Effect of free-SH containing compounds on allyl isothiocyanate antimicrobial activity against Escherichia coli O157:H7

Allyl Isothiocyanate in the Volatiles of Brassica juncea Inhibits the Growth of Root Rot Pathogens of Panax notoginseng by Inducing the Accumulation of ROS

The cultivation of Panax notoginseng is often seriously hindered by root rot disease caused by the accumulation of soil-borne pathogens. Here, the inhibitory activity of Brassica juncea volatiles on P. notoginseng root rot pathogens was assessed and compounds in volatiles were identified. Furthermore, the antimicrobial activity and mechanism of allyl isothiocyanate (AITC) were deciphered by integrated transcriptome and metabolome analyses. The volatiles of B. juncea showed dose-dependent antimicrobial activity against root rot pathogens. AITC, identified as the main volatile compound, not only significantly inhibited pathogen growth in vitro but also suppressed root rot disease in the field. Integrated transcriptomic and metabolomics analysis revealed that AITC inhibited Fusarium solani by interfering with energy production and induced the accumulation of ROS by decreasing the content of glutathione (GSH). In summary, B. juncea releases AITC to inhibit soil-borne pathogens and could be used as a rotation crop or soil fumigant to alleviate root rot disease.

Cardioprotective effect of allyl isothiocyanate in a rat model of doxorubicin acute toxicity

Doxorubicin (DOX) is an effective anthracycline chemotherapeutic drug. Nevertheless, the cardiotoxicity adverse effect restricts its clinical benefit. Allyl isothiocyanate (AITC) is a natural antioxidant and anti-inflammatory agent. In the present study, we investigated the effect of AITC on cardiotoxicity of DOX. Thirty-two adult male albino rats were divided into four groups; control, AITC, DOX, and AITC + DOX. AITC was administrated orally (25 mg/kg/day) for 7 days, and DOX was given as a single i.p. injection (15 mg/kg) on the third day. Mortality rate was observed during the experiment. Cardiac toxicity markers (lactate dehydrogenase (LDH), creatine kinase (CK-MB), and cardiac Troponin I (cTn-I)) were evaluated in serum samples obtained from all groups after 48 hours of DOX injection. DOX-treated group showed 40% mortality and a significant increase in cardiac enzymes. This increase was accompanied by degenerated cardiomyocytes, and inflammatory cells infiltrates. Interestingly, AITC administration alleviated myocardial oxidative stress induced by DOX as attenuated the increase in malondialdehyde (MDA), and nitric oxide (NO) while resulted in elevations of the antioxidant reduced glutathione (GSH) level as well as superoxide dismutase (SOD) activity. Furthermore, the inflammatory cytokine, TNF-α, was reduced upon administration of AITC with DOX. The cardio-protection of AITC is attributed to increase the expression of cytoprotective nuclear factor erythroid 2-related factor 2 (Nrf2). Subsequently, heme oxygenase 1 (HO-1) level was elevated by AITC to correct the oxidative stress induced by DOX in the heart. Accordingly, AITC ameliorated acute cardiotoxicity associated with DOX treatment via attenuation of oxidative stress and the induced-tissue inflammatory injury. Abbreviations: DOX: doxrubicin; Nrf2: nuclear factor erythroid 2-related factor 2; HO-1: heme oxygenase 1; AITC: ally isothiocyanate; MDA: malondialdehyde; SOD: superoxide dismutase; GSH: reduced glutathione; TNF-α: tumor necrosis factor alpha.

Symmetrical Antioxidant and Antibacterial Properties of Four Romanian Cruciferous Extracts

Four alcoholic extracts from Romanian Cruciferous species—cabbage, acclimatized broccoli, black radish and cauliflower—were obtained in a microwave field. The extracts showed good and symmetric antioxidant activity (0.97–1.13 mmol/L TE) and good phenolic content (1001–1632 mg GAE/L). For the HPLC method, the limit of detection (LOD), limit of quantitation (LOQ) and recovery degree were established. The small values of LOD and LOQ indicated a great fit of data. The HPLC method achieved satisfactory quantitative recoveries in the range of 96%–122%, except for the lowest sinigrin concentration (8.774 µg/mL). The presence of metals in the studied extracts falls within the allowed limits. The four Cruciferous extracts showed good and slightly asymmetric antibacterial activities against some Gram-positive and Gram-negative bacteria, including strains with known resistance to antibiotics. Moreover, greater inhibitory effects were exhibited against Gram-negative bacteria. Asymmetrically, no inhibition was observed on the fungal strains. Therefore, the present results may suggest that some alcoholic extract formulas of cabbage and black radish (presenting good antibacterial activity) might be helpful in the antimicrobial fight and could be successfully used on selected cases and strains.

