Removal and prevention of dental plaque with d-tagatose

Dental plaque develops when early bacterial colonizers adhere to the acquired pellicle (saliva-derived proteinous coating on the tooth surface) followed by adhesion of late interspecies colonizers to form this type of biofilm (coaggregation). In developing a d-tagatose-based toothpaste, we examined 15 oral isolates, including both early colonizers (Streptococcus and Actinomyces) and late colonizers (Fusobacterium, Porphyromonas, Prevotella, Veillonella, Capnocytophaga, and Actinobacillus), and tested them for their ability to coaggregate with each other. We then tested the ability of d-tagatose to reverse any such coaggregations. Coaggregation was examined visually and scored by using a system ranging from 0, for no visible coaggregation to 4, for maximum coaggregation. d-Tagatose, at a concentration of less than 750 mm, completely reversed the coaggregation of 17 (60%) of 28 strongly coaggregating pairs (coaggregation score = 2 or higher) tested. In contrast, d-sorbitol had little reversal effect. d-Tagatose-sensitive coaggregations were d-galactose-reversible as well. d-Tagatose acted on both early and late colonizers; both groups, especially the late colonizers, were frequently involved in periodontal diseases. Thus, d-tagatose has the potential for preventing and removing plaque development and for altering the subgingival microbiota. These effective qualities offer conservative control of gingival and periodontal disease.     

Modulation of nonspecific mechanisms of defense by lactic acid bacteria: effective dose.

The purpose of this study was to determine the effect of a fermented milk product containing Lactobacillus johnsonii La1 (formerly known as Lactobacillus acidophilus La1) on the phagocytic activity of peripheral blood leukocytes in healthy adult volunteers. Furthermore, we sought to define the effective doses of the bacteria, examine the effect on respiratory burst activity, and, finally, examine the contribution made by the starter culture to the biological effects. Volunteers were randomly distributed among three groups; each subject received one pot (150 ml) of fermented milk each day for 3 wk. The first two groups received a freshly prepared product fermented by Streptococcus thermophilus (group A) alone or S. thermophilus and 10(7) cfu/ml L. johnsonii La1 (group B). Group C received a product stored for a period of 21 to 28 d and that contained S. thermophilus and 10(6) cfu/ml of L. johnsonii La1. Ingestion of L. johnsonii La1 did not significantly increase fecal lactobacilli counts. However, L. johnsonii La1 was able to survive intestinal transit and was only recovered from the feces of the volunteers of groups B and C. The fermented base alone showed a weak effect on respiratory burst but not on phagocytic activity. However, the product containing 10(7) cfu/ml L. johnsonii La1 significantly enhanced both functions. The product containing 10(6) cfu/ml of L. johnsonii La1 had no significant effect on either function. These results suggest that fecal persistence may not necessarily reflect in vivo colonization and may not be a prerequisite for all forms of immune reactivity.     

Investigating hydrophobicity and the effect of exopolysaccharide on aggregation properties of dairy propionibacteria isolated from Turkish homemade cheeses

Propionic acid bacteria have been used widely as starter cultures. However, their potential as probiotics has received little attention. The ability to auto- and coaggregate is a desirable property for probiotics in health-promoting foods. Therefore, in the current study, we assessed the effect of exopolysaccharides produced by dairy propionibacteria strains on the aggregative and hydrophobicity properties. All propionibacteria strains tested showed auto- and coaggregation ability with Escherichia coli ATCC 11229, but the results were strain specific and dependent on exopolysaccharides production and incubation conditions. In addition, propionibacteria strains tested were determined to be highly hydrophilic. Our results indicate that the ability to autoaggregate, together with cell-surface hydrophobicity and coaggregation abilities with an E. coli strain, can be used for preliminary screening in order to identify potentially probiotic bacteria suitable for human or animal use.     

