Expression of fluorescent proteins in Lactobacillus rhamnosus to study host–microbe and microbe–microbe interactions

Probiotic Lactobacillus strains are widely used to benefit human and animal health, although the exact mechanisms behind their interactions with the host and the microbiota are largely unknown. Fluorescent tagging of live probiotic cells is an important tool to unravel their modes of action. In this study, the implementation of different heterologously expressed fluorescent proteins for the labelling of the model probiotic strains Lactobacillus rhamnosusGG (gastrointestinal) and Lactobacillus rhamnosusGR‐1 (vaginal) was explored. Heterologous expression of mTagBFP2 and mCherry resulted in long‐lasting fluorescence of L. rhamnosusGG and GR‐1 cells, using the nisin‐controlled expression (NICE) system. These novel fluorescent strains were then used to study in vitro aspects of their microbe–microbe and microbe–host interactions. Lactobacillus rhamnosusGG and L. rhamnosusGR‐1 expressing mTagBFP2 and mCherry could be visualized in mixed‐species biofilms, where they inhibited biofilm formation by Salmonella Typhimurium–gfpmut3 expressing the green fluorescent protein. Likewise, fluorescent L. rhamnosusGG and L. rhamnosusGR‐1 were implemented for the visualization of their adhesion patterns to intestinal epithelial cell cultures. The fluorescent L. rhamnosus strains developed in this study can therefore serve as novel tools for the study of probiotic interactions with their environment.     

Metabolic and proteomic adaptation of Lactobacillus rhamnosus strains during growth under cheese‐like environmental conditions compared to de Man,Rogosa, and Sharpe medium

The aim of this study was to demonstrate the metabolic and proteomic adaptation of Lactobacillus rhamnosus strains, which were isolated at different stages of Parmigiano Reggiano cheese ripening. Compared to de Man, Rogosa, and Sharpe (MRS) broth, cultivation under cheese‐like conditions (cheese broth, CB) increased the number of free amino acids used as carbon sources. Compared with growth on MRS or pasteurized and microfiltrated milk, all strains cultivated in CB showed a low synthesis of d,l ‐lactic acid and elevated levels of acetic acid. The proteomic maps of the five representative strains, showing different metabolic traits, were comparatively determined after growth on MRS and CB media. The amount of intracellular and cell‐associated proteins was affected by culture conditions and diversity between strains, depending on their time of isolation. Protein spots showing decreased (62 spots) or increased (59 spot) amounts during growth on CB were identified using MALDI‐TOF‐MS/MS or LC‐nano‐ESI‐MS/MS. Compared with cultivation on MRS broth, the L. rhamnosus strains cultivated under cheese‐like conditions had modified amounts of some proteins responsible for protein biosynthesis, nucleotide, and carbohydrate metabolisms, the glycolysis pathway, proteolytic activity, cell wall, and exopolysaccharide biosynthesis, cell regulation, amino acid, and citrate metabolism, oxidation/reduction processes, and stress responses.     

Growth,acid production and bacteriocin production by probiotic candidates under simulated colonic conditions

Aims

The aim of this study is to evaluate the capacity of three bacteriocin producers, namely Lactococcus lactis subsp. lactis biovar diacetylactis UL719 (nisin Z producer), L. lactis ATCC 11454 (nisin A producer) and Pediococcus acidilactici UL5 (pediocin PA‐1 producer), and to grow and produce their active bacteriocins in Macfarlane broth, which mimics the nutrient composition encountered in the human large intestine.

Methods and Results

The three bacteriocin‐producing strains were grown in Macfarlane broth and in De Man–Rogosa–Sharpe (MRS) broth. For each strain, the bacterial count, pH drop and production of organic acids and bacteriocins were measured for different period of time. The ability of the probiotic candidates to inhibit Listeria ivanovii HPB 28 in co‐culture in Macfarlane broth was also examined. Lactococcus lactis subsp. lactis biovar diacetylactis UL719, L. lactis ATCC 11454 and Ped. acidilactici UL5 were able to grow and produce their bacteriocins in MRS broth and in Macfarlane broth. Each of the three candidates inhibited L. ivanovii HPB 28, and this inhibition activity was correlated with bacteriocin production. The role of bacteriocin production in the inhibition of L. ivanovii in Macfarlane broth was confirmed for Ped. acidilactici UL5 using a pediocin nonproducer mutant.

