David K R Karaolis

University of Adelaide, Adelaide, South Australia, Australia

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Publications (36)156.28 Total impact

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    James P. Nataro, David K. Karaolis
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    ABSTRACT: This work tested the hypothesis that c-di-GMP is a novel immunostimulatory molecule that modulates the immune response. Intramammary treatment of mice with c-di-GMP before S. aureus challenge gave a protective effect and a 1O,OOO-fold reduction in CFUs in tissues. Intramuscular vaccination of mice with c-di-GMP coinjected with S. aureus clumping factor A (ClfA) Ag produced serum with significantly higher anti-ClfA IgG Ab titer compared with ClfA alone. Intraperitoneal injection of mice with c-di-GMP activated monocyte and granulocyte recruitment. Human immature dendritic cells (DCs) cultured in the presence of c-di-GMP showed increased expression of costimulatory molecules CD80/CD86 and maturation marker CD83, increased MHC class II and cytokines and chemokines such as IL-12, IFN-g, IL-8, MCP-l, IFN-g-inducible protein 10, and RANTES, and altered expression of chemokine receptors including CCR1, CCR7, and CXCR4. c-di-GMP-matured DCs demonstrated enhanced T cell stimulatory activity. We found that c-di-GMP activates ERK phosphorylation in human M-CSF-induced monocyte-derived macrophages , c-di-GMP is stable in human serum. We have also found that c-di-GMP acts as a potent adjuvant in vaccine studies in vivo to inhibit infection by MRSA, Streptococcus pneumoniae, and Klebsiella pneumoniae. We propose c-di-GMP can be used clinically as an immunomodulator, immune enhancer, or vaccine adjuvant.
    06/2009;
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    ABSTRACT: Cyclic diguanylate (c-di-GMP) is a novel immunomodulator and immune enhancer that triggers a protective host innate immune response. The protective effect of c-di-GMP as a vaccine adjuvant against Staphylococcus aureus infection was investigated by subcutaneous (s.c.) vaccination with two different S. aureus antigens, clumping factor A (ClfA) and a nontoxic mutant staphylococcal enterotoxin C (mSEC), then intravenous (i.v.) challenge with viable methicillin-resistant S. aureus (MRSA) in a systemic infection model. Mice immunized with c-di-GMP plus mSEC or c-di-GMP plus ClfA vaccines then challenged with MRSA produced strong antigen-specific antibody responses demonstrating immunogenicity of the vaccines. Bacterial counts in the spleen and liver of c-di-GMP plus mSEC and c-di-GMP plus ClfA-immunized mice were significantly lower than those of control mice (P<0.001). Mice immunized with c-di-GMP plus mSEC or c-di-GMP plus ClfA showed significantly higher survival rates at day 7 (87.5%) than those of the non-immunized control mice (33.3%) (P<0.05). Furthermore, immunization of mice with c-di-GMP plus mSEC or c-di-GMP plus ClfA induced not only very high titers of immunoglobulin G1 (IgG1), but c-di-GMP plus mSEC also induced significantly higher levels of IgG2a, IgG2b and IgG3 compared to alum adjuvant (P<0.01 and P<0.001, respectively) and c-di-GMP plus ClfA induced significantly higher levels of IgG2a, IgG2b and IgG3 compared to alum adjuvant (P<0.001). Our results show that c-di-GMP should be developed as an adjuvant and immunotherapeutic to provide protection against systemic infection caused by S. aureus (MRSA).
