Effect of crop management and sample year on abundance of soil bacterial communities in organic and conventional cropping systems.

AIMS: To identify changes in the bacterial community, at the phylum level brought about by varied crop management. METHODS AND RESULTS: Next-generation sequencing methods were used to compare the taxonomic structure of the bacterial community within 24 agricultural soils managed with either organic or conventional methods, over a 3-year period. Relative abundance of the proportionately larger phyla (e.g. Acidobacteria and Actinobacteria) was primarily affected by sample year rather than crop management. Changes of abundance in these phyla were correlated with changes in pH, organic nitrogen and soil basal respiration. Crop management affected some of the less dominant phyla (Chloroflexi, Nitrospirae, Gemmatimonadetes) which also correlated with pH and organic N. CONCLUSION: Soil diversity can vary with changing environmental variables and soil chemistry. If these factors remain constant, soil diversity can also remain constant even under changing land use. SIGNIFICANCE AND IMPACT OF THE STUDY: The impact of crop management on environmental variables must be considered when interpreting bacterial diversity studies in agricultural soils. Impact of land use change should always be monitored across different sampling time points. Further studies at the functional group level are necessary to assess whether management-induced changes in bacterial community structure are of biological and agronomic relevance.

Meat quality and health implications of organic and conventional beef production.

Recommendation to reduce fat consumption from ruminant meat does not consider the contribution of nutritionally beneficial fatty acids in lean beef. Here we report effects of production system (organic vs conventional) and finishing season on meat and fat quality of sirloin steaks from retail outlets and simulated fatty acid intakes by consumers. There was little difference in meat quality (pH, shear force and colour), but the fat profiles varied considerably between production systems and season. Meat fat from organic and summer finished cattle contained higher concentrations of conjugated linoleic acid, its precursor vaccenic acid and individual omega-3 fatty acids and had a lower ratio of omega-6 to omega-3 fatty acids compared with non-organic and winter finished cattle respectively. The fat profile from summer finished organic beef aligns better to recommended dietary guideline including those for long chain omega-3 fatty acids compared with that from winter finished, non-organic steak.

Improving the fatty acid profile of winter milk from housed cows with contrasting feeding regimes by oilseed supplementation.

Many studies show concentrations of nutritionally desirable fatty acids in bovine milk are lower when cows have no access to grazing, leading to seasonal fluctuations in milk quality if cows are housed for part of the year. This study investigated the potential to improve the fatty acid profiles of bovine milk by oilseed supplementation (rolled linseed and rapeseed) during a period of indoor feeding in both organic and conventional production systems. Both linseed and rapeseed increased the concentrations of total monounsaturated fatty acids, vaccenic acid, oleic acid and rumenic acid in milk, but decreased the concentration of the total and certain individual saturated fatty acids. Linseed resulted in greater changes than rapeseed, and also significantly increased the concentrations of α-linolenic acid, total polyunsaturated fatty acids and total omega-3 fatty acids. The response to oilseed supplementation, with respect to increasing concentrations of vaccenic acid and omega-3 fatty acids, appeared more efficient for organic compared with conventional diets.

Variation in nutritionally relevant components in retail Jersey and Guernsey whole milk.

This study investigates the quality of retail milk labelled as Jersey & Guernsey (JG) when compared with milk without breed specifications (NS) and repeatability of differences over seasons and years. 16 different brands of milk (4 Jersey & Guernsey, 12 non specified breed) were sampled over 2 years on 4 occasions. JG milk was associated with both favourable traits for human health, such as the higher total protein, total casein, α-casein, ß-casein, κ-casein and α-tocopherol contents, and unfavourable traits, such as the higher concentrations of saturated fat, C12:0, C14:0 and lower concentrations of monounsaturated fatty acids. In summer, JG milk had a higher omega-3:omega-6 ratio than had NS milk. Also, the relative increase in omega-3 fatty acids and α-tocopherol, from winter to summer, was greater in JG milk. The latter characteristic could be of use in breeding schemes and farming systems producing niche dairy products. Seasonality had a more marked impact on the fatty acid composition of JG milk than had NS milk, while the opposite was found for protein composition. Potential implication for the findings in human health, producers, industry and consumers are considered.

