The Journal of applied bacteriology最新文献

Lactobacillus amylovorus ATCC 33621 is an actively amylolytic bacterial strain which produces a cell-bound glucoamylase (EC 3.2.1.3). Conditions of growth and glucoamylase production were investigated using dextrose-free de Man-Rogosa-Sharpe (MRS) medium in a 1.5 l fermenter, with varying dextrin concentration (0.1-1.5% (w/v)), pH (4.5-6.5) and temperature (25-55 degrees C). Cell extracts were prepared by subjecting cells to treatment with a French Pressure cell in order to release intracellular proteins. Glucoamylase activity was then assayed. The effects of pH (4.0-9.0), temperature (15-85 degrees C) and substrate (dextrin and starch, 0-2% w/v) concentration on crude enzyme activity were investigated. Optimal growth was obtained in MRS medium containing 1% (w/v) dextrin, at pH 5.5 and 37 degrees C. Glucoamylase production was maximal at the late logarithmic phase of growth, during 16-18 h. Crude enzyme had a pH optimum of 6.0 and temperature optimum of 60 degrees C. With starch as the substrate, maximal activity was obtained at a concentration of 1.5% (w/v). The effects of ions and inhibitors on glucoamylase activity were also investigated. Enzyme activity was not significantly influenced by Ca2+ and EDTA at 1 mmol l-1 concentration; however Pb2+ and Co2+ were found to inhibit the activity at concentrations of 1 mmol l-1. The crude enzyme was found to be thermolabile when glucoamylase activity decreased after about 10 min exposure at 60 degrees C. This property can be exploited in the brewing of low calorie beers where only mild pasteurization treatments are used to inactivate enzymes. The elimination of residual enzyme effect would prevent further maltodextrin degradation and sweetening during long-term storage, thus helping to stabilize the flavour of beer.

Fructo-oligosaccharides (FOS) are claimed to have a positive effect on the intestinal flora. They are being used in functional foods in Japan and Europe. This group have tested the degradation of two commercial FOS preparations by oral streptococci in order to predict the cariogenicity of these products. Both preparations could be fermented to some extent by the species of oral streptococci tested. The enzymes necessary for the degradation of FOS were inducible. Each strain showed a specific degradation pattern. All strains, particularly Streptococcus mutans rapidly produced acid, mainly lactic acid. Streptococcus mitis also produced high concentrations of acetic acid. Plaque formation by Strep. mutans was similar to the sucrose control. It is concluded that FOS are cariogenic to a similar extent as sucrose.

A total of 241 lactic acid bacteria belonging to Lactobacillus plantarum, Pediococcus pentosaceus, Lactobacillus fermentum/reuteri and Lactobacillus brevis from various processing stages of maize dough fermentation were investigated. Results indicated that each processing stage has its own microenvironment with strong antimicrobial activity. About half of the Lact. plantarum and practically all of the Lact. fermentum/reuteri investigated were shown to inhibit other Gram-positive and Gram-negative bacteria, explaining the elimination of these organisms during the initial processing stages. Further, widespread microbial interactions amounting to 85% to 18% of all combinations tested were demonstrated amongst lactic acid bacteria within the various processing stages, i.e. raw material, steeping, 0 h and 48 h of fermentation, explaining the microbial succession taking place amongst lactic acid bacteria during fermentation. The antimicrobial effect was explained by the combined effect of acids, compounds sensitive to proteolytic enzymes and other compounds with antimicrobial activity with the acid production being the most important factor. The pattern of antimicrobial factors was not species-specific and the safety and storage stability of fermented maize seem to depend on a mixed population of lactic acid bacteria with different types of antimicrobial characteristics. This means that introduction of pure cultures as starters may impose a risk to the product.

The potential of polymerase chain reaction (PCR) for verifying the identity of colonies stained by the immunofluorescence colony-staining (IFC) procedure was investigated. Using primers directed against conserved sequences of the pectate lyase-genes coding for isozymes PLa, PLd and PLe of Erwinia chrysanthemi, the authors confirmed the identity of 96% of 20 fluorescent target colonies, punched from IFC-stained samples with pure cultures. In pour plates with mixtures of Erw. chrysanthemi and non-target colonies from potato peel extracts, the identity of 90% of 113 target colonies was confirmed. Using primers directed against sequences of the ferric-pseudobactin receptor gene pupA of Pseudomonas putida WCS358, the identity of 96% of 22 target colonies was confirmed in IFC-stained samples with pure cultures. In pour plates with mixtures of Ps. putida WCS358 and non-target bacteria from compost extracts, the identity of 59% of 108 fluorescent colonies was confirmed by PCR. It was shown that components from non-target bacteria lowered the threshold level of PCR for Ps. putida WCS358 100-fold.

