Masters Degrees (Microbiology)

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Browsing Masters Degrees (Microbiology) by Subject "Adhesion"

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    Isolation and characterization of novel Lactobacillus spp. with promising gastro-intestinal survival and adhesion properties
    (Stellenbosch : Stellenbosch University, 2017-12) Klopper, Kyle Brent; Dicks, Leon Milner Theodore; Deane, Shelly M.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH SUMMARY: The human gastrointestinal tract (GIT) is a complex organ system, and is closely associated with immunological and hormonal functions. A delicate balance needs to be maintained between the selective and beneficial colonization of allochthonous and autochthonous microorganisms, which contribute to the preservation of gut homeostasis and protect the host against infections. Lactobacillus reuteri HFI-LD5 and Lactobacillus rhamnosus HFI-K2, isolated from the feces of healthy humans, formed biofilms on a hydrophobic abiotic surface (polystyrene) under static conditions and were selected for further studies. Meaningful differences in cell surface properties were observed between the isolates, with strain HFI-K2 exhibiting a significantly greater basic surface property, in addition to a significantly higher surface hydrophobicity (37.71 %, p˂ 0.05) compared to that recorded for strain HFI-LD5 (8.82 %, p˂ 0.05). The hydrophobic nature of L. rhamnosus HFI-K2 in conjunction with better biofilm formation, may contribute to a greater GIT colonization ability. Neither of the two strains isolated degraded mucus, and their growth was not irreversibly inhibited when exposed to acidic conditions (pH 2.5) and bile salts (0.5 % and 1.0 % w/v), suggesting that they may survive conditions in the GIT. To confirm planktonic and sessile survival of L. rhamnosus HFI-K2 and L. reuteri HFI-LD5 in the human GIT, the effect of three simulated, fasting-state gastrointestinal fluids (gastric fluid, pH 2, 2 h exposure; intestinal fluid, pH 7.5, 6 h exposure and colonic fluid pH 7, 24h exposure) on both free-living and attached cell viability of the strains was assessed. Exposure to simulated gastric juice had the greatest effect on both planktonic cell viability and biofilm metabolic activity. The sequential introduction of the simulated gastrointestinal fluids initiated the detachment of biofilm biomass, accompanied by a decrease in the metabolic activity, as recorded by changes in CO2 production, by the use of the carbon dioxide measurement system (CEMS). However, as soon as the exposure was halted and sterile culture medium was reintroduced, the remaining biofilm biomass responded by producing CO2, followed by the recovery of biofilm biomass and re-establishment of pre-exposure activity within 24 h. In contrast to the complete loss of planktonic L. rhamnosus HF1-K2 viability after exposure to gastric juice, biofilms of this strain not only recovered within 24 h after exposure, but also exhibited increased metabolic activity after recovery. To our knowledge, this is the first study to assess the effect of simulated, fasting-state gastrointestinal fluids on lactobacilli biofilms. Monitoring of CO2 production as a real-time indicator of metabolic activity in a biofilm provided insight to the differential survival responses of lactic acid bacteria under fasting-state gastrointestinal conditions. The ability of L. reuteri HFI-LD5 and L. rhamnosus HFI-K2 to survive acid, bile and simulated gastrointestinal fluid induced stresses, coupled with biofilm formation under dynamic flow conditions, may contribute to improved survival and persistence of these strains within the human GIT. These characteristics, especially those exhibited by L. rhamnosus HFI-K2, are promising indicators for the application of these isolates as probiotic supplements.