The hydrogenation of unsaturated fatty acids by five bacterial isolates from the sheep rumen, including a new species.

Five strictly anaerobic bacteria able to hydrogenate unsaturated fatty acids were isolated from sheep rumen. One was characterized as Ruminococcus albus, two as Eubacterium spp. and two as Fusocillus spp., one of which is named as a new species. The Fusocillus organisms were able to hydrogenate oleic acid and linoleic acid to stearic acid, and linolenic acid to cis-octadec-15-enoic acid. The R. albus and the two Eubacteria did not hydrogenate oleic acid but converted linoleic and linolenic acids to a mixture of octadecenoic acids; trans-octadec-II-enoic acid predominated but several isomeric cis and trans octadecenoic acids were produced together with isomers of non-conjugated octadecadienoic acids. The intermediate and final products of hydrogenation by each organism were compatible with the results from mixed rumen bacteria.     

Tauroconjugation of cholic acid stimulates 7 alpha-dehydroxylation by fecal bacteria.

We examined the effect of the type of cholic acid conjugation (taurine-conjugated, glycine-conjugated, or unconjugated cholic acid) on cholic acid 7 alpha-dehydroxylation by intestinal flora. Cholic acid 7 alpha-dehydroxylation in fecal cultures, in cultures of a defined limited flora consisting of a mixture of seven bacterial species isolated from the intestinal tract, and in a binary culture of a 7 alpha-dehydroxylating Clostridium species plus a cholic acid-deconjugating Bacteroides species was studied. We found that tauroconjugation of cholic acid significantly (P < 0.05) increased bacterial 7 alpha-dehydroxylation of cholic acid into deoxycholic acid from 34 to 55% in fecal cultures, from 45 to 60% in defined limited fecal cultures, and from 75 to 100% in binary cultures. Equimolar concentrations of free taurine did not stimulate 7 alpha-dehydroxylation in fecal cultures or in the defined limited flora, but free taurine did stimulate 7 alpha-dehydroxylation in the binary culture. In the binary culture of Clostridium species strain 9/1 plus Bacteroides species strain R1, the minimal flora capable of increased 7 alpha-dehydroxylation of taurocholic acid, strain R1 deconjugated taurine and rapidly reduced it to H2S. Bacteroides species strain R1 did not grow unless taurine or another appropriate reducible sulfur source was present. Clostridium species strain 9/1 did not grow or 7 alpha-dehydroxylate unless H2S or another source of reduced sulfur was present. We conclude that the increased 7 alpha-dehydroxylation of tauroconjugated cholic acid depends on the reduction of taurine to H2S, which is a necessary growth factor for the 7 alpha-dehydroxylating bacteria.     

Isomerization increases the postprandial oxidation of linoleic acid but not alpha-linolenic acid in men

Human lipid intake contains various amounts of trans fatty acids. Refined vegetable and frying oils, rich in linoleic acid and/or alpha-linolenic acid, are the main dietary sources of trans-18:2 and trans-18:3 fatty acids. The aim of the present study was to compare the oxidation of linoleic acid, alpha-linolenic acid, and their major trans isomers in human volunteers. For that purpose, TG, each containing two molecules of [1-(13)C]linoleic acid, alpha-[1-(13)C]linolenic acid, [1-(13)C]-9cis,12trans-18:2, or [1-(13)C]-9cis,12cis,15trans-18:3, were synthesized. Eight healthy young men ingested labeled TG mixed with 30 g of olive oil. Total CO(2) production and (13)CO(2) excretion were determined over 48 h. The pattern of oxidation was similar for the four fatty acids, with a peak at 8 h and a return to baseline at 24 h. Cumulative oxidation over 8 h of linoleic acid, 9cis,12trans-18:2, alpha-linolenic acid, and 9cis,12cis,15trans-18:3 were, respectively, 14.0 +/- 4.1%, 24.7 +/- 6.7%, 23.6 +/- 3.3%, and 23.4 +/- 3.7% of the oral load, showing that isomerization increases the postprandial oxidation of linoleic acid but not alpha-linolenic acid in men.     

