Antagonistic activity of Lactobacillus acidophilus RY2 isolated from healthy infancy feces on the growth and adhesion characteristics of enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAggEC) infection is an important cause of acute diarrhea, affecting children in developing countries and travelers visiting tropical or subtropical areas. Three probiotics can exert bacteriostatic or bactericidal effects on human and animal intestinal pathogens, the efficiency of probiotics on EAggEC infection remains unclear. In this study, the antagonistic activity of probiotic bacteria isolated from infant faeces was examined against several EAggEC stains. While three isolates, Lactobacillus acidophilus RY2, Lactobacillus salivarius MM1 and Lactobacillus paracasei En4 were shown to significantly inhibit the growth of EAggEC. In addition, the antagonistic activity of the Lactobacillus species was maintained despite heating (100 °C, 15 min) of cell free culture supernatant (CFCS). The antagonistic activity of the CFCS however, could be reduced following lactate dehydrogenase treatment and at pH 7.2. Furthermore, in an adhesion–inhibition assay, L. acidophilus RY2 was shown to be more effective than L. salivarius MM1 and L. paracasei EN4. This study suggests that L. acidophilus RY2 could be used as a probiotic organism against EAggEC.     

Antagonistic activity of probiotic lactobacilli and bifidobacteria against entero- and uropathogens

AIM: To develop in vitro assays for comparing the antagonistic properties and anti-oxidative activity of probiotic Lactobacillus and Bifidobacterium strains against various entero- and urinary pathogens. METHODS AND RESULTS: The antagonistic activity of five probiotic lactobacilli (Lactobacillus rhamnosus GG, Lactobacillus fermentum ME-3, Lactobacillus acidophilus La5, Lactobacillus plantarum 299v and Lactobacillus paracasei 8700:2) and two bifidobacteria (Bifidobacterium lactis Bb12, Bifidobacterium longum 46) against six target pathogens was estimated using different assays (solid and liquid media, anaerobic and microaerobic cultivation) and ranked (low, intermediate and high). Bacterial fermentation products were determined by gas chromatography, and the total anti-oxidative activity of probiotics was measured using linolenic acid test. Pyelonephritic Escherichia coli was highly suppressed by GG and both bifidobacteria strains. Lactobacilli strains 8700:2, 299v and ME-3 were the most effective against Salmonella enterica ssp. enterica in microaerobic while ME-3 and both bifidobacteria expressed high activity against Shigella sonnei in anaerobic milieu. Lact. paracasei, Lact. rhamnosus and Lact. plantarum strains showed intermediate antagonistic activity against Helicobacter pylori under microaerobic conditions on solid media. The highest anti-oxidative activity was characteristic for Lact. fermentum ME-3 (P < 0.05). No efficient antagonist against Clostridium difficile was found. The positive correlations between the pH, lactic acid production and anti-microbial activity for all tested probiotics were assessed. CONCLUSIONS: Developed experimental assays enable to compare the anti-microbial and -oxidative activity of Lactobacillus and/or Bifidobacterium probiotics, which have been claimed to possess the ability of suppressing the growth of various enteric and urinary pathogens. SIGNIFICANCE AND IMPACT OF THE STUDY: Screening Lactobacillus and Bifidobacterium sp. strains according to their activity in various environmental conditions could precede the clinical efficacy studies for adjunct treatment with probiotics in cure of different gastrointestinal and urinary tract infections.     

