureus Small-Colony Variants Are Associated With Extensive Alterations In Regulator And Virulence Gene Expression Profiles, Barbara C. Kahl, Gunnar Belling, Petra Becker, Indranil Chatterjee, Katrin Wardecki, Karin Hilgert, Ambrose Cheung

Dartmouth Scholarship

Chronic airway infection is a hallmark of cystic fibrosis (CF) and many CF patients are infected persistently by Staphylococcus aureus. Thymidine-dependent trimethoprim-sulfamethoxazole (SXT)-resistant S. aureus small-colony variants (SCVs), often in combination with isogenic normal S. aureus phenotypes, are highly prevalent and persistent in airway secretions of CF patients due to long-term SXT therapy (B. Kahl, M. Herrmann, A. S. Everding, H. G. Koch, K. Becker, E. Harms, R. A. Proctor, and G.

Rat/Mgra, A Regulator Of Autolysis, Is A Regulator Of Virulence Genes In Staphylococcus Aureus, Susham Ingavale, Willem Van Wamel, Thanh T. Luong, Chia Y. Lee, Ambrose L. Cheung

Dartmouth Scholarship

We have previously identified mgrA (rat) as a regulator of autolysis in Staphylococcus aureus. Besides its effect on autolytic activity, we recently found alterations in the expression of regulator and target virulence genes in the mgrA mutant. Northern analysis and transcription fusion assays showed that inactivation of mgrA has led to the downregulation of RNAIII of agr and hla and upregulation of sarS and spa. Although both SarA and agr are activators of α-hemolysin and a repressors of protein A synthesis, we found that the transcription of sarA was not affected in the mgrA mutant and …