Dimorphecolic acid is synthesized by the coordinate activities of two divergent Delta12-oleic acid desaturases

Dimorphecolic acid (9-OH-18:2Delta(10)(trans)(,12)(trans)) is the major fatty acid of seeds of Dimorphotheca species. This fatty acid contains structural features that are not typically found in plant fatty acids, including a C-9 hydroxyl group, Delta(10),Delta(12)-conjugated double bonds, and trans-Delta(12) unsaturation. Expressed sequence tag analysis was conducted to determine the biosynthetic origin of dimorphecolic acid. cDNAs for two divergent forms of Delta(12)-oleic acid desaturase, designated DsFAD2-1 and Ds-FAD2-2, were identified among expressed sequence tags generated from developing Dimorphotheca sinuata seeds. Expression of DsFAD2-1 in Saccharomyces cerevisiae and soybean somatic embryos resulted in the accumulation of the trans-Delta(12) isomer of linoleic acid (18: 2Delta(9)(cis)(,12)(trans)) rather than the more typical cis-Delta(12) isomer. When co-expressed with DsFAD2-1 in soybean embryos or yeast, DsFAD2-2 converted 18:2Delta(9)(cis)(,12)(trans) into dimorphecolic acid. When DsFAD2-2 was expressed alone in soybean embryos or together with a typical cis-Delta(12)-oleic acid desaturase in yeast, trace amounts of the cis-Delta(12) isomer of dimorphecolic acid (9-OH-18:2Delta(10)(trans,)(12)(cis)) were formed from DsFAD2-2 activity with cis-Delta(12)-linoleic acid [corrected]. These results indicate that DsFAD2-2 catalyzes the conversion of the Delta(9) double bond of linoleic acid into a C-9 hydroxyl group and Delta(10)(trans) double bond and displays a substrate preference for the trans-Delta(12), rather than the cis-Delta(12), isomer of linoleic acid. Overall these data are consistent with a biosynthetic pathway of dimorphecolic acid involving the concerted activities of DsFAD2-1 and DsFAD2-2. The evolution of two divergent Delta(12)-oleic acid desaturases for the biosynthesis of an unusual fatty acid is unprecedented in plants.     

Hydrogenation of Linoleic Acid by a Rumen Spirochete

Borrelia sp. B(2)5, when grown in a medium containing [1-(14)C] linoleic acid in an atmosphere of CO(2), was found to hydrogenate linoleic acid to trans-11-octadecenoic acid.     

Deconjugation of bile salts by Bacteroids and Clostridium

Deconjugation of bile salts by four strains of Bacteroides and four strains of Clostridium was studied by use of resting cells and cell-free culture supernatants. Bacteroids strains yielded active cells but showed relatively low bile salt hydrolase (BSH) activity in the culture supernatants while the reverse was the case for the spore-forming clostridial strains. BSH was formed constitutively and was oxygen insensitive. The optimum pH was between 4.5 and 5.0. Marked substrate specificity was found in two strains, one Clostridium and one Bacteroides, which showed restricted activity against taurine conjugates. Bacteroides in general attacked the taurine conjugates of dihydroxy bile acids more readily than the trihydroxy taurine conjugates. Deconjugated bile acid moieties were further modified by some resting cells, depending on the bacterial strain while no enzymatic activity other than that of BSH was found in the culture supernatants. Cells of B. fragilis 2536 performed 7 alpha-dehydrogenation when the pH of the medium allowed the reaction, and this oxidative process was markedly enhanced in the presence of an abundant supply of oxygen as a terminal electron acceptor. C. perfringens PB 6K produced the 3- keto product in addition to the 3 beta-hydroxy derivative of the liberated bile acids and the formation of the latter derivative seemed to take place without preliminary deconjugation.     

