Antibacterial action

The accepted bactericidal actions of organic acids have long been the acidification of the bacterial cell cytoplasm following the diffusion of uncharged protonated acid across the membrane (Breidt, Jr., Hayes, and McFeeters, 2004). However, additional specific effects of organic acid on 

Bacteria are known to react differently to antibacterial agents. This is due either to inherent differences, which may be their unique cell envelope composition or proteins not being susceptible or as a result of resistance development, by adaptation exchange of genetic information. For organic acids to be effective as an antibacterial, they must be able to penetrate the cell envelope and attain a sufficiently high concentration at the target site where they will exert antibacterial action (Cloete, 2003). 

Lactic acid may pose as an example inasmuch as it can act either in a bactericidic or bacteriostatic manner, depending on the specific inhibitory conditions. This has been noted specifically for inhibition of L. monocytogenes where lactic acid is able to either kill or limit growth of the organism. Lactic acid is now included in growth prediction models for this pathogen (Gravesen et al., 2004). 

Not much is known about the effect of organic acids on another important pathogen, Salmonella spp., but E. coli and Salmonella are both enteric bacteria and seem to have a similar physiology. It is, however, known that medium chain fatty acids (C6-C12, caproic, caprylic, capric, and lauric) are much more effective against Salmonella than the short-chain fatty acids (formic, acetic, propionic, and butyric). Another important finding was that the short-chain fatty acid butyrate specifically down-regulates the expression of invasion genes in Salmonella spp. at low doses. Medium-chain fatty acids and propionate also decrease the ability of Salmonella spp. to invade epithelial cells. This has been found to be in contrast to acetic acid (Van Immerseel et al., 2006). 

Inhibitors of cell wall growth, including those that combine with the cell wall substrates, inhibit polymerization and attachment of new agents to the cell wall, combine with carrier molecules and those that inhibit enzymes critical to cell growth. Bacitracin, vancomycin, penicillins, cephalosporins  

Inhibitors of nucleic acid synthesis that include drugs that influence DNA template actions in eluding replication, inhibit RNA polymerase, and those that inhibit nucleotide metabolism (e.g., flucytosine (fungi), acyclovir (viruses), and quinolones)  

Inhibition of ribosome functions (e.g., steptomycin, kanamycin, tetracyclines, fusidic acid, and erythromycin). 

---

Mechanism of Antibacterial Action. In spite of the fact that the antibacterial activity of the amiaoglycosides has been known siace the 1940s, the mechanisms iavolved are stiU incompletely understood. Numerous reviews have appeared (eg, 108 —113) and the sequence of events seems to be as outlined below. 

Under acidic conditions, dehydration to an anhydrotetracycline [20154-34-1] (8), C22H22N20y, occurs under basic ones, ring C opens to an isotetracycline [3811-31-2] (9), C22H24N20g. The anhydrotetracyclines, such as (8), appear to exhibit a mode of antibacterial action, but it is unlike that of tetracycline (24). Epimerization (23,25,26) at C-4 occurs in a variety of solvents within the pH range 2—6, particularly in acetic acid (25). A number of anions (27) facihtate this reaction. The reverse process, from 4-epitetracycline [79-85-6] C22H24N20g, to tetracycline, is promoted by chelation with ions such as calcium and magnesium (28). 

The biochemical basis of penicillin action continues to be an area of active investigation. Penicillins are highly specific inhibitors of enzyme(s) involved in the synthesis of the bacterial cell wall, a structure not present in mammalian cells. Three principal factors are thought to be important for effective antibacterial action by a penicillin ... 

The hydrogen peroxide produced in the glucose oxidase catalyzed reaction has an antibacterial action. If the presence of hydrogen peroxide is undesirable in the product, catalase is added to remove the peroxide. 

Acetic acid, boric acid, benzalkonium chloride, aluminum acetate, benzethonium chloride—provide antifungal or antibacterial action... 

Acne medicines may contain ingredients such as salicylic acid, benzoyl peroxide, and sulfur, which remove the top layer of dead skin. They may also contain ingredients that have antibacterial action. Some ingredients reduce sebum production others reduce inflammation. 

Russell A.D. Chopra I. (1996) Understanding Antibacterial Action and Resistance, 2nd edn. Chichester Ellis Horwood. 

The possession of surface activity per se may be an important faetor in the antibacterial action of a group of drugs, for example the eationie detergents. The addition of low concentrations of surface-active compounds may potentiate the biological effect of an antibacterial agent. Thus, phenols are often more aetive in the presence of soaps. 

Russell A.D. (1995) Mechanisms of bacterial resistance to biocides. Int Biodet Biodeg, 36, 247-265. Russell A.D. Chopra I. (1996) Understanding Antibacterial Action and Resistance, 2nd edn. Chichester Ellis Horwood. 

In other cases fullerene antibacterial action takes place after photoirradiation of fulleropyrrolidinium salts. It is not yet clear if the photodynamic action implies the participation of superoxide and hydroxyl radicals (type I mechanism) or singlet oxygen (type II mechanism) but the efficacy is really interesting with the death of more than 99.9% of bacterial and fungal cells and a special selectivity for microbes over mammalian cells (Tegos et al., 2005). Also a sulfobutyl fullerene derivative is able to inhibit environmental bacteria after photoirradiation and it exerts its action on E. coli even if incorporated in coated polymer (Yu et al., 2005). 

Now we come to the question what is the basis of the antibacterial action of the sulfa drugs Many useful drugs in human medicine are enzyme inhibitors, small molecules that frequently bear a structural resemblance to the substrates or products of enzyme-catalyzed reactions. So it is with the sulfonamides. 

He shou wu, a herhal formulation has been used for the treatment of skin tumors. For topical use, the powder is mixed with sesame oil and applied. He shou wu has been used for centuries to help maintain the youthful color of one s hair and also to help diminish hair loss. Holy basil contains ursolic acid (Fig. 7) — one of the cosmetic industry s latest favorites because not only does it quickly heal the skin, it also improves elasticity and removes wrinkles. It also shows benefits for preventing skin cancer. A poultice made from the herh is used topically for its antifungal and antibacterial actions. ... 

Bacterial peptidoglycans o-amino acids and the antibacterial action of penicillins... 

---