A new strain of Salmonella typhimurium reverted by mitomycin C and N-methyl-N'-nitro-N-nitrosoguanidine--a possible universal tester for mutagenic compounds

A strain of Salmonella typhimurium, SO1007, which carries the amber mutation trpD28 plus the plasmid pKM101 was reverted very efficiently by two mutagens with different mutagenic specificities and modes of action: mitomycin C (MC) and N-methyl-N'-nitro-N-nitrosoguanidine (NG). By selecting revertants on minimal agar supplemented with anthranilic acid (AA), two distinct phenotypic classes of TrpD28 revertants can be recovered: prototrophs (MM+) and anthranilate utilizers (AA+). Since each phenotypic class is known to be caused by a variety of mutational events, reversion of trpD28 on minimal-anthranilate medium may be useful for detecting mutagenic agents regardless of the types of mutations they may cause. Thus, strains like SO1007 may be useful as 'universal' detectors of mutagenic compounds. In the course of these experiments we also observed that pKM101 does not protect but, on the contrary, sensitizes the host bacteria slightly to the toxic effects of MC.     

Structure-activity relationships for the mutagenic activity of tricyclic intercalating agents in Salmonella typhimurium

A total of 25 different tricyclic DNA-intercalating chromophores bearing a common -CONH(CH2)2N(CH3)2 solubilizing sidechain have been compared with the 'classical' frameshift mutagen 9-aminoacridine for their ability to induce revertants in Salmonella typhimurium strain TA1537 (sensitive to frameshift mutation by acridine mutagens). The compounds showed varying levels of activity in this strain. For the fused linear and fused angular tricyclics, activity varied from zero to similar levels to 9-aminoacridine, but with no discernable relationship between activity and either structure or the measured physico-chemical properties. However, the '2-1' tricyclic compounds had essentially no mutagenic activity. Since several of these compounds have high in vivo antitumor activity, this is useful knowledge.     

Toxic and mutagenic effects of formaldehyde in Salmonella typhimurium

Toxic and mutagenic activities of formaldehyde were studied in Salmonella typhimurium strain TM677, using forward mutation to 8-azaguanine (8-AG) resistance both in the absence and in the presence of Aroclor-induced rat-liver postmitochondrial supernatant (PMS). The results showed that formaldehyde was toxic and mutagenic to the bacteria in both systems, but toxicity and mutagenicity were reduced in the presence of PMS. The minimum concentration required to induce toxicity and mutagenicity was 0.17 mM in the absence of PMS and 0.33 mM in the presence of PMS.     

Induced mutagenesis in Salmonella typhimurium AG262 strain constructed for screening the mutagens

The Salmonella typhimurium strain AG262 has been constructed for screening of SOS-mutagens, such as UV-light and 4NQO, the Ames plasmidless tester strains of S. typhimurium being mutation-proof under the action of this class of mutagens. The strain AG262 has also been successfully used for screening of induced base pair change mutations occurring independently of cellular SOS-system of mutagenesis (MNNG, EMS, nitrofuran derivatives), and of the mutations induced by frame-shift mutagens (benzo/a/pyrene 7,12-dimethylbenzo/a/antracene ICR-191, 9AA, DDDTDP).     

Isolation of an azide mutagenic metabolite in Salmonella typhimurium

A scheme that employs a cation-exchange column and high-pressure liquid chromatography (HPLC) is devised to isolate and process large quantities of azide metabolite produced by S. typhimurium TA1530 strain. The mutagenic metabolite adheres strongly to the cation-exchange column, thus providing a convenient way to separate the metabolite from unreacted azide (N₃⁻). The metabolite is very polar and only sparingly soluble in most organic solvents. Recrystallization in a methanol-carbontetrachloride solvent system gave rise to microcrystalline material that decomposes with charring and gas evolution at 173–176°C. The infrared spectrum indicates the presence of a covalently bound azide moiety.     

Comparative antimutagenicity of 5 compounds against 5 mutagenic complex mixtures in Salmonella typhimurium strain TA98

Using the Ames Salmonella/microsome assay, we compared the antimutagenic activities of chlorophyllin, retinol, beta-carotene, vitamin C, and vitamin E against solvent extracts of coal dust, diesel emission particles, airborne particles, fried beef, and tobacco snuff. The results show that chlorophyllin inhibited 69% of the mutagenic activity of tobacco snuff and over 90% of that of the other 4 complex mixtures. Retinol inhibited 29-48% of the mutagenic activity of all 5 complex mixtures. beta-Carotene, vitamin C, and vitamin E inhibited, if any, less than 39% of the activity of the complex mixtures studied. Vitamin C enhanced the mutagenicity of airborne particles. These results indicate that for these dietary and environmental complex mixtures chlorophyllin is a more effective antimutagen than retinol, beta-carotene, vitamin C, and vitamin E.     