Integration of Elicitors and Less-Susceptible Hybrids for the Control of Powdery Mildew in Organic Tomato Crops.

Powdery mildew is a serious economic problem in Mediterranean tomato production. The disease is currently controlled by fungicides (especially sulfur) in both conventional and organic production. Four factorial greenhouse experiments were conducted in successive cropping seasons (autumn 2005, autumn 2006, spring 2006, and spring 2007) to assess the main and combined effects of (i) a less-susceptible hybrid ('Elpida'), (ii) chitin soil amendment, or (iii) Milsana or chitosan elicitor foliar treatments on the severity of powdery mildew and crop performance. Analysis of variance revealed significant effects of cropping season on disease severity and crop yield. All control practices reduced disease severity; reductions of approximately 40, 30, 15, and 15% were achieved by Milsana foliar treatment, the use of a less-susceptible hybrid, chitosan foliar treatment, and chitin soil amendment, respectively. In the season with the highest disease pressure, higher yields were obtained with the less-susceptible hybrid Elpida whereas, in the three seasons with no or low disease pressure, the use of the more susceptible hybrid 'Bison' produced higher yields. Milsana and sulfur treatments did not significantly affect yield (yields were slightly lower compared with untreated control plants) and, therefore, their use cannot be recommended based on the results obtained.

Crop and field boundary influences on the activity of a wide range of beneficial invertebrate groups on a split conventional/organic farm in northern England.

Activity of 12 beneficial invertebrate groups was assessed in 2005 and 2006 on a farm in northern England split into conventional and organic management halves, using pitfall and pan traps set in both crops and field boundaries. Management, crop and boundary structure influences on invertebrate activity were assessed, as was the relationship between crop and boundary type. Classification of crop and boundary assemblages produced three and two groups, respectively, in both years. Organic arable crops had well-defined assemblages in both years; and, while grass and grass/clover fields were separated from conventional arable fields in 2005, there was mixing in 2006. One boundary group, in both years, was dominated by conventional arable fields with tall herbaceous boundary vegetation. The other group had more organic arable and grassy fields with shorter boundary vegetation. Redundancy analyses showed that a number of groups (Cantharidae, Coccinellidae, Syrphidae, Ichneumonidae, Braconidae, Proctotrupoidea, Lycosidae) were more active in organic arable fields with more Staphylinidae in conventional arable crops and no obvious trend with Carabidae, Hemiptera, Neuroptera and Linyphiidae. Activity of some groups, especially Coccinellidae, Syrphidae and parasitic wasps, was strongly related to weed cover. Staphylinidae were most active in tall herbaceous boundaries by conventional arable crops with more of a number of groups (Cantharidae, Coccinellidae, parasitic wasps) in short herbaceous boundaries by organic arable crops. Organic management produced most differences in aerially-dispersed invertebrates, and management had a profound effect on activity in field boundaries. Possible management prescriptions to increase invertebrate activity include changing sowing times, weed cover manipulation and field boundary and margin management.

Fat composition of organic and conventional retail milk in northeast England.

