| 1. |
- Singh, Bhupender L., et al.
(författare)
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Cefuroxime axetil loaded solid lipid nanoparticles for enhanced activity against S. aureus biofilm
- 2014
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Ingår i: Colloids and Surfaces B. - : Elsevier BV. - 0927-7765 .- 1873-4367. ; 121, s. 92-98
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Tidskriftsartikel (refereegranskat)abstract
- The present research work is focused on the development of solid lipid nanoparticles of cefuroxime axetil (CA-SLN) for its enhanced inhibitory activity against Staphylococcus aureus produced biofilm. CA-SLN was prepared by solvent emulsification/evaporation method using single lipid (stearic acid (SA)) and binary lipids (SA and tristearin (TS)). Process variables such as volume of dispersion medium, concentration of surfactant, homogenization speed and time were optimized. The prepared SLN were characterized for encapsulation efficiency, drug polymer interaction studies (DSC and FT-IR), shape and surface morphology (SEM and AFM), in vitro drug release, stability studies and in vitro anti biofilm activity against S. aureus biofilm. Among the process variables, increased volume of dispersion medium, homogenization speed and time led to increase in particle size whereas increase in surfactant concentration decreased the particle size. SLN prepared using binary lipids exhibited higher entrapment efficiency than the single lipid. DSC and FT-IR studies showed no incompatible interaction between drug and excipients. CA-SLN showed two folds higher anti-biofilm activity in vitro than pristine CA against S. aureus biofilm.
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| 2. |
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| 3. |
- Chai, Qian, et al.
(författare)
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Organization of Ribosomes and Nucleoids in Escherichia coli Cells during Growth and in Quiescence
- 2014
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 289:16, s. 11342-11352
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Tidskriftsartikel (refereegranskat)abstract
- Background: We studied ribosome and nucleoid distribution in Escherichia coli under growth and quiescence. Results: Spatially segregated ribosomes and nucleoids show drastically altered distribution in stationary phase or when treated with drugs affecting translation, transcription, nucleoid-topology, or cytoskeleton. Ribosome inheritance in daughter cells is frequently unequal. Conclusion: Cellular growth processes modulate ribosome and nucleoid distribution. Significance: This provides insight into subcellular organization of molecular machines. We have examined the distribution of ribosomes and nucleoids in live Escherichia coli cells under conditions of growth, division, and in quiescence. In exponentially growing cells translating ribosomes are interspersed among and around the nucleoid lobes, appearing as alternative bands under a fluorescence microscope. In contrast, inactive ribosomes either in stationary phase or after treatment with translation inhibitors such as chloramphenicol, tetracycline, and streptomycin gather predominantly at the cell poles and boundaries with concomitant compaction of the nucleoid. However, under all conditions, spatial segregation of the ribosomes and the nucleoids is well maintained. In dividing cells, ribosomes accumulate on both sides of the FtsZ ring at the mid cell. However, the distribution of the ribosomes among the new daughter cells is often unequal. Both the shape of the nucleoid and the pattern of ribosome distribution are also modified when the cells are exposed to rifampicin (transcription inhibitor), nalidixic acid (gyrase inhibitor), or A22 (MreB-cytoskeleton disruptor). Thus we conclude that the intracellular organization of the ribosomes and the nucleoids in bacteria are dynamic and critically dependent on cellular growth processes (replication, transcription, and translation) as well as on the integrity of the MreB cytoskeleton.
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| 4. |
- Dongre, Mitesh, et al.
(författare)
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Flagella-mediated secretion of a novel Vibrio cholerae cytotoxin affecting both vertebrate and invertebrate hosts
- 2018
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Ingår i: Communications Biology. - : Springer Nature Publishing AG. - 2399-3642. ; 1
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Tidskriftsartikel (refereegranskat)abstract
- Using Caenorhabditis elegans as an infection host model for Vibrio cholerae predator interactions, we discovered a bacterial cytotoxin, MakA, whose function as a virulence factor relies on secretion via the flagellum channel in a proton motive force-dependent manner. The MakA protein is expressed from the polycistronic makDCBA (motility-associated killing factor) operon. Bacteria expressing makDCBA induced dramatic changes in intestinal morphology leading to a defecation defect, starvation and death in C. elegans. The Mak proteins also promoted V. cholerae colonization of the zebrafish gut causing lethal infection. A structural model of purified MakA at 1.9 Å resolution indicated similarities to members of a superfamily of bacterial toxins with unknown biological roles. Our findings reveal an unrecognized role for V. cholerae flagella in cytotoxin export that may contribute both to environmental spread of the bacteria by promoting survival and proliferation in encounters with predators, and to pathophysiological effects during infections.
