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Biomedical subjects

F C Fang

Publications and source records attributed to F C Fang.

At least 19 recordsLinked to original sources
PubMed1997

Periplasmic superoxide dismutase protects Salmonella from products of phagocyte NADPH-oxidase and nitric oxide synthase.

Superoxide dismutase (SOD) catalyzes the conversion of superoxide radical to hydrogen peroxide. Periplasmic localization of bacterial Cu,Zn-SOD has suggested a role of this enzyme in defense against extracellular phagocyte-derived reactive oxygen species. Sequence analysis of regions flanking the Salmonella typhimurium sodC gene encoding Cu,Zn-SOD demonstrates significant homology to lambda phage proteins, reflecting possible bacteriophage-mediated horizontal gene transfer of this determinant among pathogenic bacteria. Salmonella deficient in Cu,Zn-SOD has reduced survival in macrophages and attenuated virulence in mice, which can be restored by abrogation of either the phagocyte respiratory burst or inducible nitric oxide synthase. Moreover, a sodC mutant is extremely susceptible to the combination of superoxide and nitric oxide. These observations suggest that SOD protects periplasmic or inner membrane targets by diverting superoxide and limiting peroxynitrite formation, and they demonstrate the ability of the respiratory burst and nitric oxide synthase to synergistically kill microbial pathogens in vivo.

Animals↗
PubMed1997

The transcriptional regulator SoxS is required for resistance of Salmonella typhimurium to paraquat but not for virulence in mice.

In Escherichia coli, the SoxRS regulon is required for resistance to redox-cycling agents which elevate cytosolic superoxide levels, as well as for resistance to nitric oxide-dependent macrophage killing. In Salmonella typhimurium, SoxS is also required for enhanced expression of Mn-superoxide dismutase and resistance to paraquat, but not for resistance to nitric oxide donor compounds in vitro, resistance to macrophage killing, or virulence in mice. Differences in other antioxidant defense systems or compensation by homologous regulons may account for species-specific differences in the role of SoxS.

Animals↗
PubMed1997

SlyA, a transcriptional regulator of Salmonella typhimurium, is required for resistance to oxidative stress and is expressed in the intracellular environment of macrophages.

Appropriate regulation of genes enables Salmonella typhimurium to adapt to the intracellular environment of the host. The Salmonella slyA gene is in a family of transcriptional regulators that may play an important role in this adaptation. We have previously shown that slyA mutant Salmonella strains are profoundly attenuated for virulence and do not survive in macrophages. In this study, we demonstrate that the expression of multiple Salmonella proteins is regulated by SlyA during stationary phase and during infection of macrophages. Both of these conditions also induced the expression of a slyA::lacZ transcriptional fusion. Expression of the slyA::lacZ transcriptional fusion increased 15-fold in stationary phase and was not dependent on the stationary-phase sigma factor, RpoS. slyA mutant Salmonella strains were sensitive to oxidative products of the respiratory burst, including hydrogen peroxide and the products of the redox cycling compound paraquat, but not to nitric oxide donors. These results suggest that the SlyA regulon is activated during infection of the host and is required for resistance to toxic oxidative products of the reticuloendothelial system.

Animals↗
PubMed1997

Diverse presentation of aberrant origin of the right subclavian artery: two case reports.

Aberrant origin of the right subclavian artery occurs in up to 1% of the population and can result in a wide range of symptoms. In this report, two cases of this anomaly are presented. In the first case, a patient developed fatal group A streptococcal aortitis. In the second case, the patient complained of chronic cough and intermittent dyspnea. The embryologic genesis of this abnormality is discussed and the current literature is summarized. Although relatively uncommon, it is important to consider this vascular anomaly in the differential diagnosis of patients with dysphagia, dyspnea, chest pain, fever, or mediastinal widening evidenced on chest roentgenography.

Adult↗
PubMed1996

Homocysteine antagonism of nitric oxide-related cytostasis in Salmonella typhimurium.

Nitric oxide (NO) is associated with broad-spectrum antimicrobial activity of particular importance in infections caused by intracellular pathogens. An insertion mutation in the metL gene of Salmonella typhimurium conferred specific hypersusceptibility to S-nitrosothiol NO-donor compounds and attenuated virulence of the organism in mice. The metL gene product catalyzes two proximal metabolic steps required for homocysteine biosynthesis. S-Nitrosothiol resistance was restored by exogenous homocysteine or introduction of the metL gene on a plasmid. Measurement of expression of the homocysteine-sensitive metH gene indicated that S-nitrosothiols may directly deplete intracellular homocysteine. Homocysteine may act as an endogenous NO antagonist in diverse processes including infection, atherosclerosis, and neurologic disease.

Animals↗
PubMed1996

Donor-to-host transmission of Mycoplasma hominis in lung allograft recipients.