This study of UK retail milk identified highly significant variations in fat composition. The survey, conducted over 2 yr replicating summer and winter, sampled 22 brands, 10 of which indicated organic production systems. Results corroborate earlier farm-based findings considering fat composition of milk produced under conventional and organic management. Organic milk had higher concentrations of beneficial fatty acids (FA) than conventional milk, including total polyunsaturated fatty acids (PUFA; 39.4 vs. 31.8 g/kg of total FA), conjugated linoleic acid cis-9,trans-11 (CLA9; 7.4 v 5.6 g/kg of FA), and α-linolenic acid (α-LN; 6.9 vs. 4.4 g/kg of FA). As expected, purchase season had a strong effect on fat composition: compared with milk purchased in winter, summer milk had a lower concentration of saturated fatty acids (682 vs. 725 g/kg of FA) and higher concentrations of PUFA (37.6 vs. 32.8 g/kg of FA), CLA9 (8.1 vs. 4.7 g/kg of FA), and α-LN (6.5 vs. 4.6 g/kg of FA). Differences identified between sampling years were more surprising: compared with that in yr 2, milk purchased in year 1 had higher concentrations of PUFA (37.5 vs. 32.9 g/kg of FA), α-LN (6.0 vs. 5.1 g/kg of FA), and linoleic acid (19.9 vs. 17.5 g/kg of FA) and lower concentrations of C16:0 and C14:0 (332 vs. 357 and 110 vs. 118 g/kg of FA, respectively). Strong interactions were identified between management and season as well as between season and year of the study. As in the earlier farm studies, differences in fat composition between systems were greater for summer compared with winter milk. Large between-year differences may be due to changes in weather influencing milk composition through forage availability, quality, and intake. If climate change predictions materialize, both forage and dairy management may have to adapt to maintain current milk quality. Considerable variation existed in milk fat composition between brands.

Milk quality as affected by feeding regimens in a country with climatic variation.

To investigate the influence of climatic conditions and season on milk composition, bulk tank milk was sampled on 5 occasions during a period of 15 mo from 20 Swedish dairy farms. These farms included 5 organic and 5 conventional farms in central Sweden and 7 traditional conventional farms and 3 conventional farms growing maize for silage in southern Sweden. Feed data and milk yield were recorded and milk was analyzed for content of fatty acids, carotenoids, and tocopherol. Differences between milk from the 2 regions and between summer and winter seasons were shown. Milk from central Sweden differed from milk from southern Sweden in that it had a higher content of carotenoids, tocopherol, short-chain fatty acids (C4-C14), C18:0, and C18:3 n-3 and a lower content of C16. Summer milk samples had a lower fat content and contained higher amounts of C18:1 cis-9 and conjugated linoleic acid cis-9,trans-11, and lower amounts of C4 to C16 compared with winter milk. Differences between farm types from central Sweden were lower content of conjugated linoleic acid cis-9,trans-11 and higher content of C18:3 n-3 in organic milk compared with conventional milk. In southern Sweden the use of maize silage caused lower milk content of carotenoids and C18:3 n-3 when compared with traditional feeding. Differences in milk composition could be related to climatic differences because legumes are more dominating in the leys of central Sweden and maize growing is limited to southern Sweden.

Potentials to differentiate milk composition by different feeding strategies.

To investigate the effect of the dietary intake of the cow on milk composition, bulk-tank milk was collected on 5 occasions from conventional (n = 15) and organic (n = 10) farms in Denmark and on 4 occasions from low-input nonorganic farms in the United Kingdom, along with management and production parameters. Production of milk based on feeding a high intake of cereals, pasture, and grass silage resulted in milk with a high concentration of alpha-linolenic acid (9.4 +/- 0.2 mg/kg of fatty acids), polyunsaturated fatty acids (3.66 +/- 0.07 mg/kg of fatty acids), and natural stereoisomer of alpha-tocopherol (RRR-alpha-tocopherol, 18.6 +/- 0.5 mg/kg of milk fat). A milk production system using a high proportion of maize silage, by-products, and commercial concentrate mix was associated with milk with high concentrations of linoleic acid (LA; 19.7 +/- 0.4 g/kg of fatty acids), monounsaturated fatty acids (27.5 +/- 0.3 mg/kg of fatty acids), and a high ratio between LA and alpha-linolenic acid (4.7 +/- 0.2). Comparing these 2 production systems with a very extensive nonorganic milk production system relying on pasture as almost the sole feed (95 +/- 4% dry matter intake), it was found that the concentrations of conjugated LA (cis-9,trans-11; 17.5 +/- 0.7 g/kg of fatty acids), trans-11-vaccenic acid (37 +/- 2 g/kg of fatty acids), and monounsaturated fatty acids (30.4 +/- 0.6 g/kg of fatty acids) were higher in the extensively produced milk together with the concentration of antioxidants; total alpha-tocopherol (32.0 +/- 0.8 mg/kg of milk fat), RRR-alpha-tocopherol (30.2 +/- 0.8 mg/kg of milk fat), and beta-carotene (9.3 +/- 0.5 mg/kg of milk fat) compared with the organic and conventional milk. Moreover, the concentration of LA (9.2 +/- 0.7 g/kg of fatty acids) in milk from the extensive milk production system was found to approach the recommended unity ratio between n-6 and n-3, although extensive milk production also resulted in a lower daily milk yield.

