Lactobacillus Viridescens Research Articles

Production of Xylooligosaccharides from Sugarcane Bagasse and Evaluation of Their Prebiotic Potency In Vitro

The purpose of study was utilization of sugarcane bagasse, waste product of sugarcane industry, for production of xylooligosaccharides (XOS) and their evaluation of their prebiotic potential. The XOS production was carried out in two steps: alkaline extraction of xylan (5, 10 and 15%KOH and NaOH) followed by acid hydrolysis (0.25 and 0.50M H2SO4; 20, 40 and 60 min) of xylan, and quantified using high performance thin layer chromatography (HPTLC). The prebiotic potency of XOS was evaluated for probiotics viz. Lactobacillus brevis, Lactobacillus acidophilus and Lactobacillus viridescens in comparison to standard fructooligosaccharides (FOS). The chemical compositional analysis indicated that bagasse contain 28.42% hemicellulose out of which 21.46% was estimated to be xylan. Maximum yield of xylan (20.5%) was obtained with 15%NaOH treatment. The best treatments for xylan hydrolysis were found to be 0.25M H2SO4 for 20 and 40 min with concentrations of xylose, xylobiose and xylotriose to be 2.014, 2.106 and 1.228 mg ml− 1, respectively, in 20 min hydrolysis and 2.138, 1.502 and 0.824 mg ml− 1, respectively, in 40 min hydrolysis. XOS were found to be better prebiotics than standard FOS. Pure xylobiose was found to have highest positive effect on growth of all three bacteria tested indicating that effects of XOS were due to presence of xylobiose, xylotriose and XOS with higher degree of polymerization in xylan hydrolysates. Sugarcane bagasse xylan can be converted into XOS only by controlled acid hydrolysis leading to increased production of XOS which can be used as good prebiotics in drugs and food ingredients after their purification eliminating all the acidic and alkaline residues and also side products.

Optimal experimental design for improving the estimation of growth parameters of Lactobacillus viridescens from data under non-isothermal conditions

In predictive microbiology, the model parameters have been estimated using the sequential two-step modeling (TSM) approach, in which primary models are fitted to the microbial growth data, and then secondary models are fitted to the primary model parameters to represent their dependence with the environmental variables (e.g., temperature). The Optimal Experimental Design (OED) approach allows reducing the experimental workload and costs, and the improvement of model identifiability because primary and secondary models are fitted simultaneously from non-isothermal data. Lactobacillus viridescens was selected to this study because it is a lactic acid bacterium of great interest to meat products preservation. The objectives of this study were to estimate the growth parameters of L. viridescens in culture medium from TSM and OED approaches and to evaluate both the number of experimental data and the time needed in each approach and the confidence intervals of the model parameters. Experimental data for estimating the model parameters with TSM approach were obtained at six temperatures (total experimental time of 3540h and 196 experimental data of microbial growth). Data for OED approach were obtained from four optimal non-isothermal profiles (total experimental time of 588h and 60 experimental data of microbial growth), two profiles with increasing temperatures (IT) and two with decreasing temperatures (DT). The Baranyi and Roberts primary model and the square root secondary model were used to describe the microbial growth, in which the parameters b and Tmin (±95% confidence interval) were estimated from the experimental data. The parameters obtained from TSM approach were b=0.0290 (±0.0020) [1/(h0.5°C)] and Tmin=−1.33 (±1.26) [°C], with R2=0.986 and RMSE=0.581, and the parameters obtained with the OED approach were b=0.0316 (±0.0013) [1/(h0.5°C)] and Tmin=−0.24 (±0.55) [°C], with R2=0.990 and RMSE=0.436. The parameters obtained from OED approach presented smaller confidence intervals and best statistical indexes than those from TSM approach. Besides, less experimental data and time were needed to estimate the model parameters with OED than TSM. Furthermore, the OED model parameters were validated with non-isothermal experimental data with great accuracy. In this way, OED approach is feasible and is a very useful tool to improve the prediction of microbial growth under non-isothermal condition.

