Evaluation of mutagenic activity in an extract of pepper tree stem bark (Schinus terebinthifolius Raddi)

An extract (decoction) from pepper tree stem bark (Schinus terebinthifolius Raddi) is widely used in Brazil as a topical antiinflammatory agent and to cicatrize wounds. The extract contains catechin, tannins, terpenes, flavonoids, and saponins; of these components, both mutagenic potential and antioxidant properties have been ascribed to flavonoids. The mutagenicity of some flavonoids is believed to be associated with the formation of reactive oxygen species and seems to depend on the number and position of hydroxyl groups. In the present study, we evaluated an extract of S. terebinthifolius in a series of cell-free and bacterial assays in order to determine its genotoxic potential. The extract was negative in a cell-free plasmid DNA test, indicating that it did not directly break DNA. Positive results, however, were obtained in the SOS chromotest, in a forward mutagenesis assay employing CC104 and CC104mutMmutY strains of Escherichia coli, and in the Salmonella reversion assay, using strains TA97, TA98, TA100, and TA102. All the bacterial tests were performed without exogenous metabolic activation due to the topical use of this preparation. The results indicate that pepper tree stem bark extract produces DNA damage and mutation in bacteria, and that oxidative damage may be responsible for the genotoxicity.     

Genotoxicity of 5-aminolevulinic and 4,5-dioxovaleric acids in the salmonella/microsuspension mutagenicity assay and SOS chromotest

5-Aminolevulinic acid (ALA) is a heme precursor that accumulates in some porphyric disorders and in lead poisoning which can undergo metal-catalyzed oxidation producing reactive oxygen species and the keto-aldehyde, 4,5-dioxovaleric acid (DOVA). Evidence in vitro of ALA-induced DNA lesions suggests that ALA and DOVA have mutagenic potential that could possibly contribute to an increased frequency of hepatocellular carcinoma (HCC) in patients with acute intermittent porphyria (AIP). In this study, we evaluated the genotoxic potential of ALA and DOVA. In the absence of exogenous metabolic activation, ALA and DOVA were mutagenic in Salmonella typhimurium tester strain TA104. ALA was also mutagenic in S. typhimurium TA102, but not in TA98, TA100, or TA1535, indicating an oxidative mechanism. Removal of H(2)O(2) with catalase gave only partial protection, suggesting generation of other mutagenic species. Both ALA and DOVA damaged the DNA of Escherichia coli PQ37, inducing the SOS response detected by an increase in beta-galactosidase activity. These results verified the potential mutagenic activity of ALA and DOVA and reinforce the hypothesis that DNA damage induced by ALA may be associated with the development of HCC in individuals suffering from AIP.     

Genotoxicity of p-nitrocinnamaldehyde and related alpha, beta-unsaturated carbonyl compounds in two bacterial assays

Seventeen cinnamaldehydes, cinnamic acids, 2-furylacroleins and related compounds were tested in the Salmonella preincubation reversion assay and in the SOS chromotest. Of eight compounds containing nitrogroups, seven were clearly mutagenic in the presence of S9 mix and six in its absence; whereas none of the parent compounds not containing a nitrogroup and none of the congeners containing chlorine, methoxy or amino groups were mutagenic. Metabolic epoxidation was excluded in additional experiments using SKF525, an inhibitor of mono-oxygenases, and trichloropropene oxide, an inhibitor of epoxide hydrolases. Less or no mutagenicity was found in the nitroreductase deficient strains Salmonella typhimurium TA100NR or TA98NR and in the O-acetyltransferase deficient strains TA100/1,8-DNP6 or TA98/1,8-DNP6 except with 5-nitro-2-furylacrolein which exhibited decreased mutagenicity in TA100NR when compared with TA100 but the highest mutagenicity in TA100/1,8-DNP6. Less or no genotoxic activity was found in the SOS chromotest when using the nitroreductase deficient Escherichia coli strain PQ253 whereas all seven compounds tested were positive in strain PQ37. The results demonstrate the importance of the nitro group and that the compounds are activated either by bacterial nitroreductase or by the nitroreductase in the S9 mix. A chemical activation of the acrolein moiety by the negative inductive effect of the nitro group is unlikely. The genotoxicity of the cinnamyl compounds is dependent on the position of the nitro group in the phenyl ring. The genotoxicities of the p-nitro compounds were about two orders of magnitude higher than those of the ortho and meta congeners. The comparison between the Ames test and the SOS chromotest showed good agreement.     

