Development of new tester strains derived from E. coli WP2uvrA for the determination of mutational specificity

Acute and subacute toxicity and genotoxicity of schizonepetin, a naturally occurring monoterpene with antiviral activity

In the present study, the acute, subacute and genetic toxicity of schizonepetin was assessed. The median lethal dose (LD(50)) of schizonepetin after oral administration was 478 mg/kg body weight in mice. Studies on dose toxicity were repeatedly conducted at 0, 60, 120, and 240 mg/kg bw/day in rats for 35 days after oral administration. Based on the results of this study, a dose level of 120 mg/kg bw/day is considered the no-observed-adverse-effect-level (NOAEL) in rats. Schizonepetin was negative in Salmonella typhimurium tester strains TA97, TA98, TA100, TA102 and TA1535, nonclastogenic in Chinese hamster lung (CHL) cells in the mammalian chromosome aberration test, and micronucleus formation were observed and no clinical signs or adverse effects were detected, and our results illustrated that schizonepetin is not genotoxic.

Safety assessment of Lactobacillus brevis KB290 as a probiotic strain

Lactobacillus brevis KB290 (KB290), a plant-derived probiotic lactic acid bacterium, reportedly improves gut health and stimulates immune function. Here we extensively investigated the geno-, acute, subacute, and subchronic toxicity of KB290 and its bacterial translocation potential. KB290 was non-mutagenic in the bacterial reverse mutation assay by the preincubation method. In the single oral dose toxicity test, KB290 at 10(9) cfu/ml was nontoxic at maximum capacity (20 ml/kg). When 10(8), 10(9), or 10(10) cfu/kg was administered daily to rats by gavage for 2 weeks (subacute assay), we observed no clear treatment-related effect and no evidence of bacterial translocation from the gastrointestinal tract. When it was administered for 13 weeks (subchronic assay), we again observed no clear treatment-related effect and no significant toxicological effect. Based on those results, we consider 10(10) cfu/kg per day, the highest dose tested, to be the no observed adverse effect level (NOAEL). These results suggest that KB290 is safe for human consumption.

Acute and subchronic toxicity and genotoxicity of SE5-OH, an equol-rich product produced by Lactococcus garvieae

The consumption of soy-based products is associated with a number of health benefits and much of these benefits are proposed to be due to the soy isoflavones daidzein, genistein, glycitein, their glycosides, and equol, an isoflavone naturally produced from daidzein. Equol is a naturally bacterially-derived metabolite of daidzein and is produced by bacteria in the gut of those humans capable of hosting the particular organism. To allow all humans to enjoy the health benefits of equol, a new functional food ingredient has been developed that relies on bacterial conversion of daidzein to equol under strictly controlled conditions. This new food substance, termed SE5-OH, has been studied extensively for its acute and subchronic toxicity in Sprague-Dawley rats, as well as for its potential genotoxicity. The oral LD(50) is >4,000 mg/kg. In a 91-day, subchronic study, the no-observed-adverse-effect-level (NOAEL) was 2,000 mg/kg/day, the highest dose tested. SE5-OH was negative in Salmonella typhimurium tester strains TA98, TA100, TA1535 and TA1537 and in Escherichia coli tester strain WP2uvrA with and without metabolic activation. SE5-OH was negative for chromosome aberrations in Chinese hamster lung cells up to 3,000 microg/ml with and without metabolic activation and did not induce increases in micronucleated polychromatic erythrocytes taken from Sprague-Dawley rats administered (via gavage) up to 4,000 mg/kg SE5-OH twice daily for two consecutive days.

Investigations into the in vitro antimicrobial activity and mode of action of the phenazine antibiotic d-alanylgriseoluteic acid

D-Alanylgriseoluteic acid (AGA) is a potent antimicrobial phenazine compound produced by Pantoea agglomerans (Erwinia herbicola) Eh1087. Susceptibility tests against a range of microbes indicated that AGA had a broad spectrum of antimicrobial activity and was particularly active against Gram-positive pathogens. Comparison of the in vitro efficacy of AGA with eight other antibiotics against 119 clinical isolates of Streptococcus pneumoniae demonstrated that all were inhibited by low concentrations of AGA (minimal inhibitory concentration range <or=0.06-0.75 microg/mL), regardless of their susceptibility to other antimicrobials. Investigations into the mode of action of AGA revealed that it induced the SOS response in Escherichia coli and slightly increased the frequency of GC-AT transition mutations. In cell-free assays, both AGA and griseoluteic acid reduced cytochrome c in the presence of a redox recycler (ferredoxin-NADP(+) reductase), but AGA was six to seven times more readily reduced than griseoluteic acid in the absence of the reductase. The potency and broad spectrum of AGA activity suggest that AGA may warrant further investigation.

