Rechargeable antimicrobial surface modification of polyethylene.

Polyethylene films were surface modified, to incorporate amine and amide functionalities, and subsequently were evaluated for their ability to recharge the antimicrobial N-halamine structures after contact with sodium hypochlorite, a common food-approved sanitizer. Surfaces were tested for chlorine retention and release, as well as antimicrobial activity against microorganisms relevant to food quality and food safety, including Escherichia coli K-12, Pseudomonas fluorescens, Bacillus cereus, and Listeria monocytogenes. N-Halamine functionalized polyethylene exhibited chlorine rechargeability, maintaining 5 to 7 nmol/cm2 N-halamine structures for six successive charges. The N-halamine functionalized films achieved a 4-log reduction for all organisms tested and maintained a greater than 3-log reduction for four successive uses, suggesting that the modified polyethylene films are capable of providing rechargeable antimicrobial activity. The modified films exhibited antimicrobial activity in aqueous suspensions (P < 0.05) and reduced microbial growth in diluted broth (P < 0.05), suggesting the potential for biocidal action even in the presence of organic matter. Such a rechargeable antimicrobial surface could supplement existing cleaning and sanitation programs in food processing environments to reduce the adhesion, growth, and subsequent cross-contamination of food pathogens, as well as food spoilage organisms.

Release of 1-methylcyclopropene from heat-pressed polymer films.

Gaseous 1-methylcyclopropene (1-MCP) is an inhibitor of ethylene perception that is being used extensively for apples and ornamental products, and under intensive investigation for its potential benefits for other fruits and vegetables. 1-MCP is currently used in closed environments that maintain stable concentrations for several hours in order to be effective. However, food packaging materials that release 1-MCP at a predictable rate into the package headspace might be useful for application in inhibiting the deleterious effects of ethylene in the postharvest packaging and storage of some horticultural products. A 1-MCP/alpha-cyclodextrin (1-MCP-cd) complex was incorporated into several common packaging films by heat-pressing (dry-blend, lamination) and solution-casting methods. The release of 1-MCP from the films was quantified by gas chromatography with respect to time, loading of 1-MCP, temperature, relative humidity (RH), type of film, and film-forming method. Release of 1-MCP was rapid and high in films held at RH >/= 75%. The rate of release was slow during the 1st 12 h and then increased during the next 24 to 36 h. Higher temperatures resulted in higher and faster release. A loading of 8 mg of 1-MCP-cd per 140 mg of polymer was found to be optimal. Pressing 1-MCP-cd containing films above 100 degrees C reduced the amount of 1-MCP remaining in the film. Incorporation into LDPE resulted in a higher and faster release than from PS, PVC, and PP polymers. 1-MCP release from a film matrix appears to be within the acceptable range for produce packaging applications.

Covalent attachment of lactase to low-density polyethylene films.

Polymer films to which bioactive compounds such as enzymes are covalently attached offer potential for in-package processing of food. Beta-galactosidase (lactase) was covalently attached to surface-functionalized low-density polyethylene films. A two-step wet chemical functionalization introduced 15.7 nmol/cm2 primary amines to the film surface. Contact angle, dye assays, X-ray photoelectron spectroscopy, and appropriate protein assays were used to characterize changes in film surface chemistry after each step in the process of attachment. Glutaraldehyde was used to covalently attach lactase to the surface at a density of 6.0 microg protein per cm2 via reductive amination. The bond between the covalently attached lactase and the functionalized polyethylene withstood heat treatment in the presence of an ionic denaturant with 74% enzyme retention, suggesting that migration of the enzyme into the food product would be unlikely. The resulting polyethylene had an enzyme activity of 0.020 lactase units (LU)/cm2 (approximately 4500 LU/g). These data suggest that enzymes that may have applications in foods can be covalently attached to inert polymer surfaces, retain significant activity, and thus have potential as a nonmigratory active packaging materials.

Continuous flow nonthermal CO2 processing: the lethal effects of subcritical and supercritical CO2 on total microbial populations and bacterial spores in raw milk.

