Micro-organisms resistance

Manipulation of the A, FT, and />, values in Eq. (11) will naturally produce different values of B. Accordingly, if it is desirable that B be as low as possible, this may be accomplished in one of three ways (1) reducing the bioburden A of the bulk product, (2) increasing the equivalent exposure time FT, or (3) employing a micro-organism with a lower D value at the specified temperature. Since option 3 most likely is impossible, as the most resistant micro-organisms of a fixed D value must be used in sterilizer validation, one must either employ techniques to assure the lowest possible measurable microbial bioburden prior to sterilization or simply increase the sterilization cycle time. 

The micro-organisms must have high resistance to the sterilization treatment which they are being used to validate. This does not mean that they must be the most resistant micro-organism known to man. B. stearothermophilus has D i-values of l min according to conditions of culture and the substrate upon which they are mounted. This is higher than most spores of Bacillus spp., which tend to have Di2i-values below 0.5 min. 

Resistance of pathogens to antimicrobial treatment is a major concern in veterinary medicine, just as in human medicine. Antimicrobial resistance negatively impacts both the current use and future development of pharmaceuticals for animals. For sick animals, antimicrobial resistance directly impairs the success of treatment to control disease. This can affect the prognosis and suffering for an individual animal and often the productivity, survival, and economic returns for an entire herd. Resistance may make it difficult to find effective, already approved drugs as active controls for preapproval clinical trials. The ability of resistant micro-organisms to move between humans and animals raises serious public health concerns. 

Effectiveness against already existing antibiotic-resistant micro-organisms ... 

Table 30.1 Themo-resistant micro-organisms T = temperature of D-value, D-value see text [4]...

The bioburden process is based on the initial contamination before sterilisation, and thus it is a tailored sterilisation process. Bioburden based sterilisation cycles are not commonly used in Europe. Prerequisite is that the number and thermo-resistance of the micro-organisms in the product are documented, based on which the customised sterilisation time can be calculated. An example can be found for parenteral solutions (for injection, for infusion) in reference [4]. In this example. No is 1 (rounded up) and the D-value at 100 °C of the most resistant micro-organism is approximately 2 min. Using equation 30.3, it can be calculated that a SAL of 10 will be obtained after 12 min. 

Normally two disinfectants are used alternately to prevent accumulation of resistant micro-organisms, however there is little evidence to support this [23]. 

Resistance to penetration by micro-organisms is covered by EN 374-2 and protection from low temperatures in EN 511. Careful handling and regular inspection are essential since chemicals and abrasion will eventually cause deterioration of gloves. Rinsing in clean water and drying naturally will prolong their life. 

As other cheaper materials usually give satisfactory performance, nickel and nickel alloys are not normally required for applications involving resistance to corrosion underground. Data on their behaviour in these circumstances are therefore sparse in particular, whether micro-organisms responsible for the accelerated corrosion of ferrous and other metals in certain anaerobic soils have any influence on nickel and its alloys, is uncertain. 

Micro-organisms with resistance to environmental stresses such as solvents, extremes of pH, high salt concentration, and having broad temperature and dissolved oxygen optima are more suited to process applications. Improved process instrumentation and... 

To achieve overproduction of phenylalanine, the micro-organism should be derepressed at the pheA level and free of inhibition at the arcG level. Both genes are located on the chromosomal DNA of the micro-organism and, by means of amino add analogues such as p-fluoro-DL-phenylalanine, it is possible to make (phenylalanine) feedback resistant mutants of E.cdi (pheA and oroF mutants). The following procedure can be used ... 

The ability of micro-organisms to produce pectic enzymes in vitro constitutes no proof of their pathogenicity. Some micro-organisms produce pectic enzymes on synthetic-nutrient media, but do not always possess the ability to produce them in vivo. An important role is here played by the susceptibility or resistance of the plant to the effect of the pathogen. Production of D-galacturonanase and pectines-terase by Fusarium oxysporum f. lycopersici was found to be much higher on susceptible than on resistant tomato-stems.287 Likewise,... 

Lignin comprises about 17-33% of the dry weight of wood. It is a complex aromatic polymer which appears to function both as a strengthening agent in the composite wood structure and also as a component which assists in the resistance of the wood towards attack by micro-organisms and decay. 

Antibiotics are routinely added to animal feed in conventional agriculture. This can have various effects on humans. Direct transmission of antibiotic residues in animal products to people may cause direct toxicity, i.e. allergies, or lead to the emergence of resistant strains of bacteria. Another threat is antibiotic-resistant forms of bacteria harmful to mankind that might appear in animals and pass from them to humans (Smith 1974), or may impart resistance to other bacteria by plasmid or transposon interchange (Franco et al. 1990). The resulting dmg-resistant and harmful micro-organisms can then not be treated successfully (Silverstone 1993). 

Chlorine is the oldest and most widespread method of water disinfection. In reverse osmosis systems, chlorine may be added to feedwater for control of micro-organisms and, in addition, to prevent membrane fouling by microbiological growth. According to Vos et al. [i,2], chlorine will attack cellulose diacetate membranes at concentrations above 50 ppm. Membranes were found to show a sharp increase in salt permeability and a decrease in strength after one week of continuous exposure. Under milder conditions (10 ppm chlorine for 15 days) no detectable change in performance was observed. Spatz and Friedlander [3] have also found cellulose acetate membranes to be resistant to chlorine when exposed to 1.5 ppm for three weeks. 

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