Predicting Growth of Weissella Viridescens in Culture Medium under Dynamic Temperature Conditions

The lactic acid bacteria (LAB) are among the main spoilage microorganisms of foods, and the Weissella viridescens (formerly Lactobacillus viridescens) is well known to cause deterioration on the meat surface in vacuum packed meat products, even under refrigerated conditions. Therefore, this study evaluated the predictive ability of Baranyi and Roberts dynamic model to describe W. viridescens growth in culture medium (which simulates a food rich in nutrients), subjected to dynamic temperature conditions. Baranyi and Roberts primary model was fitted to the growth curves of W. viridescens in culture medium under six different isothermal temperatures (4, 8, 12, 16, 20 and 30°C) previously obtained in our laboratory. Four secondary models (linear, square root, exponential and Arrhenius type) were assessed to describe the influence of temperature on the growth parameters. The square root was the best model to describe temperature influence on μmax parameter. For Ymax parameter, the secondary model was considered the mean values obtained experimentally in the studied temperature range. Experimental data were used to evaluate the model predictions under dynamic conditions for two different temperature profiles, NIP-1 (12-16-20-25°C) and NIP-2 (16-12-8-4°C). According to the statistical indexes, the model showed better predictive ability for NIP-1, with RMSE of 0.3341, R2 of 0.9939, bias factor of 1.0046 and accuracy factor of 1.0197; the growth of W. viridescens under NIP-2 conditions was underestimated, indicating a fail dangerous prediction. The results showed that the predictive model can be used to predict the shelf life of meat products spoiled by W. viridescens.

Predictive Modeling of the Growth of Lactobacillus Viridescens under Non-isothermal Conditions

Food spoilage by microorganisms is a major problem that can generate large economic losses to industries, making critical the application of technologies for predicting shelf life, aiming to obtain products with higher quality. The Lactic Acid Bacteria (LAB), including Lactobacillus viridescens, are among the main groups of microorganisms responsible for spoilage of refrigerated meat products, vacuum packed and under modified atmosphere. The growth of the LAB can be predicted by mathematical models, which describe the influence of various environmental factors (such as non-isothermal conditions) on microbial growth. The objective of this study was to obtain a mathematical model able to predict the growth of L. viridescens in non-isothermal conditions in culture medium (MRS broth). Six isothermal growth curves (at 4, 8, 12, 16, 20 and 30̊C) were described by Baranyi and Roberts model and the dependence of maximum specific growth rate (μmax) parameter on the temperature was described by square root secondary model. The model was validated using L. viridescens experimental data in the temperature ranging from 6 to 10°C and 5 to 11°C, changing every 12 and 24h, respectively. The results showed that it was possible to predict safely (bias factor greater than 1) the growth of L. viridescens in MRS broth under non-isothermal conditions. The observed prediction deviations may have been caused by abrupt temperature changes, generating intermediate adaptation phases.

Estimation of the Temperature Dependent Growth Parameters of Lactobacillus Viridescens in Culture Medium with Two-step Modelling and Optimal Experimental Design Approaches

In predictive microbiology, the model parameters has been estimated using the traditional two-step modeling approach (TS), in which primary models are fitted to the microbial growth data and secondary models represent the dependence of model parameters with environmental variables. The optimal experimental design approach (OED) has been used as an alternative to TS, mainly because the improvement of model identifiability and reduction of the experimental workload and costs. The fitting of mathematical model to experimental data in TS is sequential, whereas in OED is simultaneous. Lactobacillus viridescens is a lactic acid bacteria that is of great interest to the meat products preservation. The objective of this study was to estimate the growth parameters of L. viridescens in culture medium with TS and OED. For TS, the experimental data were obtained in six temperatures; for OED, the data were obtained in four optimal non-isothermal experiments, two experiments with increasing temperatures (ITOED) and two with decreasing temperatures (DTOED). The Baranyi and Roberts, and the Square Root models were used to describe the microbial growth, in which the b and Tmin parameters (± 95% confidence intervals) were estimated from the experimental data. The parameters obtained for TS were b = 0.0290 (±0.0020) h-0.5°C-1 and Tmin = -1.33 (±1.26) °C, with R2 = 0.991; for ITOED were b = 0.0314 (±0.0019) h-0.5°C-1 and Tmin = 0.12 (±0.71) °C, with R2 = 0.995; for DTOED were b = 0.0295 (±0.0019) h-0.5°C-1 and Tmin = -1.57 (±1.05) °C, with R2 = 0.999. The parameters obtained in the OED approach presented smaller confidence intervals, higher R2 and less experimental time than the parameters obtained in the traditional TS approach. In this way, it is possible to answer positively that OED approach is feasible and could be widely applied in predictive microbiology.