The effect of pressurized (<50 MPa) CO2 as a nonthermal process for bacterial reduction in raw skim milk was examined using a unique pressurized continuous flow system. The lethal effects of subcritical and super-critical CO2 applied at different temperatures and pressures toward total native psychrotrophic microbial populations, total inoculated Pseudomonas fluorescens, and total inoculated spore populations were studied and compared. Pressures between 10.3 and 48.3 MPa; temperatures of 15, 30, 35, and 40 degrees C; and CO2 concentrations of 0, 3, 66, and 132 g/kg of milk were studied. For both native populations and inoculated P. fluorescens, greater total microbial lethality was observed under supercritical CO2 conditions than under subcritical CO2 conditions. At 30 degrees C, there was no effect on total microbial lethality of increasing pressure up to 20.7 MPa with either 66 or 132 g/kg of CO2; at 35 degrees C, there was a positive relationship between pressure and lethality at CO2 levels of 132 g/kg, but no relationship at 66 g/kg of CO2. For total microbial populations and P. fluorescens, CO2 applied at 132 g/kg at 30 degrees C and pressures of 10.3 to 20.7 MPa resulted in an average standard plate count reduction of 3.81 and 2.93 log, respectively; at 35 degrees C and 20.7 MPa, maximum reductions achieved were 5.36 and 5.02 log, respectively. For both total microbial populations and inoculated P. fluorescens, CO2 exhibited a greater overall lethal effect at 132 g/kg than at 66 g/kg and a greater effect at 35 degrees C than at 30 degrees C. At 24.1 and 48.3 MPa and 40 degrees C, microbial lethality in raw aged milk treated with 3 g/kg of CO2 was not significantly different than that observed for uncarbonated milk; lethality achieved in milk treated with 132 g/kg of CO2 was significantly higher than that achieved in these 2 low-level CO2 treatments. No treatment studied had any significant impact on spore populations. Our work shows that, using the studied system, pressurized CO2 results in greater microbial lethality in milk above critical temperatures than below and suggests that a critical concentration threshold level of CO2 is required for lethal effects. Our work also suggests that supercritical CO2 processing in a continuous flow system can achieve reductions in some microbial populations equal to or better than that typically achieved during high-temperature, short-time pasteurization.

Inactivation of Escherichia coli (ATCC 4157) in diluted apple cider by dense-phase carbon dioxide.

Dense-phase carbon dioxide (CO2) treatments in a continuous flow through system were applied to apple cider to inactivate Escherichia coli (ATCC 4157). A response surface design with factors of the CO2/product ratio (0, 70, and 140 g/kg), temperature (25, 35, and 45 degrees C), and pressure (6.9, 27.6, and 48.3 MPa) were used. E. coli was very sensitive to dense CO2 treatment, with a more than 6-log reduction in treatments containing 70 and 140 g/kg CO2, irrespective of temperature and pressure. The CO2/product ratio was the most important factor affecting inactivation rate of E. coli. No effect of temperature and pressure was detected because of high sensitivity of the cells to dense CO2. Dense CO2 could be an alternative pasteurization treatment for apple cider. Further studies dealing with the organoleptic quality of the product are needed.

Low pressure CO2 storage of raw milk: microbiological effects.

The effects of holding raw milk under carbon dioxide pressures of 68 to 689 kPa at temperatures of 5, 6.1, 10, and 20 degrees C on the indigenous microbiota were investigated. These pressure-temperature combinations did not cause precipitation of proteins from the milk. Standard plate counts from treated milks demonstrated significantly lower growth rate compared with untreated controls at all temperatures, and in some cases, the treatment was microcidal. Raw milk treated with CO2 and held at 6.1 degrees C for 4 d exhibited reduced bacterial growth rates at pressures of 68, 172, 344, and 516 kPa; and at 689 kPa, demonstrated a significant loss of viability in standard plate count assays. The 689-kPa treatment also reduced gram-negative bacteria and total Lactobacillus spp. The time required for raw milk treated at 689 kPa and held at 4 degrees C to reach 4.30 log10 cfu/mL increased by 4 d compared with untreated controls. Total coliform counts in the treated milk were maintained at 1.95 log10 cfu/mL by d 9 of treatment, whereas counts in the control significantly increased to 2.61 log10 cfu/mL by d 4 and 2.89 log10 cfu/mL by d 9. At d 8, Escherichia coli counts had not significantly changed in treated milk, but significantly increased in the control milk. Thermoduric bacteria counts after 8 d were 1.32 log10 cfu/mL in treated milk and 1.98 log10 cfu/mL in control milk. These data indicated that holding raw milk at low CO2 pressure reduces bacterial growth rates without causing milk protein precipitation. Combining low CO2 pressure and refrigeration would improve the microbiological quality and safety of raw milk and may be an effective strategy for shipping raw single strength or concentrated milk over long distances.

