Collagen binding toEscherichia coli strain NG7C

Escherichia coli strain NG7C was shown to bind iodine-labeled human type IV collagen (Cn). The binding was rapid and saturable. The number of binding sites was estimated to be 1.5×10⁴ sites/cell and the dissociation constant 85 nM. The binding was inhibited by unlabeled type I, type IV, and type X Cn, gelatin and, at high doses by vitronectin and fibrinogen. Heat treatment of bacteria abolished the binding. A cell sonicate of strain NG7C inhibited the binding. Heat or protease treatment of the sonicate reduced its inhibitory activity by more than 50% Cell surface extracts of strain NG7C likewise inhibited Cn binding. Cells ofE. coli NG7C also bound to type IV Cn immobilized on microtiter plates. The Cn binding appears to be mediated by cell surface protein(s). Type IV Cn binding toE. coli NG7C differed from the earlier reported Cn binding mechanisms toE. coli, i.e., binding of soluble type II Cn, and from binding of immobilized type V Cn by enterobacteria.E. coli strains can thus produce different surface proteins which mediate binding to collagens. Expression of Cn binding byE. coli may enhance colonization of subepithelial tissues.     

Collagen binding by the mannose receptor mediated through the fibronectin type II domain

The macrophage mannose receptor is the prototype for a family of receptors each having an extracellular region consisting of an N-terminal cysteine-rich domain related to the R-type carbohydrate-recognition domain of ricin, a fibronectin type II domain and eight to ten domains related to C-type carbohydrate-recognition domains. The mannose receptor acts as a molecular scavenger, clearing harmful glycoconjugates or micro-organisms through recognition of their defining carbohydrate structures. Cell-adhesion assays, as well as collagen-binding assays, have now been used to show that the mannose receptor can also bind collagen and that the fibronectin type II domain mediates this activity. Neither of the two types of sugar-binding domain in the receptor is involved in collagen binding. Fibroblasts expressing the mannose receptor adhere to type I, type III and type IV collagens, but not to type V collagen, and the adherence is inhibited by isolated mannose receptor fibronectin type II domain. The fibronectin type II domain shows the same specificity for collagen as the whole receptor, binding to type I, type III and type IV collagens. This is the first activity assigned to the fibronectin type II domain of the mannose receptor. The results suggest additional roles for this multifunctional receptor in mediating collagen clearance or cell-matrix adhesion.     

Modulation of immune system cells by lactobacilli

The influence of lactobacilli on the proliferative potential of immune system cells after the intragastral administration of viable microbial cells and their native filtrates to mice CBA is evaluated. The data have been obtained on the modulating influence of lactobacilli on the formation of T- and B-cell immune response--their role in maintaining homeostatsis and specific features of cell mediated immune reactions after the intragastral administration of virulent Shigella dysenteriae for modeling experimental infection in CBA mice. The mechanisms of the immunomodulating action of lactobacilli on local and systemic reactions of the host as well as realization of the protective properties of lactobacilli against the causative agents of acute enteric infections are discussed.     

Binding of extracellular matrix proteins by lactobacilli

Ten gut and ten vaginalLactobacillus strains were investigated for their ability to bind type I collagen (Cn-I) and four selected gut lactobacilli were investigated for their binding to other extracellular matrix (ECM) molecules. Immobilized Cn-I (100 mg/L) in wells of microtitre plates was bound by all 10 autoaggregating vaginal strains and by 3 strains of gut lactobacilli from piglets in the range ofA ₅₇₀ readings 0.114–1.806.L. acidophilus strain SV31 was much more adherent than the rest of strains. All four gut lactobacilli tested for binding to other ECM molecules displayed good binding to porcine fibronectin and heparin and some of them bound weakly to fetuin and porcine mucin. No binding of these strains was observed to bovine mucin, bovine fibrinogen and bovine lactoferrin.     

Citrate utilization by homo- and heterofermentative lactobacilli

Citrate utilization by several homo- and heterofermentative lactobacilli was determined in Kempler and McKay and in calcium citrate media. The last medium with glucose permitted best to distinguish citrate-fermenting lactobacilli. Lactobacillus rhamnosus ATCC 11443, Lactobacillus zeae ATCC 15820 and Lactobacillus plantarum ATCC 8014 used citrate as sole energy source, whereas in the other strains, glucose and citrate were cometabolized. Some lactobacilli strains produced aroma compounds from citrate. Citrate transport experiments suggested that all strains studied presented a citrate transport system inducible by citrate. The levels of induction were variable between several strains. Dot blot experiment showed that lactobacilli do not present an equivalent plasmid coding for citrate permease.     

