Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Bacterial Outer Membrane”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed2026

Bacterial Outer Membrane Vesicles in Colorectal Cancer: Interdomain Communication Hubs in Pathogenesis and Immunotherapy.

The complex interaction between the intestinal microbiota and host mucosal immunity plays a defining role in colorectal cancer (CRC) development and therapeutic outcomes. Recently, bacterial outer membrane vesicles (OMVs)-nano-sized, lipid-bilayered extracellular particulates released by both commensal and pathogenic microorganisms-have emerged as critical long-range signaling vehicles within the gut. This review provides a comprehensive synthesis of the dual functionalities of OMVs in CRC pathogenesis and oncology. Mechanistically, pathogenic OMVs cross compromised mucosal barriers to drive horizontal gene transfer (HGT) of chimeric episomes, such as SPHINX DNAs and Bovine Meat and Milk Factors (BMMFs), thereby promoting genomic instability and neoplastic transformation. Conversely, there is a paradigm shift toward exploiting next-generation probiotic and engineered OMVs as highly tunable therapeutic platforms. By combining cutting-edge bioengineering strategies-such as biomimetic mineralization to neutralize local tissue acidity and chemotherapeutic packaging-these nanovectors effectively reprogram the immunosuppressive tumor microenvironment (TME). Specifically, optimized OMVs modulate macrophage polarization from an M2 to an M1 phenotype and stimulate CXCL10-mediated CD8+ T-cell infiltration, effectively turning immunologically "cold" tumors "hot." Finally, the great translational challenges regarding systemic endotoxicity, scalability, and target delivery, providing a strategic approach for the integration of OMV-based platforms into synergistic immune checkpoint inhibition regimens.

Colon cancer↗
PubMed1976

How does lysozyme penetrate through the bacterial outer membrane?

Lysozyme fails to penetrate through the outer membrane of stationary phase cells of Escherichia coli when it is simply added to suspensions of plasmolyzed cells. Lysozyme penetrates the outer membrane only when these cells are exposed to a mild osmotic shock in the presence of EDTA and lysozyme. In the presence of Mg2+, the outer membrane is stabilized sufficiently so that there is no lysozyme penetration during osmotic shock. If Mg2+ is added after an osmotic shock has been used to cause lysozyme to penetrate a destabilized outer membrane, the outer membrane is stabilized once again. In this case however, cells are converted to spheroplasts by the lysozyme which has gained access to the murein layer prior to the addition of Mg2+. Mg2+ stabilizes the outer membranes of these spheroplasts sufficiently so that they remain immune to lysis even in the absence of osmotic stabilizers such as sucrose. These results are discussed in terms of current information on the structure of the murein layer and the outer membrane.

Biological Transport↗
PubMed1979

The bacterial outer-membrane permeability of beta-lactam antibiotics.

Two penicillins and 5 cephalosporins were evaluated for their ability to pass through the outer-membranes of Proteus morganii, Citrobacter freundii and Escherichia coli. Cefazolin, ceftezole and cephaloridine showed high permeability through the outer-membranes of these Gram-negative bacteria. Benzylpenicillin and cephalothin, on the contrary, showed low permeability. The outer-membrane permeability of ampicillin and cephalexin varied from species to species. C. freundii was found to have the highest barrier against both the penicillins and the cephalosporins, and E. coli appeared to have a low barrier against the cephalosporins. The hydrophobic character of the beta-lactam antibiotics, which was estimated by a reversed-phase thin-layer chromatography was closely related to the outer-membrane permeability. In general, the more hydrophilic antibiotic showed the higher outer-membrane permeability. However, cephaloridine, the most lipophilic compound among the antibiotics tested, showed good permeability.

Anti-Bacterial Agents↗
PubMed1976

Ultrastructure and life cycle of the lipid-containing bacteriophage phi 6.

