Biology of microbes
Philip A. Geis in Cosmetic Microbiology, 2006
Gram-positive walls. Gram-positive bacteria have very thick peptidoglycan layers. The peptidoglycan has a pentaglycine bridge between the d-alanine and the l-lysine of the tetrapeptide coming off the N-acetylmuramic acid (NAM). The NAM is polymerized to N-acetylglucosamine (NAG). Gram-positive cell walls also contain teichoic acids (Figure 2.3). These are ribitol and glycerol phosphate polymers. Coming off the ribitol and glycerol may be amino acids or sugars. The teichoic acids attach to the peptidoglycan layer and extend to the outside of the cell where they give the cell a negative charge. They can even extend all the way down into the cell membrane and attach to lipids (lipoteichoic acids). They are like tie rods that hold the peptidoglycan to the membrane, but their true function has not been entirely clarified yet. They are not present in Gram-negative cell walls.
Symptom flowcharts and testing guidelines
Sarah Bekaert, Alison White in Integrated Contraceptive and Sexual Healthcare, 2018
Following solvent treatment, only Gram-positive cells remain stained, possibly because of their thick cell wall, which is not permeable to solvent. After the staining procedure, cells are treated with a counterstain, e.g. a red acidic dye such as safranin or acid fuchsin, in order to make Gram-negative (decolourised) cells visible. Counterstained Gram-negative cells appear red, and Gram-positive cells remain blue. Although the cell walls of Gram-negative and Gram-positive bacteria are similar in chemical composition, the cell wall of Gram-negative bacteria has a thin layer between an outer lipid-containing cell envelope and the inner cell membrane. This means that within the staining process, the cell wall loses the crystal violet colour during the use of the alcohol in the decolourisation process and takes on the red stain at the end part of the staining process. The Gram-positive cell wall is much thicker, and retains the crystal violet stain even through the decolourisation process.
Antibiotics: The Need for Innovation
Nathan Keighley in Miraculous Medicines and the Chemistry of Drug Design, 2020
Bacteria can be classified according to their cell wall by using a staining technique. A purple dye is added, followed by washing with acetone. Bacteria with a thick cell wall (20–40 nm) absorb the dye and are stained purple. These are defined as gram-positive bacteria. Bacteria with a thin cell wall (2–7 nm) only absorbs a small amount of dye, which is washed out with acetone. These bacteria are then stained pink with a second dye and are defined as gram-negative bacteria. Although they have a thin cell wall, the important difference between these bacteria and gram-positive bacteria is that they have an outer cell membrane made up of lipopolysaccharides. This difference has important implications for the different vulnerabilities of gram-positive and gram-negative bacteria to antibiotics.
Comparing membrane and spacer biofouling by Gram-negative Pseudomonas aeruginosa and Gram-positive Anoxybacillus sp. in forward osmosis
Published in Biofouling, 2019
Anne Bogler, Douglas Rice, Francois Perreault, Edo Bar-Zeev
Biofilms that form in wastewater facilities are often found to be site-specific and to constitute a highly diverse community (Al Ashhab et al. 2014; Vanysacker et al. 2014; Zhang et al. 2014). Although most strains on FO membranes have been found to be Gram-negative, Gram-positive strains have also been observed (Qiu and Ting 2013; Zhang et al. 2014; Ding et al. 2016). Gram-positive bacteria (eg Anoxybacillus sp.) have a simple cell wall structure surrounding the cytoplasmic membrane, primarily composed of a thick (20–80 nm) peptidoglycan layer (Madigan et al. 2012). Conversely, Gram-negative bacteria (eg Pseudomonas aeruginosa) have a complex outer cell structure comprising a thin (2–3 nm) peptidoglycan layer sandwiched between two phospholipid bilayer membranes (Madigan et al. 2012). Apart from phospholipids, the outer membrane also contains lipopolysaccharides, where the long polysaccharide chains are on the outer surface of the cell (Madigan et al. 2012). The surface properties of bacteria resulting from these outer cell structures control adhesion of cells onto surfaces, often via hydrophobic or hydrophilic interactions (Neu 1996).
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
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].
Preparation and characterization of a novel thermosensitive and bioadhesive cephalexin nanohydrogel: a promising platform for topical antibacterial delivery
Published in Expert Opinion on Drug Delivery, 2020
Sara Salatin, Farzaneh Lotfipour, Mitra Jelvehgari
The MIC value for the cephalexin-loaded NPs suggested an effective entrapment of drug into the NPs without losing its pharmacological effect as well as a favorable sustained release of cephalexin. Antibiotic-loaded NPs can target antibiotics to the site of infection and not only release the drug at the infection site but also, after phagocytosis of the pathogen, expose it to the high intracellular drug concentrations [48]. It can be assumed that the NPs adsorbed to the bacterial cell surface can act as a drug depot to decline the extent of bacterial growth [29]. After making interaction, NPs can pass through the bacterium membranes, interfere with metabolic pathways, and subsequently induce changes in the membrane shape and function [49]. Chitosan can also exhibit antibacterial activity. The cell wall of Gram-positive bacteria is mainly composed of a thick peptidoglycan layer containing teichoic acids which give a negative charge to the bacterial surface. Fu and coworkers reported that teichoic acids in the cell membrane of S. aureus interact with chitosan and its derivatives, thereby inhibiting the bacterial growth [50]. The cephalexin nanohydrogel exhibited better antibacterial activity than that of cephalexin-loaded NPs since hydrogel allowed for controllable viscoelasticity and tunable NPs release rate. Therefore, our prepared nanohydrogel with efficient antimicrobial activity can be a valuable drug delivery system for the superficial skin infection, regardless of the exact in vivo mechanism.
Related Knowledge Centers
- Alcohol
- Bacteria
- Bacteriology
- Cell Wall
- Crystal Violet
- Peptidoglycan
- Cell Membrane
- Gram Stain
- Staining
- Gram-Negative Bacteria