3411.
Mackiewicz, Barbara, et al.
(författare)
Respiratory Disorders In Two Workers Of Customs Depositories Occupationally Exposed To Mouldy Tobacco
2008
Ingår i: Annals of Agricultural and Environmental Medicine. - 1898-2263. ; 15:2, s. 317-322
Tidskriftsartikel (refereegranskat) abstract
Work-related respiratory symptoms, including dyspnoea, cough, fever, tiredness and malaise, were recorded in two customs officers employed in 2 depositories of confiscated cigarettes, of which one showed signs of dampness. Microbiological sampling of the air and the cigarettes stored in a damp depository revealed the presence of potentially pathogenic fungi and bacteria and the biochemical markers of bacterial lipopolysaccharide and fungal biomass. The Penicillium species (P. simplicissimum, P. inflatum, P commune) dominated in the damp depository, while in the other one Aspergillus fumigatus was prevalent. The patients under study did not show a specific sensitization to microbial allergens in the precipitin test, the test for inhibition of leukocyte migration and the bronchial provocation challenge, except for a weak reaction to fungal allergens in the test for inhibition of leukocyte migration. Moreover, one patient responded with subjective symptoms after exposure to inhalation of increased doses of Penicillium simplicissimum antigen. Both cases were diagnosed as a specific form of organic dust toxic syndrome (ODTS). It is hypothesized that the symptoms were evoked most probably by the non-specific action of low molecular fungal metabolites, such as mycotoxins or VOCs (volatile organic compounds), with the possible contribution of bacterial endotoxin. However, as there is no a direct proof to support this presumption, and the effects of nicotine and other tobacco constituents cannot be excluded, further studies are needed to elucidate etiopathogenesis of the disorders associated with the exposure to stored tobacco.
3412.
Macrae, Fraser L., et al.
(författare)
A fibrin biofilm covers blood clots and protects from microbial invasion
2018
Ingår i: Journal of Clinical Investigation. - 0021-9738. ; 128:8, s. 3356-3368
Tidskriftsartikel (refereegranskat) abstract
Hemostasis requires conversion of fibrinogen to fibrin fibers that generate a characteristic network, interact with blood cells, and initiate tissue repair. The fibrin network is porous and highly permeable, but the spatial arrangement of the external clot face is unknown. Here we show that fibrin transitioned to the blood-air interface through Langmuir film formation, producing a protective film confining clots in human and mouse models. We demonstrated that only fibrin is required for formation of the film, and that it occurred in vitro and in vivo. The fibrin film connected to the underlying clot network through tethering fibers. It was digested by plasmin, and formation of the film was prevented with surfactants. Functionally, the film retained blood cells and protected against penetration by bacterial pathogens in a murine model of dermal infection. Our data show a remarkable aspect of blood clotting in which fibrin forms a protective film covering the external surface of the clot, defending the organism against microbial invasion.
3413.
Macvanin, Mirjana, et al.
(författare)
Fusidic acid-resistant EF-G perturbs the accumulation of ppGpp
2000
Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 37:1, s. 98-107
Tidskriftsartikel (refereegranskat) abstract
Reductions in growth rate caused by fusidic acid-resistant EF-G mutants in Salmonella typhimurium correlate strongly with increased mean cell size. This is unusual because growth rate and cell size normally correlate positively. The global transcription regulator molecule ppGpp has a role in co-ordinating growth rate and division, and its basal level normally correlates inversely with cell size at division. We show that fusidic acid-resistant EF-G mutants have perturbed ppGpp basal levels during steady-state growth and perturbed induced levels during starvation. One mutation, fusA1, associated with the slowest growth rate and largest cell size, causes a reduction in the basal level of ppGpp to one-third of that found in the wild-type strain. Other fusA mutants with intermediate or wild-type growth rates and cell sizes have either normal or increased basal levels of ppGpp. There is an inverse relationship between the basal level of ppGpp in vivo and the degree to which translation dependent on mutant EF-G is inhibited by ppGpp in vitro. This enhanced interaction between mutant EF-G and ppGpp correlates with an increased KM for GTP. Our results suggest that mutant EF-G modulates the production of ppGpp by the RelA (PSI) pathway. In conclusion, fusidic acid-resistant EF-G mutations alter the level of ppGpp and break the normal relationship between growth rate and cell size at division. It would not be surprising if other phenotypes associated with these mutants, such as loss of virulence, were also related to perturbations in ppGpp levels effected through altered transcription patterns.
