A note on survival of salmonellas during anaerobic digestion of cattle dung

Anaerobic digestion of night soil with cattle dung slurry in biogas plants is advocated in Indian villages as a means of disposal of human excreta in the absence of conventional sanitary systems. Although intestinal pathogens are likely to be eliminated during anaerobic digestion, there is no conclusive evidence that this is so. Large numbers of saprophytic organisms in the fermenting mass make it impossible to detect the residual pathogens. Use of an antibiotic-resistant strain of Salmonella typhimurium as a test organism to study its survival during anaerobic digestion showed that the organism is totally eliminated in nine days.     

A note on survival of salmonellas during anaerobic digestion of cattle dung

Anaerobic digestion of night soil with cattle dung slurry in biogas plants is advocated in Indian villages as a means of disposal of human excreta in the absence of conventional sanitary systems. Although intestinal pathogens are likely to be eliminated during anaerobic digestion, there is no conclusive evidence that this is so. Large numbers of saprophytic organisms in the fermenting mass make it impossible to detect the residual pathogens. Use of an antibiotic-resistant strain of Salmonella typhimurium as a test organism to study its survival during anaerobic digestion showed that the organism is totally eliminated in nine days.     

Diffusibility of selenate, selenite, seleno-methionine, and seleno-cystine during simulated gastrointestinal digestion

The present study was undertaken to evaluate the in vitro availability of chemically varying forms of selenium (Se), supplemented in cow's milk. Two inorganic (selenite and selenate) and two organic (seleno-methionine [Se-Met] and seleno-cystine [Se-Cys]) Se sources were evaluated. The in vitro availability was estimated by the diffusibility of Se during simulated gastrointestinal digestion. First, the diffusibility was compared after adding a constant amount of Se as either selenate, selenite, seleno-methionine, or Se-Cys in milk samples. Se-Met and selenate were found to be significantly more diffusible than selenocystine and selenite under the simulated gastrointestinal conditions. The tendency for superior in vitro availability of selenate and Se-Met compared to selenite and Se-Cys was confirmed for a supplementation range of 5–40 ng/g of Se. This study suggests that the high diffusibility of selenate and Se-Met in a simulated gastrointestinal environment may contribute to their high absorption in vivo.     

Anthocyanins from red cabbage--stability to simulated gastrointestinal digestion

Anthocyanins were the main polyphenol components in extracts of fresh and pickled red cabbage. The composition of anthocyanins in red cabbage was studied using liquid chromatography mass-spectrometry. Eleven major peaks absorbing at 520 nm were discerned, which represented 18 different anthocyanin structures. Another five minor anthocyanin components could be identified by searching at their respective m/z values but only in anthocyanin-enriched concentrates produced by sorption to solid phase extraction matrices. The predominant anthocyanins were constructed of cyanidin-3-diglucoside-5-glucoside "cores" which were non-acylated, mono-acylated or di-acylated with p-coumaric, caffeic, ferulic and sinapic acids. Pelargonidin-3-glucoside and novel forms of cyanidin-3-O-triglucoside-5-O-glucoside di-acylated with hydroxycinnamic acids were also detected in extracts of raw red cabbage, commercially pickled red cabbage and anthocyanin-enriched concentrates. The stability of the anthocyanins to simulated gastrointestinal digestion was assessed. The anthocyanins were effectively stable in the acidic gastric digestion conditions but the total recovery after simulated pancreatic digestion was around 25% compared to around 100% recovery of phenol content. As anthocyanins make up the majority of red cabbage polyphenols, this suggested that anthocyanins broke down to form new phenolic components. The recovery of the individual anthocyanins was monitored by LC-MS(n). All of the anthocyanins were reduced in content after pancreatic digestion but acylated forms were notably more stable than non-acylated forms. There was also a relationship between the type of acylated hydroxycinnamic acid and stability to pancreatic digestion.     

