Minimum biocidal concentrations

This study has shown that typical coating biocides can be encapsulated within modified silica frameworks. These porous frameworks offer a means to inhibit the aqueous extraction of the biocide. In such combinations the biocides retain their anti-microbial properties, while controlled delivery facilitates a dynamic equilibrium to maintain a minimum inhibitory concentration at the coating interface, over an extended time period. There is evidence that biocide housed in such frameworks has a longer effective activity for a given initial concentration, since it is to some extent protected from the usual environmental degradation processes. 

In order to provide a biostatic effect for any particular organism, nonoxidizers are required to be present at a certain minimum inhibitory concentration (MIC), and for a biocidal effect, at a minimum kill concentration... 

Are biocides dosed by hand or via pumps What is the most suitable for the circumstances If pumps are used, how long does it take to dispense an adequate minimum inhibitory concentration (MIC) dose Are there timers installed ... 

Further to these results, the microbicidal activities of FIBCIDE-KF and KATHON WT were evaluated. The minimum inhibitory concentrations (MIC) for Pseudomonas aeruginosa, Pseudomonas putida, Bacillus subtilis and Microbacterium sp. are identical for both compounds, so the microbicidal effect has not diminished (Figure 10). It appears that the biocidal effects are similar because the Cl-MIT in the inclusion complex is released into water, as shown in Figure 6. 

The question of whether or not a polymer-anchored biocide can be active against microorganism growth was first tested by comparing the minimum inhibitory concentrations (MIC) of pentachlorophenol, its acrylate, 8, and the homopolymer of pentachlorophenyl acrylate 8. An agar dilution method was used. To a sterilized agar, a solution of the compound to be tested was added in the appropriate amount to make final concentrations of 1000, 500, 250, 100, 50, and 10 ppm. Following inoculation, the... 

Table 1 Minimum inhibitory concentration values of some biocide actives in ppm...

Minimum inhibition concentration (ppm of the active ingredient in PVC film) against a number of bacteria Citrobacter freundii, Escherichia coli, Proteus vulgaris, Staphylococcus aureus, Salmonella choleraesuis. Enterococcus faecalis. Pseudomonas aeruginosa, Klebsiella pneumoniae) varied between (<200 and 400-600 ppm (<0.02-0.06%). It should be noted here that these bacteria are practically not relevant to WPCs, but rather to plasic-made biomedical devices. This example just shows a range of active antibacterial concentrations of the biocide. 

Essential oils are active in the inhibition of Gram positive and Gram negative bacteria, yeast, and fungi. These oils usually show weak to moderate activity when compared with chemical biocides such as antibiotics, quaternary ammonium salts, or chlorinated phenols such as triclosan. When the major components are isolated, they usually show improved activity compared to the essential oils. The test methods employed commonly determine inhibition activity via an MIC, but do not usually address the issue of MLC (minimum lethal concentration) or how quickly viable organisms are reduced over a short period of time. In order to determine this, other test methods need to be employed. Differences in... 

Those products that have good biocidal action against these microorganisms can be considered effective. Yet, surprisingly, many manufacturers of over-the-counter (OTC) formulations do not have documented evidence of effectiveness from in vitro studies [time-kill and minimum inhibitory concentration (MIC)] to support their label claims for preoperative skin preps. In vivo studies performed on human volunteers are designed to assure that the products are anti-microbially effective within 10 minutes of application and are antimicrobially persistent for up to 6 hours postapplication. 

Concern has been expressed about whether microorganisms could become resistant as a result of increased usage of antimicrobials, but it has been pointed out that they are different from antibiotics, because their attack on microorganisms is carried out by multiple mechanisms, and the development of resistance would therefore need more than one mutation. Moreover if the concentration of biocidal agent used in an inanimate material is higher than the minimum inhibitory concentration by a sufficiently large factor, any small decrease in susceptibility would be of little relevance. 