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| 5. |
- Ghosh, Jaydip, et al.
(författare)
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Sporulation in mycobacteria
- 2009
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 106:26, s. 10781-10786
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Tidskriftsartikel (refereegranskat)
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| 6. |
- Ghosh, Jaydip, et al.
(författare)
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Sporulation in mycobacteria
- 2009
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 106:26, s. 10781-10786
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Tidskriftsartikel (refereegranskat)abstract
- Mycobacteria owe their success as pathogens to their ability to persist for long periods within host cells in asymptomatic, latent forms before they opportunistically switch to the virulent state. The molecular mechanisms underlying the transition into dormancy and emergence from it are not clear. Here we show that old cultures of Mycobacterium marinum contained spores that, upon exposure to fresh medium, germinated into vegetative cells and reappeared again in stationary phase via endospore formation. They showed many of the usual characteristics of well-known endospores. Homologues of well-known sporulation genes of Bacillus subtilis and Streptomyces coelicolor were detected in mycobacteria genomes, some of which were verified to be transcribed during appropriate life-cycle stages. We also provide data indicating that it is likely that old Mycobacterium bovis bacillus Calmette-Guérin cultures form spores. Together, our data show sporulation as a lifestyle adapted by mycobacteria under stress and tempt us to suggest this as a possible mechanism for dormancy and/or persistent infection. If so, this might lead to new prophylactic strategies.
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| 7. |
- Joshi, Bishnu, et al.
(författare)
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Transcriptome Profiling of Staphylococcus aureus Associated Extracellular Vesicles Reveals Presence of Small RNA-Cargo
- 2021
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Ingår i: Frontiers in Molecular Biosciences. - : Frontiers Media S.A.. - 2296-889X. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial extracellular vesicles (EVs) have a vital role in bacterial pathogenesis. However, to date, the small RNA-cargo of EVs released by the opportunistic pathogen Staphylococcus aureus has not been characterized. Here, we shed light on the association of small RNAs with EVs secreted by S. aureus MSSA476 cultured in iron-depleted bacteriologic media supplemented with a subinhibitory dosage of vancomycin to mimic infection condition. Confocal microscopy analysis on intact RNase-treated EVs indicated that RNA is associated with EV particles. Transcriptomic followed by bioinformatics analysis of EV-associated RNA revealed the presence of potential gene regulatory small RNAs and high levels of tRNAs. Among the EV-associated enriched small RNAs were SsrA, RsaC and RNAIII. Our finding invites new insights into the potential role of EV-associated RNA as a modulator of host-pathogen interaction.
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| 8. |
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| 9. |
- Mortezaei, Narges, et al.