    Vaccine 05/2009; 27(35):4867-73. · 3.77 Impact Factor
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    ABSTRACT: Cyclic diguanylate (c-di-GMP) is a unique bacterial intracellular signaling molecule capable of stimulating enhanced protective innate immunity against various bacterial infections. The effects of intranasal pretreatment with c-di-GMP, or intraperitoneal coadministration of c-di-GMP with the pneumolysin toxoid (PdB) or pneumococcal surface protein A (PspA) before pneumococcal challenge, were investigated in mice. We found that c-di-GMP had no significant direct short-term effect on the growth rate of Streptococcus pneumoniae either in vitro or in vivo. However, intranasal pretreatment of mice with c-di-GMP resulted in a significant decrease in bacterial load in lungs and blood after serotypes 2 and 3 challenge, and a significant decrease in lung titers after serotype 4 challenge. Potential cellular mediators of these enhanced protective responses were identified in lungs and draining lymph nodes. Intraperitoneal coadministration of c-di-GMP with PdB or PspA before challenge resulted in significantly higher antigen-specific antibody titers and increased survival of mice, compared to that obtained with alum adjuvant. These findings demonstrate that local or systemic c-di-GMP administration stimulates innate and adaptive immunity against invasive pneumococcal disease. We propose that c-di-GMP can be used as an effective broad spectrum immunomodulator and vaccine adjuvant to prevent infectious diseases.
    Vaccine 08/2008; 26(36):4676-85. · 3.49 Impact Factor
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    ABSTRACT: Innate immunity is the primary mechanism by which extracellular bacterial pathogens are effectively cleared from the lung. We have previously shown that cyclic di-GMP (c-di-GMP [c-diguanylate]) is a novel small molecule immunomodulator and immunostimulatory agent that triggers protective host innate immune responses. Using a murine model of bacterial pneumonia, we show that local intranasal (i.n.) or systemic subcutaneous (s.c.) administration of c-di-GMP prior to intratracheal (i.t.) challenge with Klebsiella pneumoniae stimulates protective immunity against infection. Specifically, i.n. or s.c. administration of c-di-GMP 48 and 24 h prior to i.t. K. pneumoniae challenge resulted in significantly increased survival. Pretreatment with c-di-GMP resulted in a 5-fold reduction in bacterial CFU in the lung (P < 0.05) and an impressive >1,000-fold decrease in CFU in the blood (P < 0.01). c-di-GMP administration stimulated a robust innate response to bacterial challenge, characterized by enhanced accumulation of neutrophils and alphabeta T cells, as well as activated NK and alphabeta T lymphocytes, which was associated with earlier and more vigorous expression of chemokines and type I cytokines. Moreover, lung macrophages recovered from Klebsiella-infected mice pretreated with c-di-GMP expressed greater quantities of inducible nitric oxide synthase and nitric oxide ex vivo than did macrophages isolated from infected mice pretreated with the control, c-GMP. These findings demonstrate that c-di-GMP delivered in either a compartmentalized or systemic fashion stimulates protective innate immunity in the lung and protects mice against bacterial invasion. We propose that the cyclic dinucleotide c-di-GMP may be used clinically as an effective immunomodulator, immune enhancer, and vaccine adjuvant to protect against respiratory infection and pneumonia in humans and animals.
    Infection and Immunity 11/2007; 75(10):4942-50. · 4.07 Impact Factor
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    ABSTRACT: Cyclic diguanylate (c-di-GMP) is a bacterial intracellular signaling molecule. We have shown that treatment with exogenous c-di-GMP inhibits Staphylococcus aureus infection in a mouse model. We now report that c-di-GMP is an immodulator and immunostimulatory molecule. Intramammary treatment of mice with c-di-GMP 12 and 6 h before S. aureus challenge gave a protective effect and a 10,000-fold reduction in CFUs in tissues (p < 0.001). Intramuscular vaccination of mice with c-di-GMP coinjected with S. aureus clumping factor A (ClfA) Ag produced serum with significantly higher anti-ClfA IgG Ab titers (p < 0.001) compared with ClfA alone. Intraperitoneal injection of mice with c-di-GMP activated monocyte and granulocyte recruitment. Human immature dendritic cells (DCs) cultured in the presence of c-di-GMP showed increased expression of costimulatory molecules CD80/CD86 and maturation marker CD83, increased MHC class II and cytokines and chemokines such as IL-12, IFN-gamma, IL-8, MCP-1, IFN-gamma-inducible protein 10, and RANTES, and altered expression of chemokine receptors including CCR1, CCR7, and CXCR4. c-di-GMP-matured DCs demonstrated enhanced T cell stimulatory activity. c-di-GMP activated p38 MAPK in human DCs and ERK phosphorylation in human macrophages. c-di-GMP is stable in human serum. We propose that cyclic dinucleotides like c-di-GMP can be used clinically in humans and animals as an immunomodulator, immune enhancer, immunotherapeutic, immunoprophylactic, or vaccine adjuvant.