Conclusions

The data provide some evidence that these bacteria can produce bacteriocins in a complex medium with carbon source similar to those found in the colon.

Significance and Impact of the Study

This study demonstrates the capacity of lactic acid bacteria to produce their bacteriocins in a medium simulating the nutrient composition of the large intestine.     

Reduction of Sulfide, Ammonia Compounds, and Adhesion Properties of Lactobacillus casei Strain KE99 In Vitro

The ability of Lactobacillus casei strain KE99 to reduce sulfide, ammonia, and to adhere to bio-surfaces was characterized and compared with three lactobacillus reference strains. Sulfide reduction by strain KE99 in MRS broth increased exponentially after 10-h growth and reached a maximum (>300 ppm reduction) within 48 h. KE99 demonstrated a maximum reduction of sulfide under anaerobic (341 ppm) growth conditions at pH 6.0-8.0 range. Maximum anaerobic reduction of sulfide was demonstrated by L. casei 393 at pH 7.0 (272 ppm); L. rhamnosus at pH 8.0 (277 ppm); and L. reuteri at pH 7.0 (244 ppm). KE99 reduced sulfide more (p < 0.0001) in MRS broth spiked with Na₂S (374 ppm) than (NH₄)₂S (340 ppm) salts. Ammonia reduction by strain KE99 and the three lactobacillus reference strains in MRS broth was low. Ammonia reduction reached a maximum within 36 h and remained unchanged over extended incubations of 48 h to 72 h or further. KE99 reduced ammonium sulfate (37 ppm) more readily than the nitrate (31 ppm), hypophosphate (29 ppm), or chloride (20 ppm) salts of ammonia. KE99 and the three reference strains of lactobacilli demonstrated avid binding to Bio-coat™ (Cn type-I, Cn type-IV, laminin, fibronectin), Matrigel™, and Caco-2 cell monolayers in vitro. The number of lactobacilli binding to Caco-2 was estimated at 74/cell with strain KE99, which was significantly higher compared with 40/cell (p < 0.0001), 26/cell (0.0001), and 64/cell (p < 0.002) with L. casei 393, L. reuteri, and L. rhamnosus, respectively. The interaction of KE99 to immobilized Cn type-I was saturable and reached an equilibrium within 1 h at room temperature. KE99 binding to Cn type-I occurred at a wide pH range and was biphasic with maximum binding at pH 5.5 and 7.5. Inhibition and binding-displacement experiments with different salts and sugars suggested that the KE99 binding to immobilized Cn type-I may involve a combination of electrostatic and lectin-type interactions. KE99 effectively detached the Cn-adherent E. coli O157:H7 in the range of 55% (ATCC43895) to 76% (ATCC43894). The binding-displacement values for L. casei 393, L. reuteri and L. rhamnosus to detach Cn-adherent E. coli O157:H7 (ATCC43894) were 66 ± 4%, 59 ± 2%, and 64 ± 2%, respectively. Also, a reconstituted solution of the freeze-dried KE99 preparation effectively detached the Cn-adherent E. coli O157:H7 in a dose-dependent manner that reached a binding-displacement equilibrium of 85% at a 1% wt/vol KE99 concentration. Received: 25 May 2001 / Accepted: 2 July 2001     

Antibiotic resistance of potential probiotic bacteria of the genus <Emphasis Type="Italic">Lactobacillus</Emphasis> from human gastrointestinal microbiome

