Bacteria
Julius P. Kreier in 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.
Antimicrobial mechanisms of selected preservatives and the bacterial response
Philip A. Geis in Cosmetic Microbiology, 2006
Precious few studies support or dispute that assumption. Porin-deficient bacteria have been shown to exhibit reduced susceptibility to parabens1 and isothiazolone-resistant bacteria isolated from consumer products were shown to lack porins.2 These observations support the role of porins in preservatives gaining access to the periplasm, at least. Once within the periplasm, several possibilities exist. The molecules may diffuse through the cytoplasmic membrane, either in a passive manner driven by mass action or in a facilitated manner in which the cell has some role in aiding the diffusion of the preservative through the membrane. The preservatives may be actively transported by the cell using an energy-requiring process with specific or general transport mechanisms. Finally (and possibly heretically), the possibility exists that the preservatives do not have to enter cells to exert their antimicrobial action. The periplasm may contain targets whose inhibition may be sufficient to inhibit cell growth, or for which the downstream effects of reacting with the preservative result in growth inhibition and cell death.
Brucella: A Foodborne Pathogen
Dongyou Liu in 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.
Recent advances in antibacterial applications of metal nanoparticles (MNPs) and metal nanocomposites (MNCs) against multidrug-resistant (MDR) bacteria
Published in Expert Review of Anti-infective Therapy, 2019
Mehran Alavi, Mahendra Rai
In first step, identification of morphological features in MNPs and bacteria is required to understand interaction of MNPs or metal oxide NPs with bacteria. Based on cell wall morphology, there are two major types of bacteria involving Gram-positive and Gram-negative, which are used for evaluation of antibiotics. In Gram-positive bacteria, cell wall of bacteria is composed of thick peptidoglycan layer and cell membrane. In contrast, in Gram-negative bacteria, plasma membrane, outer membrane, and thin peptidoglycan are components of cell wall. In these bacteria, there is periplasmic space between plasma and outer membranes. Bacterial cell walls of Gram-positive and Gram-negative bacteria are 20–80 and 10–30 nm thick, respectively. This difference is related to 95% and 5–10% amount of peptidoglycan for Gram-positive and Gram-negative bacteria, respectively [79].
N-terminal α-amino group modification of antibodies using a site-selective click chemistry method
Published in mAbs, 2018
De-zhi Li, Bing-nan Han, Rui Wei, Gui-yang Yao, Zhizhen Chen, Jie Liu, Terence C.W. Poon, Wu Su, Zhongyu Zhu, Dimiter S. Dimitrov, Qi Zhao
Sequences of anti-HER2 monoclonal antibodies were identified using a phage-displayed human antibody library. Fabs of anti-HER2 antibodies were expressed and purified as previously described.17 Fab sequences in pComb3x vectors were expressed in HB2151. Expression was induced with isopropyl-L-thio-h-D-galactopyranoside. Soluble proteins were released from the periplasm. The clear supernatant was recovered for the purification on Ni-NTA column (QIAGEN). IgGs of anti-HER2 antibodies were expressed in mammalian suspension cells following the previously published protocol.33 IgGs were expressed in 293 FreeStyle cells. Polyetherimide was used to transfect 293 FreeStyle cells according to manufacturer's instruction (Thermo Fisher). After four days post-transfection, the culture supernatant was harvested. IgGs were purified on protein A resins (GE Healthcare).
Antibiotic uptake through porins located in the outer membrane of Gram-negative bacteria
Published in Expert Opinion on Drug Delivery, 2021
Mathias Winterhalter
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].
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