    The Journal of Immunology 02/2007; 178(4):2171-81. · 5.52 Impact Factor
  • Mamoru Hyodo, Yoshihiro Hayakawa, David K. R. Karaolis
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
    ChemInform 01/2006; 37(37).
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    ABSTRACT: The cyclic dinucleotide 3',5'-cyclic diguanylic acid (c-di-GMP) is a naturally occurring small molecule that regulates important signaling systems in bacteria. We have recently shown that c-di-GMP inhibits Staphylococcus aureus biofilm formation in vitro and its adherence to HeLa cells. We now report that c-di-GMP treatment has an antimicrobial and antipathogenic activity in vivo and reduces, in a dose-dependent manner, bacterial colonization by biofilm-forming S. aureus strains in a mouse model of mastitis infection. Intramammary injections of 5 and 50 nmol of c-di-GMP decreased colonization (bacterial CFU per gram of gland) by 0.79 (P > 0.05) and 1.44 (P < 0.01) logs, respectively, whereas 200-nmol doses allowed clearance of the bacteria below the detection limit with a reduction of more than 4 logs (P < 0.001) compared to the untreated control groups. These results indicate that cyclic dinucleotides potentially represent an attractive and novel drug platform which could be used alone or in combination with other agents or drugs in the prevention, treatment, or control of infection.
    Antimicrobial Agents and Chemotherapy 09/2005; 49(8):3109-13. · 4.57 Impact Factor
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    ABSTRACT: The novel cyclic dinucleotide, 3',5'-cyclic diguanylic acid, cGpGp (c-di-GMP), is a naturally occurring small molecule that regulates important signaling mechanisms in prokaryotes. Recently, we showed that c-di-GMP has "drug-like" properties and that c-di-GMP treatment might be a useful antimicrobial approach to attenuate the virulence and pathogenesis of Staphylococcus aureus and prevent or treat infection. In the present communication, we report that c-di-GMP (50 microM) has striking properties regarding inhibition of cancer cell proliferation in vitro. c-di-GMP inhibits both basal and growth factor (acetylcholine and epidermal growth factor)-induced cell proliferation of human colon cancer (H508) cells. Toxicity studies revealed that exposure of normal rat kidney cells and human neuroblastoma cells to c-di-GMP at biologically relevant doses showed no lethal cytotoxicity. Cyclic dinucleotides, such as c-di-GMP, represent an attractive and novel "drug-platform technology" that can be used not only to develop new antimicrobial agents, but also to develop novel therapeutic agents to prevent or treat cancer.
    Biochemical and Biophysical Research Communications 05/2005; 329(1):40-5. · 2.41 Impact Factor
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    ABSTRACT: Staphylococcus aureus is an important pathogen of humans and animals, and antibiotic resistance is a public health concern. Biofilm formation is essential in virulence and pathogenesis, and the ability to resist antibiotic treatment results in difficult-to-treat and persistent infections. As such, novel antimicrobial approaches are of great interest to the scientific, medical, and agriculture communities. We recently proposed that modulating levels of the cyclic dinucleotide signaling molecule, c-di-GMP (cyclic diguanylate [3',5'-cyclic diguanylic acid], cGpGp), has utility in regulating phenotypes of prokaryotes. We report that extracellular c-di-GMP shows activity against human clinical and bovine intramammary mastitis isolates of S. aureus, including methicillin-resistant S. aureus (MRSA) isolates. We show that chemically synthesized c-di-GMP is soluble and stable in water and physiological saline and stable following boiling and exposure to acid and alkali. Treatment of S. aureus with extracellular c-di-GMP inhibited cell-to-cell (intercellular) adhesive interactions in liquid medium and reduced (>50%) biofilm formation in human and bovine isolates compared to untreated controls. c-di-GMP inhibited the adherence of S. aureus to human epithelial HeLa cells. The cyclic nucleotide analogs cyclic GMP and cyclic AMP had a lesser inhibitory effect on biofilms, while 5'-GMP had no major effect. We propose that cyclic dinucleotides such as c-di-GMP, used either alone or in combination with other antimicrobial agents, represent a novel and attractive approach in the development of intervention strategies for the prevention of biofilms and the control and treatment of infection.