Mutagenicity spectra in Salmonella typhimurium strains of glutathione, L-cysteine and active oxygen species

Glutathione and L-cysteine, in the presence of rat kidney post-mitochondrialsupernatant (S9) fraction, and various forms of active oxygenwere investigated for mutagenicity in seven his^– strainsof Salmonella typhimurium. Glutathione and L-cysteine showedqualitatively and quantitatively virtually identical mutagenicactivities. The number of mutants induced in strain TA97 was3–4 times higher than in TA100, the strain in which themutagenicity was originally detected. Mutagenic effects werealso observed in strains TA92, TA102 and TA104, but not in TA1535and TA1537. Hydrogen peroxide, superoxide and glucose/glucoseoxidase in the presence and absence of kidney S9 fraction showedpronounced mutagenic effects in strains TA104 and TA102. Additionally,weak mutagenic effects were observed in TA100, while the remainingstrains, including TA97, were not responsive. These mutagenicityspectra suggest that the mutagenic species formed from glutathioneand L-cysteine are similar, if not identical, and are differentfrom hydrogen peroxide, superoxide and other oxygen speciesderived from them. Further support for this notion was givenwhen it was observed that catalase did not affect the mutagenicityof glutathione and that superoxide dismutase showed a significanteffect only when used in milligram quantities. This study showsthat mutagenicity spectra may be useful in the elucidation ofactivation pathways. Furthermore, it is interesting to notethat all the compounds and preparations showing a positive responsein the Ames test in the present study occur endogenously inorganisms: glutathione, L-cysteine, hydrogen peroxide, superoxide,glucose, glucose oxidase and kidney S9 fraction (which was mutagenicin several strains).     

Evaluation of the genotoxicity of gentian violet in bacterial and mammalian cell systems

Previous studies indicate that gentian violet (GV), a triphenylmethane dye used in agriculture and human medicine, is a clastogen in vitro and a carcinogen in chronically exposed mice and rats. Data on its genotoxic activity, however, have been incomplete and partly contradictory. Mutagenesis and DNA damage experiments were conducted to re-evaluate the genotoxic potential of GV in both bacterial and mammalian cell systems. GV was mutagenic in Salmonella typhimurium tester strains TA97 and TA104, but there was little mutagenic activity detected in strains TA98 and TA100. A rat liver homogenate fraction (S9) tended to increase mutagenicity. The major microsomal metabolites of GV, pentamethylpararosaniline and N,N,N',N'-tetramethylpararosaniline were less mutagenic in TA97 and TA104, while N,N,N',N"-tetramethylpararosaniline was a weak mutagen in Salmonella. GV was not mutagenic in Chinese hamster ovary (CHO) cell strain CHO-K1-BH4, and was a questionable mutagen in CHO-AS52 cells. While GV produced DNA damage as measured by sedimentation of nucleotids derived from B6C3F1 mouse lymphocytes treated in vitro, no damage was found in lymphocytes isolated from mice dosed with GV. GV was also a weak producer of gene amplification in an SV40-transformed Chinese hamster cell line. The results indicate that GV is a point mutagen in bacteria; however, since similar exposure conditions produced weak mutagenic activity in mammalian cells, GV may be carcinogenic by virtue of its clastogenic activity.     

