The effects of microbial contamination

1 Effects on products. The effects of microbial contamination on polymer dispersions themselves are listed as items 1-8 in Table 10 with other effects on production plants and the environment. 

The author has also, unusually, seen examples of polymer dispersions where an inerease in viscosity has occurred as a result of microbial infection. The mechanism of this has not been investigated but is thought to be due to microbial add production (see below), causing a reduction in pH and flocculation of one or more of the dispersion s ingredients. 

2 pH changes. pH ehanges, most usually a reduetion in pH, can arise due to fermentative metabolic processes of microbial cells, breaking down eolloidal eomponents of the product. The most common metabolic products are simple organie aeids eausing a reduetion in pH by one or more full pH units. As noted above, this acid production can lead to produet destabilisation as well as possible corrosion to storage vessels and containers. 

Occasionally an increase in pH has been noted and this is thought to be as a result of seeondary infection with one of the ammonia-producing bacteria, e.g. Brevibacterium sp., although there is no evidence that this is the case. 

3 Gas formation. Most commonly, any initial gas production will be of carbon dioxide, resulting principally from the metabolism of fermentative bacteria breaking down colloidal thickeners, e.g. cellulose to 

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The effects of microbial contamination on the coolants and the surrounding area in the factory can result in expensive problems. 

Environmental effects. As with plant related problems, the effects of microbial contamination on the environment both inside and outwith the production area are several and varied. One most noticeable effect is that of foul odour with potential associated health risks. 

Effect on the manufacturer s business. It must not be forgotten that we exist in a commercial world. The effect of microbial contamination on product quality can severely damage a manufacturer s reputation in the market to the extent that they may lose the business in part or totally, or even suffer high financial claims for the end-user s losses, which may be settled in or out of court. All this can lead to interrupted work in production, additional time which must be put in to rectify the quality incident and disposal costs. Unwanted microorganisms are expensive ... 

As distinct as most other physical or chemical parameters in production, which can be controlled immediately, the effects of microbial contamination may not become apparent until it is too late to take efficient actions to keep the product in specification. 

In the general chapter on microbial attributes of nonsterile pharmaceutical products, the guidance suggests that the presence of microbial contaminants in nonsterile products [25] can reduce or inactivate the therapeutic activity of the product and has the potential to adversely effect the health of the patients and recommends manufacturers to ensure that contamination levels are as low as possible for finished dosage forms. Microbial enumeration limits for raw materials (total aerobic microbial count and total combined yeasts and molds count) and finished dosage forms are described. For inhalation, nasal, and topical routes of administration, tests for total aerobic microbial count and total combined and yeast and mold count,... 

The main factors influencing CP remediation include temperature, the properties of the environmental matrix, the toxicity of CPs or other compounds, and the composition of indigenous or added microbial cultures (Crawford Mohn, 1985). Unlike many other xenobiotics, CPs undergo insignificant volatilization (Valo Salkinoja-Salonen, 1986 Lamar et al., 1990b Mueller et al., 1991a). The temperature, the contaminant bioavailability, the possible process amendments and the effects of additional contaminants are discussed below. 

The parasites which cause plant diseases may be spread by wind, rain, insects, birds, snails, slugs, and earthworms, transplant soil, nursery grafts, vegetative propagation (especially in strawberries, potatoes, and many flowers and ornamentals), contaminated equipment and tools, infected seed stock, pollen, dust storms, irrigation water, and people. Figure 3.8 illustrates the effects of microbial infection of various fruit trees. 

It can therefore be concluded that all plastics are capable of sterilisation but need the selection of the most suitable process. Plastics will not support the growth of microbial contaminants unless the surface is wet or a high storage RH is involved. The bioburden may be increased by certain particulates, particularly if these consist of materials which will support growth. Material cleanliness and low particulate levels are therefore a prerequisite for a fully effective sterilisation process. 

Sinks and drains should be avoided wherever posable and should be exduded from areas where aseptic operations are earned out Where installed they should be designed, located, and maintained so as to minimize the risks of microbial contamination they should be fitted with effective, easily deanable traps with air breaks to prevent back-flow. Any floor channel should be open and easily deanable and be connected to drains outside the area in a manner that prevents ingress of microbial contaminants. 

In the case when it is necessary to do some intervention it is necessary to ponder the possible side effects. One needs to assess the global impact on the object of the intervention (there could be also other impacts on the surrounding environment). This applies to all possible interventions even preventive ones. In Fig. 1.2 it is possible to observe a situation where the use of a metallic net to protect the statuary of a church has contribute to the development of brownish stains in the statues. This must be kept on mind to be alert to some proposals such as the application of brass strips on object sites exposed to run-off rainwater having in mind the control of microbial contamination that, as discussed in Warscheid, and Braams (2000) could lead to greenish stains. Of course sometimes is a question of choosing the lesser of two evils (however in the previous case one could be altical about which would be... 

Microbial contamination is a universal concern. In most studies, microbial metabolic activity on plant tissue surfaces contributes negligibly to overall metabolic activity and can be ignored. Contamination in plant cell cultures and plant tissues that have been severely damaged may be significant, however, and should be carefully considered. Microbial infection within tissue sections may have a significant effect on measured heat rate, but this has only been studied in a few tissues [29, 30]. Usually, the presence of microbial contamination can be detected by the characteristic exponential increase in heat rates with time characteristic of microbial growth. 

The effect of various pHs has been well known for some time. Acidic foods such as fmits tend to retard microbial growth and resist certain types of contamination. For this reason, the standards adopted industry-wide have been based on the processing of foods of high acidity (low pH). In the United States, the FDA has regulatory responsibiUty over the preparation, sterilization, and distribution of foods. 

An entirely different type of contamination arises from the presence of microbiota in a product. As in the case of chemical contamination, compendial requirements for microbiological purity exists. Pharmacopoeial standards vary from country to country, and manufacturers must use the specifications and kill times that meet local requirements. As of this writing, the criteria in the British Pharmacopoeia are more stringent than those estabUshed by the CTFA, which are stricter than those in the United States Pharmacopoeia. In order to meet commonly accepted standards of microbial purity, manufacturing faciUties must be periodically cleaned and all products that can support microbial growth must contain an effective preservative (6). 

Wu Q, DL Bedard, J Wiegel (1997a) Effect of incubation temperature on the route of microbial reductive dechlorination of 2,3,4,6-tetrachlorobiphenyl in polychlorinated biphenyl (PCB)-contaminated and PCB-free freshwater sediments. Appl Environ Microbiol 63 2836-2843. 

PBBs are therefore not only debrominated microbially under anaerobic conditions, but are also able to induce effective dechlorination of their chlorinated analogs. Debromination may, however, be limited in the presence of other contaminants. 

There has been considerable interest in the use of plants for bioremediation and this merits a rather extensive discussion. Plants can play an important role in bioremediation for several reasons (1) they can transport contaminants from the soil, (2) they can metabolize the contaminants after uptake, or (3) they can produce exudes that support microbial activity for degradation of the contaminants. In addition, bacteria can produce metabolites that counter the effect of toxins produced by fungi, and serve as biocontrol agents that diminish the need for the application of agrochemicals. Plant exudates play an important role in supporting the growth and activity of bacteria that carry out the degradation of contaminants in the rhizosphere and rhizoplane (the external surface of roots... 

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