Antiseptics and disinfectants are extensively used in hospitals and other health care settings for a variety of topical and hard-surface applications A wide variety of active chemical agents (biocides) are found in these products, many of which have been used for hundreds of years, including alcohols, phenols, iodine, and chlorine Most of these active agents demonstrate broad-spectrum antimicrobial activity; however, little is known about the mode of action of these agents in comparison to antibiotics This review considers what is known about the mode of action and spectrum of activity of antiseptics and disinfectants The widespread use of these products has prompted some speculation on the development of microbial resistance, in particular whether antibiotic resistance is induced by antiseptics or disinfectants Known mechanisms of microbial resistance (both intrinsic and acquired) to biocides are reviewed, with emphasis on the clinical implications of these reports

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Antiseptics and Disinfectants: Activity, Action, and Resistance

The antibacterial effect and mechanism of action of a silver ion solution that was electrically generated were investigated for Staphylococcus aureus and Escherichia coli by analyzing the growth, morphology, and ultrastructure of the bacterial cells following treatment with the silver ion solution. Bacteria were exposed to the silver ion solution for various lengths of time, and the antibacterial effect of the solution was tested using the conventional plate count method and flow cytometric (FC) analysis. Reductions of more than 5 log10 CFU/ml of both S. aureus and E. coli bacteria were confirmed after 90 min of treatment with the silver ion solution. Significant reduction of S. aureus and E. coli cells was also observed by FC analysis; however, the reduction rate determined by FC analysis was less than that determined by the conventional plate count method. These differences may be attributed to the presence of bacteria in an active but nonculturable (ABNC) state after treatment with the silver ion solution. Transmission electron microscopy showed considerable changes in the bacterial cell membranes upon silver ion treatment, which might be the cause or consequence of cell death. In conclusion, the results of the present study suggest that silver ions may cause S. aureus and E. coli bacteria to reach an ABNC state and eventually die.

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Antibacterial Activity and Mechanism of Action of the Silver Ion in Staphylococcus aureus and Escherichia coli

Here we review studies that provided important information about conformational properties of DNA using circular dichroic (CD) spectroscopy. The conformational properties include the B-family of structures, A-form, Z-form, guanine quadruplexes, cytosine quadruplexes, triplexes and other less characterized structures. CD spectroscopy is extremely sensitive and relatively inexpensive. This fast and simple method can be used at low- as well as high-DNA concentrations and with short- as well as long-DNA molecules. The samples can easily be titrated with various agents to cause conformational isomerizations of DNA. The course of detected CD spectral changes makes possible to distinguish between gradual changes within a single DNA conformation and cooperative isomerizations between discrete structural states. It enables measuring kinetics of the appearance of particular conformers and determination of their thermodynamic parameters. In careful hands, CD spectroscopy is a valuable tool for mapping conformational properties of particular DNA molecules. Due to its numerous advantages, CD spectroscopy significantly participated in all basic conformational findings on DNA.

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Circular dichroism and conformational polymorphism of DNA

Publisher Summary This chapter discusses antimicrobial activity and action of silver. Silver and its compounds have long been used, in one form or another, as antimicrobial agents. The silver compound of major therapeutic interest at the present time is silver sulphadiazine. Many in healthcare know that other silver compounds are still in use. It is worth stating that the treatment of ophthalmia neonatorum was revolutionized by the instillation of silver derivatives into the eyes of new-born sufferers. Several factors influence the antimicrobial activity of silver salts. Silver has a marked tendency to adsorb to surfaces and bactericidal activity is reduced in the presence of phosphates, chlorides, sulphides and hard water. Activity is increased as the temperature is raised and is pH-dependent, increasing with increasing pH. Sodium thioglycollate has been recommended as a suitable neutralizing agent for use in bactericidal testing although other SH compounds also fulfil this role. Silver, one of the native metals and second only to gold in its stability amongst the metals of antiquity, has provided several therapeutic agents which have been employed since the beginning of recorded history. These agents range from the metal itself, its salts and complexes with proteins and other macromolecules to the latest, silver sulphadiazine (AgSD).

Antimicrobial activity and action of silver

Publisher Summary This chapter summarizes recent information on the function of high-mobility-group (HMG) proteins. Advances in this field were made primarily by elucidating the structure of these proteins and by understanding their mode of interactions with DNA and chromatin. Renewed interest in these proteins is because of the finding that the DNA-binding domains of many regulatory proteins share common elements with the HMG-1/-2 chromosomal protein family. The HMG proteins are among the largest and best characterized group of nonhistone chromosomal proteins. Members of this protein group are found in all the cells of higher eukaryotes. Most of the data suggest that HMG proteins are associated with selected regions in chromatin and this association affects the architecture and increases the structural complexity of the chromatin fiber. The human HMG-I(Y) gene is located on the short arm of chromosome 6 in a region involved in rearrangements, translocations, and other abnormalities correlated with a number of human cancers.