Control of pathogenic and spoilage bacteria in meat and meat products by high pressure: Challenges and future perspectives

High-pressure processing is among the most widely used nonthermal intervention to reduce pathogenic and spoilage bacteria in meat and meat products. However, resistance of pathogenic bacteria strains in meats at the current maximum commercial equipment of 600 MPa questions the ability of inactivation by its application in meats. Pathogens including Escherichia coli, Listeria, and Salmonelle, and spoilage microbiota including lactic acid bacteria dominate in raw meat, ready-to-eat, and packaged meat products. Improved understanding on the mechanisms of the pressure resistance is needed for optimizing the conditions of pressure treatment to effectively decontaminate harmful bacteria. Effective control of the pressure-resistant pathogens and spoilage organisms in meats can be realized by the combination of high pressure with application of mild temperature and/or other hurdles including antimicrobial agents and/or competitive microbiota. This review summarized applications, mechanisms, and challenges of high pressure on meats from the perspective of microbiology, which are important for improving the understanding and optimizing the conditions of pressure treatment in the future.

The antioxidant power of horseradish, Armoracia rusticana, underlies antimicrobial and antiradical effects, exerted in vitro

Armoracia rusticana (AR) was tested for antimicrobial and antioxidants power. The compound demonstrated to inhibit fish pathogens such as Vibrio anguillarum, V. harvey, V. alginolyticus, Aeromonas hydrophila, A. salmonicida, Photobacterium damselae subspecie piscicida, Tenacibaculum marinum and Pseudomonas anguilliseptica,. The total phenolic content and the reducing power resulted higher in the water extract of AR, respect to the hydroalcoolic. In vitro test demonstrated that AR significantly protect cells against death, induced by oxidative stress.

Glucoraphanin and sulforaphane evolution during juice preparation from broccoli sprouts

Broccoli sprouts are considered functional food as they are naturally enriched in glucoraphanin (GR) that is the biological precursor of the anticancer compound sulforaphane (SFN). Due to its health promoting value, also broccoli sprout juice is becoming very popular. The present study aimed to quantitatively assess the conversion of GR to its hydrolysis products, SFN and SFN-nitrile, during the juice preparation process. We demonstrated that SFN plus SFN-nitrile yield from glucoraphanin is quite low (≈25%) and that some SFN is lost during the juice preparation partially due to the spontaneous conversion to sulforaphane-amine or conjugation to GSH and proteins naturally present in the juice. Our results demonstrate that the detection of the sole SFN free form does not provide reliable information about the real concentration of this functional compound in the juice.

Glutathione protects Candida albicans against horseradish volatile oil

Horseradish essential oil (HREO; a natural mixture of different isothiocyanates) had strong fungicide effect against Candida albicans both in volatile and liquid phase. In liquid phase this antifungal effect was more significant than those of its main components allyl, and 2-phenylethyl isothiocyanate. HREO, at sublethal concentration, induced oxidative stress which was characterized with elevated superoxide content and up-regulated specific glutathione reductase, glutathione peroxidase, catalase and superoxide dismutase activities. Induction of specific glutathione S-transferase activities as marker of glutathione (GSH) dependent detoxification was also observed. At higher concentration, HREO depleted the GSH pool, increased heavily the superoxide production and killed the cells rapidly. HREO and the GSH pool depleting agent, 1-chlore-2,4-dinitrobenzene showed strong synergism when they were applied together to kill C. albicans cells. Based on all these, we assume that GSH metabolism protects fungi against isothiocyanates.