(författare)
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Antibodies Change the Mechanics of Adhesion Fimbriae : a Case Study of CS20 Fimbriae Expressed by Enterotoxigenic Escherichia Coli
- 2015
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Ingår i: Biophysical Journal. - : Cell Press. - 0006-3495 .- 1542-0086. ; 108, s. 602-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Enterotoxigenic Escherichia coli (ETEC) express a variety of fimbriae that mediate adhesion to host epithelial cells. It has been shown that the ability of a fimbriated bacterial cell to attach and stay attached to host cells does not merely depend on the adhesin expressed distal of the fimbriae but also the biomechanical properties of the fimbriae are vital for sustained adhesion. Fimbriae can significantly extend under a constant force when exposed to an external force and therefore reduce the load on the adhesin, which is believed to help bacteria to withstand external forces applied by various body defense systems. Thus, it is thought that the fimbrial shaft and adhesin have co-evolved for optimal function when bacteria attach to host cells. To investigate if antibodies, normally found in the intestines, affects the biomechanical properties of fimbriae, we exposed CS20 fimbriae expressed by ETEC to anti-fimbrial antibodies and measured these properties using optical tweezers force spectroscopy. Our data show a change in the force required to extend the fimbriae and that the elasticity is significantly reduced by the presence of antibodies. The reduced elasticity, likely due to cross-linking of fimbrial subunits, could thus be another assignment for antibodies; in addition to their mission in marking bacteria as foreign, our data indicate that antibodies physically compromise fimbrial function. To further confirm interaction of antibodies to their specific target we performed western blot analysis, transmission electron microscopy and immunofluoresence microscopy. In the presence of antibodies, we suggest that our assay and results will be a starting point for further studies aimed at inhibiting bacterial adhesion by antibodies.
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| 10. |
- Mortezaei, Narges, 1985-, et al.
(författare)
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Biomechanical and Structural features of CS2 fimbriae of Enterotoxigenic Escherichia coli
- 2015
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Ingår i: Biophysical Journal. - : Elsevier. - 0006-3495 .- 1542-0086. ; 109:1, s. 49-56
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Tidskriftsartikel (refereegranskat)abstract
- Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrhea worldwide, and infection of children in underdeveloped countries often leads to high mortality rates. Isolated ETEC express a plethora of colonization factors (fimbriae/pili), of which CFA/I and CFA/II that are assembled via the alternate chaperone pathway (ACP), are amongst the most common. Fimbriae are filamentous structures, whose shafts are primarily composed of helically arranged single pilin-protein subunits, with a unique biomechanical capability allowing them to unwind and rewind. A sustained ETEC infection, under adverse conditions of dynamic shear forces, is primarily attributed to this biomechanical feature of ETEC fimbriae. Recent understandings about the role of fimbriae as virulence factors are pointing to an evolutionary adaptation of their structural and biomechanical features. In this work, we investigated the biophysical properties of CS2 fimbriae from the CFA/II group. Homology modelling its major structural subunit CotA reveals structural clues and these are related to the niche in which they are expressed. Using optical tweezers force spectroscopy we found that CS2 fimbriae unwind at a constant force of 10 pN and have a corner velocity of 1300 nm/s, i.e., the velocity at which the force required for unwinding rises exponentially with increased speed. The biophysical properties of CS2 fimbriae assessed in this work classify them into a low-force unwinding group of fimbriae together with the CFA/I and CS20 fimbriae expressed by ETEC strains. The three fimbriae are expressed by ETEC, colonize in similar gut environments, and exhibit similar biophysical features, but differ in their biogenesis. Our observation suggests that the environment has a strong impact on the biophysical characteristics of fimbriae expressed by ETEC.
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| 11. |
- Mortezaei, Narges, et al.
(författare)
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P-fimbriae in the presence of anti-PapA antibodies : new insight of antibodies action against pathogens
- 2013
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- Uropathogenic strains of Escherichia coli establish urinary tract infections by attaching to host epithelial cells using adhesive organelles called fimbriae. Fimbriae are helix-like structures with a remarkable adaptability, offering safeguarding for bacteria exposed to changing fluid forces in the urinary tract. We challenged this property of P-fimbriae by cross-linking their subunits with shaft-specific antibodies and measuring the corresponding force response at a single organelle level. Our data show compromised extension and rewinding of P-fimbriae in the presence of antibodies and reduced fimbrial elasticity, which are important properties of fimbriae contributing to the ability of bacteria to cause urinary tract infections. The reduced elasticity found by cross-linking fimbrial subunits could thus be another assignment for antibodies; in addition to marking bacteria as foreign, antibodies physically compromise fimbrial function. We suggest that our assay and results will be a starting point for further investigations aimed at inhibiting sustained bacterial adhesion by antibodies.
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| 12. |
- Mortezaei, Narges, et al.