The minimum inhibitory concentration (MIC) of the biocides used in plastics varies enormously. OBPA has a low MIC value for most of the common organisms, but OIT requires mueh less biocide than OBPA for some species, and much more for others. 

The minimum inhibition concentrations of PCP listed in Table 43 demonstrate its extraordinary broad and equalized activity spectrum. Moreover PCP exhibits strong algicidal effectiveness in concentrations of 2-5-5 mg/litre. It is indeed more than a simple microbicide, namely a biocide that is also highly toxic for plants, fish, molluscs, insects and mammals. 

OBPA is a biocide, that means it is not only toxic to microbes but also to fish and other living species. Its antimicrobial effectiveness is similar to that of organo-mercurials covering a broad spectrum of bacteria, yeasts and mould producing fungi (minimum inhibition concentrations approx. 10 mg OBPA/litre). Among the fungal species Scopulariopsis brevicaule is relatively resistant to OBPA under use conditions. 

Table 13 Minimum microbicidal concentration (%) of glutaraldehyde (50%) (with and without soiling —0.2% albumin -) at contact time (source THOR Biocides Division)...

Before considering the mechanisms by which microorganisms exhibit resistance, it is well documented that different microorganisms have different responses or susceptibility to biocides. This is commonly known as the MIC or minimum inhibitory concentration that will affect the microbe. For example, hexachlorophene has a MIC of only 0.05 ug/ml with S. aureus, 12.5 ug/ml with E. coli, but a value of 250 ug/ml with P. aeruginosa conversely, the antimicrobial agent bronopol (2-bromo-2-nitro-1,3-propanediol) has a much narrower MIC range for these three bacteria (31.5 ug/ml for E. coli and P. aeruginosa and 62.5 ug/ml for S. aureus) [16]. 

Iodine is still commonly used in liquid and sofid forms for use in emergency preparation of drinking water sources. The solid forms are sold commercially by various vendors, and are widely distributed by the U.S. Army for use in austere environments. The U.S. Army iodine water purification tablets release 8 mg/1 iodine per tablet (Department of the Army, 2002). Current guidefines specify two tablets per 1-quart canteen of water with a minimum contact time of 35 min to disinfect and prevent giardiasis (Department of the Army, 2002). Among the species of iodine, elemental iodine (fy) and hypoiodous acid (HIO) are the forms with the greatest biocidal efficacy (White, 1999). At pH 8.0 and 25°C, the concentrations of fy and HIO are approximately equal (Snoeyink and Jenkins, 1980). 

It is important to note that antimicrobial and biofilm resistance are two different characteristics though some materials show both properties at the same time. Antimicrobial materials do not automatically prevent biofilm formation and vice versa. Antimicrobial surfaces could kill bacteria on contact but if dead bacteria cell debris blocks the active biocidal surface, biofilm formation could eventually occur. For example, quaternary anunonium polymers can effectively kill bacteria but when the surface is fouled with dead bacteria debris, biofilm formation is inevitable [188]. Materials with antibiofilm properties will repel the bacterial adhesion very effectively but may not kill the bacteria when they do colonize the surface. PEG surfaces are well known to repel bacteria adhesion. However, PEG surfaces show little antimicrobial activity. Quantitative antibiofilm efficacy tests can be divided into two categories static (minimum biofilm eradication concentration assay, MBEC) and dynamic (flow cell assay). In addition, SEM is a semiquantitative assay, which is discussed in Section 2.5. 

The total concentration of HOCl + OCl , expressed as the equivalent CI2 concentration in ppm or mg/L, is called free chlorine. The free chlorine disinfection level in residential swimming pools is maintained between 0.5 and 3 ppm and is usually controlled by simple colorimetric analysis. The biocidal activity of the acid form, HOCl or active chlorine, is more than 20 times stronger than the activity of the ionized OCl— form [2]. It is therefore critical to maintain a pH lower than 7.6-7.8 where the HOCl form is significant (see Fig. 1). The minimum recommended pH is 7 for bather comfort and pool material compatibility reasons. 

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