Identification of Proteins Possibly Involved in Glucosinolate Metabolism in L. agilis R16 and E. coli VL8

This study was aimed to identify sinigrin-induced bacterial proteins potentially involved in the metabolism of glucosinolate in two glucosinolate-metabolising bacteria Lactobacillus agilis R16 and Escherichia coli VL8. Sinigrin (2 mM) was used to induce the proteins in both bacteria under anaerobic incubation for 8 h at 30 °C for L. agilis R16 and 37 °C for E. coli VL8 and the controls without sinigrin were performed. Allyl isothiocyanate and allyl nitrile as two degradation products of sinigrin were detected in sinigrin-induced cultures of L. agilis R16 (27% total products) and E. coli VL8 (38% total products) from a complete sinigrin degradation in 8 h for both bacteria. 2D gel electrophoresis was conducted to identify induced proteins with at least twofold increased abundance. Sinigrin-induced L. agilis R16 and the control produced 1561 and 1543 protein spots, respectively. For E. coli VL8, 1363 spots were detected in sinigrin-induced and 1354 spots in the control. A combination of distinct proteins and upregulated proteins of 32 and 35 spots in L. agilis R16 and E. coli VL8, respectively were detected upon sinigrin induction. Of these, 12 and 16 spots from each bacterium respectively were identified by LC-MS/MS. In both bacteria most of the identified proteins are involved in carbohydrate metabolism, oxidoreduction system and sugar transport while the minority belong to purine metabolism, hydrolysis, and proteolysis. This indicated that sinigrin induction led to the expressions of proteins with similar functions in both bacteria and these proteins may play a role in bacterial glucosinolate metabolism.

Antibacterial activity and mode of action of selected glucosinolate hydrolysis products against bacterial pathogens

Plants contain numerous components that are important sources of new bioactive molecules with antimicrobial properties. Isothiocyanates (ITCs) are plant secondary metabolites found in cruciferous vegetables that are arising as promising antimicrobial agents in food industry. The aim of this study was to assess the antibacterial activity of two isothiocyanates (ITCs), allylisothiocyanate (AITC) and 2-phenylethylisothiocyanate (PEITC) against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes. The antibacterial mode of action was also characterized by the assessment of different physiological indices: membrane integrity, intracellular potassium release, physicochemical surface properties and surface charge. The minimum inhibitory concentration (MIC) of AITC and PEITC was 100 μg/mL for all bacteria. The minimum bactericidal concentration (MBC) of the ITCs was at least 10 times higher than the MIC. Both AITC and PEITC changed the membrane properties of the bacteria decreasing their surface charge and compromising the integrity of the cytoplasmatic membrane with consequent potassium leakage and propidium iodide uptake. The surface hydrophobicity was also non-specifically altered (E. coli and L. monocytogenes become less hydrophilic; P. aeruginosa and S. aureus become more hydrophilic). This study shows that AITC and PEITC have strong antimicrobial potential against the bacteria tested, through the disruption of the bacterial cell membranes. Moreover, phytochemicals are highlighted as a valuable sustainable source of new bioactive products.

The inhibitory effects of sorbate and benzoate against Clostridium perfringens type A isolates

This study evaluated the inhibitory effects of sorbate and benzoate against Clostridium perfringens type A food poisoning (FP) and non-food-borne (NFB) disease isolates. No significant inhibition of germination of spores of both FP and NFB isolates was observed in rich medium (pH 7.0) supplemented with permissive level of sodium sorbate (0.3% ≈ 0.13 mM undissociated sorbic acid) or sodium benzoate (0.1% ≈ 0.01 mM undissociated benzoic acid) used in foods. However, these levels of sorbate and benzoate effectively arrested outgrowth of germinated C. perfringens spores in rich medium. Lowering the pH of the medium increases the inhibitory effects of sorbate and benzoate against germination of spores of NFB isolates, and outgrowth of spores of both FP and NFB isolates. Furthermore, sorbate and benzoate inhibited vegetative growth of C. perfringens isolates. However, the permissible levels of these organic salts could not control the growth of C. perfringens spores in chicken meat stored under extremely abusive conditions. In summary, although sorbate and benzoate showed inhibitory activities against C. perfringens in the rich medium, no such effect was observed in cooked chicken meat. Therefore, caution should be taken when applying these organic salts into meat products to reduce or eliminate C. perfringens spores.