Control of enteric pathogens in ready-to-eat vegetable crops in organic and 'low input' production systems: a HACCP-based approach.

Risks from pathogens such as Salmonella, Yersinia, Campylobacter and Escherichia coli O157 have been identified as a particular concern for organic and 'low input' food production systems that rely on livestock manure as a nutrient source. Current data do not allow any solid conclusions to be drawn about the level of this risk, relative to conventional production systems. This review describes six Risk Reduction Points (RRPs) where risks from enteric pathogens can be reduced in ready-to-eat vegetables. Changes can be made to animal husbandry practices (RRP1) to reduce inoculum levels in manure. Outdoor livestock management (RRP2) can be optimized to eliminate the risk of faecal material entering irrigation water. Manure storage and processing (RRP3), soil management practices (RRP4) and timing of manure application (RRP5), can be adjusted to reduce the survival of pathogens originating from manure. During irrigation (RRP6), pathogen risks can be reduced by choosing a clean water source and minimizing the chances of faecal material splashing on to the crop. Although preventive measures at these RRPs can minimize enteric pathogen risk, zero risk can never be obtained for raw ready-to-eat vegetables. Good food hygiene practices at home are essential to reduce the incidence of food-borne illnesses.

Effect of alternative treatments on seed-borne Didymella lycopersici in tomato.

AIMS: To quantify the phytotoxicity and effect of alternative seed treatments based on acidified nitrite and elicitors of plant resistance (Tillekur and Chitosan) against seed-borne inocula of Didymella lycopersici. METHODS AND RESULTS: Treatments tested were: nitrite [sodium nitrite in citric acid buffer (pH 2)] at 30, 100 and 300 mmol l(-1) and three exposure times (10, 20 and 30 min); Tillekur (in water) at 12.5, 25, 50, 100 and 200 mg ml(-1); Chitosan (in 0.05% acetic acid) at 2.5, 5, 10 and 50 mg ml(-1). Efficacy of treatments was determined in growth chamber experiments. Nitrite at 300 mmol l(-1) was completely effective, as was the fungicide, at controlling disease when applied for less than 20 min. Tillekur was as effective as the fungicide postemergence, but proved to be phytotoxic pre-emergence. Chitosan was significantly less effective than the other treatments. CONCLUSIONS: The high efficacy and low cost of acidified nitrite indicates that it is a suitable alternative to fungicides. SIGNIFICANCE AND IMPACT OF THE STUDY: There is currently a lack of effective seed treatments that can be used in organic and low-input crops. Treatments identified in this study can be considered as an effective alternative to chemical control against seed-borne fungal pathogens.

Salivary nitrate--an ecological factor in reducing oral acidity.

Human oral cavities represent a novel environment with a constant supply of concentrated nitrate. For humans, over 80% of dietary nitrate originates from fruit and vegetables. With a healthy, balanced diet, rich in fruit and vegetables, the concentration of nitrate in saliva can reach up to more than three times the European drinking water standard. The physiological function of the active excretion of salivary nitrate is unknown. Furthermore, little is known of the ecological function of oral nitrate and the effect on the oral environment during its subsequent oral microbial conversions. The objectives of the research were to investigate the effect on salivary pH coupled with oral microbial nitrate and/or nitrite reduction. Human saliva samples were incubated anaerobically in the presence of 111.0 mmol glucose (2%), with and without 1.5 mmol nitrate/nitrite, and pH and nitrate/nitrite consumption were measured during the time-course of the incubations. We found that anaerobic incubation of saliva containing a mixture of oral bacteria in the presence of nitrate/nitrite substrates and glucose resulted in a higher pH than was found in controls in the absence of nitrate/nitrite. These results suggest that the presence of these electron acceptors repressed acid fermentation, or increased alkali production, or consumed acid produced, thus reducing salivary acidity. This finding identifies salivary nitrate as a possible ecological factor in reducing oral acidity. The possibility that a symbiotic relationship between host nitrate excretion and nitrate-reducing microorganisms might help to protect against tooth decay should be explored further.