9 cis,11 trans conjugated linoleic acid (CLA) is synthesised and desaturated into conjugated 18:3 in bovine adipose tissues

Although endogenous synthesis of conjugated linoleic acid (CLA) in the mammary gland of lactating cows has been already well documented, no study has determined so far as to which tissue and/or organ is involved in CLA synthesis in the growing ruminant except one study showing that CLA synthesis does not occur in ruminant liver. In this context, adipose tissue appears to be a good candidate for endogenous synthesis of CLA in the growing ruminant. The aim of this study was to compare the respective metabolisms of 11trans 18:1 (vaccenic acid, VA) and 9cis,11trans 18:2 (rumenic acid) to that of stearic acid (the preferential substrate of Δ9 desaturase) in adipose tissues (subcutaneous, SC and intermuscular, IM) of six Charolais steers by using the in vitromethod of incubated tissue slices. Samples of SC and IM adipose tissues were incubated at 37°C for 16 h under an atmosphere of 95% O2/5% CO2 in a medium supplemented with 0.75 mM of fatty acid (FA) mixture (representative of circulating non-esterified FA) and 186 μM [1-14C]-18:0 or 58.6 μM [1-14C]-VA or 56 μM [1-14C]-9cis,11trans CLA. Viability of explants was verified by measuring metabolic functions (glucose uptake and glucose-6-phosphate dehydrogenase activity). After 16 h of incubation, FA uptake was similar for all FA (18:0, VA and 9cis,11trans 18:2) in both SC and IM adipose tissues (around 40%). Once in adipose tissue, all FA were preferentially esterified (>80% of cell FA) favouring neutral lipid synthesis (around 90% of esterified FA). Stearic acid was highly (27%) desaturated into oleic acid in SC adipose tissue whereas this desaturation was much lower (6.8%) in IM adipose tissue (P < 0.0001). VA was desaturated into 9cis,11trans CLA at a low extent of about 2.5% to 4.4% in both adipose tissues probably because of a limited affinity of Δ9 desaturase for VA. 9cis,11trans CLA was itself converted by desaturation into 6cis, 9cis,11trans 18:3 at the intensity of 10.8% and 14.5% of cell 9cis,11trans CLA in SC and IM adipose tissues, respectively. In conclusion, bovine adipose tissues of the growing ruminant were especially involved in the endogenous synthesis of CLA from VA and in its desaturation into conjugated derivative, mainly 6cis, 9cis,11trans 18:3, of which biological properties need to be elucidated.     

The biohydrogenation of α-linoleic acid and oleic acid by rumen micro-organisms

1. α-[U-¹⁴C]Linolenic acid was incubated with the rumen contents of sheep and the metabolic products were characterized by thin-layer chromatography, gas–liquid chromatography and absorption spectroscopy in the ultraviolet and infrared. 2. A tentative scheme for the biohydrogenation route to stearic acid is presented. The main pathway is through diconjugated cis–cis–cis-octadecatrienoic acid, non-conjugated trans–cis (cis–trans)-octadecadienoic acid and trans-octadecenoic acid, but other pathways are apparent. 3. Washed rumen micro-organisms possessed only a limited capacity to hydrogenate α-linolenic acid and oleic acid but the rate was greatly stimulated by a factor(s) present in the supernatant rumen liquor. 4. Pure cultures of Clostridium perfringens, Streptococcus faecalis, Escherichia coli and a coliform organism isolated from sheep faeces possessed negligible ability to hydrogenate unsaturated fatty acids compared with a mixed population of rumen micro-organisms. Butyrivibrio fibrisolvens slowly converted linoleic acid into octadecenoic acid.     