Effect of allyl isothiocyanate on developmental toxicity in exposed Xenopus laevis embryos

The pungent natural compound allyl isothiocyanate isolated from the seeds of Cruciferous (Brassica) plants such as mustard is reported to exhibit numerous beneficial health-promoting antimicrobial, antifungal, anticarcinogenic, cardioprotective, and neuroprotective properties. Because it is also reported to damage DNA and is toxic to aquatic organisms, the objective of the present study was to determine whether it possesses teratogenic properties. The frog embryo teratogenesis assay-Xenopus (FETAX) was used to determine the following measures of developmental toxicity of the allyl isothiocyanate: (a) 96-h LC50, defined as the median concentration causing 50% embryo lethality; (b) 96-h EC50, defined as the median concentration causing 50% malformations of the surviving embryos; and (c) teratogenic malformation index (TI), equal to 96-h LC50/96-h EC50. The quantitative results and the photographs of embryos before and after exposure suggest that allyl isothiocyanate seems to exhibit moderate teratogenic properties. The results also indicate differences in the toxicity of allyl isothiocyanate toward exposed embryos observed in the present study compared to reported adverse effects of allyl isothiocyanate in fish, rodents, and humans. The significance of the results for food safety and possible approaches to protect against adverse effects of allyl isothiocyanate are discussed.

New amino acid germinants for spores of the enterotoxigenic Clostridium perfringens type A isolates

Clostridium perfringens spore germination plays a critical role in the pathogenesis of C. perfringens-associated food poisoning (FP) and non-food-borne (NFB) gastrointestinal diseases. Germination is initiated when bacterial spores sense specific nutrient germinants (such as amino acids) through germinant receptors (GRs). In this study, we aimed to identify and characterize amino acid germinants for spores of enterotoxigenic C. perfringens type A. The polar, uncharged amino acids at pH 6.0 efficiently induced germination of C. perfringens spores; L-asparagine, L-cysteine, L-serine, and L-threonine triggered germination of spores of most FP and NFB isolates; whereas, L-glutamine was a unique germinant for FP spores. For cysteine- or glutamine-induced germination, gerKC spores (spores of a gerKC mutant derivative of FP strain SM101) germinated to a significantly lower extent and released less DPA than wild type spores; however, a less defective germination phenotype was observed in gerAA or gerKB spores. The germination defects in gerKC spores were partially restored by complementing the gerKC mutant with a recombinant plasmid carrying wild-type gerKA-KC, indicating that GerKC is an essential GR protein. The gerKA, gerKC, and gerKB spores germinated significantly slower with L-serine and L-threonine than their parental strain, suggesting the requirement for these GR proteins for normal germination of C. perfringens spores. In summary, these results indicate that the polar, uncharged amino acids at pH 6.0 are effective germinants for spores of C. perfringens type A and that GerKC is the main GR protein for germination of spores of FP strain SM101 with L-cysteine, L-glutamine, and L-asparagine.

Study of the chemical reduction of the fumonisins toxicity using allyl, benzyl and phenyl isothiocyanate in model solution and in food products

Fumonisins (FBs) are bioactive compounds produced by several strains of Fusarium spp. which contain a polyketide structure similar to sphinganine. These mycotoxins contain a free amino group that could work as an electron donor and react with the electrophile carbon present within the isothiocyanate (ITC) group. The objective of this study was to determine the effect of ITCs (allyl, benzyl and phenyl) on the stability of FB(1), FB(2) and FB(3). Firstly, PBS solutions at three pH levels (4, 7 and 9) were prepared and added with pairs of one FB (1 mg/L) plus one ITC (1 mg/L). Then, gaseous ITC was used to fumigate corn kernels and corn flour contaminated with FBs produced by Gibberella moniliformis CECT 2987 in situ. Mycotoxin levels were evaluated using liquid chromatography coupled to mass spectrometry in tandem (LC-MS/MS), while products formed from the reaction of FBs and ITCs were examined by liquid chromatography coupled to mass spectrometry-linear ion trap (LC-MS-LIT). The reduction of FB(1) and FB(2) in solution ranged from 42 to 100% on a time-dependent manner. This variance was greatly influenced by pH. In general, lower pH levels eased the reaction between ITCs and FBs. ITC fumigation treatment (50, 100 and 500 μL/L) was able to reduce 53-96% of FB(1) levels, 29-91% of FB(2) and 29-96% of FB(3). Four reaction products between the bioactive compounds employed in this study were identified, corresponding to FB + ITC conjugates.