体外拮抗幽门螺杆菌的人嗜酸乳杆菌菌株的选育

目的 探讨人嗜酸乳杆菌对幽门螺杆菌（Ｈｅｌｉｃｏｂａｃｔｅｒ ｐｙｌｏｒｉ,ＨＰ）毒力株的体外拮抗作用,筛选出对ＨＰ毒力株有明显拮抗作用的嗜酸乳杆菌菌株。方法 从健康人胃肠道中分离出５２株嗜酸乳杆菌可疑株,通过其培养特性,生理特性,生化反应及代谢产物测定等进行鉴定,获得２６株嗜酸乳杆菌。同时,从临床患者胃活检标本中分离出２３株ＨＰ菌株,用ＰＣＲ方法筛选出ｃａｇＡ阳性ＨＰ毒力株,然后,采用打孔法进行嗜酸乳杆菌培养上清拮抗ＨＰ毒力株的实验,以１％的乳酸作对照。结果 筛选出４株对ＨＰ毒力株有明显拮抗作用的嗜酸乳杆菌,这种拮抗作用不依赖嗜酸乳杆菌分泌的乳酸。结论 人嗜酸乳杆菌在体外对ＨＰ毒力株具有明显拮抗作用。该研究为应用微生态疗法治疗ＨＰ感染提供了理论基础。     

Selecting lactic acid bacteria for their safety and functionality by use of a mouse colitis model

Studies showed that specific probiotics might provide therapeutic benefits in inflammatory bowel disease. However, a rigorous screening of new probiotics is needed to study possible adverse interactions with the host, particularly when intended for administration to individuals with certain health risks. In this context, the objective of this study was to investigate the role of three lactobacilli (LAB) on intestinal inflammation and bacterial translocation using variations of the mouse model of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced acute colitis. We first compared the in vitro ability of LAB to survive gastrointestinal tract (GIT) conditions and their ability to persist in the GIT of mice following daily oral administration. As a control, we included a nonprobiotic Lactobacillus paracasei strain, previously isolated from an endocarditis patient. Feeding high doses of LAB strains to healthy and to TNBS-treated mice did not induce any detrimental effect or abnormal translocation of the bacteria. Oral administration of Lactobacillus salivarius Ls-33 had a significant preventive effect on colitis in mice, while Lactobacillus plantarum Lp-115 and Lactobacillus acidophilus NCFM did not. None of the three selected LAB strains translocated to extraintestinal organs of TNBS-treated mice. In contrast, L. paracasei exacerbated colitis under severe inflammatory conditions and translocated to extraintestinal organs. This study showed that evaluations of the safety and functionality of new probiotics are recommended. We conclude that not all lactobacilli have similar effects on intestinal inflammation and that selected probiotics such as L. salivarius Ls-33 may be considered in the prevention or treatment of intestinal inflammation.     

Diversity and mechanisms of alkali tolerance in lactobacilli

We determined the maximum pH that allows growth (pHmax) for 34 strains of lactobacilli. High alkali tolerance was exhibited by strains of Lactobacillus casei, L. paracasei subsp. tolerans, L. paracasei subsp. paracasei, L. curvatus, L. pentosus, and L. plantarum that originated from plant material, with pHmax values between 8.5 and 8.9. Among these, L. casei NRIC 1917 and L. paracasei subsp. tolerans NRIC 1940 showed the highest pHmax, at 8.9. Digestive tract isolates of L. gasseri, L. johnsonii, L. reuteri, L. salivarius subsp. salicinius, and L. salivarius subsp. salivarius exhibited moderate alkali tolerance, with pHmax values between 8.1 and 8.5. Dairy isolates of L. delbrueckii subsp. bulgaricus, L. delbrueckii subsp. lactis, and L. helveticus exhibited no alkali tolerance, with pHmax values between 6.7 and 7.1. Measurement of the internal pH of representative strains revealed the formation of transmembrane proton gradients (DeltapH) in a reversed direction (i.e., acidic interior) at alkaline external-pH ranges, regardless of their degrees of alkali tolerance. Thus, the reversed DeltapH did not determine alkali tolerance diversity. However, the DeltapH contributed to alkali tolerance, as the pHmax values of several strains decreased with the addition of nigericin, which dissipates DeltapH. Although neutral external-pH values resulted in the highest glycolysis activity in the presence of nigericin regardless of alkali tolerance, substantial glucose utilization was still detected in the alkali-tolerant strains, even in a pH range of between 8.0 and 8.5, at which the remaining strains lost most activity. Therefore, the alkali tolerance of glycolysis reactions contributes greatly to the determination of alkali tolerance diversity.     

