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S Venitt

Publications and source records attributed to S Venitt.

At least 55 records · Page 3Linked to original sources
PubMed1989

A study of the heterogeneity of bacterial fluctuation-test data and the effects of auxotrophic-growth enhancement.

Microtitre fluctuation tests using Salmonella typhimurium TA100 and TA98 and Escherichia coli WP2uvrApKM101 were performed to determine the heterogeneity of spontaneous mutagenicity data and how this affects interpretation of results. Assays were performed in the absence and presence of additional amino acids to simulate the effects of the auxotrophic growth enhancement characteristic of tests of complex biological mixtures. The results indicate that the heterogeneity of the data did not depart significantly from that expected from binomial theory and that two criteria must be satisfied in order to define a positive result: (i) a net increase which significantly exceeds the background mutation and which takes account of its heterogeneity; and (ii) a statistically significant dose response.

Data Interpretation, Statistical↗
PubMed1988

The bacterial mutagenicity of synthetic all-trans fecapentaene-12 changes when assayed under anaerobic conditions.

Fecapentaenes are potent mutagens produced in the anaerobic environment of the human colon. The aim of this study was to determine the effect of anaerobic conditions on the bacterial mutagenicity of all-trans fecapentaene-12, a synthetic fecapentaene. Fecapentaene-12 was tested aerobically and anaerobically at doses from 0.25 to 4 micrograms/plate in agar-overlay assays with Salmonella typhimurium TA98 and TA100 and Escherichia coli WP2uvrA(pKM101), and 0.01 to 2 micrograms/ml in fluctuation test with TA100. In agar-overlay tests, fecapentaene-12 was less mutagenic to the frameshift mutant TA98 under aerobic conditions than under anaerobic conditions (average slopes of 3.8 and 31.6 revertants/micrograms respectively). Aerobic assays using TA100 and E. coli WP2uvrA-(pKM101) gave respective slopes of 62.9 and 167.6. Anaerobic assays with these base-substitution mutants gave negative results under conditions in which positive controls were mutagenic. However, the numbers of spontaneous revertants in these anaerobic assays were substantially lower than normal. Microtitre fluctuation tests, known to perform equally well under both aerobic and anaerobic conditions, were conducted with TA100 to confirm that the activity of fecapentaene-12 as a base-substitution mutagen was attenuated under anaerobic conditions. Replicate aerobic assays gave an average slope (revertants/well/microgram) of 0.41, compared with 0.056 for anaerobic assays--a greater than 7-fold difference. There was no significant difference in slope between aerobic and anaerobic positive controls. Thus, fecapentaene-12 may have two distinct modes of action, acting as a base-substitution mutagen and as a frameshift mutagen. Anaerobic conditions suppress the base-substitution activity but not the frameshift activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobiosis↗
PubMed1987

Lack of mutagenic activity of bile acids in bacterial fluctuation tests.

3 bile acids (cholic acid, chenodeoxycholic acid and deoxycholic acid) were assayed for mutagenicity in Salmonella typhimurium TA98 and TA100 in fluctuation tests in the absence of an external source of metabolic activation. At the doses tested, there were no dose-related statistically significant increases in mutagenicity compared with appropriate controls. These results do not support the claim (Watabe, J., and H. Bernstein (1985) Mutation Res., 158, 45-51) that these bile acids are mutagenic.

Bile Acids and Salts↗
PubMed1987

The toxicity and mutagenicity of the anti-tumour drug 5-aziridino-2,4-dinitrobenzamide (CB1954) is greatly reduced in a nitroreductase-deficient strain of E. coli.