Characterization of products from the reaction of glucosinolate-derived isothiocyanates with cysteine and lysine derivatives formed in either model systems or broccoli sprouts

Glucosinolates, present in Brassica vegetables, are thought to contribute to human health prevention because of their enzymatically induced breakdown products, primarily isothiocyanates (ITCs). ITCs are reactive substances that readily react with nucleophilic (food) compounds. The reactivity of allyl-ITC and 4-(methylsulfinyl)butyl-ITC (sulforaphane) toward thiol and amino groups of cysteine and lysine derivatives was studied in buffered model systems as well as broccoli sprouts. The thiol group is the preferred reaction site, and it was demonstrated that even endogenously released sulforaphane is able to react very fast with cysteine in broccoli sprouts. Amino groups reacted slower and only under basic conditions. However, great differences in the reactivity between the different amino compounds were revealed. The aliphatic allylamine reacted very fast with allyl-ITC, forming N,N'-diallylthiourea, a compound identified as a main thermal degradation product of allyl-ITC.

Essential oils in food preservation: mode of action, synergies, and interactions with food matrix components

Essential oils are aromatic and volatile liquids extracted from plants. The chemicals in essential oils are secondary metabolites, which play an important role in plant defense as they often possess antimicrobial properties. The interest in essential oils and their application in food preservation has been amplified in recent years by an increasingly negative consumer perception of synthetic preservatives. Furthermore, food-borne diseases are a growing public health problem worldwide, calling for more effective preservation strategies. The antibacterial properties of essential oils and their constituents have been documented extensively. Pioneering work has also elucidated the mode of action of a few essential oil constituents, but detailed knowledge about most of the compounds' mode of action is still lacking. This knowledge is particularly important to predict their effect on different microorganisms, how they interact with food matrix components, and how they work in combination with other antimicrobial compounds. The main obstacle for using essential oil constituents as food preservatives is that they are most often not potent enough as single components, and they cause negative organoleptic effects when added in sufficient amounts to provide an antimicrobial effect. Exploiting synergies between several compounds has been suggested as a solution to this problem. However, little is known about which interactions lead to synergistic, additive, or antagonistic effects. Such knowledge could contribute to design of new and more potent antimicrobial blends, and to understand the interplay between the constituents of crude essential oils. The purpose of this review is to provide an overview of current knowledge about the antibacterial properties and antibacterial mode of action of essential oils and their constituents, and to identify research avenues that can facilitate implementation of essential oils as natural preservatives in foods.

Influence of NaCl and NaNO3 on sinigrin hydrolysis by foodborne bacteria

The glucosinolate sinigrin (SNG) is converted by endogenous plant myrosinase or by bacterial myrosinase-like activity to form the potent antimicrobial allyl isothiocyanate. In order to use SNG as a natural antimicrobial precursor in food, it became important to better understand the ability of bacteria to synthesize the enzyme(s) and understand factors influencing this synthesis at a constant SNG concentration. Eight spoilage, pathogenic, or starter culture bacteria were grown separately in medium containing individual or combined salts with SNG. SNG degradation by the bacteria and the formation of its major degradation product, allyl isothiocyanate, were followed for 12 days at 30 or 35°C. The bacterial strains varied in their ability to metabolize SNG, and this was enhanced by NaCl and/or NaNO(3). SNG hydrolysis took place after 4 days, and the greatest amount occurred by day 12. At 12 days, Escherichia coli O157:H7 showed the greatest capacity to hydrolyze SNG (45.3% degradation), followed by Staphylococcus carnosus (44.57%), while Pseudomonas fluorescens was not active against SNG. The ability of tested strains to metabolize SNG, in decreasing order, was as follows: Escherichia coli O157:H7 > Staphylococcus carnosus > Staphylococcus aureus > Pediococcus pentosaceus > Salmonella Typhimurium > Listeria monocytogenes > Enterococcus faecalis > Pseudomonas fluorescens.

Multidirectional time-dependent effect of sinigrin and allyl isothiocyanate on metabolic parameters in rats