Determination of thermal inactivation kinetics of microorganisms with a continuous microflow apparatus.

Use of a continuous microflow submerged microcoil (CSMC) apparatus was compared with the capillary tube (CT) method for measuring the thermal inactivation kinetics of Pseudomonas fluorescens at 61 degrees C for 3 to 29 s. Inocula were continuously pumped through a microbore (< or = 0.0762 cm inside diameter) thin-walled stainless steel capillary tube submerged in a heated oil bath. The heating time was set by changing the flow rate, tube dimensions, or both. With the use of microthermo-couples, the time for the inocula to reach within 1 degree C of the set temperature was <3 s, and shorter than that with capillary tubes or vials. Inactivation curves (61 degrees C) for P. fluorescens prepared by the CSMC method were not different from curves prepared by the CT method, as determined by analysis of variance (P > 0.05). Inactivation of Bacillus cereus spores (105 degrees C) and native microflora found in raw milk (72 degrees C) over heating times of 3 to 42 s were determined by CSMC. CSMC can measure thermal inactivation kinetics of microorganisms efficiently and simply at high temperatures and in short times. Survivors can be enumerated in 1-ml volumes of heat-treated samples, making it useful for determining inactivation kinetics of low numbers of microorganisms, such as those found in high-quality raw milk. Inactivation kinetics were generally more accurately described by the Weibull function (R2 > or = 0.97) than the linear kinetic model.

Effects of carbon dioxide on bacterial growth parameters in milk as measured by conductivity.

Inhibition of bacterial growth by dissolved carbon dioxide (CO2) has been well established in many foods including dairy foods. However, the effects of dissolved CO2 on specific growth parameters such as length of lag phase, time to maximum growth rate, and numbers of organisms at the stationary phase have not been quantified for organisms of concern in milk. The effect of dissolved CO2 concentrations of 0.6 to 61.4 mM on specific bacterial growth parameters in raw or single organism inoculated sterile milk was determined at 15 degrees C by conductance. Commingled raw or sterile milks were amended to a final concentration of 0.5 mg/ml each of urea and arginine HCl. Sterile milks were inoculated singly with one of six different microorganisms to a final concentration of approximately 10(2) to 10(3) cfu/ml; raw milk was adjusted to a final indigenous bacterial population of approximately 10(3) cfu/ml. Conductivity of the milk was recorded every 60 s over 4 to 5 d in a circulating apparatus at 15 degrees C. Conductivity values were fit to Gompertz equations and growth parameters calculated. Conductance correlated with plate counts and was satisfactory for monitoring microbial growth. Data fit the Gompertz equation with high correlation (R2 = 0.96 to 1.00). In all cases, dissolved CO2 significantly inhibited growth of raw milk bacteria, influencing lag, exponential, and stationary growth phases as well as all tested monocultures.

Effect of cooking on the formation of N-nitrosodimethylamine in Korean dried seafood products.

Only N-nitrosodimethylamine (NDMA) was detected when N-nitrosamines (NA) were analysed in seven dried seafood products, either uncooked or cooked. The cooking methods used were a briquet fire, a gas range, an electric oven, a microwave oven, a steam cooker and an electric coil cooker. The contents of NDMA ranged from 1.0 to 46.9 microgram kg(-1) in uncooked products. When these samples were cooked, regardless of the cooking method, the content of NDMA tended to increase, ranging from 1.1 to 630.5 microgram kg(-1). In general, indirect heating such as a steam cooker and a microwave oven, as compared with direct heating such as a gas range and a briquet fire, caused less increase in NDMA during cooking.

Effect of dissolved carbon dioxide on thermal inactivation of microorganisms in milk.

Postpasteurization addition of CO2 inhibits growth of certain microorganisms in dairy products, but few workers have investigated the effect of CO2 on the thermal inactivation of microorganisms during pasteurization. Concentrations of CO2 ranging from 44 to 58 mM added to raw whole milk significantly (P < 0.05) reduced the number of surviving standard plate count (SPC) organisms in milk heated over the range of 67 to 93 degrees C. A decrease in thermal survival rates (D-values) for Pseudomonas fluorescens R1-232 and Bacillus cereus ATCC 14579 spores in milk was positively correlated with CO2 concentrations (1 to 36 mM). D(50 degrees C)-values for P. fluorescens significantly decreased (P < 0.05) in a linear fashion from 14.4 to 7.2 min. D(89 degrees C)-values for B. cereus spores were significantly (P < 0.05) decreased from 5.56 min in control milk to 5.29 min in milk containing 33 mM CO2. The Weibull function was used as a model to describe the thermal inactivation of P. fluorescens, B. cereus spores, and SPC organisms in raw milk. Nonlinear parameters for the Weibull function were estimated, and survival data fitted to this model had higher R2 values than when fitted to the linear model, further providing support that the thermal inactivation of bacteria does not always follow first-order reaction rate kinetics. These results suggest that CO2 could be used as a processing aid to enhance microbial inactivation during pasteurization.