    Antimicrobial Agents and Chemotherapy 04/2005; 49(3):1029-38. · 4.57 Impact Factor
  • Mamoru Hyodo, Yumi Sato, Yoshihiro Hayakawa, David K R Karaolis
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    ABSTRACT: This paper describes unique behavior of bis(3'-5')diguanylic acid (c-di-GMP) under some conditions. Thus, c-di-GMP exists as the monomer in aprotic organic solvents such as DMSO. By contrast, c-di-GMP smoothly aggregates in water and in low-concentration aqueous solutions of some salts, such as sodium chloride and ammonium acetate, to give a mixture of many aggregates. The resulting multiple aggregates converge to the single compound (provably the monomer) in a >154 mM (0.9%) sodium chloride aqueous solution, in a >100 mM ammonium acetate buffer, and in a >100 mM phosphate buffer.
    Nucleic Acids Symposium Series 01/2005;
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    ABSTRACT: Vibrio cholerae is an important human pathogen and the cause of cholera. Since genetic variation and antibiotic resistance of strains have implications for effective treatment of the disease, we examined the genetic diversity and antibiotic resistance profile in 92 clinical strains (serogroup O1) and 56 environmental strains (O1 antigen, 42 strains; non-O1 antigen, 14 strains) isolated in Brazil between 1991 and 1999. Clinical and environmental O1 strains showed greater drug resistance compared to environmental non-O1 strains. Nearly all clinical O1 strains were resistant to one or more antibiotics while half of the environmental O1 and non-O1 strains were resistant to one or more antibiotics. No plasmids or class 1 integrons were detected in the strains by PCR analysis. Multilocus enzyme electrophoresis analysis (MLEE) suggests most of the O1 strains belong to a single (South American) clone that is related but different to seventh-pandemic strains isolated from other parts of the world. Our results show that there is a close genetic relationship between clinical and environmental O1 strains and that many serogroups and the environment can be a reservoir for antibiotic resistance.
    Epidemiology and Infection 11/2004; 132(5):985-92. · 2.87 Impact Factor
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    Dalin Zhang, Jim Manos, Xinrong Ma, Robert Belas, David K R Karaolis
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    ABSTRACT: The Vibrio pathogenicity island (VPI) in epidemic Vibrio cholerae is an essential virulence gene cluster. The VPI can excise from the chromosome and form extrachromosomal circular excision products. The VPI is 41.2-kb in size and encodes 29 potential proteins, several of which have no known function and whose regulation is not well understood. To determine the transcriptional organization of the tagA-orf2-orf3-mop-tagD region located at the 5'-(left) end of the VPI, we used reverse-transcriptase-PCR (RT-PCR), Northern blot analysis and DNA sequencing. RT-PCR primers were designed to transcribe and amplify regions spanning two or more open reading frames so as to establish the transcriptional organization. RT-PCR and Northern blot results demonstrated that the tagA-tagD region is transcribed as a polycistronic message and organized into several potential operons including tagA-orf2, orf3-mop, orf3-mop-tagD and tagD alone. Transcriptional lacZ fusions supported the existence of a promoter upstream of orf3 that was toxT-dependent. Interestingly, our data suggests that the orf3 promoter can drive the expression of either a long transcript (orf3-mop-tagD) or a short transcript (orf3-mop) without tagD. Our data also suggests that tagD can be expressed from two different promoters and that tagD is either transcribed alone or co-expressed with orf3-mop under certain conditions. These studies provide new insight into the genetic structure, transcriptional organization and regulation of a cluster of virulence genes on the VPI of epidemic V. cholerae.