SOS induction in Escherichia coli and Salmonella mutagenicity: a comparison using 330 compounds

To examine the concordance of two microbial genotoxicity short-termassays, 330 experimental results for the SOS chromotest usingtester strain Escherichia coli PQ37 were compared with the resultsof the Salmonella/mammalian microsome mutagenicity assay withSalmonella typhimurium TA97, TA98, TA100, TA102, TA104, TA1535,TA1537 and/or TA1538. With respect to qualitative features,the concordance between SOS chromotest and Salmonella mutagenicitytest results was 86.4% (sensitivity, 78.6%; specificity, 100%;     

Studies on the induction of gene mutations in bacterial and mammalian cells by the ring-opened benzene metabolites trans,trans-muconaldehyde and trans,trans-muconic acid

t,t-Muconaldehyde and t,t-muconic acid have been investigated for the induction of gene mutations in Salmonella typhimurium (reversion of the his- strains TA97, TA98, TA100, TA102, TA104 and TA1535), Escherichia coli (reversion of the trp- strain WP2 uvrA) and Chinese hamster V79 cells (acquisition of resistance toward 6-thioguanine). t,t-Muconaldehyde proved weakly mutagenic in strain TA104 in the presence and absence of NADPH-fortified postmitochondrial fraction from rat liver homogenate (S9 mix). In strains TA97, TA100 and TA102, weak positive responses were observed only in the presence of S9 mix. In strains TA98, TA1535 and WP2 uvrA, the result was negative. In V79 cells, the mutation frequency was increased from approximately 7 X 10(-6) to 90 X 10(-6) in cultures exposed to t,t-muconaldehyde at optimal concentration (1.7-3 microM in separate experiments). The concentration-response curve showed pronounced hyperlinearity, with no mutagenic effect being observed at a third of the optimal concentration. t,t-Muconic acid was greater than 100 times less toxic than t,t-muconaldehyde in both bacteria and mammalian cells, and it did not show any mutagenic effect. These results complete a previous mutagenicity study, carried out on benzene and 13 metabolites. It is concluded that the newly investigated metabolites cannot account for the bacterial mutagenicity of bioactivated benzene and benzene-trans-1,2-dihydrodiol, since these compounds exhibited their strongest response in strain TA1535. t,t-Muconaldehyde showed similarities in its mutagenicity to p-benzoquinone and hydroquinone. All three compounds showed, at most, weak effects in bacteria, but were strongly mutagenic in V79 cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Assessment of oxidative DNA damage in the oxyR-deficient SOS chromotest strain Escherichia coli PQ300.

The SOS chromotest is a simple short-term genotoxicity assay measuring the induction of gene sfiA in Escherichia coli K-12. The recent availability of SOS tester strains with additional mutations in DNA repair or protection systems allows testing of DNA damaging compounds for genotoxic specificity. E. coli PQ300 differs from the standard SOS tester strain PQ37 in that it contains an additional mutation in gene oxyR that renders it more sensitive to oxidative genotoxins. The generation of reactive oxygen intermediates (ROI) by hydroperoxides (H2O2, t-butyl hydroperoxide, cumene hydroperoxide), gamma-radiation, glucose oxidase, and xanthine oxidase resulted in a more vigorous SOS response in strain PQ300 compared to strain PQ37. PQ300 was also more sensitive than PQ37 for the detection of reducing agents such as ascorbic acid, cysteine, and glutathione, which also alter the redox status of the bacterial cells. However, intercalating agents (adriamycin, bleomycin, and mitomycin C) and the UV- and radiomimetic compound 4-nitroquinoline-1-oxide whose DNA damaging potential are known also to involve ROI did not show significant differences between strains PQ37 and PQ300. It is concluded that the oxyR-deficient strain PQ300 is useful for detecting certain classes of genotoxins that change the oxidative/antioxidative balance of tester bacteria in the SOS chromotest.     

Effects of Salmonella genotypes and testing protocols on H2O2-induced mutation

Hydrogen peroxide (H2O2) was shown to be mutagenic in a number of strains of Salmonella typhimurium. Strain SB1106p (hisC3108, hisO1242, pKM101), a newly-constructed strain carrying the histidine mutation at a UGA chain-terminating codon, was more responsive to H2O2 than TA104 or TA102, the two hisG428 strains originally developed for detecting oxidative mutagens. The largest proportional increase in revertants of strain TA104 was in the fraction of intragenic deletions. Three other strains (TA97, SB1111 and SB1106) gave unequivocal positive responses to H2O2 in both the liquid pre-incubation procedure and standard plate incorporation procedure. The response of TA100 varied among experiments, ranging from negative to a weak positive. Variations in the catalase content among the tester strains did not correlate with the relative responses obtained in the mutagenicity assays.     