Mathematical Modeling of Lactobacillus Viridescens Growth in Vacuum Packed Sliced Ham under non Isothermal Conditions

Lactic acid bacteria (LAB) are responsible for the spoilage of vacuum packed meat products, as ham. Temperature is the main factor affecting the microbial dynamics and its variation during the production, distribution and storage of foods is considerable. Thus, the use of mathematical models to describe the microbial behavior under variable temperatures can be very useful in predicting the food shelf life. This study evaluated the growth of Lactobacillus viridescens in sliced ham under non isothermal conditions, and assessed the predictive ability of the Baranyi and Roberts model using parameters obtained isothermally in culture medium (MRS). To obtain the BAL growth, the fresh ham piece was sterilized, sliced, inoculated with bacteria and stored in a temperature-controlled incubator. For the establishment of the secondary models, the primary model parameters were obtained isothermally in the culture medium at 4, 8, 12, 16, 20 and 30° C, in which there was no lag phase observed; the square root model was selected to describe the dependence of the μmax parameter (maximum specific growth rate) with the temperature, and the ymax parameter (maximum population) was represented by an average because there was no significant influence of the temperature. The mathematical models were validated with L. viridescens growth data in ham under five variable temperature conditions (NI-1 (4-8-12-16°C), NI-2 (12-16-20-25°C), NI-3 (25-20-16-12-8-4°C), NI-4 (16-12-8-4°C) and NI-5 (12-8-4-8-12°C)), and its predictive ability were assessed through statistical indexes (bias factor, accuracy factor and RMSE), with good results (bias factor between 0.9450 and 1.0326; accuracy factor between 1.0382 and 1.0682, and RMSE between 0.7641 and 1.3317), especially in increasing temperature, where the prediction was safe. The validated model can be used to estimate the shelf life of a commercial ham under different temperature conditions.

Production of Antilisterial Bacteriocins from Lactic Acid Bacteria in Dairy-Based Media: A Comparative Study.

One hundred and eight strains of lactic acid bacteria (LAB) were screened for bacteriocin production by the modified deferred antagonism and agar well diffusion methods. When the modified deferred antagonism method was employed, 82 LAB strains showed inhibitory action against Listeria monocytogenes v7 ½a, whereas 26 LAB strains expressed no inhibition. Only 12 LAB strains exhibited inhibitory activity when the agar well diffusion method was used, 11 of which had been previously recognized as bacteriocin production positive (Bac(+)). Lactobacillus viridescens NRRL B-1951 was determined, for the first time, to produce an inhibitory compound with a proteinaceous nature. The inhibitory activity was observed in the presence of lipase, α-chymotrypsin, and trypsin, but no inhibition zone could be detected in the presence of proteinase K, indicating the proteinaceous nature of the inhibitory compound. The inhibitory compound was active against Lact. sake ATCC 15521 and Lact. plantarum NCDO 995. Bacteriocin production by the Bac(+) LAB strains was assessed in Lactobacillus MRS Broth as well as in dairy-based media such as nonfat milk, demineralized whey powder, and cheddar cheese whey supplemented with complex nutrient sources that are rich in nitrogen. Lact. sake ATCC 15521 and L. monocytogenes CWD 1002, CWD 1092, CWD 1157, CWD 1198, and v7 ½a were used as indicators. The inhibitory activities of the bacteriocins varied depending on the indicator strains and the growth media used. The LAB indicator strains were found to be more sensitive to inhibition by bacteriocins when compared to the listerial indicator strains. Among the listerial indicators, L. monocytogenes CWD 1002 and CWD 1198 were the most sensitive strains to the bacteriocins investigated in this study. Media composition had a significant influence on bacteriocin production and activity. When compared to demineralized whey powder medium and cheddar cheese whey medium supplemented with whey protein concentrate, cheddar cheese whey medium supplemented with complex nutrient sources such as yeast extract, polypeptone, proteose peptone nr. 3, or soytone appeared to be more supportive of bacteriocin production.