Enhancement of nisin, lysozyme, and monolaurin antimicrobial activities by ethylenediaminetetraacetic acid and lactoferrin

A microtiter plate assay was employed to systematically assess the interaction between ethylenediaminetetraacetic acid (EDTA) or lactoferrin and nisin, lysozyme, or monolaurin against strains of Listeria monocytogenes, Escherichia coli, Salmonella enteritidis, and Pseudomonas fluorescens. Low levels of EDTA acted synergistically with nisin and lysozyme against L. monocytogenes but EDTA and monolaurin interacted additively against this microorganism. EDTA synergistically enhanced the activity of nisin, monolaurin, and lysozyme in tryptic soy broth (TSB) against two enterohemorrhagic E. coli strains. In addition, various combinations of nisin, lysozyme, and monolaurin with EDTA were bactericidal to some gram-negative bacteria whereas none of the antimicrobials alone were bactericidal. Lactoferrin alone (2000 microg ml(-1)) did not inhibit any of the bacterial strains, but did enhance nisin activity against both L. monocytogenes strains. Lactoferrin in combination with monolaurin inhibited growth of E. coli O157:H7 but not E. coli O104:H21. While lactoferrin combined with nisin or monolaurin did not completely inhibit growth of the gram-negative bacteria, there was some growth inhibition. All combinations of EDTA or lactoferrin with antimicrobials were less effective in 2% fat UHT milk than in TSB. S. enteritidis and P. fluorescens strains were consistently more resistant to antimicrobial combinations. Resistance may be due to differences in the outer membrane and/or LPS structure.     

Addition of reducing agent dithiothreitol improves 4-decanolide synthesis by the genus Sporidiobolus

Two species of the genus Sporidiobolus, S. johnsonii and S. ruinenii, were used to study the effect of the reducing agent, dithiothreitol (DTT), on 4-decanolide production using ricinoleic acid as the substrate. The results indicate that the addition of DTT into the cultures significantly enhanced 4-decanolide biosynthesis by the two species.     

优势菌群强化好氧活性污泥处理制浆中段废水的研究

利用实验室构建的优势菌群(B.subtilis∶B.cereus∶V.pantothenticus=35%∶50%∶15%,质量比)强化好氧活性污泥以处理制浆中段废水。污泥驯化实验表明,投加优势菌群体系的CODCr去除率和污泥的理化特性均优于不投加优势菌群体系的。当优势菌群投加量为0.3 g/L时,废水处理效果最好,处理周期为8 h,比不投加优势菌群的体系缩短了1 h,CODCr去除率达72.9%。降解动力学实验结果表明,好氧活性污泥处理制浆中段废水符合一级降解动力学模型,优势菌群投加量为0.3 g/L的体系降解速率常数最大,为0.0487 min-1,且大于不投加优势菌群的体系。     

一株自然发酵甘薯酸浆的促淀粉絮凝酵母菌的分离鉴定及其共凝集特性

通过PDA固体培养基进行平板涂布、分离,在自然发酵甘薯酸浆中纯化筛选出一株具有促进副干酪乳杆菌L1絮凝淀粉的酵母菌,根据个体、群体形态观察、生理生化实验和26S rDNA分子测序对其进行鉴定,鉴定该酵母菌为季也蒙氏毕赤酵母(Meyerozyma guilliermondii),并命名为M.guilliermondii J616。通过测定共凝集率确定了四种可促进M.guilliermondii J616与副干酪乳杆菌L1共凝集的因素为:孵育前以无菌蒸馏水作缓冲液、做超声分散处理;孵育条件为pH=5、温度为35 ℃。其孵育24 h时共凝集率分别为68.8%、74.8%、70.4%、72.7%。不同生长期的酵母菌对共凝集没有显著影响。     

Indigenous dadih lactic acid bacteria: cell-surface properties and interactions with pathogens

ABSTRACT:  Cell surface properties of dadih lactic acid bacteria strains were studied for adhesion to hydrocarbons (BATH) and aggregation abilities. Autoaggregation correlates with adhesion, which is a prerequisite for colonization and infection of the gastrointestinal tract by many pathogens, whereas coaggregation has been related to the ability to interact closely with pathogens. The results demonstrated significant differences in cell surface properties among the tested natural lactic acid bacteria food strains. Hydrophobicity increased when the cells were heat inactivated. All strains showed aggregation abilities with the pathogen strains tested, but the coaggregation properties were strain-specific. Our results indicate that the ability to autoaggregate, together with cell surface hydrophobicity and coaggregation abilities with pathogen strains, can be used for preliminary screening in order to identify potentially probiotic bacteria suitable for human or animal use. This study suggest the importance to identify and characterize bacterial cell-wall properties to understand their role in adhesion to hydrocarbons, autoaggregation and relation to coaggregation mechanisms, and also the relevance to future probiotic food development from natural strains.     