An electron microscopic study of the lipid-containing bacteriophage phi 6 revealed an electron dense compact inner core of 30 nm in diam., which apparently contains the nucleic acid of the virus. This inner particle is surrounded by a complex polyhedral capsid with an outer diam. of 50 nm. Outside this is the envelope, which gives the virus a total diam. of 65 to 75 nm. The envelope, which has a thickness of a unit membrane, could be removed by treating the phage with Triton X-100. A definite structure is seen inside the envelope of the phage tail. In infection, phages are attached by their tails to the host cell pili. Occasional pili with a few attached phages were seen in a phage resistant mutant. In the course of the infection phages were also seen attached to the outer membrane of the cell. In a phage-tolerant mutant many normal-looking pili with adsorbed phages were visible, but we could never see phage-cell membrane associations. The membrane of the phage appears to fuse with the bacterial outer membrane and 50 nm virus particles could be seen in the periplasmic space of the bacterium, probably attached to the cytoplasmic membrane. Newly formed 50 nm particles appeared 45 min post infection (p.i.) cnetrally in the host cell. Assembly of the envelope also began at this time and by 80 minutes p.i. all the 50 nm particles were covered by the virus membrane. At no stage were phages seen in the periphery of the bacterium. Mature phages were finally released by a rupture of the host cell without spheroplast formation.

Adsorption↗
PubMed1976

Association of the folded chromosome with the cell envelope of E. coli: characterization of the proteins at the DNA-membrane attachment site.

Gentle lysis of E. coli cells in the presence of a DNA counterion (either 1.0 M NaCl or 5 mM spermidine) permits the isolation of the folded intact bacterial chromosome associated with membrane fragments. Most of the proteins in these chromosomes are also found in purified membrane preparations, and they can be identified as belonging to either the inner or the outer bacterial membrane. Ultraviolet irradiation of the membrane-attached chromosomes causes the formation of a stable complex between two inner membrane proteins (molecular weight 80,000 and 56,000 daltons) and 5-bromodeoxyuridine (BrdU)-substituted DNA. The photochemical attachment of BrdU-substituted DNA to specific membrane proteins suggests that these proteins may be bound to the DNA in vivo. Such DNA-membrane-binding proteins may have a role in the attachment of the folded chromosome to the bacterial envelope.

Bacterial Proteins↗
PubMed1977

Alteration of the Escherichia coli membrane by addition of bacteriophage T4 protein synthesized after infection.

Many T4-induced proteins were found associated with the Escherichia coli membrane during infection. Some of these were apparently ionically bound, but many could be identified as integral parts of the inner and outer bacterial membranes by their selective solubilities in guanidine or Sarkosyl. The synthesis and insertion of these proteins into the bacterial membrane were temporally controlled and, once in the membrane, these proteins were stably integrated. Host membrane protein synthesis continued after infection of non-UV-irradiated cells, but was not present, if the cells were irradiated. There were no major redistribution or loss of bacterial proteins from E. coli membranes as a consequence of T4 infection.

Cell Membrane↗
PubMed2026

Phage vB_KpnM_NB cocktail synergizing with amikacin in inhibiting persister cells of Klebsiella pneumoniae.

UNLABELLED: The emergence of multidrug-resistant Klebsiella pneumoniae (KPN) and antibiotic-tolerant persister cells poses a significant challenge to existing anti-infection therapies. Given the urgent need for sustainable alternatives to antibiotics, phage cocktails are emerging as a promising alternative to control K. pneumoniae infections. We isolated three lytic phages vB_KpnM_NB (1-3) from Ningbo environmental samples, classified them into the Drexlerviridae family, and determined the biological characteristics of two representative phages. Genomic analysis confirmed that these phages are closely related and lack resistance and virulence genes, ensuring biosafety. Subsequently, a stable KPN persister model was established using amikacin, with a biphasic killing pattern observed during treatment. At a multiplicity of infection of 10, the phage cocktail eliminated 99.00% of persister cells, while individual phages were less effective. The phage cocktail also inhibited persister-derived biofilm formation, showing improved results when combined with amikacin. This combination significantly reduced capsule polysaccharide production in persisters, weakening the outer membrane barrier. These findings demonstrate that the phage cocktail-amikacin combination effectively targets planktonic cells, persister cells, and biofilms, providing a promising strategy against persisters and recurrent K. pneumoniae infections. IMPORTANCE: This study fills the critical gap in understanding how phage cocktails synergize with amikacin against K. pneumoniae persister cells. By constructing a highly specific phage vB_KpnM_NB cocktail, establishing a stable persister model, and performing in vitro bactericidal and biofilm assays, we demonstrate that the cocktail effectively eliminates planktonic cells, persisters, and biofilms. We clarify the core synergistic mechanism: inhibiting capsular polysaccharide synthesis, improving phage adsorption, and disrupting the bacterial outer membrane barrier. These findings provide experimental evidence for the prevention and control of multidrug-resistant and carbapenem-resistant K. pneumoniae persister infections, establishing a safe and effective phage-antibiotic combination therapy. The results are crucial for addressing antibiotic tolerance and controlling chronic, recurrent infections. They hold significant theoretical and translational value for the treatment of refractory infections in clinical settings and offer new insights into the development of novel antimicrobial strategies.