On the specifity and stereospecificity of the conversion of different 2,3-unsaturated acids by Clostridium kluyveri (author's transl)]

Further 2,3-unsaturated acids are revealed which can be reduced by Clostridium kluyveri with crotonate or butyrate as hydrogen donors. Unsaturated and saturated 3-halogenated acids are transformed into the saturated halogen-free acids. The following reaction sequence is proposed: a) hydrogenation, b) elumination of HX and c) again hydrogenation. Tiglinate ((E)-2-methyl-2-butenoate) and (E)-2-methyl-2-pentenoate are stereospecifically reduced to the (S)-2-methyl substituted acids. C. kluyveri contains endogenous material; in the presence of hydrogen acceptors such as 2,3-unsaturated acids this is degraded to acetate, and the reducing equivalents liberated hydrogenate the unsaturated acid. In a transient phase the hydration products of the unsaturated acids are present in the non-activated form in appreciable amounts. Tiglinate as well as crotonate is partially converted to ethyl methyl ketone and aceton and/or propanol, respectively.     

Regiospecific effect of 1-octanol on cis-trans isomerization of unsaturated fatty acids in the solvent-tolerant strain Pseudomonas putida S12

The solvent-tolerant bacterium Pseudomonas putida S12, which adapts its membrane lipids to the presence of toxic solvents by a cis to trans isomerization of unsaturated fatty acids, was used to study possible in vivo regiospecificity of the isomerase. Cells were supplemented with linoleic acid (C18:2delta9-cis,delta12-cis), a fatty acid that cannot be synthesized by this bacterium, but which was incorporated into membrane lipids up to an amount of 15% of total fatty acids. After addition of 1-octanol, which was used as an activator of the cis-trans isomerase, the linoleic acid was converted into the delta9-trans,delta12-cis isomer, while the delta9-cis,delta12-trans and delta9-trans,epsilon12-trans isomers were not synthesized. Thus, for the first time, regiospecific in vivo formation of novel, mixed cis/trans isomers of dienoic fatty acid chains was observed. The maximal conversion (27-36% of the chains) was obtained at 0.03-0.04% (v/v) octanol, after 2 h. The observed regiospecificity of the enzyme, which is located in the periplasmic space, could be due to penetration of the enzyme to a specific depth in the membrane as well as to specific molecular recognition of the substrate molecules.     

Characterization of an antibiotic resistant Clostridium hathewayi strain from a continuous-flow exclusion chemostat culture derived from the cecal contents of a feral pig

The chemostat model has been an important tool in studying intestinal microflora. To date, several competitive exclusion products have been developed from such studies as prophylactic treatment against pathogenic bacteria. A continuous-flow chemostat model of a feral pig was developed using inocula from the cecal contents of a wild boar caught in East Texas. Several strains of antibiotic-sensitive bacteria were isolated including Bacteroides, Lactobacillus, Enterococcus and Clostridium sp. This study reports on the characterization of a multidrug-resistant Clostridium hathewayi strain that was isolated from this feral pig's cecal contents maintained in a continuous-flow chemostat system showing high resistance to carbapenems and macrolides (including the growth promoter tylosin). Clostridium hathewayi has been documented to be pathogenic to both humans and animals. Feral pigs may be an important source of pathogenic and antibiotic resistant bacteria and may pose potential risk to domestic species. Further work is needed to elucidate the prevalence of these reservoirs and assess the contribution these may play in the spread of disease and resistance.     

Phosphatase Activity of Anaerobic Organisms

Anaerobic organisms were tested for phosphatase activity in different pH ranges. Several groups of organisms displayed characteristic patterns. Bacteroides fragilis, B. melaninogenicus, and B. ruminicola produced phosphatase with strongest activity at pH 8.6. Fusobacterium mortiferum was the only species of this genus to show strong hydrolysis. The enzyme was active in both acid and alkaline ranges. The activity of gram-positive organisms was variable, the most active groups being Clostridium perfringens, Peptostreptococcus intermedius, P. micros, and Peptococcus constellatus. The incorporation of phosphatase activity into the identification scheme of anaerobes seems feasible. There was a correlation of hydrolysis with several important pathogens.     