(författare)
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Structural and biophysical comparison of UPEC and ETEC adhesion fimbriae
- 2015
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Ingår i: Biophysical Journal. - : Cell Press. - 0006-3495 .- 1542-0086. ; 108:2, suppl 1, s. 527A-527A
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Tidskriftsartikel (refereegranskat)abstract
- Adhesion fimbriae (pili) of uropathogenic and enterotoxigenic Escherichia coli (UPEC and ETEC, respectively) facilitate adherence of the bacteria to target cells. Fimbriae are absolutely necessary for colonization and biofilm formation in the initiation of disease. The types of fimbriae expressed on the bacterial surface vary with the preferred environmental niche of the bacterial strain. For example, UPEC that express P-pili are most frequently associated pyelonephritis, an infection in the upper urinary tract, whereas bacteria that express type 1 fimbriae commonly cause cystitis through infection of the lower urinary tract. In contrast, ETEC expressing CFA/I and CS2 pili are associated with diarrheal diseases, initiating disease in the small intestines.Although expressed in different enviroments, these fimbriae share basic structural and biomechanical features. Structurally, they are all long (1-4 μm), thin (7-8 nm diameter) helix-like filaments that extend from the bacterial surface. Biomechanically, they share the ability to be extended into a thinner filament (2-3 nm diameter) by unwinding of the helical filament under a constant force. However, the force required to unwind is specific to each fimbrial type. In addition, the dependence of the force required to unwind a fimbria on the velocity of this unwinding, (that is, the kinetics of unwinding), is also type-specific and highly variable. These biomechanical parameters are dissimilar for UPEC and ETEC expressed fimbriae, separating them into two distinct groups. Using force spectroscopy data, helical reconstructions from electron microscopy data, and computational simulations, we show in this work how these pronounced biomechanical differences may be beneficial for bacterial survival in a given environment.
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| 13. |
- Mortezaei, Narges, et al.
(författare)
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Structure and function of enterotoxigenic Escherichia coli fimbriae from differing assembly pathways
- 2015
-
Ingår i: Molecular Microbiology. - : John Wiley & Sons. - 0950-382X .- 1365-2958. ; 95:1, s. 116-126
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Tidskriftsartikel (refereegranskat)abstract
- Pathogenic enterotoxigenic Escherichia coli (ETEC) are the major bacterial cause of diarrhea in young children in developing countries and in travelers, causing significant mortality in children. Adhesive fimbriae are a prime virulence factor for ETEC, initiating colonization of the small intestinal epithelium. Similar to other Gram-negative bacteria, ETEC express one or more diverse fimbriae, some assembled by the chaperone-usher pathway and others by the alternate chaperone pathway. Here, we elucidate structural and biophysical aspects and adaptations of each fimbrial type to its respective host niche. CS20 fimbriae are compared with colonization factor antigen I (CFA/I) fimbriae, which are two ETEC fimbriae assembled via different pathways, and with P-fimbriae from uropathogenic E.coli. Many fimbriae unwind from their native helical filament to an extended linear conformation under force, thereby sustaining adhesion by reducing load at the point of contact between the bacterium and the target cell. CFA/I fimbriae require the least force to unwind, followed by CS20 fimbriae and then P-fimbriae, which require the highest unwinding force. We conclude from our electron microscopy reconstructions, modeling and force spectroscopy data that the target niche plays a central role in the biophysical properties of fimbriae that are critical for bacterial pathophysiology.
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| 14. |
- Sharma, Atul, et al.
(författare)
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Helicobacter pylori single-stranded DNA binding protein - functional characterization and modulation of H-pylori DnaB helicase activity
- 2009
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Ingår i: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 276:2, s. 519-531
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Tidskriftsartikel (refereegranskat)abstract
- Helicobacter pylori, an important bacterial pathogen, causes gastric ulcer and gastric adenocarcinoma in humans. The fundamentals of basic biology such as DNA replication are poorly understood in this pathogen. In the present study, we report the cloning and functional characterization of the single-stranded DNA (ssDNA) binding protein from H. pylori. The N-terminal DNA binding domain shows significant homology with E. coli single-stranded DNA binding protein (SSB), whereas the C-terminal domain shows less homology. The overall DNA-binding activity and tetramerization properties, however, remain unaffected. In in vitro experiments with purified proteins, H. pylori (Hp) SSB bound specifically to ssDNA and modulated the enzymatic ATPase and helicase activity of HpDnaB helicase. HpSSB and HpDnaB proteins were co-localized in sharp, distinct foci in exponentially growing H. pylori cells, whereas both were spread over large areas in its dormant coccoid form, suggesting the absence of active replication forks in the latter. These results confirm the multiple roles of SSB during DNA replication and provide evidence for altered replicative metabolism in the spiral and coccoid forms that may be central to the bacterial physiology and pathogenesis.