In the 1970s it was shown that the monofunctional alkylating agent CB1954 (5-aziridino-2,4-dinitrobenzamide) kills the Walker rat carcinoma 256 in vivo and in vitro, but is inactive against several other tumours. In studies with bacteria, the large differences in survival in DNA-repair-proficient and deficient strains of Escherichia coli B treated with CB1954 were characteristic of a difunctional cross-linking agent. It was concluded that DNA was the only target large enough to receive significantly more than one lethal hit per molecule and that mono-alkylation alone could not account for the lethal effects of CB1954. In 1986 it was shown that CB1954 induced DNA interstrand cross-links in CB1954-sensitive cultured Walker 256 cells, but not in resistant Chinese hamster V79 cells, suggesting that the sensitivity of Walker cells results mainly from their activation of the drug to a difunctional agent by nitroreduction. To test this, we assayed the toxicity and mutagenicity of CB1954 in nitroreductase-plus and -minus strains of E. coli WP2uvrA. Agar-overlay assays showed that CB1954 was mutagenic to several strains of E. coli WP2, in a dose range 1-100 micrograms per plate, with slopes (mutants/nmol) of 7.1, 1.05 and 0.16 for WP2uvrA pKM101, WP2uvrA and WP2. Assays with nitrofurazone showed that these strains possessed nitroreductase activity. However, E. coli NFR-343, a nitrofurazone-resistant mutant of WP2uvrA which lacks nitroreductase activity was markedly less sensitive to the mutagenicity of CB1954, giving a mean slope of 0.12 compared with 1.15 for WP2uvrA. Aroclor-induced rat-liver S9 did not change these responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Antineoplastic Agents↗
PubMed1987

A forward mutation assay using ampicillin-resistance in Escherichia coli designed for investigating the mutagenicity of biological samples.

The development of a bacterial mutation assay using forward mutation to ampicillin-resistance is described. It is a technically simple assay using Escherichia coli D494uvrB transformed with a multi-copy mutator plasmid pGW1700. Mutation is detected by an increase in the frequency of ampicillin-resistant colonies following treatment of bacteria with the test material during logarithmic growth. The determination of viable counts allows a correction factor to be applied to compensate for the effects of sample-induced growth enhancement or toxicity on the bacterial population. The assay has been tested with a range of reference mutagens. It is particularly sensitive to base-pair substitution mutagens, detecting these at doses equal to or less than those detected in the Salmonella/microsome assay or the SOS Chromotest. The assay also detects frameshift mutagens but with lower sensitivity than the Salmonella/microsome assay.

4-Nitroquinoline-1-oxide↗
PubMed1986

Carcinogenicity and mutagenicity of chromium compounds: the association between bronchial metaplasia and neoplasia.

Over the last 40 years, experiments with animals and epidemiology of exposed human populations have established that certain hexavalent chromium-containing compounds are capable of causing cancer whilst trivalent materials are not. More recently, a variety of short-term genotoxicity tests (predictive of carcinogenicity) have clearly demonstrated that Cr[VI] is genotoxic per se, and that all Cr[VI]-containing materials which have been tested are genotoxic. What experiments have failed to demonstrate clearly, however, is which of the myriad of industrially available hexavalent materials are carcinogenic and which are not. In this long-term study we have looked at the incidence of squamous metaplasia in the bronchial epithelium of rats exposed to a range of chromium-containing materials by intrabronchial implantation. Squamous metaplasia is generally considered to be a transformed state from which squamous carcinoma may arise. We have shown that its incidence is increased in all groups exposed to Cr[VI]-materials, and in rats exposed to the reference carcinogen 20-methylcholanthrene. Squamous metaplasia was not increased in rats exposed to Cr[III] materials. Of rats exposed to Cr[VI], only those receiving materials of sparing aqueous solubility developed bronchial squamous carcinoma at statistically significant levels. These results strongly support the hypothesis that although Cr[VI] per se is biologically active, producing genotoxic effects and pathological changes which may predispose to the development of cancer, only Cr[VI] materials of sparing aqueous solubility seem to be capable of evoking a carcinogenic response.

Animals↗
PubMed1986

Further studies on the detection of mutagenic and genotoxic activity in human faeces: aerobic and anaerobic fluctuation tests with S. typhimurium and E. coli, and the SOS Chromotest.