    FEMS Microbiology Letters 07/2004; 235(1):199-207. · 2.05 Impact Factor
  • Dalin Zhang, Jim Manos, Xinrong Ma, Robert Belas, David K.R. Karaolis
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    ABSTRACT: The Vibrio pathogenicity island (VPI) in epidemic Vibrio cholerae is an essential virulence gene cluster. The VPI can excise from the chromosome and form extrachromosomal circular excision products. The VPI is 41.2-kb in size and encodes 29 potential proteins, several of which have no known function and whose regulation is not well understood. To determine the transcriptional organization of the tagA–orf2–orf3–mop–tagD region located at the 5′-(left) end of the VPI, we used reverse-transcriptase-PCR (RT-PCR), Northern blot analysis and DNA sequencing. RT-PCR primers were designed to transcribe and amplify regions spanning two or more open reading frames so as to establish the transcriptional organization. RT-PCR and Northern blot results demonstrated that the tagA–tagD region is transcribed as a polycistronic message and organized into several potential operons including tagA–orf2, orf3–mop, orf3–mop–tagD and tagD alone. Transcriptional lacZ fusions supported the existence of a promoter upstream of orf3 that was toxT-dependent. Interestingly, our data suggests that the orf3 promoter can drive the expression of either a long transcript (orf3–mop–tagD) or a short transcript (orf3–mop) without tagD. Our data also suggests that tagD can be expressed from two different promoters and that tagD is either transcribed alone or co-expressed with orf3–mop under certain conditions. These studies provide new insight into the genetic structure, transcriptional organization and regulation of a cluster of virulence genes on the VPI of epidemic V. cholerae.
    FEMS Microbiology Letters 05/2004; 235(1):199 - 207. · 2.05 Impact Factor
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    ABSTRACT: Vibrio cholerae, the causative agent of cholera can produce an exopolysaccharide (EPS). Some strains can also phenotypically switch from a smooth to a 'rugose' phenotype characterized by small wrinkled colonies, overproduction of EPS, increased biofilm formation in vitro and increased resistance to various stressful conditions. High frequency switching to the rugose phenotype is more common in epidemic strains than in non-pathogenic strains, suggesting EPS production and the rugose phenotype are important in cholera epidemiology. VpsR up-regulates Vibrio polysaccharide (VPS) genes and the synthesis of extracellular EPS (VPS). However, the function of VPS, the rugose phenotype and VpsR in pathogenesis is not well understood. We report that rugose strains of both classical and El Tor biotypes of epidemic V. cholerae are defective in the in vitro production of extracellular collagenase activity. In vivo studies in rabbit ileal loops suggest that VpsR mutants are attenuated in reactogenicity. Intestinal colonization studies in infant mice suggest that VPS production, the rugose phenotype and VpsR have a role in pathogenesis. Our results indicate that regulated VPS production is important for promoting in vivo biofilm formation and pathogenesis. Additionally, VpsR might regulate genes with roles in virulence. Rugose strains appear to be a subpopulation of cells that might act as a 'helper' phenotype promoting the pathogenesis of certain strains. Our studies provide new insight into the potential role of VPS, the rugose phenotype and VpsR in the pathogenesis of epidemic V. cholerae.
    FEMS Microbiology Letters 02/2004; 230(1):105-13. · 2.05 Impact Factor
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    C Rajanna, J Wang, D Zhang, Zheng Xu, A Ali, Y-M Hou, D K R Karaolis
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    ABSTRACT: The Vibrio pathogenicity island (VPI) in epidemic Vibrio cholerae is an essential virulence gene cluster. Like many pathogenicity islands, the VPI has at its termini a phage-like integrase gene (int), a transposase-like gene (vpiT), and phage-like attachment (att) sites, and is inserted at a tRNA-like locus (ssrA). We report that the VPI precisely excises from the chromosome and that its left and right ends join to form an extrachromosomal circular excision product (pVPI). Two-stage nested PCR analysis and DNA sequencing confirmed the int-att-vpiT junction and that the core attP of pVPI is identical to the chromosomal VPI attR site. Excision was independent of toxR and toxT. Excision was independent of recA, suggesting that it is mediated by site-specific recombination. Interestingly, while excision was detected in int and vpiT mutants, excision was abolished in a double (int vpiT) mutant and was restored by plasmids containing genes for either recombinase. Excision results in deletion of A361 in the ssrA locus, which flanks the right junction of the VPI. Since A361 encodes U70 in the critical G. U base pair in the acceptor stem of the ssrA RNA that is the determinant for aminoacylation with alanine, this deletion might have deleterious effects on ssrA function. Also, vpiT may have undergone interchromosomal translocation or may represent an independent integration event, as it was found downstream of hutA in some isolates. Our results provide new insight into the molecular biology of the VPI, and we propose that the process of excision and circularization is important in the emergence, pathogenesis, and persistence of epidemic V. cholerae.
