Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-06-18
2002-07-16
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06420455
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of microbiology, and in particular to antimicrobial compositions, particularly to antimicrobial compositions that yield polymeric films, coatings, or shaped articles having prolonged antimicrobial activity, particularly in both the light and the dark.
BACKGROUND
The potential for the presence of pathogenic bacteria and viruses in biological fluids such as saliva, tears, blood, and lymph is of significant concern as is the potential for the transfer of such microorganisms to the surfaces of medical devices (and vice versa). For these reasons, methods for minimizing the transmission of pathogens in the home and in hospitals, as well no as in daycare centers, are important.
Microorganisms (e.g., viruses, bacteria, fungi) can be killed or rendered static by a number of physical and chemical methods. Physical methods include heat and radiation. There are a number of chemicals that have been used to limit viral, fungal, and bacterial growth. Examples include alcohols (usually as 70% by volume aqueous ethyl- or isopropyl alcohol), phenol (carbolic acid) and phenol derivatives such as hexachlorophene, formaldehyde, glutaraldehyde, ethylene oxide, ether, detergents, chlorhexidine gluconate, heavy metals such as silver, copper, and mercury, organic compounds of mercury such as mercurochrome, oxidizing agents such as hydrogen peroxide, iodine, hypochlorite, and chlorine. A number of antiviral agents are also known, including amantadine, nucleoside analogs such as AZT, aciclovir, ganciclovir, and vidarabine.
Antibiotics, such as bacitracin, the cephalosporins, cycloserine, the penicillins, vancomycin, chloramphenicol, the erythromycins, the tetracyclines, the sulfonamides, and the aminoglycosides (such as streptomycin, neomycin, and gentamycin), have traditionally been defined as chemicals made by microorganisms that kill bacteria. Antibiotics have no effect on viruses.
Such treatment methods are neither permanent nor continuous. thus repeated treatments may be needed. Compositions intended for imparting a continuously antimicrobial, self-disinfectinig property to surfaces or liquids have been disclosed, most of which involve covalent attachment of an antimicrobial moiety to a polymer or mixture of an antimicrobial agent with a polymer to impart controlled release of the antimicrobial agent.
Generally, known compositions intended for imparting continuous antimicrobial, self-disinfecting activity require intimate contact of the antimicrobial agent or antimicrobial moiety with a given bacterium, fungus, or virus. Since surfaces, in particular, inevitably become soiled, potentially precluding intimate contact of an antimicrobial agent or moiety with the contaminating microbe, it would be of potential benefit to have a method for imparting continuous antimicrobial, self-disinfecting activity at-a-distance,
Such a method was disclosed by Dahl et al.,
Photochemistry and Photobiology
, 46, 3, 345-352 (1987) in which
E. coli
were separated from a surface by about 0.65 mm, wherein the surface included rose bengal. The method involved irradiating the rose bengal using visible light. The antimicrobial activity at-a-distance was ascribed to the diffusion of toxic singlet oxygen through air to the bacteria. Singlet oxygen itself is known to be generated by irradiation of rose bengal and other so-called triplet sensitizers.
Singlet oxygen is generated in neutrophils and macrophages for use in killing microorganisms. Superoxide dismutases, catalases, and peroxidases are defenses against radical- and reduced-oxygen species, but are not effective against singlet oxygen. A few microorganisms, such as Cercospora, are inherently resistant to singlet oxygen, and Gram-positive bacteria are generally more easily killed by singlet oxygen than Gram-negative bacteria. Enveloped viruses are inactivated by singlet oxygen more readily than nonenveloped viruses. It is notable that not a single documented case of acquired resistance by a bacterium, fungus, or virus to singlet oxygen is known.
The “photodynamic effect” is the term used to describe destruction of cells and microbes by triplet-sensitizers in the presence of light. Under conditions where oxygen concentration is high and there are no reducing agents present, singlet oxygen is believed to be the destructive agent. This is the predominant mechanism (the so-called Type II mechanism) for cell destruction in cases where the photosensitizer cannot enter the cell. The Type II mechanism is known to be the predominant means of phototoxicity to
E. coli
for the xanthene dyes, such as rose bengal, for example, which upon irradiation generates reactive oxygen species. 80% of which are singlet oxygen, and 20% of which are superoxide radical anions. For photosensitizers that can pass through the lipid bilayer membrane into the interior of the cell where reducing agent concentrations, such as NADPH and glutathione, are high, the so-called Type I mechanism has been determined to be the predominant one leading to cell destruction. This mechanism involves, ultimately, the formation of a photosensitizer free radical and hydrogen peroxide, hydroxyl radical, and superoxide radical anion.
Some effort has been directed toward utilization of a combination of light and triplet-sensitizers (e.g., phthalocyanine, porphyrin hypericin, and rose bengal) for killing bacteria and fungi and for inactivating viruses. For example, photoinactivation of influenza virus by rose bengal and light was disclosed by Lenard et al.,
Photochemistry and Photobiology
, 58, 527-531 (1993). Also, International Patent Application No. WO 94/02022 discloses improved germicidal compositions utilizing rose bengal in photodynamic killing of microorganisms on surfaces.
As stated above, chemical attachment (e.g., covalent or ionic) of photosensitizers to, or physical mixing of photosensitizers with, polymers has been of significant interest to workers in this field. Incorporation of dyes, such as xanthene dyes like rose bengal, into polymer matrices has been described in U.S. Pat. No. 5,830,526 (Wilson et al.), for example, which describes a woven or nonwoven fabric bound with a non-leachable light-activated dye by a cationic or anionic binder such as a water soluble polymer or carrageenan. Upon exposure to normal light, the dye generates singlet oxygen that kills microorganisms and viruses. As shown in Example 4 of U.S. Pat. No. 5,820,526, no dark antimicrobial activity is observed for the compositions comprising binder, and as Comparative Example 1 shows (below), when no binder is used, the dyes leach from the substrate to such a great extent that the compositions colorize articles with which they come in contact. Japanese Patent Application No. 5-39004 discloses ionic bonding of rose bengal to a positively charged polymer carrier and killing of microbes in the presence of oxygen and light. Bezman et al.
Photochemistry and Photobiology
, 28, 325-329 (1978) disclose the photodynamic inactivation of
E. coli
by rose bengal immobilized on polystyrene beads. It is believed that none of these examples of polymer-bound photosensitizers such as rose bengal, however, would have antimicrobial activity in the dark.
Generally, triplet-sensitizing dye compositions intended for imparting continuous antimicrobial, self-disinfecting activity utilize the dye in combination with light, thus severely limiting applications of these compositions to those where irradiation is feasible. Thus, as an example, a floor finish comprising one of the photodynamic compositions discussed above could impart antimicrobial activity to a floor during the day, or while the flooring is otherwise irradiated with visible light, but would not impart antimicrobial activity to the flooring during dark periods. Some dyes, however, such as methylene blue and halogenated xanthene dyes such as rose bengal, possess light-independent (dark) cytotoxic activity, and thus are effective antimicrobial agents in the dark as well as in the light. See, for example, Smith et al.,
Soil. Sci
., 58, 47 (
Hastings David J.
Lalonde Monserrat R.
Landgrebe Kevin D.
Loperfido John C.
Olson Linda K.
3M Innovative Properties Company
Florczak Yen Tong
Michl Paul R.
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