Pathogen survival during anaerobic digestion: Fatty acids inhibit anaerobic growth ofEscherichia coli

Summary The fate of pathogens in anaerobic digesters has been studied in a laboratory model system in which glucose-nutrient broth cultures of genetically-defined strains ofEscherichia coli received additions of fatty acids at concentrations similar to those attained during anaerobic treatment of farm wastes. Marked concentration-dependent inhibition of growth was observed for both antibiotic resistant and sensitive strains, and the effects increased with increasing chain lengths up to C₈. Survival of enteric organisms during anaerobic digestion may be limited by fatty acid toxicity.     

Anthocyanins from red wine--their stability under simulated gastrointestinal digestion

The stability of anthocyanins from red wine was assessed using an in vitro digestion system that simulated the physiochemical changes that occur in the upper gastrointestinal tract. Anthocyanins in red wine were stable to gastric conditions whereas there was a small loss in total phenol content. After pancreatic digestion, the total anthocyanins were very poorly recovered compared to the bulk phenols in the IN sample, which was previously described as the "serum-available" fraction, and the majority of the anthocyanins and phenols were recovered in the OUT fraction, previously described as the "colon-available" fraction. Removing alcohol from the wine samples prior to the procedure did not markedly affect this pattern. The composition of anthocyanins in the post gastric, IN and OUT samples was analysed using liquid chromatography mass-spectrometry. The red wine used contained over 20 identifiable anthocyanins of which the main components were 3-O-glucosides of malvidin, peonidin, petundin, delphidin and cyanidin. Coumaroylated-glucoside derivatives of malvidin, petundin, peonidin, and delphinidin were observed and acetylated glucosides of peonidin, petundin and malvidin were also identified. Anthocyanins with modified aglycones similar to vitisin A derivatives of delphinidin, peonidin, petunidin and malvidin were also identified. After the in vitro digestion procedure, only five anthocyanins could be detected in the IN (serum-available) and the OUT (colon-available) fractions, which were confirmed as malvidin-3-O-glucoside and the vitisin A adducts of malvidin-3-O-glucoside, malvidin-3-O-acetylglucoside, malvidin-3-O-coumaroylglucoside and peonidin-3-O-glucoside. Malvidin-3-O-glucoside was recovered at 0.2% in the IN fraction and 0.9% in the OUT fraction. However, the vitisin derivatives were much more stable to pancreatic digestion. Assuming that the vitisin A derivatives display similar biological properties to their parent anthocyanins, their enhanced gastrointestinal stability could lead to enhanced bioavailability and bio-effectiveness in vivo.     

Modeling active mass in aerobic sludge digestion

Aerobic digestion of waste-activated sludge was carried out in lab-scale reactors for both batch and semicontinuous flow patterns. The reactors were monitored at three different temperatures: 10, 20, and 30 degrees C. During the course of digestion, significant solubilization of volatile suspended solids was observed, and its effect on the magnitude of kinetic coefficients was examined. Differences in metabolic activity and sludge stabilization were found between batch and semicontinuous flow patterns. An Arrhenius-type relationship was not found to apply to rate constants for the semicontinuous reactors.     

Modeling anaerobic digestion of microalgae using ADM1

The coupling between a microalgal pond and an anaerobic digester is a promising alternative for sustainable energy production by transforming carbon dioxide into methane using solar energy. In this paper, we demonstrate the ability of the original ADM1 model and a modified version (based on Contois kinetics for the hydrolysis steps) to represent microalgae anaerobic digestion. Simulations were compared to experimental data of an anaerobic digester fed with Chlorella vulgaris. The modified ADM1 fits adequately the data for the considered 140 day experiment encompassing a variety of influent load and flow rates. It turns out to be a reliable predictive tool for optimising the coupling of microalgae with anaerobic digestion processes.     

Myricitrin degraded by simulated digestion inhibits oxidation of human low-density lipoprotein

The inhibitory effects of myricitrin on the oxidation of human low-density lipoprotein were investigated before and after its degradation by simulated digestion. Myricitrin strongly inhibited the low-density lipoprotein oxidation induced by either 2,2'-azobis (2-amidinopropane) dihydrochloride or CuSO4 in a concentration-dependent manner. Myricitrin was very stable under an acidic condition (pH 1.8) corresponding to the gastric environment, but it was easily degraded under an alkaline condition (pH 8.5) corresponding to the intestinal environment. However, degraded myricitrin also had a strong inhibitory effect on the oxidative degradation of alpha-tocopherol, cholesterol and apolipoprotein B-100 in low-density lipoprotein. Our study revealed that myricitrin was degraded into many components under a mildly alkaline condition, but the degraded myricitrin still retained the free radical-scavenging and copper-chelating activities toward low-density lipoprotein.     