Mycoplasma hominis is a significant pathogen in immunocompromised hosts, particularly organ transplant recipients. We describe two recipients of lung allografts from the same donor who had M. hominis pleuropulmonary infection during the immediate postoperative period. The most likely source of infection in these cases was the donor's respiratory tract. The slow-growing pinpoint colonies formed by M. hominis on routine bacterial culture medium may be easily overlooked and should be subcultured to mycoplasmal medium for definitive identification. The recommended management of this infection consists of drainage and antimicrobial therapy with tetracycline, clindamycin, or a fluoroquinolone. This report highlights the potential for M. hominis to be transmitted from donor to recipient during organ transplantation.

Adult↗
PubMed1996

Expression of Salmonella typhimurium rpoS and rpoS-dependent genes in the intracellular environment of eukaryotic cells.

Adaptation to the intracellular environment of host cells is crucial for the pathogenesis of Salmonella infections. The alternative sigma factor RpoS is a global regulator of gene expression during starvation and stress conditions and is required for virulence in Salmonella spp. We have used lacZ reporter fusions to rpoS and rpoS-dependent genes to study rpoS regulation after entry of Salmonella typhimurium into macrophages and epithelial cells. The results demonstrate that expression of an rpoS::lacZ translational fusion increases rapidly in S. typhimurium after phagocytosis. Activity of RpoS also increases after bacterial entry into both macrophages and epithelial cells, as demonstrated by the induction of the rpoS-regulated genes katE and spvB. A control rpoS-independent promoter for neomycin resistance does not show significant induction after cell entry. These results demonstrate that the regulatory system mediated by RpoS in S. typhimurium is activated by the intracellular environment of eukaryotic cells.

Animals↗
PubMed1996

Identification of sigma S-regulated genes in Salmonella typhimurium: complementary regulatory interactions between sigma S and cyclic AMP receptor protein.

sigma S (RpoS)-regulated lacZ transcriptional fusions in Salmonella typhimurium were identified from a MudJ transposon library by placing the rpoS gene under the control of the araBAD promoter and detecting lacZ expression in the presence or absence of arabinose supplementation. Western blot (immunoblot) analysis of bacteria carrying PBAD::rpoS demonstrated arabinose-dependent rpoS expression during all phases of growth. sigma S-dependent gene expression of individual gene fusions was confirmed by P22-mediated transduction of the MudJ insertions into wild-type or rpoS backgrounds. Analysis of six insertions revealed the known sigma S-regulated gene otsA, as well as five novel loci. Each of these genes is maximally expressed in stationary phase, and all but one show evidence of cyclic AMP receptor protein-dependent repression during logarithmic growth which is relieved in stationary phase. For these genes, as well as for the sigma S-regulated spvB plasmid virulence gene, a combination of rpoS overexpression and crp inactivation can result in high-level expression during logarithmic growth. The approach used to identify sigma S-regulated genes in this study provides a general method for the identification of genes controlled by trans-acting regulatory factors.

Amino Acid Sequence↗
PubMed1995

HIV gp120-specific cell-mediated immune responses in mice after oral immunization with recombinant Salmonella.

Salmonella is of great interest as a potential human immunodeficiency virus vaccine vector because of its ability to elicit potent mucosal and systemic immune responses when administered orally. To determine whether such a vaccine could elicit an immune response in mice, plasmids expressing HIV gp120-LAI were introduced into attenuated S. typhimurium. Three serial doses of 10(10) recombinant organisms were administered orally to BALB/c mice at 2-week intervals. Immunized mice but not control mice demonstrated proliferative T cell responses to gp120-LAI, comparable in magnitude to the proliferative responses to Salmonella antigens. Immunized mice had detectable serum and intestinal Salmonella-specific IgA and serum Salmonella-specific IgG. However, no gp120-specific antibody was detected in either serum or intestinal washes. These results indicate that live recombinant Salmonella-based vaccine constructs can induce HIV-specific cellular immune responses in vivo.

AIDS Vaccines↗
PubMed1995

Genetic and redox determinants of nitric oxide cytotoxicity in a Salmonella typhimurium model.

Paradoxically, nitric oxide (NO) has been found to exhibit cytotoxic, antiproliferative, or cytoprotective activity under different conditions. We have utilized Salmonella mutants deficient in antioxidant defenses or peptide transport to gain insights into NO actions. Comparison of three NO donor compounds reveals distinct and independent cellular responses associated with specific redox forms of NO. The peroxynitrite (OONO-) generator 3-morpholinosydnonimine hydrochloride mediates oxygen-dependent Salmonella killing, whereas S-nitrosoglutathione (GSNO) causes oxygen-independent cytostasis, and the NO. donor diethylenetriamine-nitric oxide adduct has no antibacterial activity. GSNO has the greatest activity for stationary cells, a characteristic relevant to latent or intracellular pathogens. Moreover, the cytostatic activity of GSNO may best correlate with antiproliferative or antimicrobial effects of NO, which are unassociated with overt cell injury. dpp mutants defective in active dipeptide transport are resistant to GSNO, implicating heterolytic NO+ transfer rather than homolytic NO. release in the mechanism of cytostasis. This transport system may provide a specific pathway for GSNO-mediated signaling in biological systems. The redox state and associated carrier molecules are critical determinants of NO activity.