Bacteriocin production by spray-dried lactic acid bacteria

AIMS: Cell survival and antagonistic activity against Listeria innocua, Listeria monocytogenes and Staphylococcus aureus were investigated after spray-drying three bacteriocin-producing strains of lactic acid bacteria: Carnobacterium divergens, Lactobacillus salivarius and Lactobacillus sakei. METHODS AND RESULTS: Bacterial cell concentrates were spray-dried and stored at 4 degrees C and 18 degrees C and 0.3% ERH (equilibrium relative humidity). Enumeration and antagonistic activity were evaluated before and after spray-drying and at regular intervals during storage. CONCLUSIONS: A higher survival rate was obtained when survival was performed at 4 degrees C. With the exception of Carnobacterium divergens which lost the inhibitory activity against Staph. aureus after drying, antagonistic production was not affected by the process nor by the storage. Of the three species studied, Lact. salivarius showed the highest resistance to the spray-drying and storage processes. SIGNIFICANCE AND IMPACT OF THE STUDY: Spray-drying is a potentially useful process for large scale production of dried powders containing viable organisms with antagonistic activity against pathogens.     

Rapid identification of 11 human intestinal Lactobacillus species by multiplex PCR assays using group- and species-specific primers derived from the 16S-23S rRNA intergenic spacer region and its flanking 23S rRNA

Rapid and reliable two-step multiplex polymerase chain reaction (PCR) assays were established to identify human intestinal lactobacilli; a multiplex PCR was used for grouping of lactobacilli with a mixture of group-specific primers followed by four multiplex PCR assays with four sorts of species-specific primer mixtures for identification at the species level. Primers used were designed from nucleotide sequences of the 16S-23S rRNA intergenic spacer region and its flanking 23S rRNA gene of members of the genus Lactobacillus which are commonly isolated from human stool specimens: Lactobacillus acidophilus, Lactobacillus crispatus, Lactobacillus delbrueckii (ssp. bulgaricus and ssp. lactis), Lactobacillus fermentum, Lactobacillus gasseri, Lactobacillus jensenii, Lactobacillus paracasei (ssp. paracasei and ssp. tolerans), Lactobacillus plantarum, Lactobacillus reuteri, Lactobacillus rhamnosus and Lactobacillus salivarius (ssp. salicinius and ssp. salivarius). The established two-step multiplex PCR assays were applied to the identification of 84 Lactobacillus strains isolated from human stool specimens and the PCR results were consistent with the results from the DNA-DNA hybridization assay. These results suggest that the multiplex PCR system established in this study is a simple, rapid and reliable method for the identification of common Lactobacillus isolates from human stool samples.     

唾液乳杆菌ZDY159a抑菌机制的研究

目的对唾液乳杆菌(Lactobacillus salivarius)ZDY159a的产酸能力和体外抑菌影响因素进行初步研究。方法采用共培养法和牛津杯法,以大肠埃希菌(Escherichia coli O157:H7)NCTC 12900和金黄色葡萄球菌(Staphylococcus aureus)CMCC 26003作为指示菌。结果唾液乳杆菌ZDY159a发酵产生的乳酸和乙酸均具有较强抑菌活性;发酵全液的抑菌活性强于发酵上清液;低p H与发酵上清液的抑菌活性呈正相关;蛋白酶和过氧化氢酶处理可降低发酵上清液的抑菌活性。结论唾液乳杆菌ZDY159a的抑菌活性与发酵过程中产生的有机酸、细菌素(蛋白或多肽类物质)和过氧化氢有关,且菌体可提高发酵上清液的抑菌活性。     

Detection and activity of lactacin B, a bacteriocin produced by Lactobacillus acidophilus

