Bactericidal processes

Bactericidal processes which can be most effectively and practically used to eliminate salmonellae from foods appear to be mainly limited to the application of heat or of irradiation. As discussed by Mossel and Ley , ionising radiation is particularly technically attractive with its highly penetrative biocidal properties and because it can uniquely be used to terminally pasteurise previously frozen or packaged food products. On the theoretical basis of reducing the population of salmonellae by a factor of 10, i.e. 6 log cycles, the most probable effective dose (MPED) has been estimatedto be 0-4 0-2 Mrad (4 0 2 0kGy) and 0-25 Mrad has been shown to inactivate at least 3 log cycles of salmonellae on deep-frozen boiler carcasses under simulated commercial conditions A cautionary note was introduced by Urbain in 1978, however, who considers that salmonellae radicidation may be uneconomic unless universally required by government legislation and Davies Sinskey have shown that radiation-resistant mutants of S. typhimurium potentially exist and can be selectively isolated in extreme, cyclic irradiation circumstances. 

Acetic anhydride is a useful solvent in certain nitrations, acetylation of amines and organosulfur compounds for mbber processing, and in pesticides. Though acetic acid is unexceptional as a fungicide, small percentages of anhydride in acetic acid, or in cold water solutions are powerful fungicides and bactericides. There are no reports of this appHcation in commerce. It is possible that anhydride may replace formaldehyde for certain mycocidal apphcations. 

Antibiotics are produced by fermentation. The process may take a few days to obtain an extractable amount of product. Antibiotic production is done by the batch process. Oxygen transport is the major concern therefore sufficient polymeric sugar and protein with a trace amount of elemental growth factors are used to enhance production. An anti-biogram test is used to observe the amount of antimicrobial agent in the fermentation broth. A bioassay determines the activity unit of the bactericides. 

The tetracyclines exert their effect by inhibiting bacterial protein syndiesis, which is a process necessary for reproduction of die microorganism. The ultimate effect of diis action is tiiat the bacteria are either destroyed or dieir multiplication rate is slowed. The tetracyclines are bacteriostatic (capable of slowing or retarding die multiplication of bacteria), whereas die macrolides and lincosamides may be bacteriostatic or bactericidal (capable of destroying bacteria). 

The reason for this varied behaviour is not difficult to find. A population of bacteria does not possess the uniformity of properties inherent in pure chemical substances. This fact, together with the varied manner in which bactericides exert their effect and the complex nature of the bacterial cell, should provide adequate and satisfying reasons why the precise theories of reaction kinetics should have failed to explain the disinfeclion process. 

In 1880, the bacteriologist Robert Koch had noted that anthrax spores were more rapidly killed by the same concentrahons of phenol if the temperature was elevated. A former pharmacopoeial sterilizahon process heating with a bactericide used an elevated temperature, 80-100°C, maintained for 30 minutes, to ensure that quite low concentrations of bactericides would sterilize parenteral injections and eye-drops. 

Table 1 below represents the types of biocides that were used during the pulping process and subsequent biocides that have been introduced over the last few years to assist in the reduction of microbial contamination. In general, they types of biocides that are now being utilised are fast acting bactericides to prevent the anaerobic activity which results in the production of odours and blackened pulp. 

Siloxane compounds, in vitreous silica manufacture, 22 414 Siloxane materials, 20 240 Siloxane oligomers, in silicone polymerization, 22 555-556 Siloxanols, silylation and, 22 703 Silsesquioxane hybrids, 13 549 Silsesquioxanes, 15 188, 22 589-590 SilvaGas process, 3 696, 697 Silver (Ag), 22 636-667. See also Silver compounds. See Ag entries Argentothiosulfate complexes Batch desilverizing Lead-silver alloys Palladium-silver alloy membranes analytical methods for, 22 650-651 applications of, 22 636-637, 657-662 as bactericide, 22 656, 657, 660 barium alloys with, 3 344 in bimetallic monetary system, 22 647-648 in cast dental gold alloys, 8 307t coke formation on, 5 266 colloidal precipitation color, 7 343t colloidal suspensions, 7 275 color, 7 334, 335... 

Other components of the formulated catalyst were also tested for their germicidal properties. The desiccant is a good bactericide and cloth coated with the desiccant maintained a sixty percent reduction during the entire test as shown in Fig. 12.9-9a. The desiccant deactivates and kills the bacteria by rapid dehydration. However, this process is not as effective for airborne fungi (Fig. 12.9-9b). 

Ozone might interfere with the intracellular bactericidal capabilities of alveolar macrophages by inactivating lysosomal hydrolases, or perhaps through the destruction of heme-containing enzymes that are apparentiy involved in producing superoxide anion radical. Further evaluation of the process by which relatively low concentrations of ozone potentiate bacterial infection would be of value. 

TiOj coated fabric filters were prepared in a one-step process by the solvothermal method, and their properties were compared with those electrosprayed with Degussa P25. Filters coated with TiO nanoparticles prepared by the solvothermal method were superior to the commercial TiO powder in terms of particle size and homogeneity. A significant amount of bactericidal activity towards E. coli was successfully implanted into fabric filters by dip coating a solvothermally prepared TiO dispersion. 

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