Isolation and Identification of Yeasts and Lactic Acid Bacteria from Local Traditional Fermented Camel Milk, Chal

The yeasts and lactic acid bacteria in samples of the Iranian traditional fermented camel milk, Chal were identified on the basis of physiological and morphological properties. Yeast species were identified including Pichia. anamala, Pichia. jadinii, Debaryomyces. hansenii, Pichia. guilliermondii, Kluyvermyces. marxianus, Candida. fermentati, Pichia. ciferrii, Torulospora. delbrueckii, Candida. versatilis, Kluyvermyces. lactis, Candida. kefir, Saccharomyces. pastorianus, Saccharomyces. serevisiae, Candida. friedrichii, Kluyvermyces. polysporus, Rhodotorula. musilaginosa, Candida. lipolytica and Candida. lusitaniae. All of them could assimilate the glucose and liquefacted the gelatin, but could not production starch, tolerated 1% acetic acid, growth in the presence of Nacl 16% (except Debaryomyces. hansenii), anassimilateed the nitrat (except Rhodotorula. musilaginosa). Within the yeasts species, Kluyvermyces. lactis (8.57%) and Kluyvermyces. marxianus (8.57%) were the predominant. Also 93 different lactic acid bacteria species were identified including 64 bacilli as lactobicallus and wieselia, 8 cocci, leuconostoc, 11 coccobacili, leuconostoc, lactococcus and wieselia, 2 streptococci, streptoccus and 8 tetrad cocci shapes, pediococci. All isolates fermented galactose, except Lactobacillus delbrueckii subsp. Bulgaricus, Lactobacillus kefir, Lactobacillus viridescens. All the isolates could growth at 37°C, only Leuconostoc mesenteroides subsp. Cremoris and Leuconostoc paramesenteroides could not growth at 30°C. This study revealed Chal contained a wide variety of yeasts and lactic acid bacteria.

The investigation of probiotic potential of lactic acid bacteria isolated from cow milk

Probiotic strains can be isolated from many sources, for human applications one of the main criteria is being mammal origin. Cow milk is an important nutrient source for human. Lot of studies showed that this fluid has beneficial effects on the health of human. One reason of being beneficial is explaining by the microflora of cow milk including beneficial lactic acid bacteria. In this research work, 12 isolate were identified as lactic acid bacteria by biochemical characterization and further studied for probiotic activity. Among them 9 lactic acid bacteria was posseses probiotic activity. Six Lactobacilli stains were identified as Lactobacillus gasseri(1),Lactobacillus rhamnosus(1),Lactobacillus fermentum(2),Lactobacillus viridescens(3),Lactobacillus farciminis(1), Lactobacillus buchner(4). All of the bacilli isolates were selected to observe potential probiotic activity. These isolates showed resistance to stomach pH (pH 3.0), tolerance against 0.3% bile salt concentration and antimicrobial activity against Escherichia coli, Salmonella enteritids, Staphylococcus aureus, Listeria monocytogenes. The isolates were used to investigate the tolerances of the isolates to other stress conditions, such as, growth at different NaCl solution, growth at different temperatures and in the presence of 0.5% CaCO3. All of the isolate showed good tolerances in stress conditions. After investigation the probiotic properties of these isolates, they were identified by biochemical characterization techniques. It is observed that, cow milk is a source of potential probiotic strains.