A total of 52 strains of Lactobacillus acidophilus were examined for production of bacteriocins. A majority (63%) demonstrated inhibitory activity against all members of a four-species grouping of Lactobacillus leichmannii, Lactobacillus bulgaricus, Lactobacillus helveticus, and Lactobacillus lactis. Four L. acidophilus strains with this activity also inhibited Streptococcus faecalis and Lactobacillus fermentum, suggesting a second system of antagonism. Under conditions eliminating the effects of organic acids and hydrogen peroxide, no inhibition of other gram-positive or -negative genera was demonstrated by L. acidophilus. The agent produced by L. acidophilus N2 and responsible for inhibition of L. leichmannii, L. bulgaricus, L. helveticus, and L. lactis was investigated. Ultrafiltration studies indicated a molecular weight of approximately 100,000 for the crude inhibitor. The agent was sensitive to proteolytic enzymes and retained full activity after 60 min at 100 degrees C (pH 5). Activity against sensitive cells was bactericidal but not bacteriolytic. These characteristics identified the inhibitory agent as a bacteriocin, designated lactacin B. Examination of strains of L. acidophilus within the six homology groupings of Johnson et al. (Int. J. Syst. Bacteriol. 30:53-68, 1980) demonstrated that production of the bacteriocin lactacin B could not be used in classification of neotype L. acidophilus strains. However, the usefulness of employing sensitivity to lactacin B in classification of dairy lactobacilli is suggested.     

Functional and safety characterization of autochthonous Lactobacillus paracasei FS103 isolated from sheep cheese and its survival in sheep and cow fermented milks during cold storage

The main objective of this study was to evaluate some probiotic characteristics of Lactobacillus spp. isolated from traditional sheep cheese, and to investigate the fermentative ability and viability in sheep and cow milks of a selected potential probiotic Lactobacillus (L.) strain, i.e., L. paracasei FS103. A total of 54 autochthonous Lactobacillus isolates were characterized for (i) acidity and bile salt resistance, (ii) tolerance to gastric and intestinal juice models, and (iii) antagonistic activity against pathogens and antibiotic resistance. Potential probiotic Lactobacillus has been used in sheep and cow milks for the manufacturing of experimental fermented milks. In these latter, pH value, microbial count, and sensory analysis were carried out. Lactobacillus FS103 classified as L. paracasei subsp. paracasei had a good survival in gastric and intestinal juice models, inhibited the growth of undesirable bacteria, and was susceptible to chloramphenicol, clindamycin, penicillin, amoxicillin, erythromycin, tetracycline, and ampicillin. Moreover, when used to produce experimental sheep and cow fermented milks, L. paracasei FS103 was able to acidify both milk types leading to a continuous pH decrease during all fermentation time (24 h). FS103 population remains viable at a level > 108 CFU mL−1 after 21 days of cold (4 °C) storage. The results of sensory analysis showed that scores related to consistency, taste, and astringent were significantly higher in sheep fermented milk while animal-like was less acceptable compared to cow fermented milk. Lactobacillus paracasei FS103 isolated from sheep cheese exhibited potential probiotic properties and suitable features for sheep and cow fermented milks maintaining high vitality during cold storage.     

Probiotic properties of Lactobacillus strains isolated from the feces of breast-fed infants and Taiwanese pickled cabbage