High-Mobility-Group Chromosomal Proteins: Architectural Components That Facilitate Chromatin Function

Salt-induced conformational transition of poly[d(A-T)]·poly[d(A-T)]

The article reviews data indicating that poly(dA-dT).poly(dA-dT) is able of adopting three distinct double helical structures in solution, of which only the A form conforms to classical notions. The other two structures have dinucleotides as double helical repeats. At low salt concentrations poly(dA-dT).poly(dA-dT) adopts a B-type alternating conformation which is exceptionally variable. Its architecture can gradually move in the limits demarcated by the CD spectra with inverted long wavelength CD bands and the 31P NMR spectra with a very low and a 0.6 ppm separation of two resonances. Contrary to Z-DNA, the 31P NMR spectrum of the limiting alternating B conformation of poly(dA-dT).poly(dA-dT) is characterized by an upfield shift of one resonance. We attribute the exceptional conformational flexibility of the alternating B conformation to the unequal tendency of bases in the dA-dT and dT-dA steps to stack. However, by assuming the limiting alternating B conformation, the variability of the synthetic DNA is not exhausted. Specific agents make it isomerize into another conformation by a fast, two-state mechanism, which is reflected by a further deepening of the negative long wavelength CD band and a downfield shift of the 31P NMR resonance of poly(dA-dT).poly(dA-dT) that was constant in the course of the gradual alterations of the alternating B conformation. These changes are, however, qualitatively different from the way poly(dG-dC).poly(dG-dC) behaves in the course of the B-Z isomerization. Poly(dG-dC).poly(dG-dC) displays purine-pyrimidine (dGpdC) resonance in the characteristic downfield position, while the downfield resonance of poly(dA-dT).poly(dA-dT) belongs to the pyrimidine-purine (dTpdA) phosphodiester linkages. Consequently, phosphodiester linkages in the purine-pyrimidine steps play a similar role in the appearance of the Z form to the pyrimidine-purine phosphodiesters in the course of the isomerization of poly(dA-dT).poly(dA-dT). This excludes that the high-salt structures of poly(dA-dT).poly(dA-dT) and poly(dG-dC).poly(dG-dC) are members of the same conformational family. We call the high-salt conformation of poly(dA-dT).poly(dA-dT) X-DNA. It furthermore follows from the review that synthetic molecules of DNA with alternating purine-pyrimidine sequences of bases can adopt either the Z form or the X form, or even both, depending on the environmental conditions. This introduces a new dimension into the DNA double helix conformational variability. The possible biological relevance of the X form is suggested by experiments with linear molecules of natural DNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Conformational variability of poly(dA-dT).poly(dA-dT) and some other deoxyribonucleic acids includes a novel type of double helix.

Examination of circular dichroic and phosphorus nuclear magnetic resonance spectra showed that poly(dA-dT)-poly(dA-dT) exhibited an ethanol-induced transition to the A form in an Na+ containing medium like natural DNAs. A mere replacement of the Na+ by Cs+ counterions meant that the polynucleotide was with a little cooperativity transformed into a novel conformation displaying a deep negative band in the long wavelength part of the CD spectrum. The presence of very low concentration of Cs2+ shifted the midpoint of the transition to a lower content of ethanol.

Conformational transitions of poly(dA-dT).poly(dA-dT) in ethanolic solutions

Cooperative changes in the chiroptical properties of DNA induced by methanol.

Conformational changes of poly(dA-dT) . poly(dA-dT) induced by increasing ionic strength were studied using CD spectroscopy. It was found that a pronounced noncooperative inversion of the long-wavelength part of the CD spectrum of poly(dA-dT) . poly(dA-dT) occurred at high concentrations of CsF in solution. It was suggested that a great difference between the geometries of the purine and pyrimidine residues in the helix was characteristic of the structure of poly(dA-dT) . poly(dA-dT) in concentrated CsF solutions.

Michaela Vorlíčková

Papers

Salt-induced conformational transition of poly[d(A-T)]·poly[d(A-T)]

Conformational variability of poly(dA-dT).poly(dA-dT) and some other deoxyribonucleic acids includes a novel type of double helix.

Conformational transitions of poly(dA-dT).poly(dA-dT) in ethanolic solutions

Cooperative changes in the chiroptical properties of DNA induced by methanol.

Salt-induced conformational changes of poly(dA-dT).