Isolation, characterization and identification of lactic acid bacteria involved in traditional fermentation of borde, an Ethiopian cereal beverage

Changes in pH, titratable acidity, Enterobacteriaceae, aerobic mesophiles, lactic acid bacteria (LAB) and yeast counts were investigated during borde fermentation. A rapid decrease in pH was associated with accelerated growth rate of LAB and inhibition of Enterobacteriaceae. Wide diversities of LAB strains were present at early stage of borde fermentation. The number of species reduced as the fermentation progressed. Representatives of LAB involved in borde fermentation were isolated at 6 h intervals, characterized and identified using physiological and biochemical methods including API 50CH kit. The LAB strains were grouped into 3 major and 2 minor clusters. Most of the LAB strains were heterofermentative lactobacillus (79.4%), while pediococcus species dominating the cocci (20.6%). Weissella confusa, Lactobacillus brevis, Lactobacillus viridescens, Pediococcus pentosaceus and P. pentosaceus subsp. intermedius were identified throughout borde fermentation as dominant LAB. The frequency of dominating strains were: W. confusa (30.9%), Lb. viridescens (26.5%), Lb. brevis (10.3%) and P. pentosaceus (7.4%) and P. pentosaceus subsp. intermedius (8.8%), while sporadically isolated species of Lactobacillus curvatus, P. acidilactici, Lactobacillus collinoides, Lactobacillus sanfrancisco, Lactobacillus pontis and Lactobacillus delbrueckii subsp. delbrueckii were 16.3%. The dominating LAB strains can be potential starter cultures for borde fermentation.

The combined effect of high pressure and nisin on inactivation of microorganisms in milk

The behaviour of both Gram-negative and Gram-positive bacteria associated with milk, in response to application of high pressure (HP) combined with nisin, was evaluated. Escherichia coli, Pseudomonas fluorescens, Listeria innocua, and Lactobacillus viridescens grown separately in skim milk were pressure-treated at 250–500 MPa for 5 min at 20 °C in the presence of 0, 250, or 500 IU/ml nisin. Combining HP and nisin gave a greater inactivation of all four bacteria than when either was applied individually. A reduction of ≥ 8 log of L. viridescens and L. innocua in milk was achieved at 500 MPa for 5 min at 20 °C, in the presence of 500 IU/ml nisin. The Gram-negative bacteria were more sensitive to HP, either alone or in combination with nisin, than Gram-positive bacteria. Treatment at 400 MPa for 5 min with 500 IU/ml nisin, or at 250 MPa for 5 min with 500 IU/ml nisin, gave a > 8 log reduction of E. coli and P. fluorescens, respectively. By adding nisin to cell suspensions after HP treatment, it was shown that the effect of HP on cells of a single species can vary; some HP-induced sublethal injury is irreversible, allowing the sensitisation of Gram-negative bacteria to nisin post HP treatment. Reversible membrane damage in P. fluorescens caused by HP was demonstrated using fluorescent dye uptake before, after, or during HP treatment. Industrial relevance The synergistic microbial inactivation that can be achieved by HP treatment in the presence of nisin has applications not only for liquid milk but many other dairy and low-acid products. Such a combination of hurdles may allow lower pressures and shorter treatment times without compromising product safety.

Kinetic and Mechanistic Characterization of Recombinant Lactobacillus viridescens FemX (UDP-N-acetylmuramoyl Pentapeptide-lysine N6-Alanyltransferase)

The FemABX family encodes enzymes that incorporate l-amino acids into the interchain peptide bridge of Gram-positive cell wall peptidoglycan and are novel nonribosomal peptidyl transferases that use aminoacyl-tRNA as the amino acid donor. We previously reported the identification of the femX gene from Lactobacillus viridescens and recombinant expression of active FemX (LvFemX) that catalyzes the transfer of l-Ala from Ala-tRNAAla to the epsilon-amino group of l-lysine of UDP-MurNAc pentapeptide (Hegde, S. S., and Shrader, T. E. (2001) J. Biol. Chem. 276, 6998-7003). Recombinant LvFemX exhibits Km values of 42 and 15 microm for UDP-MurNAc pentapeptide and Escherichia coli Ala-tRNAAla, respectively, and exhibited a kcat value of 660 min-1. Initial velocity and inhibition kinetic studies support an ordered sequential mechanism for the enzyme, and we propose that catalysis proceeds via a ternary complex. The pH dependence of the activity was bell-shaped, depending on the ionization state of two groups exhibiting apparent pKa values of 5.5 and 9.3. Chemical modification of the enzyme and the kinetics of inactivation, and protection by substrate, indicated the involvement of carboxyl groups in the catalytic function of the enzyme. Site-directed mutagenesis identified Asp109 as a candidate for the catalytic base and Glu320 plays an additional important role in the catalytic function of the enzyme.