Environmental survival mechanisms of the foodborne pathogen Campylobacter jejuni

Campylobacter spp. continue to be the greatest cause of bacterial gastrointestinal infections in humans worldwide. They encounter many stresses in the host intestinal tract, on foods and in the environment. However, in common with other enteric bacteria, they have developed survival mechanisms to overcome these stresses. Many of the survival mechanisms used by Campylobacter spp. differ from those used by other bacteria, such as Escherichia coli and Salmonella spp. This review summarizes the mechanisms by which Campylobacter spp. adapt to stress conditions and thereby increase their ability to survive on food and in the environment.     

Effects of inhibition gastric acid secretion on arterial acid-base status during digestion in the toad Bufo marinus

Digestion affects acid-base status, because the net transfer of HCl from the blood to the stomach lumen leads to an increase in HCO3(-) levels in both extra- and intracellular compartments. The increase in plasma [HCO3(-)], the alkaline tide, is particularly pronounced in amphibians and reptiles, but is not associated with an increased arterial pH, because of a concomitant rise in arterial PCO2 caused by a relative hypoventilation. In this study, we investigate whether the postprandial increase in PaCO2 of the toad Bufo marinus represents a compensatory response to the increased plasma [HCO3(-)] or a state-dependent change in the control of pulmonary ventilation. To this end, we successfully prevented the alkaline tide, by inhibiting gastric acid secretion with omeprazole, and compared the response to that of untreated toads determined in our laboratory during the same period. In addition, we used vascular infusions of bicarbonate to mimic the alkaline tide in fasting animals. Omeprazole did not affect blood gases, acid-base and haematological parameters in fasting toads, but abolished the postprandial increase in plasma [HCO3(-)] and the rise in arterial PCO2 that normally peaks 48 h into the digestive period. Vascular infusion of HCO3(-), that mimicked the postprandial rise in plasma [HCO3(-)], led to a progressive respiratory compensation of arterial pH through increased arterial PCO2. Thus, irrespective of whether the metabolic alkalosis is caused by gastric acid secretion in response to a meal or experimental infusion of bicarbonate, arterial pH is being maintained by an increased arterial PCO2. It seems, therefore, that the elevated PCO2, occuring during the postprandial period, constitutes of a regulated response to maintain pH rather than a state-dependent change in ventilatory control.     

Determinants of non-toxicity in the gastric pathogen Helicobacter pylori

The Helicobacter pylori vacuolating cytotoxin gene, vacA, is naturally polymorphic, the two most diverse regions being the signal region (which can be type s1 or s2) and the mid region (m1 or m2). Previous work has shown which features of vacA make peptic ulcer and gastric cancer-associated type s1/m1 and s1/m2 strains toxic. vacA s2/m2 strains are associated with lower peptic ulcer and gastric cancer risk and are non-toxic. We now define the features of vacA that determine the non-toxicity of these strains. To do this, we deleted parts of vacA and constructed isogenic hybrid strains in which regions of vacA were exchanged between toxigenic and non-toxigenic strains. We showed that a naturally occurring 12-amino acid hydrophilic N-terminal extension found on s2 VacA blocks vacuolating activity as its removal (to make the strain s1-like) confers activity. The mid region of s2/m2 vacA does not cause the non-vacuolating phenotype, but if VacA is unblocked, it confers cell line specificity of vacuolation as in natural s1/m2 strains. Chromosomal replacement of vacA in a non-toxigenic strain with vacA from a toxigenic strain confers full vacuolating activity proving that this activity is entirely controlled by elements within vacA. This work defines why H. pylori strains with different vacA allelic structures have differing toxicity and provides a rational basis for vacA typing schemes.     