Effect of carbon dioxide on the growth of Bacillus cereus spores in milk during storage.

The effects of the addition of 11.9 mM CO2 on the growth of Bacillus cereus spores inoculated into sterile homogenized whole milk at 101 and 106 spores/ml and stored at 6.1 degrees C, was examined weekly for 35 d. Colony-forming units from CO2 treated inoculated milks decreased over 35 d at a rate similar to that of untreated inoculated milk, as defined by linear regression. Plate counts for treated and control milks inoculated at 10(1) cfu/ml were not significantly different on sampling d 0, 14, 21, and 28. Plate counts at d 7 were significantly different and counts at d 35 were at undetectable levels for both treated and control milks. Plate counts for milk inoculated at 10(6) cfu/ml were not significantly different on d 0, 28, and 35; they were significantly different on d 7, 14, and 21. There was no consistency as to whether the control or test milks were higher in counts on days when the differences were significant. Added CO2 reduced the pH of the milk from an average value of 6.61 to an average value of 6.31; however, this drop did not correlate with changes in any other parameter measured. These data suggest that moderate levels of CO2 do not enhance the outgrowth of B. cereus spores over long-term storage and do not increase the risk of foodborne illness due to the organism.

Impact of CO2 addition to milk on selected analytical testing methods.

The addition of CO2 to raw milk and dairy products controls the growth of psychrotrophic bacteria at refrigeration temperatures. The objective of this study was to determine the effects of dissolved CO2 in milk on the performance of four important routine testing methods: antibiotic residue test, freezing point test, infrared milk component analysis, and alkaline phosphatase test. Raw or pasteurized whole milk was carbonated at <4 degrees C to contain approximately 0 (control), 200, 400, 600, and 1000 ppm of CO2. The addition of CO2 to raw milk up to 1000 ppm had no effect on the performance of the three antibiotic (beta-lactams) residue tests: IDEXX SNAP, Charm II Sequential Tablet, and Delvo-P Ampule. Milk freezing point decreased linearly with increasing concentration of dissolved CO2, from -0.543 degrees H (control) to -0.595 degrees H (1000 ppm). Carbonation to 1000 ppm decreased milk pH (measured at 38 degrees C) from 6.61 (control) to 6.15 (1000 ppm). The effects of CO2 on milk freezing point and pH were reversible upon removal of dissolved CO2. Increased CO2 levels in milk changed the infrared absorption spectrum of milk and caused the corrected lactose readings to decrease and the corrected fat B readings to increase. For the alkaline phosphatase tests, 0 (none), 0.05, 0.1, and 0.2% raw milk were deliberately added to pasteurized milks of six levels of carbonation (0 to 1000 ppm). The addition of CO2 did not influence the ability of Fluorophos, Charm PasLite, and Scharer Modified Rapid tests to differentiate between a pasteurized milk and a pasteurized milk with raw milk contamination.

Antimicrobial activity of a 14-residue synthetic peptide against foodborne microorganisms.

A chemically synthesized short-chain peptide composed of six leucine and eight lysine (6K8L) residues was demonstrated to be biocidal against several foodborne organisms including Escherichia coli O157:H7, Listeria monocytogenes, Pseudomonas fluorescens, and Kluyveromyces marxianus suspended in phosphate buffer at concentrations of 5 to 50 microg/ml. All strains were reduced by 3 log10 CFU/ml within 10 min at peptide concentrations of <10 microg/ml. The peptide reduced by 3 log10 CFU/ml E. coli O157:H7 counts in apple juice and was active over the pH range of 3.5 to 7. Peptide concentrations of 100 microg/ml inhibited the aerobic and anaerobic microorganisms present in meat exudate liquid. However, the peptide was not effective against E. coli O157:H7 in skim milk at concentrations up to 100 microg/ml.

