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Bacteria
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
The cell wall has a rigid three-dimensional structure composed of cross-linked peptidogiyean, which consists of repeating units of N-acetylglucosamine and N-acetylmuramic acid. These repeating polymeric units are bound together by cross-linked pentaglycine residues. The cell envelopes of Gram-positive cells are structurally simpler than are Gram-negative cell envelopes even though they are generally thicker. In addition to an inner cytoplasmic membrane and a thick peptidoglycan layer, the Gram-positives have an outer glycocalyx or capsular layer. Gram-negative bacteria also have an inner membrane and a second membrane separated by a periplasmic space, providing a higher lipid content in Gram-negative cells (fifteen to twenty percent) compared to that (two to four percent) in Gram-positives. Figure 15.4 is an electron micrograph of a thin section of a Gram-positive bacterium, Mycobacterium flavum, and Figure 15.5 is an electron micrograph of an unidentified species of Pseudomonas, a Gram-negative bacterium.
Recombinant Antibodies
Published in Siegfried Matzku, Rolf A. Stahel, Antibodies in Diagnosis and Therapy, 2019
Melvyn Little, Sergey M. Kipriyanov
A major problem for the export of antibodies or any other proteins to the cell surface of Gram-negative bacteria such as E. coli is the double membrane. After secretion through the cytoplasmic membrane and cleavage of their signal peptide, they are then confronted by the largely impermeable outer membrane, which is characterized by an outer leaf of lipopolysaccharides. A rigid peptidoglycan network in the periplasmic space between the inner and outer membranes forms the cell wall. It is apparently anchored to the outer membrane by lipoproteins such as the major lipoprotein, Lpp, modified at its N-terminus by a lipid moiety that is integrated into the outer membrane. A large number of trimeric protein complexes formed by a channel-forming class of proteins known as the porins are also integrated into the outer membrane, where they permit the diffusion of molecules up to a molecular weight of about 500 Da. The porins and several other outer membrane proteins, including the abundant outer membrane protein A (OmpA), appear to contain several membrane-spanning β-sheets joined by surface loops.
Brucella: A Foodborne Pathogen
Published in Dongyou Liu, Handbook of Foodborne Diseases, 2018
Brucella are nonmotile and do not have spores. The cell wall of Brucella is typical for gram-negative bacteria. The outer membrane, approximately 4–5 nm in thickness, is composed of asymmetric layers of LPS and phospholipids and is supported by an underlying 3–5 nm layer of peptidoglycan. Some proteins, such as OmpA, are covalently bound to the peptidoglycan layer and stabilize the outer membrane. The hydrophobic region of the membrane provides an anchor for proteins and forms a functional and structural barrier between the periplasm and the exterior of the cell. The periplasmic space varies from 3 to 30 nm. Porins in the outer membrane function as channels to the interior of the cell. Other proteins, such as lipoproteins, are also embedded in the outer membrane.
Tracing the origins of extracellular DNA in bacterial biofilms: story of death and predation to community benefit
Published in Biofouling, 2021
Davide Campoccia, Lucio Montanaro, Carla Renata Arciola
Thus, in various Gram-positive and Gram-negative bacteria eDNA secretion appears to be linked to competence and to the DNA uptake machinery. The formation of complexes between single strand DNA (ssDNA) and the ComE secretin, its homologs found in other bacterial species (e.g. ComEA) or other unrelated proteins (e.g. single-stranded binding protein SsbB), has been hypothesized to act as a putative reservoir function. Under this hypothesis, periplasmic ComE/ComEA/SsbB-DNA clusters would be accumulated and stored until needed and become available on demand. This periplasmic accumulation could serve not only for transformation but also as a food source (Seitz & Blokesch 2014). Moreover, periplasmic accumulation would support the hypothesis that, in Gram-negative bacteria, vesiculation could generate DNA-containing OMVs.
New perspectives in the antibiotic treatment of mechanically ventilated patients with infections from Gram-negatives
Published in Expert Review of Anti-infective Therapy, 2021
Marios Karvouniaris, Konstantinos Pontikis, Thomas Nitsotolis, Garyphallia Poulakou
Though chemically related to ceftazidime and cefepime, this novel cefalosporin possesses unique properties that enable the molecule to remain stable in the presence of all classes of β-lactamases, Ambler classes A, C, D, and B class metallo-β-lactamases as well. The side chain at position 3 of the drug contains a catechol moiety, forms complexes with ferric iron, and the drug is transported as a siderophore (‘Trojan horse strategy’). This process facilitates high concentrations of the antibiotic in the periplasmic space to inhibit the synthesis of peptidoglycans. The spectrum of activity is broad, and the corresponding MIC90 values in 2016 for A. baumannii, K. pneumoniae, P. aeruginosa, and Stenotrophomonas maltophilia were 4, 1, 0.5, and 0.25 mg/L, respectively (all within the range of susceptibility) [102]. More in vitro data from Canadian ICUs, during 2015–17, confirmed universal susceptibility of Enterobacterales, MDR P. aeruginosa, and A. baumannii to cefiderocol [103].
Antibiotic uptake through porins located in the outer membrane of Gram-negative bacteria
Published in Expert Opinion on Drug Delivery, 2021
Using microfluidic devices allows to handle single bacteria in a reliable manner [42,43]. For example, in combination with autofluorescent antibiotics (fluoroquinolones) and a strong light source single-cell detection became possible and has been successfully implemented to study the accumulation of antibiotics in single bacterial cells [44–48]. Suspending bacterial cells within a microfluidic chamber and using a tuneable deep UV light source allowed them to study in a label-free manner the accumulation of fluoroquinolones in Enterobacteriaceae. In these studies, the authors achieved with careful controls to separate cellular autofluorescence and crosstalk from the drug signals [45]. The same group has also worked with fluorescent derivatives of ceftazidime to study intracellular accumulation at the single-cell level [47–48]. The derivatives accumulated in the periplasm once the outer membrane was permeabilised, and periplasmic accumulation was found to correlate with antibiotic activity. However, the authors also noted that modifications of the compounds with fluorophores changed the antibiotic activity of the drug in E. coli strains, which needs to be accounted for when interpreting permeation rates for fluorescent derivatives. For basic studies fluorescent labeled molecules has been prepared and characterized [49–51].