This study assessed potential probiotic Lactobacillus strains isolated from the feces of breast-fed infants and from Taiwanese pickled cabbage for their possible use in probiotic fermented foods by evaluating their (i) in vitro adhesive ability, resistance to biotic stress, resistance to pathogenic bacteria, and production of β-galactosidase; (ii) milk technological properties; and (iii) in vivo adhesive ability, intestinal survival and microbial changes during and after treatment. Five Lactobacillus isolates identified as Lactobacillus reuteri F03, Lactobacillus paracasei F08, Lactobacillus rhamnosus F14, Lactobacillus plantarum C06, and Lactobacillus acidophilus C11 that showed resistance to gastric juice and bile salts were selected for further evaluation of their probiotic properties. All the strains demonstrated the ability to adhere to Caco-2 cells, particularly, strain L. plantarum C06 and L. reuteri F03 showed satisfactory abilities, which were similar to that of the reference strain L. rhamnosus GG. The strains L. paracasei F08 and L. acidophilus C11 had the highest β-galactosidase activity. Most of the strains were resistant to aminoglycosides and vancomycin but sensitive to ampicillin, erythromycin, and penicillin. All the 5 strains elicited antibacterial activity against both Gram-positive (Bacillus cereus, Listeria monocytogenes and Staphylococcus aureus) and -negative (Escherichia coli and Salmonella enterica) pathogens. Moreover, the strains L. reuteri F03, L. paracasei F08, and L. plantarum C06 could grow rapidly in milk without nutrient supplementation and reached 10? cfu/mL after 24 h of fermentation at 37 °C. The viable cell counts of the 3 strains remained above 10? cfu/mL after 21 d of storage at 4 °C. In the animal feeding trial, the number of intestinal lactobacilli increased significantly after administration of milk fermented with the 3 strains, and the counts of fecal coliforms and Clostridium perfringens were markedly reduced. Lactobacillus strains could also survive in the ileal intestinal tissue of the treated rats. Technologically interesting Lactobacillus isolates may be used in the future as probiotic starter cultures for manufacturing novel fermented foods.     

Lactobacillus paracasei subsp. paracasei 8700:2 degrades inulin-type fructans exhibiting different degrees of polymerization

Ten strains of lactobacilli were assessed for their capacity to degrade inulin-type fructans, which are well-known prebiotics. Both oligofructose and inulin were tested. The dairy isolate Lactobacillus acidophilus IBB 801 degraded only oligofructose. The human isolate Lactobacillus paracasei subsp. paracasei 8700:2 degraded oligofructose and long-chain inulin and grew rapidly on both energy sources. In both cases, fractions of different degrees of polymerization were fermented. Moreover, large and short fractions of oligofructose were degraded simultaneously. When L. paracasei subsp. paracasei 8700:2 grew on oligofructose-enriched inulin, oligofructose was preferentially metabolized. In all cases, lactic acid was the main metabolic end product. Significant amounts of acetic acid, formic acid, and ethanol were produced when long-chain inulin or oligofructose-enriched inulin was used as the sole energy source.     

Lactobacillus acidophilus LAP5 able to inhibit the Salmonella choleraesuis invasion to the human Caco-2 epithelial cell

The mechanisms for lactic acid bacteria (LAB) to inhibit Salmonella invasion appear to be multifactorial and include the adhesion of LAB to host intestine epithelium, the production of organic acids, or bacteriocin by LAB cells. Previously, we found a strain of Lactobacillus acidophilus isolated from swine, i.e. strain LAP5, was with antagonistic effect against Salmonella typhimurium. This strain LAP5 was also found to meet the requirements for probiotic use. In this study, we evaluate the potential of LAP5 strain to protect the human or swine from infection by Salmonella choleraesuis. We present evidence that the culture of LAP5 was able to inhibit the invasion of S. choleraesuis to human Caco-2 cell line. The LAP5 cell culture showed a higher inhibitory effect on the invasion of S. choleraesuis to Caco-2 cells than the spent culture supernatant (SCS) of LAP5 did. Also, the pH, organic acids or the bacteriocin, which act at low pH conditions, may play the role of antagonistic effect. The addition, adhesion of LAP5 cells to Caco-2 cell line may also play roles to reduce the invasion of S. choleraesuis.     