Antimicrobial activity of a 14-residue peptide against Escherichia coli O157:H7.

An amphiphilic, cationic peptide composed of eight leucines and six lysines was synthesized by solid phase peptide synthesis (SPPS). The synthetic peptide was bactericidal within 10 min at concentrations as low as 3 microg ml - 1 against mid-exponential Escherichia coli O157:H7 suspended in buffer. Concentrations of 25 microg ml - 1 caused up to 7 log10 cfu ml - 1 reductions. When tested against E. coli O157:H7 grown in TSB, the peptide was bactericidal and bacteriostatic at concentrations of 50 and 25 microg ml - 1, respectively. An inhibitory effect was also observed against stationary phase cells. The synthetic peptide caused the release of u.v.-absorbing materials from the E. coli O157:H7 as well as an increase in its O.D.600 nm. Intracellular K+ and ATP depletion were also observed. These results suggest that the peptide increased the cell membrane permeability but it did not lyse the cells.

The effect of lipids on bongkrekic (Bongkrek) acid toxin production by Burkholderia cocovenenans in coconut media.

Tempe bongkrek is an Indonesian food made by fermentation of coconut presscake or coconut milk residue Rhizopus oligosporus. Consumption of tempe bongkrek is associated with a food-borne human intoxication and significant numbers of deaths annually. The bacterium Burkholderia cocovenenans, which is the causative organism, produces two toxins, toxoflavin and bongkrekic acid (also commonly referred to as bongkrek acid). The reasons why these poisonings occur only in a very limited number of foods and only in isolated regions of the world are unclear. Our preliminary experiments in defined media and coconut investigated several compositional and environmental factors and suggested that lipid type and/or concentration were important. The effect of lipid concentration and fatty acid type on the production of bongkrekic acid by B. cocovenenans was examined by adding different amounts of coconut fat or individual free fatty acids to defatted and sterilized Rich Coconut Media (dRCM). The dRCM with added lipid was inoculated with B. cocovenenans, incubated at 30 degrees C for 5 days and the amount of bongkrekic acid formed quantified by HPLC. Coconut fat concentrations of 10% (dry basis) or less did not result in detectable amounts of bongkrekic acid even though the B. cocovenenans grew to high levels. Forty and 50% coconut fat resulted in as much as 1.4 mg/g bonkrekic acid (dry weight) at the same level of growth. Of eight saturated fatty acids tested, only lauric (12:0), myristic (14:0), and palmitic (16:0) acids stimulated the production of detectable amounts of toxin. When four 18-carbon free fatty acids with different degrees of saturation were compared, significant amounts of bongkrekic acid (2.62 mg/g dry weight) were produced only with oleic acid (18:1). These data indicate that the concentration and type of lipid in the substrate is critical for bongkrekic acid formation. This may explain why bongkrekic acid intoxication is limited to certain foods. Outbreaks associated with foods containing less than 20% fat may be a result of toxoflavin formation and not bongkrekic acid formation.

Combined effects of carbon dioxide addition and barrier films on microbial and sensory changes in pasteurized milk.

The growth of psychrotrophic microorganisms is an important factor in the deterioration of refrigerated pasteurized milk. Dissolved CO2 inhibits certain spoilage microorganisms in foods provided that the packaging offers a sufficient barrier to CO2 evolution. The objectives of this work were, first, to estimate the sensory threshold for dissolved CO2 in 2% milk and, second, to determine the relationship between microbial growth and package barrier properties for pasteurized milk to which CO2 had been added at concentrations near the flavor threshold. The sensory threshold, as determined by a trained panel, for CO2 in 2% pasteurized milk was > 2.8 mM and < 9.1 mM. Pasteurized milk was inoculated with a cocktail of spoilage microorganisms, packaged in different barrier film pouches, and stored at 6.1 degrees C for up to 28 d. The addition of CO2 at concentrations of 8.7 and 21.5 mM increased the time needed to reach 10(6) cfu/ml from 6.4 d (no CO2) to 8.0 and 10.9 d, respectively, in low barrier pouches. In high barrier pouches, the time needed to reach 10(6) cfu/ml was increased to 9.7 and 13.4 d, respectively, at CO2 concentrations of 8.7 and 21.5 mM. This increase represents an increase in shelf-life of approximately 25 to 200%. Microbial counts had longer lag times and lower growth rates and took longer to reach stationary growth as the concentration of CO2 increased in all films than did the control milk. The control milk curdled in less than 17 d, but the test milk in the high barrier packaging had not curdled at 28 d. These data suggest that the shelf-life of pasteurized refrigerated milk could be extended by at least 25 to 200% at CO2 concentrations near the sensory threshold. The major variables in shelf-life are the amount of added CO2 and the barrier properties of the package.