Preliminary characterization of a food-borne multiple-antibiotic-resistant Salmonella typhimurium strain

Plasmid characterization studies were conducted on a Salmonella typhimurium strain isolated from pasteurized milk and from a symptomatic patient during the 1985 Illinois salmonellosis outbreak. This strain (Hf) was reported to possess an unusual plasmid profile which distinguished it from all Salmonella strains isolated in the United States prior to 1984. Antibiotic susceptibility testing revealed that the strain was resistant to tetracycline, erythromycin, clindamycin, sulfisoxazole, sulfadiazene, triple sulfa, cefoperazone, streptomycin, mezlocillin, piperacillin, carbenicillin, penicillin, ampicillin, and kanamycin. Plasmid analysis revealed that the strain possessed four plasmids with sizes of approximately 158, 98, 10.2, and 6.0 kilobase pairs (kb). Successive transfer at 43 degrees C led to increased antibiotic sensitivity in 75.5% of the isolates screened. Electroporation and calcium chloride treatment were each used to transform plasmid-free Escherichia coli strains with the plasmid pool from S. typhimurium Hf. Plasmids introduced by transformation ranged in size from 4.4 to 23.2 kb and correlated with resistance to penicillin G, ampicillin, carbenicillin, cephalothin, cefoperazone, cefamandole, mezlocillin, piperacillin, and in some cases, tetracycline and kanamycin. DNA-DNA hybridization experiments localized these resistance genes to a highly duplicated 6.3-kb fragment of the total EcoRI restriction digest of the S. typhimurium Hf plasmid pool.     

Cloning of Salmonella typhimurium DNA encoding mutagenic DNA repair.

Mutagenic DNA repair in Escherichia coli is encoded by the umuDC operon. Salmonella typhimurium DNA which has homology with E. coli umuC and is able to complement E. coli umuC122::Tn5 and umuC36 mutations has been cloned. Complementation of umuD44 mutants and hybridization with E. coli umuD also occurred, but these activities were much weaker than with umuC. Restriction enzyme mapping indicated that the composition of the cloned fragment is different from the E. coli umuDC operon. Therefore, a umu-like function of S. typhimurium has been found; the phenotype of this function is weaker than that of its E. coli counterpart, which is consistent with the weak mutagenic response of S. typhimurium to UV compared with the response in E. coli.     

Preliminary characterization of a food-borne multiple-antibiotic-resistant Salmonella typhimurium strain.

Plasmid characterization studies were conducted on a Salmonella typhimurium strain isolated from pasteurized milk and from a symptomatic patient during the 1985 Illinois salmonellosis outbreak. This strain (Hf) was reported to possess an unusual plasmid profile which distinguished it from all Salmonella strains isolated in the United States prior to 1984. Antibiotic susceptibility testing revealed that the strain was resistant to tetracycline, erythromycin, clindamycin, sulfisoxazole, sulfadiazene, triple sulfa, cefoperazone, streptomycin, mezlocillin, piperacillin, carbenicillin, penicillin, ampicillin, and kanamycin. Plasmid analysis revealed that the strain possessed four plasmids with sizes of approximately 158, 98, 10.2, and 6.0 kilobase pairs (kb). Successive transfer at 43 degrees C led to increased antibiotic sensitivity in 75.5% of the isolates screened. Electroporation and calcium chloride treatment were each used to transform plasmid-free Escherichia coli strains with the plasmid pool from S. typhimurium Hf. Plasmids introduced by transformation ranged in size from 4.4 to 23.2 kb and correlated with resistance to penicillin G, ampicillin, carbenicillin, cephalothin, cefoperazone, cefamandole, mezlocillin, piperacillin, and in some cases, tetracycline and kanamycin. DNA-DNA hybridization experiments localized these resistance genes to a highly duplicated 6.3-kb fragment of the total EcoRI restriction digest of the S. typhimurium Hf plasmid pool.     

Evaluation of alternariol and alternariol methyl ether for mutagenic activity in Salmonella typhimurium.

Alternariol and alternariol methyl ether were tested in the Ames Salmonella typhimurium assay, and both were shown, with and without metabolic activation, to be nonmutagenic to strains TA98 and TA100. The finding of other investigators that alternariol methyl ether is weakly mutagenic to TA98 without metabolic activation could have resulted from the presence of a small amount of one of the highly mutagenic altertoxins in the alternariol methyl ether originally tested.     

Testing of 2,4,5-T-amino acid conjugates for mutagenic activity in Salmonella typhimurium strains

Since amino acid conjugates are plant metabolites of the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 5 amino acid conjugates (aspartic acid, glutamic acid, leucine, methionine and tryptophan) of 2,4,5-T were tested for possible mutagenic activity utilizing 5 strains of Salmonella typhimurium (TA97, TA98, TA100, TA1535 and TA1538) with and without rat-liver microsomal and cytosolic enzymes. These compounds did not cause any significant increase in reversions when compared with controls in the presence or absence of the activating system. Further, linear regression analysis showed no significant (p less than 0.05) dose-response relationships. Thus, it was concluded that the tested amino acid conjugates of 2,4,5-T are not mutagens or promutagens in these assays.