Microbial cell membrane disruption

Microbes also have a plasma membrane that resides adjacent to their cell wall. Polymyxins are amphipathic agents (containing both nonpolar, lipophilic and polar, lipophobic groups) that interact with phospholipids in microbial cell membranes. The result is disruption of the membrane and increased permeability. However, because microbial and mammalian cell membranes are not exceedingly dissimilar, polymixins can produce significant toxicity in humans (i.e., they have low selective toxicity). This is also true for the related drug nystatin. This is why these particular antibiotics are not generally used systemically and are usually restricted to topical application. 

The polypyrrole (Ppy)/dextrin nanocomposite is synthesised via in situ polymerisation and the preparation of this nanocomposite is shown in Figure 5.4. The backbone chain of this nanocomposite polymer contains hydrophobic side chains, which disrupt the microbial cell membrane leading to leakage of the cytoplasm in bacteria including Escherichia coli. Pseudomonas aeruginosa. Staphylococcus aureus and Bacillus subtilis. This material can be implemented in the fields of biomedicine, biosensors and food packaging due to the biodegradable property of dextrin as well as the antibacterial properties of the Ppy [79]. 

Antibiotics are generally toxic to microbes (although the general term antibiotic can be used as well for substances to combat nonmicrobial pathogens and others). Antibiotics are often based upon naturally occurring substances produced by some BU to combat other BU, and often disrupt microbial cell membranes or metabolism. Microbial immunity to antibiotics can be built by the following mechanisms ... 

Chlorinated derivatives of phenols, cresol, and xylenol elicit the release of [ C]-glutamate from E. colt [92]. These compounds are effective bactericides and are used in crude disinfectant and antiseptic preparations such as LysoT and Det-tol . Their abUity to denature protein is probably responsible for their disruptive action upon microbial cell membranes. In addition to damaging the membrane [92], phenol exerts a lytic action upon the cell wall lysis occurs in growing cultures of E. coll [93] and is particularly noted in synchronous cultures at the point of cell division [94]. 

It has been generally observed that the mechanical effects due to cavitational events are more responsible for the microbial disinfection and the chemical and heat effects play only a supporting role [56]. Microstreaming resulting from stable cavitation has been shown to produce stresses, sufficient to disrupt cell membranes... 

Daptomycin (15 Cubicin ) Daptomycin (15) Lipopeptide NP Microbial Antibacterial Disrupts multiple aspects of bacterial cell membrane function 211-225... 

Most enzymes of industrial importance like amylase, protease, cellulase, etc. are extracellular. By the addition of surface-active agents, enzyme excretion through cell membranes and consequently the yield of these enzymes can be increased 38). Extracellular enzymes are separated from microbial cells by filtration and, if necessary, in addition by enrichment. Intracellular enzymes are released by disruption of the cells... 

Divalent cations (e.g. Mg2+, Ca2+) present in hard water may also interact with the microbial cell surface and block disinfectant adsorption sites necessary for activity. On the other hand, cationic compounds may disrupt the outer membrane of Gram-negative bacteria and facilitate their own entry. 

Surfactant Effects on Microbial Membranes and Proteins. Two major factors in the consideration of surfactant toxicity or inhibition of microbial processes are the disruption of cellular membranes b) interaction with lipid structural components and reaction of the surfactant with the enzymes and other proteins essential to the proper functioning of the bacterial cell (61). The basic structural unit of virtually all biological membranes is the phospholipid bilayer (62, 63). Phospholipids are amphiphilic and resemble the simpler nonbiological molecules of commercially available surfactants (i.e., they contain a strongly hydrophilic head group, whereas two hydrocarbon chains constitute their hydrophobic moieties). Phospholipid molecules form micellar double layers. Biological membranes also contain membrane-associated proteins that may be involved in transport mechanisms across cell membranes. 

P NMR has been used to investigate the effects of three anti-microbial peptides isolated from Australian tree frogs Litoria caerulea and L. genimacu-lata on the cell membranes of Bacillus cereus and Staphylococcus epidermidis. The wide-spectrum antibiotic peptides caerin 1.1 and maculatin 1.1 disrupted cell membranes causing an increase in the isotropic P NMR signal. However, caerin 4.1, a narrow-spectrum antibiotic, did not affect the P spectra of these bacteria. ... 

Upon contact with the microbial cells, the diluent molecules dissolve in the cytoplasmic membrane and cause its swelling [19]. This leads to disruption of the transmembrane potential, pH gradient across the cytoplasmic membrane, and it ultimately leads to disruption of the ion-active pumps [20]. Fluid-mosaic model has been widely accepted as the best description of the real-time structure of biological membranes, and it states that the cytoplasmic membrane exists in a fluid state under physiological conditions [21]. 

Terpenes In recent years, more data indicate the presence of terpenes in numerous representatives of hchens (Culberson 1970 Rundel 1978 Abdullah et al. 2007). One of the many functiOTis of these compounds is their antimicrobial activity, but the mechanism of action of terpenes on microorganisms is not fully understood (Cowan 1999). According to their lipophilic nature, it is assumed to act by disrupting membrane functions of microbial cells (Cowan 1999), and some authors believe that they may cause nonspecific cell membrane permeability increase for the antibiotic molecule (Byron et al. 2003). 

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