High hydrostatic pressure inactivation of Lactobacillus viridescens and its effects on ultrastructure of cells

The effect of high hydrostatic pressure treatment on Lactobacillus viridescens, a major spoilage micro‐organism of processed meat, was investigated. When pressure was applied at 400, 500 and 600 MPa for 5 min, cell survival in MRS broth was reduced approximately by 2, 7 and 8 log cycles, respectively. The combination of high pressure and temperature increase showed synergistic effects on microbial inactivation. Empty cavities in the cell and DNA denaturation were observed after pressure treatment above 400 MPa. The level of microbial inactivation when Lb. viridescens was pressured in protein‐fortified MRS broth and ham were less than half compared with the inactivation achieved in peptone water. Increasing the temperature during high‐pressure treatment solved these adverse effects in the ham.

FemABX Family Members Are Novel Nonribosomal Peptidyltransferases and Important Pathogen-specific Drug Targets

Pathogen-specific antibiotics kill the offending species without inviting the patient's flora to help develop a resistance mechanism. The current scarcity of pathogen-specific antibiotics reflects the rarity of essential genes that are also not widely represented in and conserved among species. The FemX enzyme that initiates the synthesis of the interchain peptide of the peptidoglycan in a subset of bacterial species was purified from Lactobacillus viridescens. Subsequently, the encoding femX gene was cloned and sequenced using reverse genetics. The femX gene is a member of the femAB family, a large family of genes previously implicated in interchain peptide synthesis but with unknown specific functions. Mutagenesis of the femX gene identified the members of the extended FemABX family as novel nonribosomal peptidyltransferases. Determinants of FemX complex substrate recognition and a strong stimulator of FemX activity were also identified. The FemABX family members are ideal candidates for pathogen-specific antibiotic development.

Production of histamine and tyramine by lactic acid bacteria isolated from vacuum-packed sugar-salted fish.

The incidence of histamine- or tyramine-producing lactic acid bacteria was examined in several products of vacuum-packed sugar-salted fish (salmon, halibut, mackerel). No histamine-producing isolates were observed, whereas the majority of tyramine-producing isolates were identified as Carnobacterium spp. These organisms were shown to be important members of the microbial flora during storage of vacuum-packed sugar-salted salmon at 5 degrees C. The amount of tyramine produced was reduced by lowering the temperature from 9 degrees C to 4 degrees C for all of five strains of carnobacteria or lactobacilli. The majority of tyramine was produced during the exponential growth phase for Carnobacterium piscicola N 5 and Lactobacillus viridescens N 69. The ability of these bacteria to produce tyramine may be used as an index of microbial quality/acceptability of stored vacuum-packed sugar-salted fish.

Identification and Characteristics of Lactic Acid Bacteria Isolated from Masai Fermented Milk in Northern Tanzania

Microorganisms were isolated from fermented milk manufactured by Masai men in northern Tanzania. The lactic acid bacteria isolated were identified as Lactococcus lactis ssp. lactis, Lactococcus garvieae, Enterococcus faecium, Streptococcus bovis, Lactobacillus confusus, Lactobacillus brevis, Lactobacillus plantarum, and Lactobacillus viridescens. The dominant strains were Lc. lactis ssp. lactis and Lb. confusus. Yeasts identified as Saccharomyces sp. and Candida sp. were isolated from several samples as minor strains.The binding ability of 21 strains of lactic acid bacteria to amino acid pyrolysates was investigated. 3-Amino-1,4-dimethyl-4H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), and 1-methyl-9H-pyrido[4,3-b]indole (Harmane) were bound to cells of all bacterial species.The growth of Staphylococcus aureus and Escherichia coli in the cultured milk was inhibited by Lc. lactis ssp. lactis and Lb. confusus.