Modeling of protein loops by simulated annealing.

A method is presented to model loops of protein to be used in homology modeling of proteins. This method employs the ESAP program of Higo et al. (Higo, J., Collura, V., & Garnier, J., 1992, Biopolymers 32, 33-43) and is based on a fast Monte Carlo simulation and a simulated annealing algorithm. The method is tested on different loops or peptide segments from immunoglobulin, bovine pancreatic trypsin inhibitor, and bovine trypsin. The predicted structure is obtained from the ensemble average of the coordinates of the Monte Carlo simulation at 300 K, which exhibits the lowest internal energy. The starting conformation of the loop prior to modeling is chosen to be completely extended, and a closing harmonic potential is applied to N, CA, C, and O atoms of the terminal residues. A rigid geometry potential of Robson and Platt (1986, J. Mol. Biol. 188, 259-281) with a united atom representation is used. This we demonstrate to yield a loop structure with good hydrogen bonding and torsion angles in the allowed regions of the Ramachandran map. The average accuracy of the modeling evaluated on the eight modeled loops is 1 A root mean square deviation (rmsd) for the backbone atoms and 2.3 A rmsd for all heavy atoms.     

Differential survival of macroalgae to digestion by intertidal herbivore molluscs

This study evaluates the capacity of algal propagules to survive digestion by seven intertidal herbivore molluscs. Thirty individuals of Littorina peruviana, 36 of Siphonaria lessoni, 35 of Collisella ceciliana, and 25 each of C. zebrina, Chiton granosus, Fissurella crassa and F. limbata were collected at different dates between October, 1983 and April, 1984. About half of the individuals of each species were examined for gut contents and the other half was used to provide faecal pellets for culture. Diet of these grazers ranged from 8 macroalgal species in Collisella zebrina to 17 in Fissurella limbata. In total, macroalgal propagules of 56% of the 27 algal species found in these gut contents survive digestion. There was no positive correlation between diet and number of algal taxa growing in the respective faecal cultures. Survival through Littorina peruviana and Chiton granosus was low (20–30% of the algal species consumed) while it was high (75–83%) through the two species of Collisella. No significant correlation was found between frequency of algae in the gut contents and its frequency in the faecal cultures. Algal capacity to survive digestion was almost exclusively restricted to opportunistic species, especially in the Chlorophyta and Phaeophyta. It seems that survival of algal propagules through the digestive tract of generalist grazers is a rather random phenomenon.     

Requirement for the induced expression of a cell wall associated receptor kinase for survival during the pathogen response

Pathogen infection of angiosperms must rely on some interaction between the extracellular matrix (ECM) and the invading agent, and may be accompanied by signaling between the ECM and cytoplasm. An Arabidopsis cell wall associated receptor kinase (Wak1) has an amino-terminal domain that is tightly associated with the ECM, spans the plasma membrane and has a cytoplasmic protein kinase domain. Wak1 expression is induced when Arabidopsis plants are infected with pathogen, or when the pathogen response is stimulated either by exogenous salicylate (SA) or its analog 2,2-dichloroisonicotinic acid (INA). This Wak1 induction requires the positive regulator NPR1/NIM1. Thus Wak1 is a pathogen-related (PR) protein. Expression of an antisense and a dominant negative allele of Wak1 shows that induced expression of Wak1 is needed for a plant to survive if stimulated by INA. Ectopic expression of the entire Wak1, or the kinase domain alone, can provide resistance to otherwise lethal SA levels. These experiments suggest that Wak1 expression and other PR proteins are protecting plants from detrimental effects incurred during the pathogen response. These results provide a direct link between a protein kinase that could mediate signals from the ECM, to the events that are precipitated by a pathogen infection.     

Intracellular survival mechanisms of Francisella tularensis, a stealth pathogen

Research on the highly virulent and contagious, facultative intracellular bacterium Francisella tularensis has come into the limelight recently, but still little is known regarding its virulence mechanisms. This review summarizes recent studies on its intramacrophage survival mechanisms, some of which appear to be novel.