Influence of Soil Temperature and Matric Potential on Sugar Beet Seedling Colonization and Suppression of Pythium Damping-Off by the Antagonistic Bacteria Pseudomonas fluorescens and Bacillus subtilis.

ABSTRACT Pseudomonas fluorescens B5 and Bacillus subtilis MBI 600 colonized sugar beet seedlings at matric potentials of -7 x 10(3), -140 x 10(3), and -330 x 10(3) Pa and under five temperature regimes ranging from 7 to 35 degrees C, with diurnal fluctuations of 5 to 22 degrees C. No interaction between matric potential and temperature was observed. In situ bioluminescence indicated physiological activity of Pseudomonas fluorescens B5. Colonization of the root at >/=4 cm below the seed decreased at very low matric potential (-330 x 10(3) Pa). Total population size of Pseudomonas fluorescens B5 per seedling was significantly increased at -140 x 10(3) Pa. However, matric potential had no significant effect on the population density of Pseudomonas fluorescens per gram of root fresh weight and did not affect the distribution of the population down the root. Total population size per seedling and downward colonization by Pseudomonas fluorescens B5 were significantly reduced at high temperatures (25 to 35 degrees C). Maximum colonization down the root occurred at intermediate temperature (15 degrees C) at both matric potentials (-7 x 10(3) and -140 x 10(3) Pa). Addition of B. subtilis MBI 600 to the seed had no effect on rhizosphere populations of Pseudomonas fluorescens B5. Populations of B. subtilis MBI 600, which consisted largely of spores, were slightly reduced at lower matric potentials and were not affected by temperature. Survival and dry weight of plants in soils infested with Pythium spp. decreased with increasing soil temperature and matric potential, indicating an increase in disease pressure. However, there was no significant interaction between the two factors. At -330 x 10(3) Pa, soil dryness but not Pythium infection was the limiting factor for plant emergence. At temperatures of 7 to 25 degrees C and matric potentials of -7 x 10(3) to 120 x 10(3) Pa, treatment with Pseudomonas fluorescens B5 increased plant survival and dry weight. At 7 degrees C and -120 x 10(3) Pa, there was almost complete emergence of seeds treated with Pseudomonas fluorescens B5. Antagonistic activity of Pseudomonas fluorescens B5 decreased with increasing soil temperature and decreasing matric potential. At 25 to 35 degrees C and -7 x 10(3) Pa, no effect was observed. In regimes with different day and night temperatures, the maximum (day) temperature was decisive for disease development and antagonistic activity. B. subtilis MBI 600 displayed no significant antagonistic effect against Pythium ultimum and did not influence the performance of Pseudomonas fluorescens B5 in combined inocula.

Biological control of cucumber and sugar beet damping-off caused by Pythium ultimum with bacterial and fungal antagonists.