Antimicrobial potential of immobilized Lactococcus lactis subsp. lactis ATCC 11454 against selected bacteria

Immobilization of living cells of lactic acid bacteria could be an alternative or complementary method of immobilizing organic acids and bacteriocins and inhibit undesirable bacteria in foods. This study evaluated the inhibition potential of immobilized Lactococcus lactis subsp. lactis ATCC 11454 on selected bacteria by a modified method of the agar spot test. L. lactis was immobilized in calcium alginate (1 to 2%)-whey protein concentrate (0 and 1%) beads. The antimicrobial potential of immobilized L. lactis was evaluated in microbiological media against pathogenic bacteria (Escherichia coli, Salmonella, and Staphylococcus aureus) or Pseudomonas putida, a natural meat contaminant, and against seven gram-positive bacteria used as indicator strains. Results obtained in this study indicated that immobilized L. lactis inhibited the growth of S. aureus, Enterococcus faecalis, Enterococcus faecium, Lactobacillus curvatus, Lactobacillus sakei, Kocuria varians, and Pediococcus acidilactici. Only 4 h of incubation at 35 degrees C resulted in a clear inhibition zone around the beads that increased with time. With the addition of 10 mM of a chelating agent (EDTA) to the media, results showed growth inhibition of E. coli; however, P. putida and Salmonella Typhi were unaffected by this treatment. These results indicate that immobilized lactic acid bacteria strains can be successfully used to produce nisin and inhibit bacterial growth in semisolid synthetic media.     

Aggregation and hydrophobicity properties of 6 dairy propionibacteria strains isolated from homemade Turkish cheeses

In the present study, 6 dairy Propionibacterium strains were assessed with regard to their hydrophobic characteristics and their autoaggregation and coaggregation abilities since these traits have been shown to be indicative of adherence in other microorganisms. Aggregation assays and bacterial adhesion to hydrocarbons demonstrated significant differences in cell surface properties among the tested propionibacteria strains. Almost all strains appeared relatively hydrophilic, which showed low affinity for p-xylene. Four of the tested strains showed the strong adhesion to ethyl acetate, a basic solvent, in comparison with microbial adhesion to chloroform, an acidic solvent, which demonstrated the particularity of propionibacteria to have an important electron donor and acidic character. Also, these strains simultaneously showed affinity to 3 hydrocarbons, suggesting a high complexity of the cell surface. All propionibacteria strains tested showed autoaggregation and coaggregation ability with the Escherichia coli ATTC 11229, but the results were strain-specific and dependent on incubation conditions. Anaerobic incubation conditions were determined as the best condition for aggregation abilities of propionibacteria strains. A relationship was obtained between aggregation abilities (auto- and coaggregation) and a correlation between adhesion to hydrocarbon (chloroform) and autoaggregation was possible. Our results indicate that the ability to autoaggregation together with cell surface hydrophobicity and coaggregation abilities with E. coli strain can be used for preliminary screening in order to identify potentially probiotic bacteria suitable for human or animal use. PRACTICAL APPLICATION: Autoaggregation, cell surface hydrophobicity, and coaggregation abilities with E. coli of the selected dairy propionibacteria strains could be used as probiotic in foods after in vivo studies.     

以啤酒废水处理污泥为原料发酵生产微生物肥料的研究

研究以啤酒废水处理污泥为原料液态发酵生产微生物肥料.通过单因素试验和正交试验,研究了污泥添加量、二氧化氯添加量、发酵条件和培养基对解磷菌D-P2生长繁殖的影响.结果表明,啤酒废水处理污泥添加量为水的60％,二氧化氯添加量为啤酒污泥的1.0％,接种量为8.0％,初始pH值为7.0,在32℃下培养28h就可以得到活体菌高达2.8× 109cfu/mL的解磷菌发酵液,高于国家磷细菌肥料标准.     