Thirteen Lactobacillus strains isolated from the gastrointestinal microbiome of people from the territory of the former Soviet Union have been studied for resistance to 15 antibiotics of different nature, namely, penicillins, aminoglycosides, macrolides, lincosamides, tetracyclines, chloramphenicol, and rifampicin. The strains included four strains of L. plantarum, four of L. helveticus, three of L. casei/paracasei, one of L. rhamnosus, and one of L. fermentum. All strains showed relative sensitivity to ampicillin, chloramphenicol, rifampicin, roxithromycin, erythromycin, and azithromycin, while none of them were sensitive to all tested antibiotics. L. plantarum strains had the broadest resistance spectra: one strain was resistant to tetracycline and three aminoglycosides and three strains were resistant to tetracycline and five aminoglycosides; one strain demonstrated high resistance to clindamycin and two strains to lincomycin. At the same time, two L. plantarum strains demonstrated resistance to benzylpenicillin coupled with sensitivity to ampicillin, another β-lactam antibiotic. Such resistance was clearly not related to the β-lactamase activity and could be explained by a specific mutation in one of the penicillin-binding proteins of the cell wall. Strains of L. helveticus, L. casei/paracasei, L. rhamnosus, and L. fermentum exhibited cross resistance to two to five different aminoglycosides. A PCR test of the resistance determinants for the widely clinically used antibiotics, tetracycline, chloramphenicol, and erythromycin revealed the presence of the tetM gene of conjugative transposon in L. casei/paracasei and two L. helveticus strains. Nucleotide sequence analysis of the amplified tetM fragments demonstrated their high homology with the tetM genes of Enterococcus faecalis and Streptococcus pneumoniae. The strains carrying tetM were tested for the genes of replication and conjugative transfer of plasmids in lactic acid bacteria. The results indicated that these strains contain genes identical or highly homologous to the rep and trsK genes of the plca36 plasmid and rep gene of the pLH1 and pLJ1 plasmids of lactic acid bacteria. The tetM gene is probably not expressed in strains sensitive to the corresponding antibiotic. However, the investigated lactobacilli cannot be directly used as probiotics, as they may serve as a source of genes for antibiotic resistance in the human microbiome.     

Adhesion of Vancomycin-Resistant Enterococcus to Human Intestinal Mucus

The intestinal mucus layer provides a potential niche for colonization by vancomycin-resistant Enterococcus faecium (VREF). We therefore examined the ability of six VREF strains to adhere to human intestinal mucus and determined binding kinetics. Four of six (67%) VREF strains demonstrated significant adhesion to immobilized intestinal mucus compared with a Salmonella typhimurium–negative control strain, but the level of adherence was low compared with Lactobacillus rhamnosus GG. Binding kinetics studies demonstrated that the maximum number of these four VREF strains that could adhere to a unit surface area of immobilized mucus was similar to or higher than the maximum number of L. rhamnosus GG that could adhere; however, L. rhamnosus GG demonstrated 20- to 130-times higher affinity than the VREF strains. These results demonstrate that VREF strains may adhere to human intestinal mucus and suggest that L. rhamnosus GG might be able to displace VREF strains.     

Quantification by real-time PCR of Lactococcus lactis subsp. cremoris in milk fermented by a mixed culture

During cheese making, interactions between different strains of lactic acid bacteria play an important role. However, few methods are available to specifically determine each bacterial population in mixed cultures, in particular for strains of the same species. The aim of this study was to develop a real-time PCR quantification method to monitor the population of Lactococcus cremoris ATCC 19257 in mixed culture with Lactobacillus rhamnosus RW-9595M and the bacteriocin-producing microorganism Lc. diacetylactis UL719. The specificity of the two primers 68FCa33 and 16SR308 used to amplify a 240-bp fragment of DNA from Lc. cremoris was demonstrated by conventional PCR. Using these primers for real-time PCR, the detection limit was 2 cfu/reaction or 200 cfu of Lc. cremoris ATCC 19257 per millilitre of mixed culture in milk. In pure culture batch fermentation, good correlation was obtained between real-time PCR and the conventional plating method for monitoring Lc. cremoris growth. In mixed culture batch fermentation, Lb. rhamnosus and Lc. cremoris decreased due to nisin Z production by Lc. diacetylactis. The decrease of the Lc. cremoris cell population detected by real-time PCR was not possible to observe by the plate count method in the presence of a Lc. diacetylactis population that was 1 log higher.An erratum to this article can be found at     