Vancomycin binding to cell walls of non-streptococcal vancomycin-resistant bacteria.

The availability of peptidoglycan for binding to vancomycin was investigated in intrinsically vancomycin-resistant clinical isolates of Leuconostoc mesenteroides, Lactobacillus viridescens and Pediococcus pentosaceus. Intrinsic vancomycin resistance expressed by L. mesenteroides and P. pentosaceus was the result of poor binding of vancomycin to native or SDS-treated cell walls. Pre-exposure of L. viridescens to vancomycin decreased the subsequent binding of vancomycin to the cell walls, suggesting an alternative mechanism to that found in high-level vancomycin-resistant enterococci and intrinsically-resistant L. mesenteroides and P. pentosaceus. Vancomycin binding was sensitive to substitution of larger side chains at the C-terminus. Variations of peptidoglycan peptide types found in L. mesenteroides, L. viridescens and P. pentosaceus could account for their intrinsic vancomycin resistance.

Isolation and Taxonomie Characterization of Acid Urease-producing Bacteria

About 16,000 isolates from animal feces and intestines were assayed for the production of acid urease, and the 700 strains selected as producers were examined as to their taxonomic properties. Of these 700 strains, 370 belonged to the genus Streptococcus, 312 to the genus Lactobacillus, 9 to the genus Escherichia, 6 to the genus Staphylococcus, 2 to the genus Morganella and 1 to the genus Bifidobacterium. The majority of the streptococci were identified as Streptococcus mitior, the remainder being Streptococcus salivarius, Streptococcus faecalis, Streptococcus faecium, Streptococcus avium and Streptococcus gallinarum. The majority of the lactobacilli were considered to be Lactobacillus reuteri or Lactobacillus fermentum and Lactobacillus animalis or Lactobacillus salivarius, the remainder being Lactobacillus ruminis, Lactobacillus viridescens, Lactobacillus vac- cinostercus and strains considered to be Lactobacillus acidophilus, Lactobacillus amylovorus, Lactobacillus crispatus or Lactobacillus gasseri.

Isolation and taxonomic characterization of acid urease-producing bacteria.

About 16, 000 isolates from animal feces and intestines were assayed for the production of acid urease, and the 700 strains selected as producers were examined as to their taxonomic properties. Of these 700 strains, 370 belonged to the genus Streptococcus, 312 to the genus Lactobacillus, 9 to the genus Escherichia, 6 to the genus Staphylococcus, 2 to the genus Morganella and 1 to the genus Bifidobacterium. The majority of the streptococci were identified as Streptococcus mitior, the remainder being Streptococcus salivarius, Streptococcus faecalis, Streptococcus faecium, Streptococcus avium and Streptococcus gallinarum. The majority of the lactobacilli were considered to be Lactobacillus reuteri or Lactobacillus fermentum and Lactobacillus animalis or Lactobacillus salivarius, the remainder being Lactobacillus ruminis, Lactobacillus viridescens, Lactobacillus vaccinostercus and strains considered to be Lactobacillus acidophilus, Lactobacillus amylovorus, Lactobacillus crispatus or Lactobacillus gasseri.

The Effect of Salt on Growth of Attached and Unattached Cells of Lactobacillus viridescens

The growth rates of attached and unattached cells of Lactobacillus viridescens were determined in a meat extract broth ce:supplemented with 0 to 4% (w/v) NaCl. Attached growth rates were obtained by computer enhanced microscopy of cells adhering to glass flow chambers. Growth rates of unattached cells were determined by turbidity measurement in batch culture. Attached cells of Lactobacillus viridescens were capable of maintaining higher growth rates than unattached cells at all salt concentrations. The growth rate of attached cells was stimulated by 1 and 2% salt.