Bacterial Community of Koumiss from Mongolia Investigated by Culture and Culture-Independent Methods

The bacterial community of fermented horse milk (koumiss) from Mongolia was studied using three methods: cultivation, direct identification by 16S rRNA clone library and denaturing gradient gel electrophoresis (DGGE). Ninety-eight strains were isolated by traditional cultivation and 61 of those were randomly selected for further identification by 16S rRNA gene sequencing. The strains were dominated by lactic acid bacteria (LAB; six different lactobacilli), Acinetobacter, Bacillus and Psychrobacter. Construction of the clone library analysis revealed that 16S sequences of 220 clones, genus Lactobacillus was dominant, but Streptococcus thermophilus, Acetobacter pasteurianus and uncultured clones were also detected. Ten unique bands were sequenced from the DGGE and revealed: Lactococcus lactis, Lactococcus lactis subsp. lactis, Clostridium acidurici, Acinetobacter johnsonii, Dickeya sp., Enterobacter sp., Pseudomonas sp., Raoultella sp., and Ruminococcus sp.. In vitro growth inhibition of three human pathogens, Escherichia coli, Enterobacter sakazakii and Staphylococcus aureus by 14 culturable bacteria displayed that only three of the isolates tested inhibit growth of E. sakazakii while most of the other bacteria delayed growth of the target bacteria.     

Lytic and nonlytic mechanism of inactivation of gram-positive bacteria by lysozyme under atmospheric and high hydrostatic pressure

A different behavior was observed in three gram-positive bacteria exposed to hen egg white lysozyme by plate counts and phase-contrast microscopy. The inactivation of Lactobacillus johnsonii was accompanied by spheroplast formation, which is an indication of peptidoglycan hydrolysis. Staphylococcus aureus was resistant to lysozyme and showed no signs of peptidoglycan hydrolysis, and Listeria innocua was inactivated and showed indications of cell leakage but not of peptidoglycan hydrolysis. Under high hydrostatic pressure, S. aureus also became sensitive to lysozyme but did not form spheroplasts and was not lysed. These results suggested the existence of a nonlytic mechanism of bactericidal action of lysozyme on the latter two bacteria, and this mechanism was further studied in L. innocua. Elimination of the enzymic activity of lysozyme by heat denaturation or reduction with beta-mercaptoethanol eliminated this bactericidal mechanism. By means of a LIVE/DEAD viability stain based on a membrane-impermeant fluorescent dye, the nonlytic mechanism was shown to involve membrane perturbation. In the absence of lysozyme, high-pressure treatment was shown to induce autolytic activity in S. aureus and L. innocua.     

Reduction of Escherichia coli population following treatment with bacteriocins from lactic acid bacteria and chelators

The inhibitory activity of lactocin 705/AL705 (2133 arbitrary units per ml (AU ml(-1))), two bacteriocins produced by Lactobacillus curvatus CRL705 and nisin (1066AU ml(-1)) produced by Lactococcus lactis CRL1109 in combination with chelating agents against Escherichia coli strains in TSB medium at 21 and 6 degrees C was investigated. Treatment with EDTA (500 and 1000 mm) and Na lactate (800 mm) alone produced a variable effect depending on the strain, Na lactate being inhibitory against E. coli NCTC12900 at both assayed temperatures while EDTA (1000 mm) led to its inactivation only at 6 degrees C. Direct and deferred strategies using EDTA and Na lactate showed that the direct addition of bacteriocins and chelators was not as effective as compared to deferred treatments. When the deferred treatment effectiveness was evaluated at 6 degrees C, the use of EDTA (500 and 1000 mm) and Na lactate (800 mm) in combination with lactocin 705/AL705 demonstrated to be the most inhibitory strategy against both E. coli strains. Nevertheless, treatments with chelators and bacteriocins was highly dependent upon strain sensitivity. Permeabilization of the outer membrane of E. coli strains with EDTA and Na lactate combined with lactocin 705/AL705 showed to be valuable in controlling this foodborne bacteria at low temperatures.     