3414.
Macvanin, Mirjana, et al.
(författare)
Fusidic acid-resistant mutants of Salmonella enterica serovar Typhimurium with low fitness in vivo are defective in RpoS induction
2003
Ingår i: Antimicrobial Agents and Chemotherapy. - 0066-4804 .- 1098-6596. ; 47:12, s. 3743-3749
Tidskriftsartikel (refereegranskat) abstract
Mutants of Salmonella enterica serovar Typhimurium resistant to fusidic acid (Fusr) have mutations in fusA, the gene encoding translation elongation factor G (EF-G). Most Fusr mutants have reduced fitness in vitro and in vivo, in part explained by mutant EF-G slowing the rate of protein synthesis and growth. However, some Fusr mutants with normal rates of protein synthesis still suffer from reduced fitness in vivo. As shown here, Fusr mutants could be similarly ranked in their relative fitness in mouse infection models, in a macrophage infection model, in their relative hypersensitivity to hydrogen peroxide in vivo and in vitro, and in the amount of RpoS production induced upon entry into the stationary phase. We identify a reduced ability to induce production of RpoS (sigmas) as a defect associated with Fusr strains. Because RpoS is a regulator of the general stress response, and an important virulence factor in Salmonella, an inability to produce RpoS in appropriate amounts can explain the low fitness of Fusr strains in vivo. The unfit Fusr mutants also produce reduced levels of the regulatory molecule ppGpp in response to starvation. Because ppGpp is a positive regulator of RpoS production, we suggest that a possible cause of the reduced levels of RpoS is the reduction in ppGpp production associated with mutant EF-G. The low fitness of Fusr mutants in vivo suggests that drugs that can alter the levels of global regulators of gene expression deserve attention as potential antimicrobial agents.
3415.
Macvanin, Mirjana, 1973-
(författare)
The Physiological Cost of Antibiotic Resistance
2003
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Becoming antibiotic resistant is often associated with fitness costs for the resistant bacteria. This is seen as a loss of competitiveness against the antibiotic-sensitive wild-type in an antibiotic-free environment. In this study, the physiological alterations associated with fitness cost of antibiotic resistance in vitro (in the laboratory medium), and in vivo (in a mouse infection model), are identified in the model system of fusidic acid resistant (FusR) Salmonella enterica serovar Typhimurium.FusR mutants have mutations in fusA, the gene that encodes translation elongation factor G (EF-G). FusR EF-G has a slow rate of regeneration of active EF-G·GTP off the ribosome, resulting in a slow rate of protein synthesis. The low fitness of FusR mutants in vitro, and in vivo, can be explained in part by a slow rate of protein synthesis and resulting slow growth. However, some FusR mutants with normal rates of protein synthesis still suffer from reduced fitness in vivo. We observed that FusR mutants have perturbed levels of the global regulatory molecule ppGpp. One consequence of this is an inefficient induction of RpoS, a regulator of general stress reponse and an important virulence factor for Salmonella. In addition, we found that FusR mutants have reduced amounts of heme, a co-factor of catalases and cytochromes. As a consequence of the heme defect, FusR mutants have a reduced ability to withstand oxidative stress and a low rate of aerobic respiration.The pleiotropic phenotypes of FusR mutants suggest that antibiotic resistance can be associated with broad changes in bacterial physiology. Knowledge of physiological alterations that reduce the fitness of antibiotic-resistant mutants can be useful in identifying novel targets for antimicrobial agents. Drugs that alter the levels of global transcriptional regulators such as ppGpp or RpoS deserve attention as potential antimicrobial agents. Finally, the observation that FusR mutants have increased sensitivity to several unrelated classes of antibiotics suggests that the identification of physiological cost of resistance can help in optimizing treatment of resistant bacterial populations.