Evaluation of nitric oxide production by lactobacilli

Six strains of Lactobacillus fermentum and Lactobacillus plantarum were investigated for nitric oxide (NO) production. First, the potential presence of NO synthase was examined. None of the strains of L. fermentum and L. plantarum examined produced NO from L-arginine under aerobic conditions. Interestingly, all L. fermentum strains expressed strong L-arginine deiminase activity. All L. fermentum strains produced NO in MRS broth, but the NO was found to be chemically derived from nitrite, which was produced by L. fermentum from nitrate present in the medium. Indeed all L. fermentum strains express nitrate reductase under anaerobic conditions. Moreover, one strain, L. fermentum LF1, had nitrate reductase activity under aerobic conditions. It was also found that L. fermentum strains JCM1173 and LF1 possessed ammonifying nitrite reductase. The latter strain also had denitrifying nitrite reductase activity at neutral pH under both anaerobic and aerobic conditions. The LF1 strain is thus capable of biochemically converting nitrate to NO. NO and nitrite produced from nitrate by lactobacilli may constitute a potential antimicrobial mechanism. studied in a rat acute liver injury model (Adawi et al. 1997). The results indicate that Lactobacillus plantarum DSM 9842 may possess NOS (Adawi et al. 1997). However, NO production from L-arginine has not been investigated in pure cultures of L. plantarum. According to the results of a 15N enrichment experiment, traces of (NO2-+NO3-)-N (total oxidised nitrogen: TON), which seemed to be formed by the resting cells of Lactobacillus fermentum IFO3956, appeared to be derived from L-arginine (Morita et al. 1997). Therefore, it was suggested that L. fermentum may possess a NOS. However, NO produced from L-arginine was not directly measured and a NOS inhibitor test was not performed by Morita et al. (1997). It is known that L-arginine deiminase (ADI) in bacteria may convert L-arginine to NH4+ (Cunin et al. 1986), which may be further oxidised to TON via nitrification by bacteria. Therefore, 15N enrichment experiments could not definitely conclude that L. fermentum possess NOS to convert L-arginine directly to NO. In this study, six Lactobacillus strains belonging to L. plantarum and L. fermentum were measured for NO production in MRS broth. The metabolism of nitrate and L-arginine by the Lactobacillus cell suspensions was also studied. The possibility that NO and nitrite production by lactobacilli may be a potential probiotic trait is also discussed.     

Colonization by lactobacilli of piglet small intestinal mucus

The colonization potential of lactobacilli was investigated using small intestinal mucus extracts from 35-d-old pigs. Mucus-secreting tissue from the small intestine of piglets was gently rinsed to remove contents and then shaken in buffer to release mucus from the surface. Numbers of lactobacilli in different portions of the small intestine of 35-d-old pigs were enumerated. Also, mucus isolated from the small intestine of pigs was investigated for its capacity to support the growth of lactobacilli. Results indicated that Lactobacillus spp. inhabit the mucus layer of the small intestine and can grow and adhere to ileal mucus. From adhesion studies of Lactobacillus fermentum 104R to mucus analysed by Scatchard plot, it is suggested that an associating system showing positive cooperativity is involved. Proteinaceous compound(s) involved in the adhesion to mucus were detected in the spent culture fluid from the growth of strain 104R. Studies are continuing in order to identify and characterize the adhesion-promoting protein(s). From the data, it is proposed that lactobacilli colonize the mucus layer of the small intestine of pigs.     

Deconjugation of bile acids by intestinal lactobacilli.

Lactobacillus species normally found in the intestinal tract of humans varied in the ability to deconjugate bile acids, whereas laboratory strains of Lactobacillus acidophilus deconjugated both glycocholate and taurocholate. All isolates of L. acidophilus from human feces deconjugated taurocholate, whereas only one of six deconjugated glycocholate. None of 13 isolates identified as L. casei deconjugated taurocholate, whereas 9 deconjugated glycocholate. The deconjugating system of L. acidophilus appeared to be constitutive, required low oxidation-reduction potential, and was most active at pH 6. No degradation beyond deconjugation was detected.     

Inhibition of beet molasses alcoholic fermentation by lactobacilli

Summary Alcohol production rate decreases as the concentration of bacterial contaminants increases. In complex medium, such as beet molasses, an alternative mechanism can be used by homofermentative lactic bacteria (Lactobacillus casei). Lactic acid and associated products, especially acetic acid, are liberated into the medium. The inhibition induced by these metabolites was reinforced by the presence of viable lactobacilli. Offprint requests to: P. Villa     

Bacteriophages of lactobacilli

Lactobacilli are members of the bacterial flora of lactic starter cultures used to generate lactic acid fermentation in a number of animal or plant products used as human or animals foods. They can be affected by phage outbreaks, which can result in faulty and depreciated products. Two groups of phages specific of Lactobacillus casei have been thoroughly studied. 1. The first group is represented by phage PL-1. This phage behaves as lytic in its usual host L. casei ATCC 27092, but can lysogenize another strain, L. casei ATCC 334. Bacterial receptors of this phage are located in a cell-wall polysaccharide and rhamnose is the main component of the receptors. Ca2+ and adenosine triphosphate (ATP) are indispensable to ensure the injection of the phage DNA into the bacterial cell. The phage DNA is double-stranded, mostly linear, but with cohesive ends which enables it to be circularized. The vegetative growth of PL-1 proceeds according to the classical mode. Cell lysis is produced by an N-acetyl-muramidase at the end of vegetative growth. 2. The second group is represented by the temperate phage phi FSW of L. casei ATCC27139. It has been shown how virulent phages originate from this temperate phage in Japanese dairy plants. The lysogenic state of phi FSW can be altered either by point mutations or by the insertion of a mobile genetic element called ISL 1, which comes from the bacterial chromosome. This is the first transposable element that has been described in lactobacilli. Lysogeny appears to be widespread among lactobacilli since one study showed that 27% of 148 strains studied, representing 15 species, produced phage particles after induction by mitomycin C. Similarly, 23 out of 30 strains of Lactobacillus salivarius are lysogenic and produce, after induction by mitomycin C, temperate phages, killer particles, or defective phages. Temperate phages have also been found in 10 out of 105 strains of Lactobacillus bulgaricus or Lactobacillus lactis after induction by mitomycin C. Phages so far studied of the latter 2 and closely related lactobacilli, either temperate or isolated as lytic, may be divided into 4 unrelated groups called a, b, c and d. Most of these phages are found in group a and an unquestionable relationship has already been shown between lytic phages and temperate phages that belong to this group. Lytic phage LL-H of L. lactis LL 23, isolated in Finland, is one of the most representative of those of group a and has been extensively studied on the molecular level.