腌韭菜根中腐败菌的分离鉴定及防腐剂对其抑制作用

以胀袋变质的真空包装韭菜根为原料,采用纯培养法从中分离筛选腐败微生物。通过形态学观察、生理生化试验和16S rRNA基因序列分析对其主要腐败菌进行了鉴定,并研究了防腐剂对主要腐败菌的抑制作用。结果表明导致腌韭菜根胀袋变质的优势腐败菌主要为5株芽孢杆菌属细菌,经鉴定由3株Bacillus megaterium和2株Bacillus toyonensis组成;防腐剂抑菌试验得出,苯甲酸钠、山梨酸钾、脱氢乙酸钠、EDTA和焦亚硫酸钠5种防腐剂对5株腐败菌的IC₅₀分别为5.63~10.11、11.24~31.33、10.07~18.60、20.68~40.70、15.74~36.37 μg/mL,抑菌效果依次为:苯甲酸钠 > 脱氢乙酸钠 > 山梨酸钾 > 焦亚硫酸钠 > EDTA。     

鮰鱼肌肉组织中不动杆菌的分离及鉴定

将鮰鱼在4℃冷库中取得背部肌肉组织,进行真空包装,在4℃冰箱中贮藏7 d,分离得到2株细菌,分别编号为by 7-2、bs 7-3,进行细菌形态学观察、革兰氏染色、生化鉴定、16S rDNA测序及负染等。结果表明:菌株by 7-2在LB琼脂培养基上为圆形、湿润、白色菌落,菌株bs 7-3在LB琼脂培养基上为圆形、湿润、乳白色菌落;革兰氏染色镜检表明,2株细菌均为革兰氏阴性菌;负染结果表明,by 7-2为短杆菌,bs 7-3为长杆菌,且二者均无鞭毛;生化鉴定结果显示,菌株by 7-2和bs 7-3硝酸盐还原、精氨酸双水解酶、乙酰胺酶、分解木糖、分解麦芽糖、分解甘露醇、DNA酶和氧化酶实验均为阴性,菌株bs 7-3的利用柠檬酸盐和O-F实验为阳性,菌株by 7-2利用柠檬酸盐和O-F实验为阴性;进一步通过16S rDNA测序及系统发育树分析显示,by 7-2与约翰逊不动杆菌(Acinetobacter johnsonii)亲缘关系最近,相似度达99.90%,bs 7-3与抗辐射不动杆菌(Acinetobacter radioresistens)亲缘关系最近,相似度达99.79%。因此,菌株by 7-2为约翰逊不动杆菌,bs 7-3为抗辐射不动杆菌。     

Oxygen tolerance of sulfate-reducing bacteria in activated sludge

The oxygen tolerance of sulfate-reducing bacteria (SRB) present in activated sludge was studied in batch incubations using radiolabeled [35S]sulfate and a most probable number (MPN) technique employing activated sludge medium. Sulfate reduction (SR) could not be detected in activated sludge during oxic incubation or in the presence of nitrate. However, upon anoxic incubation of both freshly sampled activated sludge and activated sludge preaerated for 40 min, SR resumed immediately at an initial rate of 2 microM h(-1). During long-term aeration of activated sludge, the number of viable and culturable SRB remained constant at around 10(6) SRB mL(-1) throughout a 121 h aeration period. During the first 9 h of the 121 h aeration period, the anaerobic SR activitywas unaffected, as compared to that of an unaerated control sample, and recommenced instantaneously upon anoxic incubation. Even after 121 h of continuous aeration, SR took place within 1.5 h after anoxic incubation albeit at a rate less than 20% that of the unaerated control. As suggested by MPN estimates and the observed kinetics of SR, oxygen exposure resulted in temporary metabolic inactivation of SRB but did not cause cell death. Consequently, SRB have the potential for quick proliferation during anoxic storage of activated sludge.     