Mutagenicity,antioxidant potential,and antimutagenic activity against hydrogen peroxide of cashew (Anacardium occidentale) apple juice and cajuina

Fresh and processed cashew (Anacardium occidentale) apple juice (CAJ) are among the most popular drinks in Brazil. Besides their nutritional benefits, these juices have antibacterial and antitumor potential. The chemical constituents of both the fresh juice and the processed juice (cajuina) were analyzed and characterized as complex mixtures containing high concentrations of vitamin C, various carotenoids, phenolic compounds, and metals. In the present study, these beverages exhibited direct and rat liver S9-mediated mutagenicity in the Salmonella/microsome assay with strains TA97a, TA98, and TA100, which detect frameshifts and base pair substitution. No mutagenicity was observed with strain TA102, which detects oxidative and alkylating mutagens and active forms of oxygen. Both CAJ and cajuina showed antioxidant activity as determined by a total radical-trapping potential assay. To test whether this antioxidant potential might result in antimutagenesis, we used a variation of the Salmonella/microsome assay that included pre-, co-, and posttreatment of hydrogen peroxide-exposed Salmonella typhimurium strain TA102 with the juices. CAJ and cajuina protected strain TA102 against mutation by oxidative damage in co- and posttreatments. The antimutagenic effects during cotreatment with hydrogen peroxide may be due to scavenging free radicals and complexing extracellular mutagenic compounds. The protective effects in posttreatment may be due to stimulation of repair and/or reversion of DNA damage. The results indicate that CAJ and cajuina have mutagenic, radical-trapping, antimutagenic, and comutagenic activity and that these properties can be related to the chemical constituents of the juices.     

Base-pair mutations caused by six aliphatic epoxides in salmonella typhimurium TA100, TA104, TA4001, and TA4006

Salmonella typhimurium strains TA100, TA104, TA4001, and TA4006 were used to detect the base-pair mutations caused by six aliphatic epoxides: chloropropylene oxide, glycidyl 1-naphthyl ether, glycidyl 4-nitrophenyl ether, 1-naphthyl-propylene oxide, styrene oxide, and trichloropropylene oxide. Dose-mutagenicity relationships could be established for all six epoxides in strains TA100 and TA104 but not in strains TA4001 and TA4006. These results, together with the lack of sensitivity of the TA100 revertants to DL-1,2,4-triazole-3-alanine, indicate CG→TA transitions and/or CG→AT transversions are of major importance for mutations induced by these epoxides in Salmonella TA100 and possibly TA104. In addition, since the reproducibility of the effect of the triazole on TA104 reversions was poor, TA→AT transversions were not eliminated as also contributing to the mutagenicity of these epoxides in this Salmonella strain. © 1993 Wiley-Liss, Inc.     

Mutagenic activity in synthetic pyrethroids in Salmonella typhimurium

Four pyrethroids, allethrin, resmethrin, permethrin and fen-valerate,were tested for mutagenicity in bacterial reversion assay systemswith seven strains (TA1535, TA100, TA1538, TA98, TA1537, TA97and TA104) of Salmonella typhimurium. Our results show thatthree pyrethroids, namely resmethrin, permethrin and fenvalerate,were not found to be mutagenic in S. typhimurium in the presenceor absence of a rat liver activation system. Allethrin was foundto be mutagenic with TA100, TA104 and TA97 strains and requiredmetabolic activation (S9 mix) in order to show its activity,mainly with TA100 and TA104 strains.     