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| 15. |
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| 16. |
- Singh, Bhupender, et al.
(författare)
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Antibodies damage the resilience of fimbriae, causing them to be stiff and tangled
- 2017
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Ingår i: Journal of Bacteriology. - 0021-9193 .- 1098-5530. ; 199:1
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Tidskriftsartikel (refereegranskat)abstract
- As adhesion fimbriae are a major virulence factor for many pathogenic Gram-negative bacteria, they are also potential targets for antibodies. Fimbriae are commonly required for initiating the colonization that leads to disease, and their success as adhesion organelles lies in their ability to both initiate and sustain bacte- rial attachment to epithelial cells. The ability of fimbriae to unwind and rewind their helical filaments presumably reduces their detachment from tissue surfaces with the shear forces that accompany significant fluid flow. Therefore, the disruption of func- tional fimbriae by inhibiting this resilience should have high potential for use as a vaccine to prevent disease. In this study, we show that two characteristic biome- chanical features of fimbrial resilience, namely, the extension force and the exten- sion length, are significantly altered by the binding of antibodies to fimbriae. The fimbriae that were studied are normally expressed on enterotoxigenic Escherichia coli, which are a major cause of diarrheal disease. This alteration in biomechanical properties was observed with bivalent polyclonal antifimbrial antibodies that recog- nize major pilin subunits but not with the Fab fragments of these antibodies. Thus, we propose that the mechanism by which bound antibodies disrupt the uncoiling of natural fimbria under force is by clamping together layers of the helical filament, thereby increasing their stiffness and reducing their resilience during fluid flow. In addition, we propose that antibodies tangle fimbriae via bivalent binding, i.e., by binding to two individual fimbriae and linking them together. Use of antibodies to disrupt physical properties of fimbriae may be generally applicable to the large number of Gram-negative bacteria that rely on these surface-adhesion molecules as an essential virulence factor.I M P O R T A N C E Our study shows that the resiliency of colonization factor antigen I (CFA/I) and coli surface antigen 2 (CS2) fimbriae, which are current targets for vac- cine development, can be compromised significantly in the presence of antifimbrial antibodies. It is unclear how the humoral immune system specifically interrupts in- fection after the attachment of enterotoxigenic Escherichia coli (ETEC) to the epithe- lial surface. Our study indicates that immunoglobulins, in addition to their well- documented role in adaptive immunity, can mechanically damage the resilience of fimbriae of surface-attached ETEC, thereby revealing a new mode of action. Our data suggest a mechanism whereby antibodies coat adherent and free-floating bacteria to impede fimbrial resilience. Further elucidation of this possible mechanism is likely to inform the development and refinement of preventive vaccines against ETEC diar- rhea.
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| 17. |
- Singh, Bhupender, et al.