Klebsiella pneumoniae↗
PubMed1975

Biochemical evidence for the reversed polarity of the outer membrane of the bacterial forespore.

Measurement of certain membrane-bound enzymic activities was used to study the orientation of the outer membrane of the double-membraned forespore of Bacillus megaterium KM. 2. Adenosine triphosphatase, NADH dehydrogenase and L-malate intact protoplasts, but were readily detected in intact stage II or IV forespores, consistent with reversed polarity of the outer forespore membrane relative to the mother-cell plasma membrane. 3. Measurement of NADH oxidase activity revealed that intact stage III forespores had the same high affinity for NADH as protoplast membrane preparations and protoplast lystates, consistent with ready access of NADH to oxidation sites on the outer forespores membrane. 4. Forespores and protoplasts showed osmometric behaviour in solutions of non-permanent solutes consistent with the presence of an intact permeability barrier in these structures.

Adenosine Triphosphatases↗
PubMed1978

Precursors of three exported proteins in Escherichia coli.

Arabinose-binding protein, maltose-binding protein, and lambda receptor are synthesized in vitro on membrane-bound polysomes from Escherichia coli. All three proteins are exported from the cytoplasm of E. coli and all three are made in vitro in a form a few thousand daltons larger than the authentic protein. The larger form of arabinose-binding protein is also detected in vivo by pulse labeling. It is concluded that the larger forms of the exported proteins are precursors containing an extra sequence. In contrast to the above, when the intracellular protein elongation factor Tu is synthesized in vitro on free polysomes, it is not detectably larger than the authentic form.

Arabinose↗
PubMed1978

Streptococcal M protein extracted by nonionic detergent. III. Correlation between immunological cross-reactions and structural similarities with implications for antiphagocytosis.

Three immunologically cross-reactive and non-cross-reactive streptococcal M proteins were analyzed by a chromatographic tryptic peptide mapping system. The results indicate that cross-reactions correlate with the extent of structural similarity among the M protein molecules analyzed. The data also reveal that free lysine is released by the action of trypsin from these three M proteins, suggesting a common lys-lys or arg-lys sequence. In addition, only one peptide has been found to be common within all three M types. This limited structural relatedness among the three M proteins examined indicates that sequence variation plays a major role in the immunological specificity of the M antigens. However, despite sequence variation, all M protein molecules have a common antiphagocytic activity. The fact that no common opsonic antibody has yet been found, even against limited M types, argues against this biological activity being solely the result of a common sequence. Based on these data, it is suggested that the antiphagocytic effect of M protein may be due to a conformationally created environment on the surface of the molecule which is selected by both immunological and biological pressure.

Antigens, Bacterial↗
PubMed1979

Inhibition of alternative complement pathway opsonization by group A streptococcal M protein.

Group A streptococcal M protein is known to be antiphagocytic; however, the exact basis for this property has not been established. In this study the hypothesis was tested that cell wall--associated M protein inhibits phagocytosis by interfering with bacterial opsonization. Two strains of group A Streptococcus pyogenes, CS44 (M+) and CS64 (an M- variant of CS44), were radiolabeled, and after incubation in serum these organisms were exposed to human polymorphonuclear leukocytes. Phagocytosis was quantitated by measurement of leukocyte-associated radioactivity. The contributions of complement and of immunoglobulin to streptococcal opsonization were evaluated by use of serum from a variety of sources. The results revealed that the M- strain was efficiently opsonized via the alternative complement pathway in a relative absence of immunoglobulins. In contrast, the M+ strain was poorly opsonized by all sera tested. These findings suggest that streptococcal M protein in some way prevents bacterial opsonization via the alternative complement pathway and that this property of M protein may partly explain its antiphagocytic characteristic.

Antigens, Bacterial↗
PubMed2005

Bordetella pertussis risA, but not risS, is required for maximal expression of Bvg-repressed genes.

