Cavitation Bacteria

The above two studies with actual contaminated water (possibly containing a wide range of bacteria/microorganisms) confirm the suitability of the hydrodynamic cavitation phenomena for microbial disinfection. Cost of the treatment is another important factor, which needs to be ascertained, before cavitation can be recommended as a replacement technique for the conventional methods of... 

Many cells, especially bacteria, yeast, etc., require very drastic measures to disrupt them and various cell disintegrators are available for this purpose. Ultrasonic vibrations cause the formation of minute bubbles, a phenomenon known as cavitation, which is caused by the extreme variations in pressure generated by the sound waves, although the generation of heat may cause problems unless the samples are cooled frequently during the treatment. An additional... 

Bacterial attack is an early stage in the degradation of wood exposed in wet or moist conditions. Bacteria can be the dominant form of attack when fungal decay is suppressed by a wood-preserving treatment. Bacteria can attack the cell wall of wood by tunnelling, cavitation or erosion mechanisms (Eaton and Hale, 1993). 

Low power ultrasound offers the possibility of enhancing the effects of chlorine. The results of a study of the combined effect of low power ultrasound and chlorination on the bacterial population of raw stream water are shown (Tab. 4.2). Neither chlorination alone nor sonication alone was able to completely destroy the bacteria present. When sonication is combined with chlorination however the biocidal action is significantly improved [10]. The effect can be ascribed partly to the break-up and dispersion of bacterial clumps and floes which render the individual bacteria more susceptible to chemical attack. In addition cavitation induced damage to bacterial cell walls will allow easier penetration of the biocide. 

Clarkson et al. (1986) conclude that proteolytic enzymes contribute to root lesion formation. Accordingly, Katz et al. (1987) found root cavitation with loss of matrix to occur in mild acidic solutions only in the presence of proteases. It is conceivable that the degradation of the matrix promotes the formation of a root lesion in two ways. First, the matrix forms a barrier to ionic diffusion, which is removed by degradation. Second, the degradation of the matrix yields nutrients, which may sustain the growth of cariogenic bacteria (Hojo et al., 1991). 

The most common oral condition and dental emergency is dental caries, which is a destructive disease of the hard tissues of the teeth due to bacterial infection with Streptococcus mutans and other bacteria. It is characterized by destruction of enamel and dentine. Dental decay presents as opaque white areas of enamel with grey undertones and in more advanced cases, brownish discoloured cavitations. Dental caries is initially asymptomatic and pain does not occur until the decay impinges on the pulp, and an inflammation develops. Treatment of caries involves removal of the softened and infected hard tissues, sealing of exposed dentines and restoration of the lost tooth structure with porcelain, silver, amalgam, composite plastic, gold etc. 

Bacteria and soft rot fungi are more tolerant of the low oxygen conditions in saturated wood, and in wood that is buried in sediments bacterial decay tends to predominate. Early reports identified unicellular bacteria in foundation piling and shipwreck timbers, but more recently three bacterial decay types in wood cell walls are now recognised - erosion, tunnelling and cavitation bacterial decay. 

Cell-Wall-Degrading Bacteria. The classification of bacterial decay types is based on the micromorphology of attack. Three main types of bacterial attack have been described so far through microscopy erosion, tunneling, and cavitation. They have been named after specific characteristics of the attack. Observations suggest that further forms of attack await description. Several other decay patterns of wood cells are suspected of being caused by bacteria, but no definite evidence is available. 

Good examples of attack by cavitation bacteria have so far only been... 

Bacterial attack has been observed in wood exposed in soil. The studies have mainly concerned posts treated with copper-chrome-arsenic preservatives. The reports show that erosion, tunneling, and cavitation forms of bacterial attack may occur 91, 92, 109-112). Extensive attack by bacteria in preservative-treated water-cooling slats was also reported by Greaves (100). 

Nilsson, T. and Singh, A. P., 1984. Cavitation bacteria. International Research group on Wood Preservation. IRG/WP 1235. 

It is evident that as a result of ultrasonic treatment some of the bacteria exposed to destruction apparently accompanied by the leakage of cytoplasm. However, most of the cells keep normal form. Bacteria pretreated with Theraphthal show a change in the shape and the destruction of the membranes that cover almost all the treated cells. This is confirmed by data on the survival of bacteria. Enhancing of effect of ultrasound treatment of cells is associated with the formation of calcium salts of Theraphthal solid phase on the membranes, thereby reducing the mechanical strength of membranes and enhancing the local cavitational effects. 

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