Competitive exclusion of diarrheagenic Escherichia coli (ETEC) from human enterocyte-like Caco-2 cells by heat-killed Lactobacillus

Diarrheagenic Escherichia coli (ETEC) bearing CFA/I or CFA/II adhesive factors specifically adhere onto the brush border of the polarized epithelial human intestinal Caco-2 cells in culture. Heat-killed Lactobacillus acidophilus strain LB, that adheres onto Caco-2 cells, inhibits diarrheagenic Escherichia coli adhesion in a concentration-dependent manner. Since the L. acidophilus does not express ETEC-CFA adhesive factors, it can be postulated that the heat-killed L. acidophilus LB cells inhibit diarrheagenic E. coli attachment by steric hindrance of the human enterocytic ETEC receptors.     

Characterization and Transfer of Antibiotic Resistance in Lactic Acid Bacteria from Fermented Food Products

The study provides phenotypic and molecular analyses of the antibiotic resistance in lactic acid bacteria (LAB) from fermented foods in Xi'an, China. LAB strains (n = 84) belonging to 16 species of Lactobacillus (n = 73), and Streptococcus thermophilus (n = 11) were isolated and identified by sequencing their 16S rRNA gene. All strains were susceptible to ampicillin, bacitracin, and cefsulodin, and intrinsically resistant to nalidixic acid, kanamycin, and vancomycin (except L. bulgaricus, L. acidophilus, and S. thermophilus, which were susceptible to vancomycin). Some strains had acquired resistance for penicillin (n = 2), erythromycin (n = 9), clindamycin (n = 5), and tetracycline (n = 14), while resistance to gentamycin, ciprofloxacin, streptomycin, and chloramphenicol was species dependent. Minimum inhibitory concentrations presented in this study will help to review microbiological breakpoints for some of the species of Lactobacillus. The erm(B) gene was detected from two strains of each of L. fermentum and L. vaginalis, and one strain of each of L. plantarum, L. salivarius, L. acidophilus, L. animalis, and S. thermophilus. The tet genes were identified from 12 strains of lactobacilli from traditional foods. This is the first time, the authors identified tet(S) gene from L. brevis and L. kefiri. The erm(B) gene from L. fermentum NWL24 and L. salivarius NWL33, and tet(M) gene from L. plantarum NWL22 and L. brevis NWL59 were successfully transferred to Enterococcus faecalis 181 by filter mating. It was concluded that acquired antibiotic resistance is well dispersed in fermented food products in Xi'an, China and its transferability to other genera should be monitored closely.     

Screening of lactic-acid bacteria from South African barley beer for the production of bacteriocin-like compounds

Strains of Lactobacillus paracasei subsp. paracasei (strain ST11BR), L. pentosus (strain ST151BR), L. plantarum (strain ST13BR), and Lactococcus lactis subsp. lactis (strain ST34BR) producing bacteriocin-like peptides were isolated from barley beer produced in the Western, Northern and Eastern provinces of South Africa. The peptides (bacST11BR, bacST151BR, bacST13BR and bacST34BR) lost their activity after treatment with proteinase K, a proteinase, papain, chymotrypsin, trypsin, pepsin and pronase, but not when they were treated with alpha-amylase, suggesting that the peptides are not glycosylated. The peptides inhibited the growth of Lactobacillus casei, L. sakei, Pseudomonas aeruginosa, Escherichia coli and Enterococcus faecalis, but not Enterobacter cloacae, Lactobacillus bulgaricus subsp. delbrueckii, L. plantarum, L. salivarius, Listeria innocua, Staphylococcus aureus, Streptococcus uberis, S. agalactiae, S. caprinus and S. pneumoniae. Peptides bacST11BR and bacST13BR differed from the other 2 peptides by failing to kill Klebsiella pneumoniae and one of the E. coli strains. Peptides were stable after 2 h of incubation at pH 2.0-12.0, and after 90 min at 100 degrees C. When autoclaved (121 degrees C, 20 min), only bacST13BR lost its activity. The bacteriocin-like peptides were produced at a growth temperature of 30 degrees C, but not at 37 degrees C.     