Removal of estrogens in municipal wastewater treatment under aerobic and anaerobic conditions: consequences for plant optimization

The removal of estrogens (estrone E1, estradiol E2, and ethinylestradiol EE2) was studied in various municipal wastewater treatment processes equipped for nutrient removal. A biological degradation model is formulated, and kinetic parameters are evaluated with batch experiments under various redox conditions. The resulting model calculations are then compared with sampling campaigns performed on differenttypes of full-scale plant: conventional activated-sludge treatment, a membrane bioreactor, and a fixed-bed reactor. The results show a > 90% removal of all estrogens in the activated sludge processes. (Due to the analytical quantification limit and low influent concentrations, however, this removal efficiency represents only an observable minimum.) The removal efficiencies of 77% and > or = 90% for E1 and E2, respectively, in the fixed-bed reactor represent a good performance in view of the short hydraulic retention time of 35 min. The first-order removal-rate constant in batch experiments observed for E2 varied from 150 to 950 d(-1) for a 1 gSS L(-1) sludge suspension. The removal efficiency of E1 and EE2 clearly depends on the redox conditions, the maximum removal rate occurring under aerobic conditions when E1 was reduced to E2. Sampling campaigns on full-scale plants indicate that the kinetic values identified in batch experiments (without substrate addition) for the natural estrogens may overestimate the actual removal rates. Although this paper does not give direct experimental evidence, it seems that the substrate present in the raw influent competitively inhibits the degradation of E1 and E2. These compounds are therefore removed mainly in activated sludge compartments with low substrate loading. Theoretical evaluation leads us to expect that diffusive mass transfer inside the floc (but not across the laminar boundary layer) appreciably influences the observed degradation rates of E1 and E2, but not of EE2.     

Potential of predominant activated sludge bacteria as recipients in conjugative plasmid transfer

We investigated the possibility of conjugative plasmid transfer to the predominant bacteria in activated sludge and the factors influencing the transfer frequency in the activated sludge process. We performed conjugative transfers of a self-transmissible, broad-host-range plasmid RP4 from Escherichia coli C600 to activated sludge bacteria by broth mating. Most of the activated sludge bacteria tested could acquire plasmid RP4, although the transfer frequencies varied from 8.8 x 10(-7) to 1.3 x 10(-2) transconjugants per recipient. The transfer frequencies in several strains were similar to, or higher than, that in intraspecific transfer to E. coli HB101. Matings under various environmental conditions showed that factors relevant to physiological activity, such as temperature and nutrient conditions, seemed to affect the transfer frequency. In addition, conjugative transfer was detected even in filtered raw and treated wastewaters. Thus, the predominant activated sludge bacteria seem to have sufficient potential as recipients in conjugative plasmid transfer under the conditions likely to occur in the activated sludge process. Transfer frequency was reduced by agitation in the presence of suspended solid. This may suggest that conjugative plasmid transfer is physically inhibited in aeration tanks.     

Effect of chelators and nisin produced in situ on inhibition and inactivation of gram negatives

The ability of chelators and nisin generated in situ to inhibit and inactivate E. coli and other gram negatives in a model substrate was investigated. The effect of various chelators and different concentrations of exogenous nisin on inhibition of E. coli in broth medium showed that only EDTA and pyrophosphates were able to cause appreciable inhibition of E. coli by nisin. In a broth where L. lactis NCFB 497 produced nisin in a concentration of 250-300 IU/ml, pyrophosphates were unable to inactivate E. coli. Under the same conditions, addition of EDTA led to inactivation of E. coli at neutral and slightly acidic pH only. A cocktail of strains of E. coli was less sensitive than E. coli ATCC 25922 alone. Pseudomonas aeruginosa was more sensitive and salmonellae more resistant. EDTA also caused a slight reduction in the L. lactis population and its biochemical activity as regards pH drop and acid production. Some of the inhibition of E. coli could be ascribed to the physical presence of Lactococcus cells rather than their metabolites excreted into the medium. Failure to observe any inhibition in fermented broths at their natural pH (4.0) was ascribed to the poor chelating power of EDTA under acid conditions.