AIMS: Five bacterial strains belonging to Bacillus subtilis, Pseudomonas fluorescens and Ps. corrugata and two fungal strains belonging to Trichoderma viride and Gliocladium virens were evaluated for their efficacy in controlling sugar beet and cucumber damping-off caused by Pythium ultimum. METHODS AND RESULTS: The in vitro antagonistic activity of bacteria against various Pythium spp. was evaluated with dual cultures in various media. Pseudomonas strains inhibited the pathogen better than Bacillus strains. To identify potentially useful antagonist combinations, dual compatibility of antagonists was also evaluated, based on growth in two liquid media containing substrate previously used by other antagonists. Four pairs of bacteria were selected. Sugar beet damping-off biocontrol was attempted with bacterial seed treatments (individually and in pairs). Cucumber damping-off biocontrol was attempted with bacterial seed treatments and bacterial and fungal compost treatments. In sugar beet, satisfactory biocontrol was only achieved with Pseudomonas antagonists. Antagonist combinations did not show any superior biocontrol ability to individual antagonists and compatibility of bacteria in vitro did not correlate with compatibility in vivo. Bacterial seed treatments and fungal compost treatments failed to control cucumber damping-off. Better biocontrol in cucumber was achieved when bacterial antagonists were applied by drenching or by coating seed with bacteria in a peat carrier. CONCLUSIONS: Pseudomonas antagonists were superior to Bacillus antagonists in controlling damping-off in cucumber and sugar beet. Pseudomonas peat inocula maintained a good shelf-life 2 years after preparation. SIGNIFICANCE AND IMPACT OF THE STUDY: Pseudomonas peat formulations have the potential for development into commercial biopesticides.

Investigations into the inhibitory effects of microcystins on plant growth, and the toxicity of plant tissues following exposure.

The cyanobacterial toxins microcystins are known to affect a number of processes in plant tissues, and their presence in water used for irrigation may have considerable impact on the growth and development of crop plants. In this study, two plant bioassays were employed to investigate the phytotoxic effects of microcystins. A plant tissue culture assay revealed that the growth and chlorophyll content of Solanum tuberosum L. cultures was inhibited at microcystin-LR concentrations of 0.005 and 0.05 microg x cm(-3), respectively. A previously developed bioassay was also employed to determine the effects of three commonly occurring microcystin variants on the growth of Synapis alba L. seedlings. Microcystins-LR, -RR, and -LF inhibited the growth of seedlings, with GI50 values of 1.9, 1.6 and 7.7 microg x ml(-1), respectively. The growth of Phaseolus vulgaris was also examined in the presence of microcystin-LR. The toxin was found to have little effect on growth for up to 18 days, but impaired the development of the roots of exposed plants, causing them to take up approximately 30% less growth medium than those grown in the absence of toxin. Microcystin was also detected in the tissues of exposed plants using a commercially available ELISA kit, suggesting that the uptake of these toxins by edible plants may have significant implications for human health.

Antimicrobial effect of acidified nitrite on dermatophyte fungi, Candida and bacterial skin pathogens.

AIMS: Nitric oxide is generated from sweat nitrite in the acidic environment of the skin surface and is thought to contribute to protection against infection. This study examined the sensitivity of Trichophyton mentagrophytes, T. rubrum, Candida albicans, Streptococcus pyogenes, Staphylococcus aureus and Propionibacterium acnes to acidified nitrite. METHODS AND RESULTS: Organisms were cultured in varying concentrations of nitrite and pH for different lengths of time, before being transferred to recovery medium. With the exception of Strep. pyogenes, addition of nitrite increased the antimicrobial activity of acid solutions against all organisms tested. The rank order of sensitivity was: C. albicans < T. rubrum < T. mentagrophytes < Staph. aureus < P. acnes, with P. acnes being most sensitive. CONCLUSION: This work has shown that acidified nitrite is microbiocidal to common cutaneous pathogens. The concentrations of nitrite required to kill pathogenic fungi and bacteria in in vitro assays were higher than the concentrations of nitrite measured in sweat. However, additional co-factors in vivo and in sweat may potentiate the effect of acidified nitrite. SIGNIFICANCE AND IMPACT OF THE STUDY: Pharmacological preparations of acidified nitrite are novel antimicrobial agents. These data suggest skin organisms which may be sensitive to this treatment.

Dietary nitrate in man: friend or foe?