Specificity of base substitution mutations induced by the dietary carcinogens 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in Salmonella

The base pair substitution mutational profiles induced by the heterocyclic amine cooked food mutagens PhIP and IQ in Salmonella typhimurium strains TA100 and TA1535 were determined by colony hybridization analysis. Both PhIP and IQ induced predominantly G→TA transversions in strain TA100 (rfa,ΔuvrB/pKM101) with a pronounced preference for the second codon position (CC→CAC; 72% of total). PhIP also reverted strain TA1535 (rfa, ΔuvrB) efficiently at concentrations similar to those required for strain TA100. In contrast to the PhIP-induced mutational profile observed in strain TA100, in strain TA1535 PhIP induced exclusively G→AT transitions at the second codon position (CC→CTC; 96–99% of total). Base substitution mutagenesis induced by heterocyclic amines related to PhIP is generally SOS-dependent, requiring the presence of plasmid pKM101 in Salmonella hisG46 strains. Thus, the SOS dependent reversion of S. typhimurium strain TA100 probably reflects error-prone lesion bypass at the major PhIP- guanosine adduct at the C-8 position. The G→AT transition mutations induced by PhIP in strain TA1535 appear to be SOS-independent, however, suggesting that these mutations may arise from the formation of PhIP-DNA adducts other than the replication-blocking C8-dG lesion. Environ. Mol. Mutagen. 31:327–332, 1998 © 1998 Wiley-Liss, Inc.     

Mutation spectra of the drinking water mutagen 3-chloro-4-methyl-5-hydroxy-2(5H)-furanone (MCF) in Salmonella TA100 and TA104: comparison to MX

The chlorinated drinking water mutagen 3-chloro-4-methyl-5-hydroxy-2(5H)-furanone (MCF) occurs at concentrations similar to or greater than that of the related furanone 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). MCF and MX differ structurally only by replacement of a 3-methyl in MCF with a 3-dichloromethyl in MX; yet, MCF is significantly less mutagenic than MX and produces different adducts when reacted with nucleosides or DNA. To explore further the effects that these structural differences might have on the biological activity of MCF and MX, we determined the mutation spectra of MCF in Salmonella strains TA100 and TA104 and of MX in strain TA104; the spectrum of MX in TA100 had been determined previously. In TA100, which presents only GC targets for mutagenesis, MCF induced primarily (75%) GC --> TA transversions, with most of the remaining revertants (20%) being GC --> AT transitions. This spectrum was not significantly different from that of MX in TA100 (P = 0.07). In TA104, which presents both GC and AT targets, MCF induced a lower percentage (57%) of GC --> TA transversions, with most of the remaining revertants (33%) being AT --> TA transversions. In contrast, MX induced almost only (98%) GC --> TA transversions in TA104, with the remaining revertants (2%) being AT --> TA transversions. Thus, almost all (98%) of the MX mutations were targeted at GC sites in TA104, whereas only 63% of the MCF mutations were so targeted. These results are consistent with the published findings that MX: (1) forms an adduct on guanosine when reacted with guanosine, (2) induces apurinic sites in DNA, and (3) forms a minor adduct on adenosine when reacted with adenosine or DNA. The results are also consistent with evidence that MCF forms adenosine adducts when reacted with adenosine. Our results show that the replacement of the 4-methyl in MCF with a 4-dichloromethyl to form MX not only increases dramatically the mutagenic potency but also shifts significantly the mutagenic specificity from almost equal targeting of GC and AT sites by MCF to almost exclusive targeting of GC sites by MX. Environ. Mol. Mutagen. 35:106-113, 2000 Published 2000 Wiley-Liss, Inc.     

Molecular analyses of Salmonella hisG428 ochre revertants for rapid characterization of mutational specificity

The Salmonella typhimurium tester strains TA104 and TA102 weredeveloped primarily to aid in the detection of oxidative mutagensand other agents that react preferentially with AT base pairs.Reversion to prototrophy of strains harboring the hisG428 ochreallele can occur by (i) any of seven single base substitutionsor (ii) several tandem double base substitutions at the ochrecodon, (iii) in-frame deletions removing all or part of theochre codon or (iv) mutations at several distinct tRNA extragenicsuppressor loci. We have used allele-specific oligonucleotideprobes and DNA sequence analysis to characterize 625 revertantsof strain TA104 (hisG428, rfa,     