    Journal of Bacteriology 01/2004; 185(23):6893-901. · 3.19 Impact Factor
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    FEMS Microbiology Letters 01/2004; 230(2):291-291. · 2.05 Impact Factor
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    ABSTRACT: Vibrio cholerae, the causative agent of cholera can produce an exopolysaccharide (EPS). Some strains can also phenotypically switch from a smooth to a ‘rugose’ phenotype characterized by small wrinkled colonies, overproduction of EPS, increased biofilm formation in vitro and increased resistance to various stressful conditions. High frequency switching to the rugose phenotype is more common in epidemic strains than in non-pathogenic strains, suggesting EPS production and the rugose phenotype are important in cholera epidemiology. VpsR up-regulates Vibrio polysaccharide (VPS) genes and the synthesis of extracellular EPS (VPS). However, the function of VPS, the rugose phenotype and VpsR in pathogenesis is not well understood. We report that rugose strains of both classical and El Tor biotypes of epidemic V. cholerae are defective in the in vitro production of extracellular collagenase activity. In vivo studies in rabbit ileal loops suggest that VpsR mutants are attenuated in reactogenicity. Intestinal colonization studies in infant mice suggest that VPS production, the rugose phenotype and VpsR have a role in pathogenesis. Our results indicate that regulated VPS production is important for promoting in vivo biofilm formation and pathogenesis. Additionally, VpsR might regulate genes with roles in virulence. Rugose strains appear to be a subpopulation of cells that might act as a ‘helper’ phenotype promoting the pathogenesis of certain strains. Our studies provide new insight into the potential role of VPS, the rugose phenotype and VpsR in the pathogenesis of epidemic V. cholerae.
    FEMS Microbiology Letters 12/2003; 230(1):105 - 113. · 2.05 Impact Factor
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    ABSTRACT: Vibrio cholerae can switch to a 'rugose' phenotype characterized by an exopolysaccharide (EPS) matrix, wrinkled colony morphology, increased biofilm formation and increased survival under specific conditions. The vps gene cluster responsible for the biosynthesis of the rugose EPS (rEPS) is positively regulated by VpsR. We recently identified media (APW#3) promoting EPS production and the rugose phenotype and found epidemic strains switch at a higher frequency than non-pathogenic strains, suggesting this switch and the rugose phenotype are important in cholera epidemiology. In this study, transposon mutagenesis on a smooth V. cholerae strain was used to identify mutants that were unable to shift to the rugose phenotype under inducing conditions to better understand the molecular basis of the switch. We identified vpsR, galE and vps previously associated with the rugose phenotype, and also identified genes not previously associated with the phenotype, including rfbD and rfbE having roles in LPS (lipopolysaccharide) synthesis and aroB and aroK with roles in aromatic amino acid synthesis. Additionally, a mutation in amiB encoding N-acetylmuramoyl-L-alanine amidase caused defects in the switch, motility and cell morphology. We also found that a gene encoding a novel regulatory protein we termed RocS (regulation of cell signaling) containing a GGDEF and EAL domains and associated with c-di-GMP levels is important for the rugose phenotype, EPS, biofilm formation and motility. We propose that modulation of cyclic dinucleotide (e.g. c-di-GMP) levels might have application in regulating various phenotypes of prokaryotes. Our study shows the molecular complexity of the switch between the smooth and rugose phenotypes of V. cholerae and may be relevant to similar phenotypes in other species.