Base Sequence↗
PubMed1995

Mutational analysis of SpvR binding to DNA in the regulation of the Salmonella plasmid virulence operon.

The Salmonella plasmid-borne spvR gene encodes a 33-kDa regulatory protein that activates transcription of the spvABCD operon during the stationary phase of bacterial growth. We used gel mobility shift assays to demonstrate that SpvR recognizes a specific target DNA sequence within a 318-bp EcoRI-ApaI fragment upstream of spvA. The addition of unlabeled target DNA to the radioactive labeled DNA-SpvR complex resulted in competitive inhibition of band retardation confirming the specificity of SpvR binding. Introduction of target DNA on a high copy number plasmid into wild-type Salmonella dublin Lane resulted in a substantial decrease of SpvB synthesis, confirming the binding properties of this DNA segment in vivo. Three SpvR mutants were constructed and were shown to abolish the positive regulatory function of SpvR. By site-specific mutagenesis of spvR, three single amino acids within the putative SpvR N-terminal alpha-helix domains were substituted by prolines. This resulted in loss of binding to the spvA promoter sequence and in loss of activation of the spvABCD genes. This study demonstrates that the regulatory function of SpvR is mediated by specific binding to the promoter region of the spvABCD operon.

Amino Acid Sequence↗
PubMed1995

Growth-phase regulation of plasmid virulence genes in Salmonella.

Virulence genes in the genus Salmonella are regulated by growth phase and by environmental signals, which allows a sequential program of expression during infection. Conditions that promote the expression of loci required in systemic infection, including the plasmid-encoded spv genes, are the opposite of the factors that induce genes involved in the invasion of epithelial cells in the gastrointestinal tract.

Animals↗
PubMed1995

Biology and clinical significance of virulence plasmids in Salmonella serovars.

Non-typhoid Salmonella strains containing virulence plasmids are highly associated with bacteria and disseminated infection in humans. These plasmids are found in Salmonella serovars adapted to domestic animals, such as Salmonella dublin and Salmonella choleraesuis, as well as in the widely distributed pathogens Salmonella typhimurium and Salmonella enteritidis. Although virulence plasmids differ between serovars, all contain a highly conserved 8-kb region containing the spv locus that encodes the spvR regulatory gene and four structural spvABCD genes. Studies in mice suggest that the spv genes enhance the ability of Salmonella strains to grow within cells of the reticuloendothelial system. The spv genes are not expressed during exponential growth in vitro but are rapidly induced following entry of Salmonella strains into mammalian cells, including macrophages. Transcription of the spv genes is controlled by the stationary-phase sigma factor RpoS, and mutations in RpoS abolish virulence. These studies suggest that the ability of Salmonella strains to respond to starvation stress in the host tissues is an essential component of virulence.

Animals↗
PubMed1995

NO inhibitions: antimicrobial properties of nitric oxide.

The past decade has witnessed a veritable explosion of interest in the simple molecule nitric oxide (NO) as a vasodilator, neurotransmitter, and antimicrobial agent. NO and other reactive nitrogen intermediates exhibit cytostatic or cytocidal activity against a remarkable breadth of pathogenic microorganisms. Mammalian cells, including human cells, produce nitric oxide both constitutively and inducibly in response to inflammatory stimuli. This review will provide a brief overview of current knowledge regarding the antimicrobial activity of NO and the possible importance of this activity in infection, particularly with regard to intracellular pathogens.

Animals↗
PubMed1995

Central regulatory role for the RpoS sigma factor in expression of Salmonella dublin plasmid virulence genes.

The plasmid virulence genes spvABCD of Salmonella spp. are regulated by SpvR and the stationary-phase sigma factor RpoS. The transcription of spv genes is induced during the post-exponential phase of bacterial growth in vitro. We sought to investigate the relationship between growth phase and RpoS in spv regulation. rpoS insertion mutations were constructed in S. dublin Lane and plasmid-cured LD842 strains, and the mutants were found to be attenuated for virulence and deficient in spv gene expression. We utilized the plasmid pBAD::rpoS to express rpoS independent of the growth phase under the control of the arabinose-inducible araBAD promoter. SpvA expression was induced within 2 h after the addition of 0.1% arabinose, even when bacteria were actively growing. This suggested that the level of RpoS, instead of the growth phase itself, controls induction of the spv genes. However, RpoS did not activate transcription of spvA in the absence of SpvR protein. Using a constitutive tet promoter to express spvR, we found that the spvA gene can be partially expressed in the rpoS mutant, suggesting that RpoS is required for SpvR synthesis. We confirmed that spvR is poorly expressed in the absence of RpoS. With an intact rpoS gene, spvR expression is not dependent on an intact spvR gene but is enhanced by spvR supplied in trans. We propose a model for Salmonella spv gene regulation in which both RpoS and SpvR are required for maximal expression at the spvR and spvA promoters.

Animals↗