International Biodeterioration最新文献

The formulation of a specialised disinfectant, which produces a clear solution on addition to water, as opposed to an emulsion, and designed to meet the needs of livestock house hygiene routines is described. Laboratory tests indicated that mixed phenols are effective in controlling organisms associated with the diseases of farm livestock particularly in view of modern methods of intensive farming. Field trials substantiated the results obtained from the laboratory tests.

Biofilms are ubiquitous in nature and microorganisms often exist as members of complex consortia, rather than as pure cultures. Their localised metabolic activity can create diffusion gradients of nutrients, fermentation byproducts and possible associated corrosion products within the biofilms; together with cell lysis, these cause a mosaic of microenvironments which may be totally different to the bathing phase. Such habitats pose a major, and often ignored, constraint on the interpretation of results obtained from laboratory disinfection models which can be physically, environmentally and physiologically inappropriate. For example, the most commonly used model for inactivation of microorganisms by biocides utilises the so-called ‘Chick- Watson law’: this implies that biocide concentration and contact time, the (C × T) factor, are the two key variables determining biocide efficacy. However, applications of the ‘law’ have assumed complete and uniform mixing of microorganisms and biocide, ignoring that diffusion might be rate limiting and that biocide concentration might decrease with time. Recent results suggest that many of the viable bacteria in chlorinated potable water are attached to surfaces and under these circumstances coliforms have withstood at least 12 ppm free residual chlorine. The use and efficacy of alternative biocides such as monochloramine against aquatic biofilms is discussed.

The assessment and management of human health risk from biocides is an iterative and multidisciplinary scientific process that seeks to define the inherent hazards of the material and integrate this information with the details of potential human exposure. This paper attempts to outline the critical elements and relationships in this process while presenting the risk assessment process for Kathon microbicides (blend of isothiazolones, 3:1 ratio of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one: MCI/MC) as an illustrative example.

Samples were taken from heavily moulded walls at a range of food and drink processing plants. Quantitative estimates of the number of moulds, yeasts and bacteria were made and the moulds were identified. The floristic diversity of the germination areas and kilns of several maltings establishments was also investigated. The most commonly isolated organisms were Penicillium spp. although each environment appears to have its own characteristic flora with more than 50% of the total colony forming units isolated at each site being accounted for by three or fewer species. The results are discussed in relation to the microflora of mouldy walls in other environments.

Several of the fungi associated with the maltings establishments were not found at any other sites. The origin of these fungi is discussed in relation to the flora associated with grain and processing of malt.

The role of Cu²⁺ in enhancing 5-chloro-2-methyl-4-isothiazolin-3-one (IT) activity was investigated. This study was carried out in two directions. Firstly, the level of enhanced activity from a Cu²⁺ and IT mixture where environmental destruction of IT is minimal was examined. Secondly, the level of protection from Cu²⁺ in environments known to irreversibly reduce IT activity was studied. The bactericidal activities were determined in tryptic soy broth medium, mineral salt base-glucose medium and 0·9 NaCl solution. Under certain conditions, Cu²⁺ also stabilizes and/or protects the sensitive chlorinated IT molecule. Both synergistic activity and stabilization or protection by Cu²⁺ enhance the antimicrobial activity of IT under test conditions. Alternative sequential treatment with IT and Cu²⁺ was used to further characterize enhanced activity. The results suggest synergism. The utility of all the findings was investigated in metalworking fluid.

Four biocides were tested for their abilities to kill Legionella micdadei and Pseudomona fluorescens in a buffered saline solution. The most effective against both organisms, at concentrations of 50 ppm or above, was a phosphonium compound, but this biocide failed to produce a 99·9% kill of P. fluorescens within 24 h at concentrations below 50 ppm. All chemicals apart from an oxidisingbiocide were more effective against L. micdadei than P. fluorescens. Old cells of Legionella, but not of Pseudomonas, exhibited increased resistance against BNPD. This could be associated with an altered outer envelope, demonstrated by SDS-PAGE analysis.