A comparison of the Ames assay and Mutatox in assessing the mutagenic potential of contaminated dredged sediment.

The ability of the Ames assay and of Mutatox to identify the genotoxic potential of dredged sediments was compared. The Ames assay has been used extensively in the testing of environmental contaminants, whereas Mutatox, a new bacterial bioluminescence test, has only recently been used for this purpose. Ten sediments with varying degrees of contamination were soxhlet extracted. Each of the 10 extracts was split with half remaining in a crude form and half cleaned using silica gel chromatography, resulting in 20 extract samples. Both the Ames assay (using Salmonella typhimurium strains TA98 and TA100) and Mutatox were conducted with and without S9 metabolic activation. When metabolically activated, TA98 and TA100 indicated a positive mutagenic response in 80 and 50%, respectively, of the sediment extracts. Without S9 activation, TA98 indicated a positive mutagenic response with half the extracts, whereas only 10% did so with TA100. Mutatox indicated a positive mutagenic response with S9 activation in 75% of the extracts and no mutagenic response in any of the sediment extracts without metabolic activation. In a side-by-side comparison of the Ames assay (TA98 with S9) and Mutatox, 80% of the sediment extracts had similar responses, both positive and negative. Fifty percent of the sediment extracts had similar responses when tested with TA100 and Mutatox in the presence of S9. Mutatox compared reasonably well with the Ames assay but was insensitive to the presence of direct-acting mutagens in the sediments tested. Although Mutatox demonstrates promise as a screening tool to assess sediment genotoxicity, the authors consider it appropriate to use the Ames assay as a confirmation for definitive investigations.

The luminescent bacteria toxicity test: its potential as an in vitro alternative.

During the past several years, the use of animals for toxicity testing has come under critical surveillance. For ethical and economic reasons, various techniques have been developed and proposed as potential alternatives for some of the whole animal toxicity assays. One assay proposed as an alternative to animal testing is the luminescent bacteria toxicity test (LBT), provided under the trade name of Microtox. The sensitivity and specificity of the LBT was compared with two commonly used toxicity tests--the L-929 Minimal Eàgle's Medium (MEM) elution cytotoxicity test and the Draize test. Cytotoxicity and LBT test data from 709 medical device and biomaterial extracts were compared using a positive/negative ranking system which provided a measurement of false positive and false negative results. These data were compiled from nine separate laboratories producing or using a wide variety of biomaterials and medical device products. The LBT was more sensitive than the tissue culture assay and displayed few false negatives. LBT EC50 values were compared with eye irritancy categories for a group of 34 chemicals and 27 personal care products. As with tissue culture, the LBT was more sensitive and produced minimal false negatives. The data from this study indicate the LBT has potential as a rapid, simple method to screen biomaterials and personal care products for toxicity and irritancy.

Use of the luminescent bacterial system for the rapid assessment of aquatic toxicity.

A simple and reliable method for monitoring the toxicity of aquatic samples has been developed. The assay is based on changes in the light output of luminescent bacteria, as measured by a temperature controlled photometric device. The new assay method described here correlates well with other bioassays yet requires less than thirty minutes to obtain a complete reportable assay. The assay system is an instrumental approach in which the bioassay organisms are handled like a chemical reagent. Data are presented which verify the sensitivity of this toxicity test. Data comparing this assay method with conventional procedures such as fish toxicity assays are also present. Various applications of this new test method, Microtox TM, are discussed.

Evaluation of thallium acetate-citrate medium for isolation of enterococci.

Thallous acetate-citrate (TAC) agar, a selective medium for isolating enterococci from frozen foods, was evaluated. Two types of bacteria, micrococci and group N streptococci, were responsible for erroneously high enterococcus counts on TAC agar. Selectivity of the medium was improved by the addition of 0.01% sodium azide.