嗜酸乳杆菌GIM1.208 β-葡萄糖苷酶的异源表达、纯化及酶学性质研究

嗜酸乳杆菌(Lactobacillus acidophilus)是益生菌,前期研究发现LactobacillusacidophilusGIM1.208所产生的β-葡萄糖苷酶(BGL)具有较高活性,为探明其结构与特性,本研究采用PCR体外扩增技术获得Lactobacillusacidophilus GIM1.208BGL...     

Characterization of dominant cultivable lactobacilli and their antibiotic resistance profiles from faecal samples of weaning piglets

AIMS: To examine the lactic acid bacteria flora of weaning piglets, to define the distribution of different lactobacilli species in piglet faecal samples, and to determine the susceptibility phenotype to 11 antibiotic of different families. METHODS AND RESULTS: The faecal samples were taken from piglets with good herd status at 11 and 28 days after weaning. The Lactobacillus isolates (n = 129) from 78 animals housed in pairs in 39 pens were preliminarily identified by their morphology and biochemical characteristics. Partial 16S ribosomal DNA (16S rDNA) was used to identify the isolates to the species level, and RAPD (randomly amplified polymorphism DNA) profiles to differentiate Lactobacillus isolates to the strain level. Based on these studies, 67 strains were selected for antibiotic resistant tests. The most numerous Lactobacillus species found in the piglets was Lactobacillus reuteri (n = 43). Other lactobacilli were L. salivarius (n = 15), L. agilis (n = 4), L. johnsonii (n = 2), L. vaginalis (n = 1), L. mucosae (n = 1) and L. gallinarum (n = 1). All the strains were susceptible to chloramphenicol, ampicillin and gentamicin. Two L. salivarius isolates and two L. reuteri isolates were found to be multiresistant. CONCLUSIONS: This study indicates that the faecal Lactobacillus flora in piglets consists mainly of L. reuteri, L. salivarius and L. acidophilus group lactobacilli, and the distribution of lactobacilli is similar between individuals of the same age and with the same diet. Most of the Lactobacillus isolates tested were sensitive to the antibiotics used in this study. SIGNIFICANCE AND IMPACT OF THE STUDY: Valuable information on Lactobacillus species distribution and their antibiotic resistance profiles in piglets is obtained.     

Viability of vaginal probiotic lactobacilli during refrigerated and frozen storage

The viability of six different strains of probiotic vaginal Lactobacillus was examined in two different cryoprotective media, during refrigerated versus frozen storage, and using two traditional types of stock cultures for starting the biomass production. Freezing at -20 degrees C and -70 degrees C had much less adverse effect on viability than did storage at 7 degrees C, and the reduction in viability was greater at -20 degrees C than at -70 degrees C. The strains showed variation in the extent of the viability losses during both types of storage. Milk-yeast extract (MYE) was shown to be the more suitable protective medium to maintain viability of the strains during the storage. The vaginal Lactobacillus strains are most stable in MYE at -70 degrees C with only a small decrease of the viability observed under these conditions. The viable cell counts of Lactobacillus paracasei CRL 1251 and CRL 1289, L. crispatus CRL 1266 and L. salivarius CRL 1328 remained around 1 x 10(8) CFU/mL after 24 months of storage at -70 degrees C, or up to 18 months for L. acidophilus CRL 1259.     

乳杆菌在发酵乳饮料中的应用

为了制备更优质的乳酸菌饮料,本论文主要以鼠李糖乳杆菌、瑞士乳杆菌、副干酪乳杆菌、嗜酸乳杆菌四种典型的乳酸杆菌为研究菌种,详细分析它们在乳品发酵过程中pH、酸度变化,货架期内的活菌数变化以及代谢产生的有机酸种类和耐胃酸的能力,以确定乳杆菌在乳饮料中应用的最优条件,分析其应用于乳饮料中的可行性。本文为乳杆菌在乳饮料中的应用提供了参考依据。