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Biomedical subjects

K K Kwan

Publications and source records attributed to K K Kwan.

10 recordsLinked to original sources
PubMed1995

Toxicity of organomercury compounds: bioassay results as a basis for risk assessment.

A former mercury plant, where mercury salts and organomercurials for pesticide use were produced, caused soil contamination in high concentrations. Typical organomercurial products included ethylmercury, phenylmercury, methoxyethylmercury and ethoxyethylmercury compounds. Risk assessment of these sites must be carried out before any major clean-up processes can be planned. A sensitive speciation technique for the various organomercury species in environmental matrices is a prerequisite for toxicity investigations. In this connection, a high-performance liquid chromatography-atomic fluorescence spectrometry (HPLC-AFS) technique has been developed to differentiate between and determine the presence of eight organomercury compounds in environmental samples. Using this technique, methylmercury, ethylmercury and phenylmercury and some unknown organomercury species were found in soil samples collected from the sites of an old mercury products producing plant. With regard to risk assessment, it is necessary to assess the toxicity of the organomercurials. As different microbial metabolic pathways react differently to mercury and its compounds, batteries of bioassays are, therefore, useful to evaluate the toxicity of pollutants. To describe the toxicity and genotoxicity of MeHg+, MeOEtHg+, EtHg+, EtOEtHg+ and PhHg+, p-tolymercury chloride, nitromersol and Hg2+ six bioassays were used: resazurin reduction method, Spirillum volutans test, nematode toxicity assay Panagrellus redivivus, Toxi-Chromotest and SOS-Chromotest. A ranking of the toxicity of the organomercurial is shown. The SOS-Chromotest indicated genotoxicity for 5-7 organomercurials.

Animals↗
PubMed1985

Identification of proteolytic pseudomonads isolated from raw milk.

Proteolytic pseudomonads isolated from raw milk were classified by numerical taxonomy. Unweighted pair-group average-linkage cluster analysis was used to cluster 49 bacterial strains, of which 26 were Pseudomonas species, as described in the Bergey's Manual of Determinative Bacteriology, based on 52 characters. The milk isolates resided in two clusters; one containing Pseudomonas fluorescens and the other Pseudomonas fragi. The isolates identified with Pseudomonas fluorescens hydrolyzed milk proteins and milk fat and produced phospholipase. The Pseudomonas fragi-like isolates hydrolyzed milk proteins and milk fat but did not produce phospholipase and fluorescent pigment. The hydrolytic characteristics of milk isolates showed that the nature of the substrate and conditions under which the test was conducted were critical.

Animals↗
PubMed1984

Study of long term effects of oil and oil-dispersant mixtures on freshwater microbial populations in man made ponds.

In this paper, the results of a 19 month investigation of microbial communities subjected to the effects of oil and oil plus dispersant additions in man made ponds are reported. Microbial biomass estimations by ATP (adenosine triphosphate) and microscopic procedures using epifluorescence indicated that oil and oil plus dispersants had little or no effect on these parameters, and any effect noted was stimulatory. However, detailed examination of specific populations indicated that oil and oil plus dispersant additions were stimulatory for short periods of time to the populations studied. Seven days after the oil and dispersant additions to the ponds, no mutagenic or toxic activities to bacteria were noted.

Adenosine Triphosphate↗
PubMed1978

Health--indicator bacteria in water--surface microlayers.

The distribuution patterns of a variety of bacteria in the surface microlayer, 20 cm and 100 cm below the surface of rivers, open lake waters, and off docks are presented. Implications of this three-season study are that conventional sampling techniques underestimate the true microbiol densities.

Fungi↗
PubMed1977

Confirmation of the single-step membrane filtration procedure for estimating Pseudomonas aeruginosa densities in water.

The efficiency of two procedures, membrane filtration and most probable number, to resuscitate and enumerate Pseudomonas aeruginosa have been compared at two temperatures and varying incubation periods. Data indicate that the membrane filtration procedure using mPA or mPA medium B is more efficient than the most-probable-number procedure in estimating P. aeruginosa populations. It was also found that the specificity of the membrane filtration procedure was such that 92 to 99% of the colonies counted as P. aeruginosa were confirmed, whereas only 2.7 to 10% of the nontypical colonies were confirmed as P. aeruginosa. Furthermore, the data indicate that mPA medium B combined with a 3- to 4-day incubation period at 4.15 degrees C is slightly more specific than mPA medium and is a valid single-step procedure for the resuscitation and enumeration of P. aeruginosa from water or sewage effluent.

Culture Media↗