(författare)
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Antibody-mediated disruption of the mechanics of CS20 fimbriae of enterotoxigenic Escherichia coli
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
-
Tidskriftsartikel (refereegranskat)abstract
- Preventive vaccines against enterotoxigenic Escherichia coli (ETEC) are being developed, many of which target common fimbrial colonization factors as the major constituent, based on empirical evidence that these function as protective antigens. Particularly, passive oral administration of ETEC anti-fimbrial antibodies prevent ETEC diarrhea. Little is, however, known regarding the specific mechanisms by which intestinal antibodies against ETEC fimbriae function to prevent disease. Using coli surface antigen 20 (CS20) fimbriae as a model ETEC colonization factor, we show using force spectroscopy that anti-fimbrial antibodies diminish fimbrial elasticity by inhibiting their natural capacity to unwind and rewind. In the presence of anti-CS20 antibodies the force required to unwind a single fimbria was increased several-fold and the extension length was shortened several-fold. Similar measurements in the presence of anti-CS20 Fab fragments did not show any effect, indicating that bivalent antibody binding is required to reduce fimbrial elasticity. Based on these findings, we propose a model for an in-vivo mechanism whereby antibody-mediated disruption of the biomechanical properties of CS20 fimbriae impedes sustained adhesion of ETEC to the intestinal mucosal surface. Further elucidation of the role played by intestinal antibodies in mechanical disruption of fimbrial function may provide insights relevant to ETEC vaccine development.
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| 18. |
- Singh, Bhupender, et al.
(författare)
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Asymmetric growth and division in Mycobacterium spp. : compensatory mechanisms for non-medial septa
- 2013
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 88:1, s. 64-76
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Tidskriftsartikel (refereegranskat)abstract
- Mycobacterium spp., rod-shaped cells belonging to the phylum Actinomycetes, lack the Min- and Noc/Slm systems responsible for preventing the placement of division sites at the poles or over the nucleoids to ensure septal assembly at mid-cell. We show that the position for establishment of the FtsZ-ring in exponentially growing Mycobacterium marinum and Mycobacterium smegmatis cells is nearly random, and that the cells often divide non-medially, producing two unequal but viable daughters. Septal sites and cellular growth disclosed by staining with the membrane-specific dye FM4-64 and fluorescent antibiotic vancomycin (FL-Vanco), respectively, showed that many division sites were off-centre, often over the nucleoids, and that apical cell growth was frequently unequal at the two poles. DNA transfer through the division septum was detected, and translocation activity was supported by the presence of a putative mycobacterial DNA translocase (MSMEG2690) at the majority of the division sites. Time-lapse imaging of single live cells through several generations confirmed both acentric division site placement and unequal polar growth in mycobacteria. Our evidence suggests that post-septal DNA transport and unequal polar growth may compensate for the non-medial division site placement in Mycobacterium spp.
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| 19. |
- Singh, Bhupender
(författare)
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Dynamic Organization of Molecular Machines in Bacteria
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bacterial cells were once treated as membrane-enclosed bags of cytoplasm: a homogeneous, undifferentiated suspension in which polymers (proteins, nucleic acids, etc.) and small molecules diffused freely to interact with each other. Biochemical studies have determined the molecular mechanisms underlying the biological processes of metabolism, replication and transcription-translation, etc. However, recent advancements in optical techniques armed with fluorescent tags for proteins and nucleic acids have increased our ability to peer into the interior of live bacterial cells. This has revealed an organized layout of multi-protein complexes, or molecular machines, dedicated to specific functions at defined sub-cellular locations; the timing of their assembly and/or rates of their activity being determined by available nutrition and environmental signals from the niche occupied by the organism.In the present study, we have attempted to identify the intracellular location and organization of the molecular machines assembled for protein synthesis (ribosomes), DNA replication (replisomes) and cell division (divisome) in different bacteria. We have used the model system Escherichia coli as well as Helicobacter pylori and mycobacterial strains (Mycobacterium marinum and Mycobacterium smegmatis), which grow at different rates and move to dormancy late into stationary phaseBacterial nucleoid plays a major role in organizing the location and movement of active ribosomes, replisomes and placement of divisome. While the active ribosomes appear to follow the dynamic folds of the bacterial nucleoid during cell growth in E. coli, inactive ribosomes appear to accumulate near the periphery. The replisome in H. pylori was visualized as a sharp, single focus upon SSB and DnaB co-localization in growing helical rods but disassembled into diffused fluorescence when the cells attained non-replicative coccoid stage. Our investigation into mycobacterial life-cycle revealed unique features such as an absence of a dedicated mid-cell site for divisome assembly and endosporulation upon entry into stationary phase.In brief, we present the cell cycle-dependent subcellular organization of molecular machines in bacteria.