High-Level Expression of Heme-Dependent Catalase Gene <Emphasis Type="Italic">katA</Emphasis> from <Emphasis Type="Italic">Lactobacillus Sakei</Emphasis> Protects <Emphasis Type="Italic">Lactobacillus Rhamnosus</Emphasis> from Oxidative Stress

Lactic acid bacteria (LAB) are generally sensitive to hydrogen peroxide (H₂O₂), Lactobacillus sakei YSI8 is one of the very few LAB strains able to degrade H₂O₂ through the action of a heme-dependent catalase. Lactobacillus rhamnosus strains are very important probiotic starter cultures in meat product fermentation, but they are deficient in catalase. In this study, the effect of heterologous expression of L. sakei catalase gene katA in L. rhamnosus on its oxidative stress resistance was tested. The recombinant L. rhamnosus AS 1.2466 was able to decompose H₂O₂ and the catalase activity reached 2.85 μmol H₂O₂/min/10⁸ c.f.u. Furthermore, the expression of the katA gene in L. rhamnosus conferred enhanced oxidative resistance on the host. The survival ratios after short-term H₂O₂ challenge were increased 600 and 10⁴-fold at exponential and stationary phase, respectively. Further, viable cells were 100-fold higher in long-term aerated cultures. Simulation experiment demonstrated that both growth and catalase activity of recombinant L. rhamnosus displayed high stability under environmental conditions similar to those encountered during sausage fermentation.     

Probiotic Lactobacilli Interfere with <Emphasis Type="Italic">Streptococcus mutans</Emphasis> Biofilm Formation In Vitro

In clinical studies, probiotic bacteria have decreased the counts of salivary mutans streptococci (MS). We compared the effects of probiotic Lactobacillus strains on the biofilm formation of Streptococcus mutans. The bacterial strains used included four S. mutans strains (reference strains NCTC 10449 and Ingbritt and clinical isolates 2366 and 195) and probiotic strains Lactobacillus rhamnosus GG, L. plantarum 299v, and L. reuteri strains PTA 5289 and SD2112. The ability of MS to adhere and grow on a glass surface, reflecting biofilm formation, was studied in the presence of the lactobacilli (LB). The effect of LB culture supernatants on the viability of the MS was studied as well. All of the LB inhibited the biofilm formation of the clinical isolates of MS (P < 0.001). The biofilm formation of the reference strains of MS was also inhibited by the LB, but L. plantarum and L. reuteri PTA 5289 showed a weaker inhibition when compared to L. reuteri SD2112 and L. rhamnosus GG. Viable S. mutans cells could be detected in the biofilms and culture media only when the experiments were performed with the L. reuteri strains. The L. reuteri strains were less efficient in killing the MS also in the tests performed with the culture supernatants. The pHs of the supernatants of L. reuteri were higher compared to those of L. rhamnosus GG and L. plantarum; P < 0.001. In conclusion, our results demonstrated that four commonly used probiotics interfered with S. mutans biofilm formation in vitro, and that the antimicrobial activity against S. mutans was pH-dependent.     

