Bacterial membrane disruption

Together with sorbic acid, benzoic acid also acts as a membrane perturbing agent (Hazan, Levine, and Abeliovich, 2004). Disruption of the OM by organic acids involves the action of dissociated as well as undissociated forms (Alakomi et al., 2000). High lipoid solubility and the ability to form membrane polar/hydrogen unions are responsible for benzoic interaction with cell membranes and the modification of membrane properties (Otero-Losada, 2003). 

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Cytoplasmic membrane Polymyxins Polyenes Imidazoles and triazoles Naftidine Disrupt bacterial membranes Disrupt fungal membranes Inhibit ergosterol synthesis Inhibits ergosterol synthesis Bind to LPS and phospholipids Bind preferentially to ergosterol Pathway not in mammalian cells Pathway not in mammalian cells... 

Bacterial membrane disrupting (leakage, transport mechanisms). Therefore, loss of active transport of nutrients through the membrane. 

Different organic acids, primarily lactic acid, have been successfully used for decontamination of whole livestock carcasses, and the application of different organic acids used for decontamination has also been tested in the fruit and vegetable industry. Organic acids other than lactic acid that are known to have bactericidal effects are acetic, benzoic, citric, malic, propanoic, sorbic, succinic and tartaric acids (Betts and Everis 2005). The antimicrobial action is due to a reduction in the pH in the bacterial environment, disruption of membrane transport, anion accumulation or a reduction in the internal pH in the cell (Busta et al., 2001). Many fruits contain naturally occurring organic acids. Nevertheless, some strains, for example E. coli 0157, are adapted to an acidic environment. Its survival, in combination with its low infective dose, makes it a health hazard for humans. 

Fullerene showed antibacterial activity, which can be attributed to different interactions of C60 with biomolecules (Da Ros et al., 1996). In fact, there is a possibility to induce cell membrane disruption. The fullerene sphere seems not really adaptable to planar cellular surface, but for sure the hydrophobic surface can easily interact with membrane lipids and intercalate into them. However, it has been demonstrated that fullerene derivatives can inhibit bacterial growth by unpairing the respiratory chain. There is, first, a decrease of oxygen uptake at low fullerene derivative concentration, and then an increase of oxygen uptake, which is followed by an enhancement of hydrogen peroxide production. The higher concentration of C60 seems to produce an electron leak from the bacterial respiratory chain (Mashino et al., 2003). 

Daptomycin has a unique mechanism of action it disrupts the bacterial membrane of Gram-positive organisms by forming channels across it. These channels permit the leakage of intracellular ions, eventually leading to cell death. Resistance to daptomycin is rare, at least so far. 

Disruption of bacterial membrane structure Polymyxins Colistin Altered target Efflux... 

Polymyxins (bactericidal disrupt bacterial membrane structural integrity)... 

How do antibiotics act Some, like penicillin, block specific enzymes. Peptide antibiotics often form complexes with metal ions (Fig. 8-22) and disrupt the control of ion permeability in bacterial membranes. Polyene antibiotics interfere with proton and ion transport in fungal membranes. Tetracyclines and many other antibiotics interfere directly with protein synthesis (Box 29-B). Others intercalate into DNA molecules (Fig. 5-23 Box 28-A). There is no single mode of action. The search for suitable antibiotics for human use consists in finding compounds highly toxic to infective organisms but with low toxicity to human cells. 

Fig. 7.15 Proposed mode of antibiotic action by cyclopeptides tubes (green) form and aggregate to disrupt bacterial membranes (red)...

The isolation of bacterial DNA described in this experiment, patterned after the work of Marmur (1961), accomplishes these objectives. Bacterial cells are disrupted by initial treatment with the enzyme, egg-white lysozyme, which hydrolyzes the peptidoglycan that makes up the structural skeleton of the bacterial cell wall. The resultant cell walls are unable to withstand osmotic shock. Thus, the bacteria lyse in the hypotonic environment. The detergent, sodium dodecyl sulfate, (SDS, sodium do-decyl sulfate) then completes lysis by disrupting residual bacterial membranes. SDS also reduces harmful enzymatic activities (nucleases) by its ability to denature proteins. The chelating agents, citrate and EDTA (ethylenediamine tetraacetic acid), also inhibit nucleases by removing divalent cations required for nuclease activity. 

Among the long-chain proline-rich AMPs, diptericin that is carrying post-translational modifications (C-terminal amidation and two O-glycosylations, see for details the previous section of this chapter) has a controversial mode of action. It was shown to disrupt the bacterial membrane, but it is unlikely that it acts primarily as a pore-former, rather it is expected to target metabolic processes such as nucleic acid, protein, and cell wall synthesis [98]. 

This is the mechanism proposed by Datyner to account for CTAC antibacterial, and antifungal to a lesser extent, activity he reports [20]. Martins et al. invoke the ability of the surfactant to disrupt the cell membrane and form mixed micelles with its lipids to account for CTAB and SLS antibacterial activity [29], In contrast, the bacteria-killing efficacy of double-chain surfactants such as DHTDMAC is assigned to an alteration of the membrane protein function resulting from the adsorption of vesicles onto the bacterial membrane. This study was carried out under laboratory conditions (very low ionic strength), and the antibacterial efficacy of fabric softeners under realistic use conditions remains highly questionable. 

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