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| 20. |
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| 21. |
- Singh, Bhupender, et al.
(författare)
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Growth, cell division and sporulation in mycobacteria
- 2010
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Ingår i: Antonie van Leeuwenhoek. International Journal of General and Molecular Microbiology. - : Springer Science and Business Media LLC. - 0003-6072 .- 1572-9699. ; 98:2, s. 165-177
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Tidskriftsartikel (refereegranskat)abstract
- Bacteria have the ability to adapt to different growth conditions and to survive in various environments. They have also the capacity to enter into dormant states and some bacteria form spores when exposed to stresses such as starvation and oxygen deprivation. Sporulation has been demonstrated in a number of different bacteria but Mycobacterium spp. have been considered to be non-sporulating bacteria. We recently provided evidence that Mycobacterium marinum and likely also Mycobacterium bovis bacillus Calmette-Gu,rin can form spores. Mycobacterial spores were detected in old cultures and our findings suggest that sporulation might be an adaptation of lifestyle for mycobacteria under stress. Here we will discuss our current understanding of growth, cell division, and sporulation in mycobacteria.
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| 22. |
- Wiklund, Krister, et al.
(författare)
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A drag force interpolation model for capsule-shaped cells in fluid flows near a surface
- 2018
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Ingår i: Microbiology. - : Microbiology Society. - 1350-0872 .- 1465-2080. ; 164:4, s. 483-494
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Tidskriftsartikel (refereegranskat)abstract
- We report an interpolation model to calculate the hydrodynamic force on tethered capsule-shaped cells in micro-fluidic flows near a surface. Our model is based on numerical solutions of the full Navier–Stokes equations for capsule-shaped objects considering their geometry, aspect ratio and orientation with respect to fluid flow. The model reproduced the results from computational fluid dynamic simulations, with an average error of <0.15 % for objects with an aspect ratio up to 5, and the model exactly reproduced the Goldman approximation of spherical objects close to a surface. We estimated the hydrodynamic force imposed on tethered Escherichia coli cells using the interpolation model and approximate models found in the literature, for example, one that assumes that E. coli is ellipsoid shaped. We fitted the 2D-projected area of a capsule and ellipsoid to segmented E. coli cells. We found that even though an ellipsoidal shape is a reasonable approximation of the cell shape, the capsule gives 4.4 % better agreement, a small difference that corresponds to 15 % difference in hydrodynamic force. In addition, we showed that the new interpolation model provides a significantly better agreement compared to estimates from commonly used models and that it can be used as a fast and accurate substitute for complex and computationally heavy fluid dynamic simulations. This is useful when performing bacterial adhesion experiments in parallel-plate flow channels. We include a MATLAB script that can track cells in a video time-series and estimate the hydrodynamic force using our interpolation formula.
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| 23. |
- Zakrisson, Johan, et al.
(författare)
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Detecting Bacterial Surface Organelles on Single Cells using Optical Tweezers
- 2016
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 32:18, s. 4521-4529
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial cells display a diverse array of surface organelles that are important for a range of processes such as: intercellular communication, motility and adhesion leading to biofilm formation, infections and bacterial spread. More specifically, attachment to host cells by Gram-negative bacteria are mediated by adhesion pili, which are nm wide and µm long fibrous organelles. Since these pili are significantly thinner than the wavelength of visible light, they cannot be detected using standard light microscopy techniques. At present, there is no fast and simple method available to investigate if a single cell expresses pili while keeping the cell alive for further studies. In this study, we present a method to determine the presence of pili on a single bacterium. The protocol involves imaging the bacterium to measure its size, followed by predicting the fluid drag based on its size using an analytical model, and thereafter oscillating the sample while a single bacterium is trapped by an optical tweezer to measure its effective fluid drag. Comparison between the predicted and the measured fluid drag thereby indicate the presence of pili. Herein, we verify the method using polymer coated silica microspheres and Escherichia coli bacteria expressing adhesion pili. Our protocol, can in real time and within seconds assist single cell studies by distinguishing between piliated and non-piliated bacteria.
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| 24. |
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