The product of six complete bowel movements were collected from one man (consuming a normal western diet) over a period of 5 months. Aqueous faecal extracts were prepared (0.75 g wet wt./ml water) under aerobic and anaerobic conditions. Graded doses were assayed aerobically and anaerobically for mutagenicity in replicate microtitre fluctuation tests employing histidine reversion in Salmonella typhimurium TA100 and tryptophan reversion in Escherichia coli WP2uvrA(pKM101), and in aerobic SOS Chromotests, using E. coli PQ37. The histidine and tryptophan content of each extract was determined by (i) pre-column derivatisation with o-phthaldialdehyde followed by reverse-phase h.p.l.c. and (ii) by aerobic and anaerobic bioassays employing appropriate auxotrophic strains of S. typhimurium and E. coli. All six faecal samples contained enough histidine and tryptophan or their precursors to compromise the interpretation of fluctuation tests. The h.p.l.c. technique, though quantitatively detecting free tryptophan added to faecal extracts, did not account for growth-enhancing effects of faecal extracts detected by bioassay using bacteria with a requirement for tryptophan. However, h.p.l.c. detected histidine more efficiently than bioassays. A combination of reconstruction experiments and bioassays enabled construction of 'growth windows' within which, in fluctuation tests, dose-related increases in numbers of positive wells could be ascribed to mutation rather than to feeding of auxotrophic bacteria. Under aerobic conditions of extraction and assay, five out of six samples were mutagenic to S. typhimurium TA100, and all six were mutagenic to E. coli WP2uvrA(pKM101). None of the samples extracted and assayed anaerobically was mutagenic to S. typhimurium, but all six were positive in E. coli WP2uvrA(pKM101). There was an increase both in faecal histidine and tryptophan and in mutagenicity during the period of collection, the association between faecal tryptophan and faecal mutagenicity being statistically significant. All the samples were negative in the SOS Chromotests. We conclude that this donor regularly excretes faeces which contain at least two classes of water-soluble directly-acting mutagens which are not detected in SOS Chromotest at doses five times those giving positive effects in fluctuation tests.

Aerobiosis↗
PubMed1986

Testing human faecal extracts for genotoxic activity with the SOS Chromotest: the importance of controlling for faecal enzyme activity.

Two aqueous extracts of human faeces were prepared from a healthy male donor and assayed in the SOS Chromotest. Both extracts were positive in microtitre fluctuation tests in Salmonella typhimurium TA100 and Escherichia coli WP2uvrA(pKM101). Differences were observed in the induction factors of these samples when p-nitrophenyl-beta-D-galactopyranoside (p-NPG) and o-nitrophenyl-beta-D-galactopyranoside (o-NPG) were used as substrates for the beta-galactosidase assay in the SOS Chromotest. With one sample, a positive induction factor was reproducibly obtained using p-NPG but not o-NPG. When the bacterial cells were washed with fresh LB broth before enzyme assay, the positive induction factor obtained with p-NPG was reduced to an insignificant level. During the 2-h treatment period, both faecal samples enhanced bacterial growth above that of the zero-dose control. When SOS Chromotest assays were performed with no bacteria or with S. typhimurium TA100 or hisG46 (non-lactose fermenting organisms) in place of E. coli PQ37, it was found that the extracts contained significant levels of endogenous beta-galactosidase and alkaline phosphatase, which, due to their carry-over in the bacterial pellet (after centrifugation to remove the coloured extract) gave rise to the positive induction factor obtained with p-NPG. The results obtained in these experiments indicate that where the SOS Chromotest is applied to biological samples, care should be taken in the interpretation of the data and that a washing step should be included to prevent possible errors occurring due to exogenous enzymes in the sample.

Alkaline Phosphatase↗
PubMed1986

Pilot study of the effect of diet on the mutagenicity of human faeces.

A healthy non-smoking man, consuming a normal 'western' diet (meat, vegetables, bread and alcohol) collected five consecutive complete bowel movements. He then added an extra 150 g of fat (from butter, cheese, milk, chocolate, peanuts, bacon and eggs) to his daily diet for 2 weeks, and collected four further consecutive bowel movements in the second week. After 6 months on his normal diet, he added 30 g of wheat bran to his daily diet for 3 weeks, and collected four complete stool samples in the third week. Aqueous faecal extracts were prepared and assayed for auxotrophic growth-enhancement and bacterial mutagenicity (using fluctuation tests with Salmonella typhimurium TA100 and Escherichia coli WP2uvrApKM101). There was no significant difference in faecal wet weight between 'normal' and 'high-fat' collections, but addition of 30 g bran was associated with a 1.8-fold increase in stool weight, in good agreement with published data. Fluctuation tests showed that normal and high-fat samples were mutagenic to S. typhimurium TA100 and to E. coli WP2uvrApKM101. There was considerable variation in mutagenic activity between consecutive bowel movements. However, there was no significant difference in mutagenicity between normal and high-fat samples. Faecal samples collected during the course of the high-fibre diet were significantly less mutagenic to both bacterial strains. Changes in auxotrophic growth-enhancing activity could not account for these changes in mutagenicity, since the pattern of change in growth-enhancement was very different from that seen for mutagenicity.

Adult↗