Based on the premise that dietary nitrate is detrimental to human health, increasingly stringent regulations are being instituted to lower nitrate levels in food and water. Not only does this pose a financial challenge to water boards and a threat to vegetable production in Northern Europe, but also may be eliminating an important non-immune mechanism for host defence. Until recently nitrate was perceived as a purely harmful dietary component which causes infantile methaemoglobinaemia, carcinogenesis and possibly even teratogenesis. Epidemiological studies have failed to substantiate this. It has been shown that dietary nitrate undergoes enterosalivary circulation. It is recirculated in the blood, concentrated by the salivary glands, secreted in the saliva and reduced to nitrite by facultative Gram-positive anaerobes (Staphylococcus sciuri and S. intermedius) on the tongue. Salivary nitrite is swallowed into the acidic stomach where it is reduced to large quantities of NO and other oxides of N and, conceivably, also contributes to the formation of systemic S-nitrosothiols. NO and solutions of acidified nitrite, mimicking gastric conditions, have been shown to have antimicrobial activity against a wide range of organisms. In particular, acidified nitrite is bactericidal for a variety of gastrointestinal pathogens such as Yersinia and Salmonella. NO is known to have vasodilator properties and to modulate platelet function, as are S-nitrosothiols. Thus, nitrate in the diet, which determines reactive nitrogen oxide species production in the stomach (McKnight et al. 1997), is emerging as an effective host defence against gastrointestinal pathogens, as a modulator of platelet activity and possibly even of gastrointestinal motility and microcirculation. Therefore dietary nitrate may have an important therapeutic role to play, not least in the immunocompromised and in refugees who are at particular risk of contracting gastroenteritides.

Helicobacter pylori is killed by nitrite under acidic conditions.

BACKGROUND: Due to the expression of urease, Helicobacter pylori is able to establish itself in the human stomach under acidic conditions. A novel host defence mechanism was recently proposed, suggesting that the formation of salivary nitrite in symbiosis with facultative anaerobic bacteria in the oropharynx, is aimed at enhancing the antimicrobial activity of gastric juice. AIMS: To investigate whether the addition of nitrite in physiological concentrations influences the resistance of H pylori to acid. METHODS: H pylori cultured from fresh gastric Biopsy specimens was exposed for 30 minutes to normal saline and to HCl/KCl buffer (0.2M) at pH 2 with urea (5 mM) added. The influence of potassium nitrite (50-1000 mumol/l) on bacterial survival was determined. RESULTS: Addition of nitrite (1 mM) to acidic solutions (pH 2) resulted in complete kill of H pylori within 30 minutes exposure time whereas acid alone allowed the organism to survive (p < 0.001). The antimicrobial effect of nitrite at pH 2 against H pylori was dose dependent and complete kill of organisms occurred at concentrations > or = 500 mumol/l. CONCLUSION: Acidified nitrite has anti-bacterial activity against H pylori. This should prompt further research into the effect of salivary nitrite on the survival of H pylori in the human stomach.

Nitrate-reducing bacteria on rat tongues.

Nitrite-producing bacteria (NPB) were isolated from tongues of laboratory rats. The most commonly found nitrite-producing organism was Staphylococcus sciuri, followed by Staphylococcus intermedius, Pasteurella spp., and finally Streptococcus spp. Both morphometric quantification of bacteria on tongue sections and enumeration of culturable bacteria (CFU) showed an increase in the density of bacteria towards the posterior tongue. Up to 65% of bacteria were located in the deep clefts on the posterior tongue. The proportion of culturable NPB in the total culturable microbial population increased from 6% (10(5) CFU cm-2) on the anterior tongue to 65% (10(7) CFU cm-2) on the posterior tongue. Different species compositions of NPB were found on different tongue sections with S. intermedius populations decreasing and S. sciuri and Pasteurella populations increasing towards the posterior tongue. Nitrite production was sensitive to oxygen, and significant nitrite production was only detected on the posterior tongue where the majority of bacteria are situated in deep clefts in the tongue surface. This study suggests the importance of bacteria in nitrite production, from nitrate, on the tongue. Nitrite produced on the tongue may subsequently form nitric oxide in the acidic environment of the stomach. Because of the antimicrobial properties of nitric oxide, a key role for nitrate-reducing tongue bacteria in host animal defense against food-borne pathogens in proposed.