3416.
Maddocks, Sarah E., et al.
(författare)
Streptococcus pyogenes antigen I/II-family polypeptide AspA shows differential ligand-binding properties and mediates biofilm formation
2011
Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 81:4, s. 1034-1049
Tidskriftsartikel (refereegranskat) abstract
The streptococcal antigen I/II (AgI/II)-family polypeptides are cell wall-anchored adhesins expressed by most indigenous oral streptococci. Proteins sharing 30-40% overall amino acid sequence similarities with AgI/II-family proteins are also expressed by Streptococcus pyogenes. The S. pyogenes M28_Spy1325 polypeptide (designated AspA) displays an AgI/II primary structure, with alanine-rich (A) and prolinerich (P) repeats flanking a V region that is projected distal from the cell. In this study it is shown that AspA from serotype M28 S. pyogenes, when expressed on surrogate host Lactococcus lactis, confers binding to immobilized salivary agglutinin gp-340. This binding was blocked by antibodies to the AspA-VP region. In contrast, the N-terminal region of AspA was deficient in binding fluid-phase gp-340, and L. lactis cells expressing AspA were not agglutinated by gp-340. Deletion of the aspA gene from two different M28 strains of S. pyogenes abrogated their abilities to form biofilms on saliva-coated surfaces. In each mutant strain, biofilm formation was restored by trans complementation of the aspA deletion. In addition, expression of AspA protein on the surface of L. lactis conferred biofilm-forming ability. Taken collectively, the results provide evidence that AspA is a biofilm-associated adhesin that may function in host colonization by S. pyogenes.
3417.
Magalhaes, Ana, et al.
(författare)
Muc5ac gastric mucin glycosylation is shaped by FUT2 activity and functionally impacts Helicobacter pylori binding
2016
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
Tidskriftsartikel (refereegranskat) abstract
The gastrointestinal tract is lined by a thick and complex layer of mucus that protects the mucosal epithelium from biochemical and mechanical aggressions. This mucus barrier confers protection against pathogens but also serves as a binding site that supports a sheltered niche of microbial adherence. The carcinogenic bacteria Helicobacter pylori colonize the stomach through binding to host glycans present in the glycocalyx of epithelial cells and extracellular mucus. The secreted MUC5AC mucin is the main component of the gastric mucus layer, and BabA-mediated binding of H. pylori to MUC5AC confers increased risk for overt disease. In this study we unraveled the O-glycosylation profile of Muc5ac from glycoengineered mice models lacking the FUT2 enzyme and therefore mimicking a non-secretor human phenotype. Our results demonstrated that the FUT2 determines the O-glycosylation pattern of Muc5ac, with Fut2 knock-out leading to a marked decrease in alpha 1,2-fucosylated structures and increased expression of the terminal type 1 glycan structure Lewis-a. Importantly, for the first time, we structurally validated the expression of Lewis-a in murine gastric mucosa. Finally, we demonstrated that loss of mucin FUT2-mediated fucosylation impairs gastric mucosal binding of H. pylori BabA adhesin, which is a recognized feature of pathogenicity.
3418.
Magalhaes, Ana, et al.