The effect of conjugated linoleic acid on arachidonic acid metabolism and eicosanoid production in human saphenous vein endothelial cells

The effects of a conjugated linoleic acid (CLA) mixture of single isomers (50:50, w/w, cis9,trans11:trans10,cis12) and the individual isomers on (a) the production of resting and calcium ionophore stimulated (14)C-eicosanoids and (b) the incorporation of (14)C-arachidonic acid (AA) into membrane phospholipids of human saphenous vein endothelial cells were investigated. The CLA mixture and the individual isomers were found to inhibit resting production of (14)C-prostaglandin F(2a) by 50, 43 and 40%, respectively. A dose dependent inhibition of stimulated (14)C-prostaglandins was observed with the CLA mixture (IC(50) 100 microM). The cis9,trans11 and trans10,cis12 (50 microM) isomers individually inhibited the overall production of stimulated (14)C-prostaglandins (between 35 and 55% and 23 and 42%, respectively). When tested at a high concentration (100 microM), cis9,trans11 was found to inhibit eicosanoid production in contrast to trans10,cis12 that caused stimulation. The overall degree of (14)C-AA incorporation into membrane phospholipids of the CLA (mixture and individual isomers) treated cells was found to be lower than that of control cells and the cis9,trans11 isomer was found to increase the incorporation of (14)C-AA into phosphatidylcholine. Docosahexaenoic acid, eicosapentaenoic acid and linoleic acid did not alter the overall degree of incorporation of (14)C-AA. The results of this study suggest that both isomers inhibit eicosanoid production, and although trans10,cis12 exhibits pro-inflammatory activity at high concentrations, the CLA mixture maintains its beneficial anti-inflammatory action that contributes to its anti-carcinogenic and anti-atherogenic properties.     

Clostridium geopurificans Strain MJ1 sp. nov., A Strictly Anaerobic Bacterium that Grows via Fermentation and Reduces the Cyclic Nitramine Explosive Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX)

A fermentative, non-spore forming, motile, rod-shaped bacterium, designated strain MJ1^T, was isolated from an RDX contaminated aquifer at a live-fire training site in Northwest NJ, United States. On the basis of 16S rRNA gene sequencing and DNA base composition, strain MJ1^T was assigned to the Firmicutes. The DNA G+C content was 42.8 mol%. Fermentative growth was supported by glucose and citrate in a defined basal medium. The bacterium is a strict anaerobe that grows between at pH 6.0 and pH 8.0 and 18 and 37 °C. The culture did not grow with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) as the electron acceptor or mineralize RDX under these conditions. However, MJ1^T transformed RDX into MNX, methylenedinitramine, formaldehyde, formate, ammonium, nitrous oxide, and nitrate. The nearest phylogenetic relative with a validly published name was Desulfotomaculum guttoideum (95 % similarity). However, MJ1^T was also related to Clostridium celerecrescens DSM 5628 (95 %), Clostridium indolis DSM 755 (94 %), and Clostridium sphenoides DSM 632 (94 %). DNA:DNA hybridization with these strains was between 6.7 and 58.7 percent. The dominant cellular fatty acids (greater than 5 % of the total, which was 99.0 % recovery) were 16:0 fatty acid methyl ester (FAME) (32.12 %), 18:1cis 11 dimethyl acetal (DMA) (16.47 %), 16:1cis 9 DMA (10.28 %), 16:1cis 9 FAME (8.10 %), and 18:1cis 9 DMA (5.36 %). On the basis of morphological, physiological, and phylogenetic data, Clostridium geopurificans is proposed as a new species in genus Clostridium, with strain MJ1^T as the type strain.     