Characterization of the beneficial properties of lactobacilli isolated from bullfrog (<Emphasis Type="Italic">Rana catesbeiana</Emphasis>) hatchery

The present work addresses the isolation and partial identification of the microbial population of a R. catesbeiana hatchery in spring and summer as well as some beneficial properties of Lactobacillus strains isolated in different seasons and hatchery areas. The bacterial population was grouped into the following taxa: Lactobacillus spp., Pediococcus spp., Enterococcus faecalis and Ent. faecium, and Enterobacteriaceae (Enterobacter spp., Escherichia coli) while Pseudomonas aeruginosa and Staphylococcus epidermidis were isolated from frogs displaying red-leg syndrome. The Lactobacillus plantarum and L. curvatus strains isolated showed to inhibit the growth of red-leg syndrome associated pathogens and food-borne bacteria by organic acids. While L. plantarum CRL 1606 also inhibited red-leg syndrome related pathogens by hydrogen peroxide, meat spoilage bacteria were only inhibited by acidity. However, by using a MRS medium added with tetramethyl-benzidine and peroxidase, a high percentage of H₂O₂-producing lactobacilli were detected. The surface properties of Lactobacillus strains showed that a few strains were able to agglutinate ABO human erythrocytes, while the highest number of strains had a low to medium degree of hydrophobicity. This paper constitute the first study related to the beneficial properties of Lactobacillus isolated from a bullfrog hatchery, as well as the selection criteria applied to a group of strains, which could help to control or prevent bacterial infectious diseases in raniculture.     

Synergistic Effect Between Two Bacteriocin-like Inhibitory Substances Produced by Lactobacilli Strains with Inhibitory Activity for <Emphasis Type="Italic">Streptococcus agalactiae</Emphasis>

Group B streptococci (GBS) are bacterial species that colonize the vagina in pregnant women and as such may cause serious infections in neonates that passed through the birth channel. The objective of this work was to study the inhibitory activities produced by each bacteriocin-like inhibitory substance (BLIS) of Lactobacillus rhamnosus L60 and Lactobacillus fermentum L23, and the effects of the combined BLIS-es of these lactobacilli on GBS. The interactions between the BLIS-es were assessed by qualitative and quantitative methods on agar plates. The minimum inhibitory concentrations (MICs) and fractional inhibitory concentrations (FICs) were determined by a modification of the broth microdilution and checkerboard methods, respectively. Antibiotic susceptibilities of all S. agalactiae strains were assayed and the results of these tests were evaluated for statistical significance. A 7.5% of GBS isolates were recovered from 760 pregnant women and 91% of those strains were susceptible to each BLIS produced by L. fermentum, L. rhamnosus, and also to a mixture of them. The comparisons among the BLIS-es showed statistically significant differences, with a combination of the BLIS-es from the two Lactobacillus species being better than the BLIS of each one alone (P < 0.05) as GBS growth inhibitors. Synergistic activities between the BLIS-es were found on 100% of susceptible GBS strains, MICs ranges of BLIS of L23 and L60 were 80–160 and 160–320 UA ml⁻¹, respectively. By the checkerboard method, the BLIS-es combination showed synergistic effect on all sensitive strains tested, with values of FICs ranging from 0.131 to 0.218. The BLIS-es produced by these lactobacilli of vaginal origin were able to inhibit S. agalactiae isolates. The results indicate that these strains may have probiotic potential for the control of GBS in women and may consequently prevent GBS infections in newborns.     

Comparison of Fructose-1,6-Bisphosphatase Gene (<Emphasis Type="Italic">fbp</Emphasis>) Sequences for the Identification of <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis>

Comparative analysis of fructose-1,6-bisphosphatase gene (fbp) sequences was evaluated for the differentiation of reference and clinical strains of Lactobacillus rhamnosus. The sequences of 1,971 nucleotides of the fbp gene were determined on both DNA strands for 21 L. rhamnosus strains, representing reference, probiotic, and clinical strains. No PCR amplification of the fbp gene was observed for other species of the Lactobacillus casei complex (L. casei and L. zeae) or strains of Lactobacillus acidophilus, Streptococcus thermophilus, and Escherichia coli. Phylogenetic analysis of the fbp putative amino acid sequences of L. rhamnosus strains by the neighbor-joining method showed clear distinct positions of this species. The phylogenetic tree, derived from fbp nucleotide sequences, showed four clear divisions between strains of L. rhamnosus. From a taxonomic point of view, our results confirm for the first time that fbp gene sequences have high discriminating power for strains of L. rhamnosus that are difficult to differentiate.     