Mutagenic evaluation of the pesticides captan, folpet, captafol, dichlofluanid and related compounds with the mutants TA102 and TA104 of Salmonella typhimurium

A mutagenic evaluation of captan, folpet, captafol, dichlofluanidand related compounds was carried out using the Salmonella/mammalianmicrosome test using strains TA102 and TA104. These strainscontain A-T base pairs at the site of the mutation in contrastto the other Salmonella tester strains that detect mutagensdamaging G-C base pairs. In addition, the excision repair systemof the TA102 strain is still intact. Captan and folpet weremutagenic in strain TA104, captafol was mutagenic in strainTA102, whereas the remaining test compounds (dichlofluanid,tetrahydro-phthalimide and thiozolidine-4-carboxylic acid) werenot mutagenic in either strain. In conclusion, we consider itof value to add these two strains to those already used in theAmes test in order to increase confidence in our ability todetect mutagens and to shed further light on their mechanismof action.     

Role of the Helicobacter pylori virulence factors vacuolating cytotoxin, CagA, and urease in a mouse model of disease.

The pathogenic role of Helicobacter pylori virulence factors has been studied with a mouse model of gastric disease. BALB/c mice were treated orally with different amounts of sonic extracts of cytotoxic H. pylori strains (NCTC 11637, 60190, 84-183, and 87A300 [CagA+/Tox+]). The pathological effects on histological sections of gastric mucosae were assessed and were compared with the effects of treatments with extracts from noncytotoxic strains (G21 and G50 [CagA-/Tox-]) and from strains that express either CagA alone (D931 [CagA+/Tox-]) or the cytotoxin alone (G104 [CagA-/Tox+]). The treatment with extracts from cytotoxic strains induced various epithelial lesions (vacuolation, erosions, and ulcerations), recruitment of inflammatory cells in the lamina propria, and a marked reduction of the mucin layer. Extracts of noncytotoxic strains induced mucin depletion but no other significant pathology. Crude extracts of strain D931, expressing CagA alone, caused only mild infiltration of inflammatory cells, whereas extracts of strain G104, expressing cytotoxin alone, induced extensive epithelial damage but little inflammatory reaction. Loss of the mucin layer was not associated with a cytotoxic phenotype, since this loss was observed in mice treated with crude extracts of all strains. The pathogenic roles of CagA, cytotoxin, and urease were further assessed by using extracts of mutant strains of H. pylori defective in the expression of each of these virulence factors. The results obtained suggest that (i) urease activity does not play a significant role in inducing the observed gastric damage, (ii) cytotoxin has an important role in the induction of gastric epithelial cell lesions but not in eliciting inflammation, and (iii) other components present in strains which carry the cagA gene, but distinct from CagA itself, are involved in eliciting the inflammatory response.     

Mutagenic activity of the 4,5- and 9,10-dihydrodiols of benzo[J]fluoranthene and their syn- and anti-dihydrodiol epoxides in salmonella typhimurium