Production and characterization of pure Clostridium spore suspensions

Aims:  A general protocol was derived for optimizing the production of pure, high concentration Clostridium endospore suspensions.
Methods and Results:  Two sporulation methods were developed that yielded high concentrations of notably pure Clostridium sporogenes , C. hungatei and C. GSA-1 (Greenland ice core isolate) spore suspensions (10 ml of 10⁹ spores ml⁻¹ with >99% purity each). Each method was derived by evaluating combinations of three sporulation conditions, including freeze drying of inocula, heat shock treatment of cultures, and subsequent incubation at suboptimal temperatures that yielded the highest percentage of sporulation. Pure spore suspensions were characterized in terms of dipicolinic acid content, culturability, decimal reduction time ( D ) value for heat inactivation (100°C) and hydrophobicity.
Conclusions:  While some Clostridium species produce a high percentage of spores with heat shock treatment and suboptimal temperature incubation, other species require the additional step of freeze drying the inocula to achieve a high percentage of sporulation.
Significance and Impact of the Study:  Pure Clostridium spore suspensions are required for investigating species of medical and environmental importance. Defining the conditions for optimal spore production also provides insight into the underlying mechanisms of Clostridium sporulation.     

Phylogenetic characterization of several para- and meta-PCB dechlorinating Clostridium species: 16s rDNA sequence analyses

The genus Clostridium has more than 127 species, grouped according to their morphology and functions. Nine Clostridium species were identified based on their ability to dechlorinate meta- and para-PCB (polychlorinated biphenyl) contaminated sediments. The phylogenetic relatedness of these PCB-degrading Clostridium species was studied using ribosomal RNA genes. The diversity of small-subunit rRNA genes associated with the domain bacteria was examined using defined operational taxonomic units (OTUs) in samples from PCB contaminated sediments from Lake Medinah, New York. The RFLP (restriction fragment length polymorphism) of the OTVs was measured. OTUs B (105 clones), A (33 clones) and C (45 clones) accounted for 75% of all the 16S rDNA clones expressing anaerobic para- and meta-PCB dechlorinating activity. In this report we describe complete 16S rDNA sequences of OTU-A and OTU-B, and partial rDNA sequences of OTUs C-J. The OTU-B and OTU-I form a phylogenetically related cluster, closely affiliated with Clostridium hydroxybenzoicum strains. OTUs A, C, D, G, H and J also belong to the genus Clostridium, but they represent separate species. OTU-E, a close affiliate to Bacteroides forsynthus, is a meta-PCB dechlorinator. The Cl. hydroxybenzoicum strains (OTU-B) are primarily para-PCB dechlorinators and are the most common. Some less prevalent OTUs (- E, -G, -H and -I), are also mostly para-PCB dechlorinators. Other Clostridium species such as Cl. beijerinckii (OTU-A), Cl. intestinalis (OTU-D) and Cl. thermolacticum (OTU-J) are primarily meta-PCB dechlorinators. Cl. paraputrificum (OTU-C) and Cl. cellulosi (OTU-F), were less prevalent in the total consortium, but they could dechlorinate both para- and meta-PCB. Although a few less prevalent Clostridium species can degrade both para- and meta-PCBs, this study confirms that para- and meta-PCB dechlorinating species are generally phylogenetically different.     

Quantification of ruminal Clostridium proteoclasticum by real-time PCR using a molecular beacon approach