Food-packaging interactions influencing quality and safety.

Interactions between foods and packaging can be detrimental to quality and/or safety. Changes in product flavour due to aroma sorption and the transfer of undesirable flavours from packaging to foods are important mechanisms of deterioration when foods are packaged in polymer-based materials. Careful consideration must be given to those factors affecting such interactions when selecting packaging materials in order to maximize product quality, safety, and shelf-life while minimizing undesirable changes. Product considerations include sensitivity to flavour and related deteriorations, colour changes, vitamin loss, microbial activity, and amount of flavour available. Storage considerations include temperature, time, and processing method. Polymer considerations include type of polymer and processing method, volume or mass of polymer to product ratio, and whether the interaction is Fickian or non-Fickian. Methodology to determine the extent of such interactions must be developed. Direct interactions between food and packaging are not necessarily detrimental. The same principles governing undesirable interactions can be used to affect desirable outcomes. Examples include films which directly intercept or absorb oxygen, inhibit microorganisms, remove undesirable flavours by sorption, or indicate safety and product shelf-life.

Effect of Carbon Dioxide on the Growth of Pseudomonas fluorescens and Listeria monocytogenes in Aerobic Atmospheres.

The effects of atmospheres containing 20% O2 and 0 to 80% CO2 or 30% CO2 and 0 to 40% O2 (balance N2) on the growth rate and lag phase of Listeria monocytogenes and Pseudomonas fluorescens in buffered nutrient broth at 7.5°C were investigated. Increasing CO2 concentration lengthened the lag phase and decreased the growth rate of both organisms. CO2 levels above 20% significantly reduced the growth rate of P. fluorescens and CO2 levels of 80% significantly reduced the growth rate of L. monocytogenes . Linear and multiple regression analyses were used to describe L. monocytogenes and P. fluorescens growth curves. The R2 values of all regression analyses were greater than 93%. The regression equations indicate that CO2 inhibits the growth of both P. fluorescens and L. monocytogenes even in the presence of 20% O2, However, the effect of CO2 on P.fluorescens is greater than on L. monocytogenes .

Induction of nitric oxide synthesis in murine macrophages by Helicobacter pylori.

Intact Helicobacter pylori cells, as well as cellular components, stimulated nitric oxide (NO) synthesis in an in vitro murine macrophage system by the L-arginine-nitric oxide pathway. Macrophage-mediated NO formation was dependent on the presence of H. pylori and exhibited a dose-dependent increase at H. pylori concentrations between 10(6) and 5 and 10(7) cells/ml. H. pylori mediated NO synthesis also required L-arginine and was inhibited by NG-monomethyl-L-arginine (NMMA), a selective inhibitor of nitric oxide synthase. NO synthesis was induced by whole H. pylori cells. H. pylori media filtrate, extracted membrane proteins, and H. pylori lipopolysaccharide (LPS). Maximal NO synthesis was induced by viable H. pylori cells with media filtrate and membrane protein extracts inducing significant NO responses. NO stimulation by media filtrate and membrane protein extracts support secreted H. pylori products as potential activators of inflammatory cell NO synthesis in vivo. NO synthesis in response to H. pylori suggests that chronic H. pylori infection may increase endogenous formation of NO. Elevated NO exposure may represent an etiologic factor explaining the epidemiologic association between long-term H. pylori infection and gastric cancer.

Potential genotoxicity of chronically elevated nitric oxide: a review.

Several human cancers are associated with chronic bacterial, viral and parasitic infections. Nitric oxide, which is a short-lived free radical produced by many types of cells for a number of important physiological functions, is elevated in these infections. Long-term exposure to elevated NO. in cells could have potential genotoxic effects on hosts. There are at least three mechanisms by which intracellular elevated NO. could exert genotoxic affects after reacting with O2. These include formation of carcinogenic N-nitroso compounds, direct deamination of DNA bases, and oxidation of DNA after formation of peroxynitrite and/or hydroxyl radicals. One or more of these mechanisms could, theoretically, explain why chronic infection increases the risk of certain cancers.