The objective of this study was to determine the relative mutagenic activities of the major dihydrodiol metabolites of benzo[j]fluoranthene (B[j]F) and their corresponding syn- and anti-dihydrodiol epoxides. Salmonella typhimurium tester strains TA97a, TA98, and TA100 were used to evaluate the mutagenic potencies of the parent hydrocarbon and these suspect proximate and ultimate mutagenic metabolites. B[j]F and the trans-dihydrodiol metabolites were active only in the presence of an external metabolic activation system (S9) with the exception of the B[j]F-4,5-diol, which was weakly active in TA98 and TA100 in the absence of S9. The B[j]F-4,5-diol was more mutagenic than the B[j]F-9,10-diol in tester strains TA98 and TA100, whereas the opposite effect was observed in TA97a. In the absence of S9, the anti-B[j]F-4,5-diol epoxide was more mutagenic than the syn-B[j]F-4,5-diol epoxide and the syn- and anti-B[j]F-9,10-diol epoxides in tester strains TA97a and TA100. The exceptional mutagenic potency of the anti-B[j]F-4,5-diol epoxide in TA100 resembles that observed by epoxides located within a fjord, or by the anti-diol epoxides of bay region methylated polycyclic aromatic hydrocarbons. In contrast, the mutagenicity of the pseudo bay region dihydrodiol epoxides arising from the B[j]F-9,10-diol more closely resembles that observed with the classical bay region dihydrodiol epoxides of chrysene. In summary, both dihydrodiol metabolites of B[j]F are mutagenic in S. typhimurium, and the relative potency varies among the tester strains. The highest mutagenic response was achieved in tester strain TA100, which detects base-pair substitutions. The most potent direct-acting dihydrodiol epoxide in this tester strain was the anti-B[j]F-4,5-diol epoxide, which agrees with the results of mouse skin painting studies that indicate that the B[j]F-4,5-diol is more tumorigenic that the parent hydrocarbon or the B[j]F-9,10-diol. A cova-lent DNA adduct formed between the anti-B[j]F-4,5-diol epoxide and deoxyguanosine was the major species of DNA adduct formed in S. typhimurium. This adduct corresponds to the major DNA adduct formed in mouse skin following application B[j]F.     

Wild type agr-negative livestock-associated MRSA exhibits high adhesive capacity to human and porcine cells

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the leading causes of nosocomial infections and a major public health concern worldwide. During the last decade, MRSA of CC398 have emerged as important colonizers of livestock. These strains also represent an increasing cause of human infections. A recent study reporting a new dominant spa type among MRSA from Finish fattening pigs (CC398/t2741) identified a strain lacking both the global virulence regulator gene locus agr and the adhesion gene fnbB. The aim of this study was to characterize this agr/fnbB-negative livestock-associated MRSA strain in terms of growth, hemolysis and adhesive capacity, and to provide data on its genomic background. To this end, growth curves and hemolysis patterns were generated and adhesion assays on human keratinocyte and porcine nasal mucosa cell lines were performed. Whole genome sequencing was used to determine the nature and extent of the relevant deletions in the livestock strains. For comparison, an agr-positive, fnbB-negative CC398/t2741 strain from the same pig herd, an agr/fnbB- positive CC398/t034 strain from another pig herd and one human MRSA strain and its isogenic Δagr knockout mutant were used. The agr-negative strains adhered significantly better to human and porcine host cells than the agr-positive control strains. For the agr-positive porcine MRSA strains, cytotoxic effects on porcine mucosal cells were observed. The strong adhesive capacity of the naturally agr-negative livestock-associated MRSA, in combination with diminished cytotoxic effects, is likely favorable for inducing persistent colonization in pigs. Independently of the host cell type, similar adhesive capacities of the naturally agr-negative livestock-associated MRSA and the human MRSA strain were shown. Our results indicate that loss of agr in the livestock-associated MRSA strain investigated in this study may have increased its potential to be transmitted to and amongst humans.     

Ozone is mutagenic in Salmonella.

Ozone is a highly reactive gas that has been tested for genotoxicity in a number of systems. Induced genetic damage resulting from ozone treatment may not be readily observed because of the high toxicity of the chemical and difficulties in generating and administering controlled concentrations. The mutagenicity of ozone was investigated in Salmonella typhimurium using a plate test protocol designed for reactive vapours and gases. Ozone, at two to three consecutive doses, induced weak, albeit statistically significant, mutagenic responses in tester strain TA102 with and without Aroclor-induced rat liver S9 (lowest effective mean concentration of 0.019 ppm; 35 min total exposure). However, dose-related responses were not always obtained. No mutagenicity was detected in strains TA98, TA100, or TA1535, with or without S9. In strain TA104, ozone induced a weak response only at a single dose with S9; this response was not reproducible. Mutagenicity was dependent on the ozone flow rate and total exposure time, with variations in the optimum dose-time regimen leading to toxicity or complete inactivity. The data show that ozone is a very weak bacterial mutagen and only when tested under narrowly prescribed, subtoxic dosing conditions.