International Biodeterioration最新文献

The effect of bacterial growth products on seven industrial biocides used in metalworking fluids was evaluated. Prior bacterial growth in two typical metalworking fluids resulted in a substrate that uniformly reduced the effectiveness of all biocides when compared to the same unused metalworking fluids. Two selective results of growth in metalworking fluid, lowering of pH and production of sulfide, only affected two of the biocides.

Polysaccharides were extracted from culture supernatants and biofilms on mild steel surfaces incubated for 7 and 28 days in pure and mixed cultures of Pseudomonas fluorescens and Desulfovibrio desulfuricans P. fluorescens produced the highest quantities of free extracellular polysaccharides (EPS) but yielded the lowest hexose content in biofilms. The major neutral hexoses detected in all extracted polysaccharides were glucose and mannose, glucose being prevalent in biofilms and mannose in free EPS. Uronic acids were found only in biofilm polysaccharides.

Scanning electron microscopy and kinetic polarisation studies showed that little corrosion occurred on mild steel incubated in P. fluorescens cultures. High levels of corrosion were seen in mixed and, to a somewhat greater extent, in pure D. desulfuricans cultures. Extracellular polysaccharides on metal surfaces help to maintain the structure of the biofilm and in this way may serve to facilitate corrosion. There is no correlation between the levels of free EPS and corrosion.

The efficacy of 4,5-dichloro-2-n-octyl-3(2H) isothiazolone (C9211) was determined using fungi isolated from food and drink processing plants. The anti-fungal performance of urethane oil based paints containing C9211 was tested in (a) laboratory experiments using a humidity cabinet and (b) field trials at a UK maltings establishment and in Singapore.

The surface of the hard glossy paints without biocide proved to be inhospitable for the germination and growth of mould fungi in exposures in the humidity cabinet and reasons for this are discussed. In field trials, paints without biocide developed extensive mould growth after several months exposure whilst all paints containing C9211 remained mould-free throughout the 18 month trial.

In the culture of Vibrio cholerae in saline water containing purified chitin prepared from fresh shrimp and crab shells, it was determined that the solubility of chitin in salin water is influenced more by the salinity than by the pH, with the optimum being pH 8·0 and salinity 15 o/oo. The stimulation of growth by freshly extracted chitins and commercially available preparations was similar. All chitin preparations stimulated growth somewhat less than did alkaline peptone broth (a commonly used culture medium). All chitin sources also stimulated the production of cholera toxin by toxigenic strains to about the same extent as did alkaline peptone broth. The strains were found to be very low toxin producers in filtered bay water alone, thus indicating the need for some nutrient source for this activity.

A number of national and international methods developed during the last 15 years for evaluating the wet-state microbiological resistance of a wide range of aqueous formulations are compared and critically reviewed. General principles for testing the efficacy of biocidal additives in industrial aqueous-based products have been drawn from them and described. These principles were validated by the testing of five commonly available biocides in five different products. An emulsion paint, a metalworking fluid and a starch-based adhesive were tested for resistance to wet-state bacterial infection, and a bituminous emulsion and a ready-mixed ceramic tile adhesive were examined for resistance to wet-state surface fungal growth. The results not only indicate relative differences in the susceptibility of such products to microbiological infection but emphasise the effect of preconditioning the biocide in the test formulation prior to inoculation with the challenge organisms.