Photomutagenicity of thiabendazole, a postharvest fungicide, in bacterial assays

We investigated the photomutagenicity of thiabendazole (TBZ), a postharvest fungicide commonly used on imported citrus fruits. Using UVA light (320-400 nm), we irradiated bacterial cultures with or without TBZ in a 24-well multiplate. UVA-irradiation without TBZ was not mutagenic to the tester strains, nor was unirradiated TBZ. TBZ was strongly photomutagenic in Escherichia coli WP2uvrA and WP2uvrA/pKM101 strains, weakly photomutagenic in Salmonella typhimurium TA100 and TA98, and not photomutagenic in S. typhimurium TA1535 and TA1538. The photomutagenicity of TBZ was more evident in WP2uvrA/pKM101, which carries the trpE65 ochre mutation (TAA), than in TA100, which carries the hisG46 missense mutation (CCC). In E. coli WP3101-WP3106 and the corresponding pKM101-containing strains, photoactivated TBZ induced predominantly G:C-->A:T transitions and A:T-->T:A transversions. In the plasmid-containing strains only, TBZ induced a moderate number of A:T-->G:C transitions and a few A:T-->C:G and G:C-->T:A transversions. The observation that UVA-irradiated TBZ mutated both G:C and A:T basepairs may explain why WP2uvrA/pKM101 was more sensitive to its mutagenicity than TA100. TBZ that was irradiated before it was added to the WP2uvrA/pKM101 cells was not photomutagenic, which suggests that the photomutagenic products of TBZ were unstable or rapidly reacted with other molecules before being incorporated into cells.

Characterization of the mutational specificity of DNA cross-linking mutagens by the Lac+ reversion assay with Escherichia coli

The mutational specificities of DNA cross-linking compounds such as cisplatin, transplatin, carboplatin, mitomycin C, psoralen, and 8-methoxypsoralen were investigated in lacZ reversion assay systems of Escherichia coli. Tester strains were constructed by introducing the six kinds of F' plasmids (lacI-, lacZ461, and proAB+), each of which carries a different base-substitution mutation within the lacZ gene. Each of the six possible base-substitution mutations was assayed by Lac+ reversion. Cisplatin induced G.C-->A.T transitions and G.C-->T.A transversions, with the former predominating. Transplatin induced A.T-->G.C transitions in addition to G.C-->A.T transitions and G.C-->T.A. Carboplatin weakly induced G.C-->A.T transitions. On the other hand, mitomycin C induced only G.C-->T.A transversions, while psoralen and 8-methoxypsoralen reactivated with near-UV irradiation induced A.T-->G.C transitions preferentially. The Lac(+) reversion system was very convenient for rapidly determining mutational spectra.

The Escherichia coli lacZ reversion mutagenicity assay

The Escherichia coli lacZ reversion assay, based on the set of episomal lacZ alleles engineered by Miller et al., provides an attractive system for studies of mutagenesis and mutational specificity. Each strain in the lacZ set reverts by a specific base substitution or frameshift event. Revertants are selected by growth on lactose minimal medium. In this review, I describe the development of the assay and its subsequent modifications and improvements. Examples of its application are presented and detailed protocols for the implementation of the assay are given.

Mutation spectra of chemical mutagens determined by Lac+ reversion assay with Escherichia coli WP3101P-WP3106P tester strains

We previously reported the development of mutation-specific Escherichia coli B tester strains WP3101 to WP3106 from strain WP2uvrA. In this study we constructed their pKM101-containing derivatives WP3101P to WP3106P, and further isolated their rfa derivatives WP4101-WP4106 and WP4101P-WP4106P. The six kinds of F' plasmids (lacI-, lacZ-, proAB+), each of which carries a different lacZ allele, contained in the above strains were originally derived from E. coli K-12 strains CC101-CC106. All the tester strains show Lac- and Trp- phenotype. Assays for transitions and transversions are based upon Lac+ reversion of a specific mutation located within the lacZ gene on an F' plasmid. The trpE65(ochre) allele in the same strains enables them to be used for Trp+ reversion assays as well. In the present paper, we evaluated the sensitivity, specificity, and usefulness of the newly developed tester strains. Strains WP3101P-WP3106P were highly sensitive to determine mutational profile of heterocyclic amines with S9 mix-mediated metabolic activation and most of the oxidative mutagens and free radical generators tested. Every type of base-pair substitutions induced by 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) or 5-diazouracil were detected in strains WP3101P-WP3106P, while A:T-->C:G and G:C-->A:T mutations induced by MeIQ, and A:T-->C:G, G:C-->A:T, and G:C-->C:G by 5-diazouracil were not detected in pKM101-free tester strains. In pKM101-carrying strains, cumene hydroperoxide induced all types of base substitutions, while formaldehyde preferentially induced G:C-->T:A transversions. Phenazine methosulfate induced predominantly G:C-->A:T transitions and G:C-->T:A transversions, while H2O2 induced predominantly G:C-->T:A and A:T-->T:A transversions. Introduction of the rfa mutation considerably enhanced sensitivity to bulky mutagens such as polycyclic aromatic compounds. All six possible base substitutions induced by 9, 10-dimethyl-1,2-benzanthracene (DMBA) were detected in tester strains WP4101P-WP4106P. In conclusion, our tester strains WP3101P-WP3106P and WP4101P-WP4106P permitted rapid and simple detection of specific mutations induced by variety of mutagens.