The effects of three dyes on the colony enumeration of nine fungal strains (including members of the Deuteromycetes and Zygomycetes) in pure and mixed cultures were investigated. Using malt extract agar as basal and control medium, the following dyes and concentrations were assayed: auramine (25 ppm), gentian violet (5 ppm) and malachite green (1 ppm). The chemicals commonly used in commercial media dichloran (2 ppm) and rose bengal (50 ppm) were included in the study as reference mould-spreading inhibitors. Higher counts were usually obtained in the media containing dichloran, rose bengal or auramine, including the control medium in the absence of chemical when the mixed-conidium inocula did not include a spreading mould. Nevertheless in most cases no significant differences were observed between them. Malachite green (1 ppm) performed mainly as a strong inhibitor of spreading moulds, only allowing adequate colony development and recoveries of both Fusarium and Aspergillus strains tested.

The characteristics of two monoclonal antibodies (Mabs), A23/1221.59.44.d.3 (1221) and A23/1239.36.64.e.2 (1239), against Erwinia carotovora subsp. atroseptica serogroup I produced in this study were compared with those of two other independently obtained Mabs, 4G4 in Spain and 4F6 in Canada, using different strains as immunogen and different screening procedures. The reaction pattern of Mabs 1221 and 1239 determined by indirect ELISA on over 200 bacterial strains including five E.c. atroseptica and 36 E.c. carotovora serogroups, seven Erw. chrysanthemi biovars, 23 other plant bacterial pathogens and 33 saprophytic bacteria from potato was similar to that of 4G4. Specificity for E.c. atroseptica serogroup I was improved, especially when skimmed milk (Marvel) was used instead of bovine serum albumin as blocking agent. Mabs 1221, 1239 and 4G4 reacted positively with all 22 E.c. atroseptica serogroup I, the dominant E.c. atroseptica serogroup on potato, strains tested and only with two out of five E.c. atroseptica serogroup XXII strains, one E.c. carotovora serogroup XXI strain and one strain of a saprophytic bacterium, Comamonas sp. Essentially similar results were obtained when examined by immunofluorescence. Characterization of the four Mabs showed that they were IgG3 and SDS-PAGE/immunoblot results suggested that they were probably against the O-side chain of bacterial cell wall lipopolysaccharides. In competition ELISA between biotin-labelled and unlabelled Mabs, the competition pattern of the four Mabs was similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the fatty acid profile of Zygosaccharomyces bailii strains, isolated from different sources, after growth at increasing concentrations of ethanol and/or decreasing temperatures were determined. Differences in fatty acid composition between Zygosaccharomyces bailii strains at standard conditions (25 degrees C, 0% initial ethanol) were observed and could be related to ethanol tolerance. Zygosaccharomyces bailii strain isolated from wine showed the highest ethanol tolerance in relation to growth rate. Surprisingly, an increase in ethanol concentration or a decrease in growth temperature caused a decrease in the degree of unsaturation of total cellular fatty acids. On the other hand, the mean chain length increased (high ethanol concentration) or decreased (low temperature) depending on the stress factor. When both stress situations (high ethanol concentration and low temperature) were present at the same time, the degree of unsaturation remained approximately constant. With decreasing temperatures, the C16/C18 ratio increased in studies of initial ethanol content below 5%, and above 5% ethanol, decreased.

Various dyes were assessed for their ability to discriminate between viable and non-viable bacteria. Two methods of killing were employed: by heat treatment or by gramicidin treatment. Staining was carried out in two ways; by staining directly in the medium or by washing cells prior to staining in buffer. Carbocyanine and rhodamine 123 dyes only exhibited small changes in fluorescence between viable and non-viable populations of bacteria. Both oxonol dye (bis 1,3-dibutylbarbituric acid trimethine oxonol) and calcafluor white proved much more useful.

The roles of lipase and esterase in causing hydrolytic spoilage of milk by a highly lipolytic psychrotrophic strain of Pseudomonas fluorescens, LS107d2, has been studied. Strains of LS107d2 have been constructed that over-produce, or are specifically deficient in, a lipase (encoded by lipA) and an esterase (encoded by estA). Southern blot analysis reveals that LS107d2 contains only one esterase and one lipase (encoded by estA and lipA) and this was confirmed by the phenotypes of mutants on triolein and tributyrin-containing agar. Analysis of broth cultures showed that the lipase is secreted into the culture medium; in contrast, the esterase is not secreted. Free fatty acid (FFA) levels in whole milk cultures of wild-type, over-producing and the mutant strains of LS107d2 have been examined. From these studies it is concluded that esterase is not involved in the accumulation of FFA by hydrolysing short chain fatty acid esters; that the highly lipolytic phenotype of LS107d2 is due solely to a single secreted lipase; and that the main FFA accumulated in milk cultures of LS107d2 are C4, C16, C18 and C18: 1. Evidence is also presented demonstrating that FFA degradation, as well as production, determines the level of FFA in milk contaminated with lipolytic organisms.