Aciduric Strains of <Emphasis Type="Italic">Lactobacillus reuteri</Emphasis> and <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis>, Isolated from Human Feces,Have Strong Adhesion and Aggregation Properties

Human feces were streaked onto MRS Agar adjusted to pH 2.5, 3.0, and 6.4, respectively, and medium supplemented with 1.0% (w/v) bile salts. Two aciduric strains, identified as Lactobacillus reuteri HFI-LD5 and Lactobacillus rhamnosus HFI-K2 (based on 16S rDNA and recA sequences), were non-hemolytic and did not hydrolyze mucin. The surface of Lactobacillus reuteri HFI-LD5 cells has a weak negative charge, whereas Lactobacillus rhamnosus HFI-K2 has acidic and basic properties, and produces exopolysaccharides (EPS). None of the strains produce bacteriocins. Both strains are resistant to several antibiotics, including sulfamethoxazole-trimethoprim and sulphonamides. The ability of Lactobacillus reuteri HFI-LD5 and Lactobacillus rhamnosus HFI-K2 to grow at pH 2.5 suggests that they will survive passage through the stomach. EPS production may assist in binding to intestinal mucus, especially in the small intestinal tract, protect epithelial cells, and stimulate the immune system. Lactobacillus reuteri HFI-LD5 and Lactobacillus rhamnosus HFI-K2 may be used as probiotics, especially in the treatment of small intestinal bacterial overgrowth (SIBO).     

Strain-Dependent Augmentation of Tight-Junction Barrier Function in Human Primary Epidermal Keratinocytes by Lactobacillus and Bifidobacterium Lysates

In this study, we investigated whether probiotic lysates can modify the tight-junction function of human primary keratinocytes. The keratinocytes were grown on cell culture inserts and treated with lysates from Bifidobacterium longum, Lactobacillus plantarum, Lactobacillus reuteri, Lactobacillus fermentum, or Lactobacillus rhamnosus GG. With the exception of L. fermentum (which decreased cell viability), all strains markedly enhanced tight-junction barrier function within 24 h, as assessed by measurements of transepithelial electrical resistance (TEER). However, B. longum and L. rhamnosus GG were the most efficacious, producing dose-dependent increases in resistance that were maintained for 4 days. These increases in TEER correlated with elevated expression of tight-junction protein components. Neutralization of Toll-like receptor 2 abolished both the increase in TEER and expression of tight-junction proteins induced by B. longum, but not L. rhamnosus GG. These data suggest that some bacterial strains increase tight-junction function via modulation of protein components but the different pathways involved may vary depending on the bacterial strain.     

Antagonistic Activity of Lactic Acid Bacteria <Emphasis Type="Italic">Lactobacillus</Emphasis> spp. against Clinical Isolates of <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis>

The screening of three strains of lactic acid bacteria identified as Lactobacillus rhamnosus, Lactobacillus reuteri, and Lactobacillus helveticus showed significant antagonistic activity against Klebsiella pneumoniae strains characterized by multiple antibiotic resistance. Lactobacilli cocultivated with the Klebsiella strains inhibited their growth 20 to 86% on the first and second days, respectively. Exoproteome analysis of L. rhamnosus cocultivated with K. pneumoniae revealed the induction of peptidoglycan hydrolases, including extracellular lytic transglycosylases, family II (MltA), and endopeptidases capable of disrupting the peptidoglycan bacterial cell wall.     