    FEMS Microbiology Letters 10/2003; 227(1):113-9. · 2.05 Impact Factor
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    ABSTRACT: Vibrio cholerae can switch to a ‘rugose’ phenotype characterized by an exopolysaccharide (EPS) matrix, wrinkled colony morphology, increased biofilm formation and increased survival under specific conditions. The vps gene cluster responsible for the biosynthesis of the rugose EPS (rEPS) is positively regulated by VpsR. We recently identified media (APW#3) promoting EPS production and the rugose phenotype and found epidemic strains switch at a higher frequency than non-pathogenic strains, suggesting this switch and the rugose phenotype are important in cholera epidemiology. In this study, transposon mutagenesis on a smooth V. cholerae strain was used to identify mutants that were unable to shift to the rugose phenotype under inducing conditions to better understand the molecular basis of the switch. We identified vpsR, galE and vps previously associated with the rugose phenotype, and also identified genes not previously associated with the phenotype, including rfbD and rfbE having roles in LPS (lipopolysaccharide) synthesis and aroB and aroK with roles in aromatic amino acid synthesis. Additionally, a mutation in amiB encoding N-acetylmuramoyl-l-alanine amidase caused defects in the switch, motility and cell morphology. We also found that a gene encoding a novel regulatory protein we termed RocS (regulation of cell signaling) containing a GGDEF and EAL domains and associated with c-di-GMP levels is important for the rugose phenotype, EPS, biofilm formation and motility. We propose that modulation of cyclic dinucleotide (e.g. c-di-GMP) levels might have application in regulating various phenotypes of prokaryotes. Our study shows the molecular complexity of the switch between the smooth and rugose phenotypes of V. cholerae and may be relevant to similar phenotypes in other species.
    FEMS Microbiology Letters 09/2003; 227(1):113 - 119. · 2.05 Impact Factor
  • Dalin Zhang, Chythanya Rajanna, Weiyun Sun, David K R Karaolis
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    ABSTRACT: Epidemic Vibrio cholerae contain a large essential virulence gene cluster called the Vibrio pathogenicity island (VPI). We recently reported that no in vitro difference in virulence was found in El Tor strain N16961 containing a mutation in the VPI-encoded mop gene but this mutant was hypervirulent and reactogenic in rabbit ileal loops. In this paper, we report in vitro studies showing that independent Mop mutants of strain 3083 are significantly attenuated (approximately 40-fold) in cholera toxin (CT) production and have significantly increased motility and biofilm forming ability but appear to be unaffected in TcpA, hemagglutinin protease and hemolysin compared to their parent. The 3083 Mop mutant showed a 100-fold decrease in its in vivo intestinal colonization ability in the infant mouse competition assays. While reverse transcription polymerase chain reaction and phenotypic studies of a mop plasmid in both mutant and wild-type backgrounds suggest Mop is expressed by the plasmid, the differences in CT and biofilm formation could not be restored in any of the mutants. The inability to complement the Mop mutants in trans may be due either to the selection of secondary mutations or to mop possibly being part of an operon. Our findings that Mop is associated with CT, motility, biofilm formation and intestinal colonization support a hypothesis in which Mop has a pleiotropic role in the pathogenesis and persistence of epidemic V. cholerae.
    FEMS Microbiology Letters 09/2003; 225(2):311-8. · 2.05 Impact Factor

Publication Stats

1k Citations
156.28 Total Impact Points

Institutions

  • 2008
    • University of Adelaide
      • School of Molecular and Biomedical Sciences
      Adelaide, South Australia, Australia
  • 2005–2006
    • Nagoya University
      • Graduate School of Information Science
      Nagoya, Aichi, Japan
  • 1997–2005
    • University of Maryland, Baltimore
      • • Department of Pathology
      • • Center for Vaccine Development
      Baltimore, Maryland, United States
  • 2004
    • Fundação Oswaldo Cruz
      • Department of Bacteriology (INCQS)
      Rio de Janeiro, Rio de Janeiro, Brazil
  • 2003
    • University of Dhaka
      • Department of Microbiology
      Dhaka, Dhaka Division, Bangladesh
  • 1998
    • Malaria Vaccine Development Program
      New Dilli, NCT, India
  • 1994–1997
    • University of Sydney
      • School of Molecular Bioscience
      Sydney, New South Wales, Australia