Expression of virulence determinants by Bordetella pertussis, the primary etiological agent of whooping cough, is regulated by the BvgAS two-component regulatory system. The role of a second two-component regulatory system, encoded by risAS, in this process is not defined. Here, we show that mutation of B. pertussis risA does not affect Bvg-activated genes or proteins. However, mutation of risA resulted in greatly diminished expression of Bvg-repressed antigens and decreased transcription of Bvg-repressed genes. In contrast, mutation of risS had no effect on the expression of Bvg-regulated molecules. Mutation of risA also resulted in decreased bacterial invasion in a HeLa cell model. However, decreased invasion could not be attributed to the decreased expression of Bvg-repressed products, suggesting that mutation of risA may affect the expression of a variety of genes. Unlike the risAS operons in B. parapertussis and B. bronchiseptica, B. pertussis risS is a pseudogene that encodes a truncated RisS sensor. Deletion of the intact part of the B. pertussis risS gene does not affect the expression of risA-dependent, Bvg-repressed genes. These observations suggest that RisA activation occurs through cross-regulation by a heterologous system.

Bacterial Adhesion↗
PubMed1977

Iodination of Escherichia coli with chloramine T: selective labeling of the outer membrane lipoprotein.

Iodination of Escherichia coli cells with chloramine T preferentially labels the free and murein-bound forms of the outer membrane lipoprotein. Iodination for 15 s at 15 degrees C labels the two forms of the lipoprotein almost exclusively, whereas iodination for 60 s at 25 degrees C also labels the other major outer membrane proteins. Chloramine T iodination is a rapid, simple technique for labeling the outer membrane lipoprotein.

Arginine↗
PubMed2025

Emergence of clade 3 emm89 group A Streptococcus in Queensland, Australia.

The emergence of a new clade of emm89 group A Streptococcus (GAS) (clade 3) has been described in several countries. Strains in this clade have been reported to have genomic characteristics that lead to increased expression of virulence factors and may confer a selective advantage over previous emm89 strains. To investigate whether clade 3 GAS is present in the emm89 GAS population of Queensland, Australia, all emm89 GAS isolates received by the Queensland Public Health Microbiology Reference Laboratory since emm typing began in the early 2000s underwent genomic sequencing and analysis. Analysis of sequences from 293 emm89 GAS isolates demonstrated the presence of distinct genomic groups in the Queensland emm89 GAS population. Unlike emm89 GAS populations described in the UK and USA, which were mostly ST101 and ST407, there were a relatively high number of ST142 and ST812 strains in the Queensland emm89 GAS population. However, the majority of Queensland isolates belonged to clade 3, with 80% (n=233) of emm89 GAS isolated from 2006 onwards belonging to this clade. All Queensland clade 3 isolates had the reported genomic features associated with higher virulence potential including increased streptolysin O production and an acapsular phenotype. Clade 3, which has emerged to become the dominant clade of emm89 GAS in Europe and the USA, is now also the dominant clade in Queensland.

Streptococcus pyogenes↗
PubMed2010

Evidence that the C-terminus of OprM is involved in the assembly of the VceAB-OprM efflux pump.

Although the architecture of tripartite multiple drug resistance (MDR) efflux pumps of Gram-negative bacteria has been well characterized, the means by which the components recognize each other and assemble into a functional pump remains obscure. In this study we present evidence that the C-terminal domain of the Pseudomonas aeruginosa OprM and the alpha-helical hairpin domain of Vibrio cholerae VceA play an important role in the recognition/specificity/recruitment step in the assembly of a functional, VceAB-OprM chimeric efflux pump. To our knowledge, this is the first evidence directly linking the C-terminal domain of an outer membrane efflux protein to its recruitment during the assembly of a tripartite efflux pump.

Amino Acid Sequence↗
PubMed1979

Protein K: a new major outer membrane protein found in encapsulated Escherichia coli.

The protein composition of purified outer membranes of 47 Escherichia coli strains was examined by sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis. Of 33 encapsulated strains, all contained an outer membrane protein distinguishable from previously reported proteins. The 14 non-encapsulated strains with one exception lacked this protein. Because of its apparent association with encapsulation (K antigen) we have named it K protein. The protein was purified nearly to homogeneity by chromatography in the presence of detergents, and its composition was determined. Its amino acid composition does not differ significantly from that reported for protein I, another E. coli major outer membrane protein. Furthermore, the N-terminal amino acid sequence of protein K indicates that it is related to protein I.

Amino Acid Sequence↗