Antimicrobial enzymes, examples

A number of important papers could not be cited in this chapter, due to the length limitations and the specific target of the chapter. For example, the antimicrobial activity of chitosans [349], the chitinolytic enzymes, the preparation of cosmetics, and the occurrence of chitin in fungi [350] are some of the subjects not dealt with specifically here, notwithstanding their importance. 

Some combinations of antimicrobials are potentially antagonistic. For example, agents that are capable of inducing /1-lactamase production in bacteria (such as cefoxitin) may antagonize the effects of enzyme-labile drugs such as penicillins or imipenem. 

Enzymic inactivation The ability to destroy or inactivate the antimicrobial agent also can confer resistance on microorganisms. For example, (3-lactamases destroy many penicillins and cephalosporins and an acetyltransferase can convert chloramphenicol to an inactive compound. 

The successful isolation of primary cells is dependent on several factors, some of which are not subject to optimization, such as species, type of tissue, age and sex of donor, and presence of genetic modifications (e.g., knockout animals). Other factors such as the dissociation medium, enzymes and concentrations, temperature, and incubation times can be optimized to ensure the quality and consistency of a primary or cell line preparation. The identification and availability of key growth factors is an important determinant of which primary cells can be maintained in culture. For example lactoferrin is a pleiotropic factor with potent antimicrobial and immunomodulatory activities. Recently it has been shown that lactoferrin at physiological concentrations can also promote bone growth, potently stimulating the proliferation and differentiation of primary osteoblasts (Naot, 2005). 

As already pointed out, staphylococci and streptococci are generally more sensitive to biocides than Gram-negative bacteria examples are provided in Table 18.4. On the other hand, mycobacteria and especially bacterial spores are much more resistant. A major reason for this variation in response is associated with the chemical composition and structure of the outer cell layers such that there is restricted uptake of a biocide. In consequence of this cellular impermeability, a reduced concentration of the antimicrobial compound is available at the target site(s) so that the cell may escape severe injury. Another, less frequently observed, mechanism is the presence of constitutive, biocidedegrading enzymes. 

Liposomes have been used by the pharmaceutical industry to deliver a range of drugs. Liposomes are made of phospholipid bilayers with one of more aqueous compartments depending on whether they are unilamellar, multilamellar, or multivesicular vehicles. Because of the bilayer structures they can adopt, they are versatile vehicles as carriers of water-soluble, oil-soluble as well as amphiphilic components. Hence, they can be used to encapsulate a wide range of food components including flavors, oils, amino acids, vitamins, minerals antimicrobials, and enzymes. Their potential applications in the food industry have been discussed by Mozafari et al. (2008)). Examples of the potential applications of liposomes in food include the delivery of cheese ripening enzymes and natural antioxidants (e.g., vitamin E). 

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