Determination of the sensitivity of bacteria to barium ions,a taxonomic marker of the genus <Emphasis Type="Italic">Pseudomonas</Emphasis>

Comparative efficacy of the determination of the sensitivity of bacterial cells to barium ions was evaluated on a synthetic nutrient medium, FMH agar, Mueller-Hinton agar, and AGV agar. The synthetic nutrient medium developed for this study contained L-proline and L-glutamine as the sole nitrogen and carbon source, which promoted growth of all Pseudomonas strains and ensured the minimal level of barium binding. The sensitivity of 80 strains belonging to 11 Pseudomonas species, including the type strains, as well as of 80 strains of 22 other bacterial species, was studied. The sensitivity of bacteria to barium ions was determined by using serial dilutions of barium chloride in the nutrient medium. The highest level of analytical sensitivity of pseudomonads to barium ions was determined on the synthetic nutrient medium: the minimal inhibitory concentration (MIC) values of barium chloride ranged from 0.5 to 6 g/L, the MIC₉₀ value was 2 g/L. At the same time, 86.1% of all strains of fluorescent Pseudomonas species produced fluorescein on the control BaCl₂-free synthetic nutrient medium. For representatives of other genera grown on all the studied nutrient media, the MIC values of barium chloride ranged from 20 to 50 g/L. The proposed method for determination of the sensitivity of bacteria to barium ions using the synthetic nutrient medium with 6 g/L of barium chloride as a criterion for the classification of barium-sensitive strains to the genus Pseudomonas is suitable for standardization.     

The probiotic properties and potential of vaginal Lactobacillus spp. isolated from healthy women against some vaginal pathogens

During the last decade, probiotic research has progressed considerably and significant advances have been made in the selection and characterization of specific probiotic strains. The most studied probiotics belong to the genus Lactobacillus. In this study, 80 Lactobacillus spp. isolated from healthy women tolerated low pH and were able to grow in the presence of bile salts. RAPD PCR technique resulted in the identification of 38 different types. These isolates were then evaluated based on adhesion capacity, antibiotic susceptibility and tolerance in simulated gastrointestinal tract. Species-specific PCR and detection of bacteriocin-related genes were also surveyed. Among the isolates, five strains—Lacticaseibacillus rhamnosus NO21, Lacticaseibacillus casei NO1, Lactiplantibacillus plantarum NO4, Lactobacillus acidophilus NO7 and Lactobacillus gasseri NO38—presented acceptable antibiotic susceptibility pattern. Further analysis showed antimicrobial activity of Lacticaseibacillus culture against various bacterial pathogens and real-time PCR showed all five strains were able to prevent the colonization of bacterial pathogens. All five selected strains produced organic acids, hydrogen peroxide and were resistant to the spermicide. In addition, they lacked haemolytic activity with the ability of hydrophobicity, auto-aggregation and co-aggregation with pathogens. These results suggest that the vaginal microbiome could be a good source for the isolation of probiotics and the strains of this study may be considered as good probiotic candidates.     

The effect of cell surface components on adhesion ability of Lactobacillus rhamnosus

The aim of this study was to analyze the cell envelope components and surface properties of two phenotypes of Lactobacillus rhamnosus isolated from the human gastrointestinal tract. The ability of the bacteria to adhere to human intestinal cells and to aggregate with other bacteria was determined. L. rhamnosus strains E/N and PEN differed with regard to the presence of exopolysaccharides (EPS) and specific surface proteins. Transmission electron microscopy showed differences in the structure of the outer cell surface of the strains tested. Bacterial surface properties were analyzed by Fourier transform infrared spectroscopy, fatty acid methyl esters and hydrophobicity assays. Aggregation capacity and adhesion of the tested strains to the human colon adenocarcinoma cell line HT29 was determined. The results indicated a high adhesion and aggregation ability of L. rhamnosus PEN, which possessed specific surface proteins, had a unique fatty acid content, and did not synthesize EPS. Adherence of L. rhamnosus was dependent on specific interactions and was promoted by surface proteins (42–114 kDa) and specific fatty acids. Polysaccharides likely hindered bacterial adhesion and aggregation by masking protein receptors. This study provides information on the cell envelope constituents of lactobacilli that influence bacterial aggregation and adhesion to intestinal cells. This knowledge will help to understand better their specific contribution in commensal–host interactions and adaptation to this ecological niche.