(författare)
The glycan receptors of Helicobacter pylori : decoding the pathways underlying gastric glycophenotype modulation
2016
Ingår i: Glycobiology. - : Oxford University Press (OUP). - 0959-6658 .- 1460-2423. ; 26:12, s. 1401-1402
Tidskriftsartikel (refereegranskat) abstract
The gastrointestinal tract is covered by a complex extracellular mucus layer that protects the gastric epithelium fromexternal aggressions such as chemical agents, microorganismsand shear stress. Although this mucus barrier confers protec-tion against certain pathogens, it may also provide a niche formicrobial binding.Helicobacter pyloriexploits the host glycoconjugates present in the gastric mucus layer and lining thesurface epithelium of the gastric mucosa to colonize the stomach. Infection can persist for decades promoting chronicinflammation, and in a subset of individuals lesions cansilently progress to cancer. The secreted MUC5AC mucin isthe main component of the gastric mucus layer, andH. pyloriBabA-mediated binding to MUC5AC confers increased riskfor overt disease. We have shown that FUT2 determines theO-glycosylation pattern of Muc5ac, with Fut2 knock-outleading to a marked decrease inα1,2-fucosylated structuresand increased expression of the terminal type 1 glycan structure Lewisa. Importantly, for thefirst time, we structurallyvalidated the expression of Lewisain murine gastric mucosa(1). We further demonstrated that loss of mucin FUT2-mediated fucosylation impairs gastric mucosal binding ofH.pyloriBabA adhesin, which is a recognized feature of patho-genicity. UponH. pyloriinfection,concomitantly with tissueinflammation, there is a remodeling of the gastric glycopheno-type. We showed that increased expression of sialyl-Lewisa/xantigens is due to transcriptional up-regulation of theB3GNT5,B3GALT5,andFUT3genes. In addition, weobserved thatH. pyloriinfected individuals present a markedgastric local pro-inflammatory signature with significantlyhigher TNF-αlevels and demonstrated that TNF-induced activation of the NF-kappaB pathway results in B3GNT5 up-regulation (2). Furthermore, we showed that this gastric glycosylation shift, characterized by increased sialylation pat-terns, favors SabA-mediatedH. pyloriattachment to humaninflamed gastric mucosa. Our data provides clinically relevantinsights into the regulatory mechanisms underlyingH. pylorimodulation of host glycosylation machinery, and phenotypicalterations crucial for life-long infection and gastric disease.
3419.
Magnius, L., et al.
(författare)
ICTV Virus Taxonomy Profile: Deltavirus
2018
Ingår i: Journal of General Virology. - : Microbiology Society. - 0022-1317 .- 1465-2099. ; 99:12, s. 1565-1566
Tidskriftsartikel (refereegranskat) abstract
Hepatitis delta virus, the only member of the only species in the genus Deltavirus, is a unique human pathogen. Its -1.7 kb circular negative-sense RNA genome encodes a protein, hepatitis delta antigen, which occurs in two forms, small and large, both with unique functions. Hepatitis delta virus uses host RNA polymerase II to replicate via double rolling circle RNA synthesis. Newly synthesized linear RNAs are circularized after autocatalytic cleavage and ligation. Hepatitis delta virus requires the envelope of the helper virus, hepatitis B virus (family Hepadnaviridae), to produce infectious particles. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of Deltavirus which is available at www.ictv.global/report/deltavirus.
3420.
Magnusson, Lisa U., 1975, et al.
(författare)
Identical, independent, and opposing roles of ppGpp and DksA in Escherichia coli.
2007
Ingår i: Journal of bacteriology. - 0021-9193. ; 189:14, s. 5193-202
Tidskriftsartikel (refereegranskat) abstract
The recent discovery that the protein DksA acts as a coregulator of genes controlled by ppGpp led us to investigate the similarities and differences between the relaxed phenotype of a ppGpp-deficient mutant and the phenotype of a strain lacking DksA. We demonstrate that the absence of DksA and ppGpp has similar effects on many of the observed phenotypes but that DksA and ppGpp also have independent and sometimes opposing roles in the cell. Specifically, we show that overexpression of DksA can compensate for the loss of ppGpp with respect to transcription of the promoters P(uspA), P(livJ), and P(rrnBP1) as well as amino acid auxotrophy, cell-cell aggregation, motility, filamentation, and stationary phase morphology, suggesting that DksA can function without ppGpp in regulating gene expression. In addition, ppGpp and DksA have opposing effects on adhesion. In the course of our analysis, we also discovered new features of the relaxed mutant, namely, defects in cell-cell aggregation and motility.
