Microbiocidal activity

As a result of the contact of blood with none-ndothelial surfaces, several humoral and cellular systems can be activated. Exposure of blood proteins and cells to blood contacting medical devices can activate plasma proteolytic systems (coagulation (blood clotting system), fibrinolysis (process by which clot is broken down), complement cascade (a system of soluble proteins involved in microbiocidal activity and the release of inflammatory components), Kallekrein-kinin and contact systems) and at least three cellular elements (leukocytes, endothelial cells, and platelets). Contrary to the normal situations whereby these mechanisms are localized and intended to promote wound healing, activation of these systems by medical devices can result in nonlocalized systemic reactions. The preclinical and clinical assessments of hemocompatibility are designed to minimize modification of these systems. 

In vitro studies with purified defensins have shown microbiocidal activity at micromolar concentrations against both Gm+ and Gm- bacteria, fungi, and certain enveloped viruses such as herpes simplex. How do they work Preliminary studies with human and rabbit defensins indicate that they increase the permeability of first the outer and then the inner membranes of E. coll Whether it will be feasible to produce these substances in quantity by gene-splicing techniques in order to evaluate therapeutic efficacy by clinical studies remains to be seen. 

Many conqionents in vulcanizates, sudb as accelerators, fillers, oils, and antioxidants, are known to affect microbial activities, and protection of rubber goods against microorganisms, by the addition of chemicals with microbiocidal activities, has been an important research area. However, the use of microbioddes is b ond the scope of this review, and extensive references have been given by Zyska [24,25]. The present review mainly covers the degradation of the polymer itself. 

The possible influence of cross-link density on the microbial deterioration of vulcanized NR has been obscured by the microbiocidal activity of the curing agent. In the curing system of CBS-sulphur, however, it was observed that the resistance of the vulcanizates is in good correlation with the cross-link density, regardless of the content of sulphtir or CBS (Figure 2) [42]. 

Povidone-iodine (Betadine) is a water-soluble iodine complex which retains the broad-range microbiocidal activity of iodine without the undesirable effects of iodine tincture. However, toxicity still occurs from povidone-iodine percutaneously absorbed, mainly when it is used on large areas of burnt skin or on neonates. This subject is comprehensively dealt with by Postellon and Aronow (1990). 

The threat of accidental misuse of quaternary ammonium compounds coupled with potential harmful effects to sensitive species of fish and invertebrates has prompted some concern. Industry has responded with an effort to replace the questionable compounds with those of a more environmentally friendly nature. Newer classes of quaternaries, eg, esters (206) and betaine esters (207), have been developed. These materials are more readily biodegraded. The mechanisms of antimicrobial activity and hydrolysis of these compounds have been studied (207). AppHcations as surface disinfectants, antimicrobials, and in vitro microbiocidals have also been reported. Examples of ester-type quaternaries are shown in Figure 1. 

The activity of the sorbates at a higher pH is one distinct advantage over the two other most commonly used food preservatives, benzoic and propionic acids, because the upper pH limits for activity of these compounds are approximately pH 4.5 and 5.5, respectively. Although the effect of sorbates can be microbiocidal under certain conditions, activity is most often manifested as a microbial growth retardant. 

Quinoline derivatives of formula 115 are outstandingly active as microbiocides and can be preferentially used as agricultural fungicides and bactericides for the control of undesired plant pathogens (96EUP703234). 

MIcrobiocldes. There are several microbiocides available commercially that can perform an effective function in controlling microbial activity. Some of these chemicals are inorganic, such as chlorine, sodium hypochlorite, calcium hypochlorite, hydrogen peroxide, chromates and compounds of mercury and silver. However, the organic chemicals find the highest use as microbiocides. Some examples of these organic compounds are peracetic acid, paraformaldehyde, polychlorophenols and quaternary ammonium derivatives, to name a few [208]. 

Mlcrobiocidal Treatment. Once the microbial activity reaches a high enough level to cause problems, physical and chemical methods may be used to control the problem. In drilling operations, the most effective method is chemical treatment—the use of microbiocides [184,208]. 

This is one of the most important factors in alleviating microbial problems. A decrease in microbial activity after treatment indicates a positive response to the microbiocidal treatment. Continuous monitoring is imperative for effective control. 

Microbiocides. For a general guideline about 100 mg/L of the microbiocide with at least 50 wt% active ingredient should be added to the drilling fluid. Exact dosage and treatment frequency has to be estimated based on the severity of the problem. 

There are around 250 chemical entities that have been identified as active components of microbiocidal products in the European Union. The aim ofthis chapter is to introduce the range of chemicals in common use and to indicate their activities and applications. 

At low pH the existence of HOCl is favoured over OCl" (hypochlorite ion). The relative microbiocidal effectiveness of these forms is of the order of 100 1. By lowering the pH of hypochlorite solutions the antimicrobial activity increases to an optimum at about pH 5 however, this is concurrent with a decrease in stability of the solutions. This problem may be alleviated by addition of NaOH (see above equation) in order to maintain a high pH during storage for stability. The absence ofbuffer allows the pH to be lowered sufficiently for activity on dilution to use-strength. It is preferable to prepare use-dilutions of hypochlorite on a daily basis. 

Prevention of HIV transmission is a major worldwide concern. A recent recommendation by the International Working Group on Vaginal Microbiocides states [34] that .. . It is desirable that an agent be evaluated for activity against HIV and other STD regardless of its intended HIV indication since a clinical outcome of HIV prevention may be achieved by the prevention... 

Neyts, J. and De Clercq, E. Effect of polyanionic componnds on intracntaneons and intravaginal herpesvirns infection in mice impact on the search for vaginal microbiocides with anti-HfV activity. Journal of Acquired Immune Deficiency Syndromes and Human Retrovirology 1995, 10, 8-12. 

Propenaldehyde. Aldehyde group. Typically available as a 92% active, liquid. It is flammable, volatile, lachrymatory, and a strong irritant. Acrolein is a protein and enzyme poison. It is stabilized against polymerization by the addition of hydroquinone (oxidation results in polymerization, rendering acrolein inactive as a microbiocide). Although only small dose levels are required (1.5 to 3.0 ppm) to achieve threshold toxicity, rapid microbial resistance can occur. This product is seldom used today as the effort is often not worth the gain. 

Use This microbiocide is active against a broad spectrum of microorganisms, including bacteria, fungi, yeasts, and algae. 

The Intercide OBF microbiocides are based on the active ingredient 2-n-octyl-4-isothiazolin-3-one (OIT). The products are effective fungicides which are widely used in paints and coatings. Characteristics and applications are described for Intercide grades OBF-8-DINP, and OBF-8-ED6. OIT is highly compatible with PVC and offers advantages over OBPA in terms of resistance to UV radiation. 

Isothiazole and its derivatives have a broad range of biological activities (81PMC117, 97JPR1, 03PHMD617). Especially, isothiazol-3(2//)-ones 1 are potent industrial microbiocides because of their antifungal and antibacterial activities (02SUR79). 

Its fungicidal action is moderate in vitro, but it has a high chemotherapeutic potency (Dimond and Davis, 1953). It should be mentioned that its parent compound, mercaptobenthiazole, is not a systemic microbiocide, and its activity is partly due to its chelate-forming properties (Horsfall, 1957). It has not become important in agriculture. 

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