AIMS: All members of the ruminal Butyrivibrio group convert linoleic acid (cis-9,cis-12-18:2) via conjugated 18:2 metabolites (mainly cis-9,trans-11-18:2, conjugated linoleic acid) to vaccenic acid (trans-11-18:1), but only members of a small branch, which includes Clostridium proteoclasticum, of this heterogeneous group further reduce vaccenic acid to stearic acid (18:0, SA). The aims of this study were to develop a real-time polymerase chain reaction (PCR) assay that would detect and quantify these key SA producers and to use this method to detect diet-associated changes in their populations in ruminal digesta of lactating cows. METHODS AND RESULTS: The use of primers targeting the 16S rRNA gene of Cl. proteoclasticum was not sufficiently specific when only binding dyes were used for detection in real-time PCR. Their sequences were too similar to some nonproducing strains. A molecular beacon probe was designed specifically to detect and quantify the 16S rRNA genes of the Cl. proteoclasticum subgroup. The probe was characterized by its melting curve and validated using five SA-producing and ten nonproducing Butyrivibrio-like strains and 13 other common ruminal bacteria. Analysis of ruminal digesta collected from dairy cows fed different proportions of starch and fibre indicated a Cl. proteoclasticum population of 2-9% of the eubacterial community. The influence of diet on numbers of these bacteria was less than variations between individual cows. CONCLUSIONS: A molecular beacon approach in qPCR enables the detection of Cl. proteoclasticum in ruminal digesta. Their numbers are highly variable between individual animals. SIGNIFICANCE AND IMPACT OF THE STUDY: SA producers are fundamental to the flow of polyunsaturated fatty acid and vaccenic acid from the rumen. The method described here enabled preliminary information to be obtained about the size of this population. Further application of the method to digesta samples from cows fed diets of more variable composition should enable us to understand how to control these bacteria in order to enhance the nutritional characteristics of ruminant-derived foods, including milk and beef.     

Susceptibility of Clostridium perfringens to C-C fatty acids

AIMS: To determine susceptibility of Clostridium perfringens strains CCM 4435(T) and CNCTC 5459 to C(2)-C(18) fatty acids, and evaluate influence of pH in cultures grown on glucose. Straw particles were added to cultures to simulate the presence of solid phase of the digestive tract milieu. METHODS AND RESULTS: Antimicrobial activity of fatty acids was expressed as a concentration at which only 50% of the initial glucose was utilized. Lauric acid showed the highest antimicrobial activity, followed by myristic, capric, oleic and caprylic acid. Only strain CNCTC 5459 was susceptible to linoleic acid. Neither caproic acid and acids with a shorter carbon chain nor palmitic and stearic acid influenced substrate utilization. The antimicrobial activity of myristic, oleic and linoleic acid decreased when clostridia were grown in the presence of straw particles. In cultures of both strains treated with capric and lauric acid at pH 5.0-5.3, the number of viable cells was <10(2) ml(-1). Only lauric acid reduced number of viable cells of both strains below 10(2) ml(-1) at pH > 6. Transmission electron microscopy revealed separation of inner and outer membranes and cytoplasma disorganization in cells treated with lauric acid. CONCLUSIONS: Lauric acid had the highest activity towards C. perfringens among fatty acid tested. Its activity was not influenced by the presence of solid particles and did not cease at pH > 6. SIGNIFICANCE AND IMPACT OF THE STUDY: Lauric acid might be a means for control of clostridial infections in farm animals.     

实时荧光定量PCR法研究结直肠癌患者肠道拟杆菌属、梭杆菌属和梭菌属量的变化

目的通过研究结、直肠癌患者肠道拟杆菌属、梭杆菌属和梭菌属量的变化,揭示肠道相关菌群改变在大肠癌发病中的作用及意义。方法收集术前结、直肠癌患者粪便标本40例及正常对照标本40例,根据细菌的靶基因序列设计特异性引物。提取待测粪便标本细菌DNA,应用SYBR Green I实时荧光定量PCR测定不同细菌的数量。结果正常对照组与实验组粪便中细菌数量分别为拟杆菌属(8.76±0.77;9.85±0.88)、梭杆菌属(7.94±1.25;10.0±1.65)、梭菌属(3.54±0.70;6.56±0.68),拟杆菌属中的脆弱拟杆菌为(2.12±0.48;4.07±1.77)、梭杆菌属中的坏死梭杆菌为(2.31±0.26;7.62±2.68)及梭菌属中的肉毒梭菌为(2.76±1.16;5.43±1.21),实验组数量均明显增多(P0.05)。结论结、直肠癌患者粪便中拟杆菌属、梭杆菌属和梭菌属的数量较正常对照明显增多,提示结、直肠癌的发生发展与肠道菌群有明显关系。