Sinigrin (SIN) and allyl isothiocyanate (AITC) are compounds found in high concentrations in Brassica family vegetables, especially in Brussels sprouts. Recently, they have been used as a nutrition supplement for their preventive and medicinal effect on some types of cancer and other diseases. In this research, nutritional significance of parent glucosinolate sinigrin 50 μmol/kg b. w./day and its degradation product allyl isothiocyanate 25 μmol/kg b. w./day and 50 μmol/kg b. w./day was studied by the evaluation of their influence on some parameters of carbohydrate and lipid metabolism in an animal rat model in vivo after their single (4 h) and 2 weeks oral administration. Additionally, the aim of this trial was to evaluate the direct action of AITC on basal and epinephrine-induced lipolysis in isolated rat adipocytes at concentration 1 μM, 10 μM and 100 μM in vitro. Sole AITC after 4 h of its ingestion caused liver triacylglycerols increment at both doses and glycaemia only at the higher dose. Multiple SIN treatment showed its putative bioconversion into AITC. It was found that SIN and AITC multiple administration in the same way strongly disturbed lipid and carbohydrate homeostasis, increasing esterified and total cholesterol, free fatty acids and lowering tracylglycerols in the blood serum. Additionally, AITC at both doses elevated insulinaemia and liver glycogen enhancement. The in vitro experiment revealed that AITC potentiated basal lipolysis process at 10 μM, and had stimulatory effect on epinephrine action at 1 μM and 10 μM. The results of this study demonstrated that the effect of SIN and AITC is multidirectional, indicating its impact on many organs like liver as well as pancreas, intestine in vivo action and rat adipocytes in vitro. Whilst consumption of cruciferous vegetables at levels currently considered "normal" seems to be beneficial to human health, this data suggest that any large increase in intake could conceivably lead to undesirable effect. This effect is potentiated with time of action of the examined compounds, whose influence is rather adverse for the majority of metabolic pathways (liver steatosis at short duration and insulinaemia, cholesterolaemia at long time treatment). Beneficial action of AITC concerned intensified hydrolysis of TG in the blood serum with a simultaneous lipolysis in adipocytes.

Allyl isothiocyanate as a cancer chemopreventive phytochemical

Allyl isothiocyanate (AITC), which occurs in many common cruciferous vegetables, is widely and often frequently consumed by humans. Besides antimicrobial activity against a wide spectrum of pathogens, it showed anticancer activity in both cultured cancer cells and animal models, although the underlining mechanisms remain largely undefined. Bioavailability of AITC is extremely high, as nearly 90% of orally administered AITC is absorbed. AITC absorbed in vivo is metabolized mainly through the mercapturic acid pathway and excreted in urine. Available data suggest that urinary concentrations of AITC equivalent are at least ten times higher than in the plasma, and tissue levels of AITC equivalent in the urinary bladder were 14-79 times higher than in other organs after oral AITC administration to rats. These findings suggest that AITC may be most effective in the bladder as a cancer chemopreventive compound. AITC at high-dose levels also exhibit a low degree of cytotoxicity and genotoxicity in animal studies, but such adverse effects are unlikely in humans exposed to dietary levels of AITC. Overall, AITC exhibits many desirable attributes of a cancer chemopreventive agent, and further studies are warranted in order to elucidate its mechanism of action and to assess its protective activity in humans.

Enzymatic inhibition by allyl isothiocyanate and factors affecting its antimicrobial action against Escherichia coli O157:H7

Allyl isothiocyanate (AIT) is derived from the glucosinolate sinigrin found in plants of the family Brassicaceae. It is a well-recognized antimicrobial agent against a variety of organisms, including foodborne pathogens such as Escherichia coli O157:H7. The efficiency of this natural agent in reducing E. coli O157:H7 numbers in food products have been reported. However, few have examined the mechanism by which AIT, and perhaps most of the isothiocyanates, kill E. coli O157:H7. In the present report, AIT showed greater antimicrobial activity at low pH values. For example, at pH 4.5 and 5.5 the MIC was 25 microL/L, while at pH 8.5, 500 microL/L was required to inhibit bacterial growth. This mustard-derived compound exhibited a high decomposition rate in water at 37 degrees C. Its degradation profile contained 3 major products and of these, diallylthiourea represented the largest ( approximately 80%) component. The decomposition products did not show antimicrobial activity towards E. coli O157:H7, even when combined with a sub-lethal dose of AIT (10 microL/L). AIT may only be antimicrobial in its original form and any further degradation in water is undesirable. AIT interactions with thioredoxin reductase and acetate kinase were also subjects of this study. AIT at 10 to 100 microL/L was able to significantly inhibit both enzymes, but only 1 microL/L was needed to decrease the activity of thioredoxin reductase. From these results, it can be postulated that: 1) AIT is a more effective antimicrobial at low pH values and its degradation reduces this activity; 2) decomposition products in water might not participate in the antimicrobial action of AIT; and 3) AIT seems to have a multi-targeted mechanism of action, perhaps inhibiting several metabolic pathways and damaging cellular structures.