Julius Maina Mathara

Functional Properties of Lactobacillus plantarum Strains Isolated from Maasai Traditional Fermented Milk Products in Kenya

Lactobacillus plantarum was the major species among the lactic acid bacterial strains isolated from traditional fermented milk of the Maasai in Kenya. Selected strains were characterized for their functional properties using in vitro standard procedures. All strains expressed acid tolerance at pH 2.0 after 2-h exposure of values that ranged from 1% to 100%, while bile tolerance of acid-stressed cells at 0.3% oxgal varied from 30% to 80%. In vitro adhesion to the mucus-secreting cell line HT 29 MTX and binding capacity to extracellular protein matrices was demonstrated for several strains. The four strains tested in a simulated stomach duodenum passage survived with recovery rates ranging from 17% to 100%. Strains were intrinsically resistant to several antibiotics tested. From these in vitro studies, a number of Lb. plantarum strains isolated from the Maasai traditional fermented milk showed probiotic potential. The strains are good candidates for multifunctional starter culture development.

Use of homogenisation pressure to improve quality and functionality of probiotic fermented milks containing Lactobacillus rhamnosus BFE 5264

The effects of 60-MPa milk homogenisation treatment were investigated on the viability of the probiotic strain Lactobacillus rhamnosus BFE5264, when used as yoghurt co-starter, as well as on the aroma profile, texture and microstructure of the resulting set-type fermented milks. The results demonstrated that the combined use of homogenisation pressure and co-inoculation of the probiotic strain with the traditional yoghurt starters allowed the reduction in the product coagulation time, the increase of the probiotic strain viability and the improvement of the product volatile molecule profiles. The rheological indices and the microstructure results indicated the positive effects of the milk homogenisation treatment on the product viscosity index and exopolysaccharide production.

Influence of gastrointestinal stress on autoinducer-2 activity of two Lactobacillus species

Quorum sensing is a bacterial communication signalling system that regulates the expression of certain target genes with autoinducers in a cell density-dependent manner. The universal luxS-mediated quorum sensing using the autoinducer-2 (AI-2) signal is present in a wide variety of bacteria with only sparse information on probiotic lactobacilli. Effective probiotics should exhibit tolerance and adaptation to stress conditions typical of the GIT. Adhesion to human intestinal epithelial cells and competitive exclusion of pathogens are also considered important. The AI-2 signal system plays an important role in the response of probiotic lactobacilli to the surrounding environment. Intraspecies-related changes in quorum signalling in the GIT were determined by monitoring the AI-2 activity of two strains each of Lactobacillus rhamnosus and L. plantarum under various stress conditions. Modulation of the AI-2 activity of all the strains was induced by stress responses to pH, bile acid, temperature, osmotic pressure and starvation, and was both species- and strain-specific. AI-2 inhibition correlated with a reduction in the stress-related genes of L. rhamnosus. We therefore suggest that AI-2 quorum signalling of probiotic lactobacilli may represent one way of adapting to the hosts ecosystem and of interacting within the intestinal environment.

Characterization of pMRI 5.2, a rolling-circle-type plasmid from Lactobacillus plantarum BFE 5092 which harbours two different replication initiation genes.

Plasmid pMRI 5.2 from Lactobacillus plantarum BFE 5092 was sequenced and analysed. The sequence consists of 5206bp with a mol% G+C content of 35.8%. Nine putative open reading frames were identified. A typical pC194 family double strand origin (dso) and a putative single strand origin (sso) were predicted upstream of a rep gene. This rep gene encoded a replication protein of 314 amino acids exhibiting 98% amino acid sequence identity to the Rep protein of plasmid pLAB1000 from Lactobacillus hilgardii. A mob gene encoding a mobilization protein was also identified and this protein showed high amino acid similarity to Mob proteins from various L. plantarum plasmids. Downstream of the mob gene, a second putative replication region was identified that is similar to the pMV158 family of plasmids. It contains a dso as well as a putative sso, and encodes the 52 amino acid repressor-like protein RepA, the replication initiation protein RepB of 215 amino acids, and the 48 amino acid RepC that is similar to ORFD of the lactococcal plasmid pWVO1. RT-PCR and qRT-PCR expression analyses of the rep and repB genes showed that the repB gene was expressed at a higher level. To confirm that the plasmid replicated by the rolling-circle-type mechanism, the presence of a characteristic single strand intermediate DNA was shown to be produced during replication. Plasmid copy number was ca. 30 per equivalent chromosome copy number based on qRT-PCR analyses. The plasmid also encodes four additional putative proteins of unknown function. The unusual feature of a rolling-circle plasmid having two different plasmid-encoded replication initiation proteins from different replicon families suggests that the genes for these may have originated from different plasmids.