Fundamental principles of bacteriology , Fundamental principles of bacteriology , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Non-pathogenic lactic acid bacteria are economically important Gram-positive bacteria used extensively in the food industry. Due to their “generally regarded as safe” status, certain species from the genera Lactobacillus and Lactococcus are also considered desirable as candidates for the production and secretion of recombinant proteins, particular those with therapeutic applications.

The hypothesis examined by this thesis is that Lactococcus lactis can be modified to be an effective antimicrobial agent. Therefore, the aims of this thesis were to investigate the optimisation of the expression, secretion and/or activities of potential heterologous antimicrobial proteins by the model lactic acid bacterium, Lactococcus lactis subsp. cremoris MG1363.

L. lactis strains were engineered to express and secrete the recombinant CyuC surface protein from Lactobacillus reuteri BR11, and a fusion protein consisting of CyuC and lysostaphin using the Sep promoter and secretion signal. CyuC has been characterised as a cystine-binding protein, but has also been demonstrated to have fibronectin binding activity. Lysostaphin is a bacteriolytic enzyme with specific activity against the Gram-positive pathogen, Staphylococcus aureus. These modified L. lactis strains were then investigated to see if they had the ability to inhibit the adhesion of S. aureus to host extracellular matrix (ECM) proteins. It was observed that the cell extracts of the L. lactis strain with the vector only (pGhost9:ISS1) was able to inhibit the adhesion of S. aureus to fibronectin, whilst the cell extracts of the L. lactis strain expressing lysostaphin was able to inhibit adhesion to keratin.

Finally, this thesis has identified specific lactococcal genes that affect the secretion of lysostaphin through the use of random transposon mutagenesis. Ten mutants with higher lysostaphin activity contained insertions in four different genes encoding: (i) an uncharacterised putative transmembrane protein (llmg_0609), (ii) an enzyme catalysing the first step in peptidoglycan biosynthesis (murA2), (iii) a homolog of the oxidative defence regulator (trmA), and (iv) an uncharacterised putative enzyme involved in ubiquinone biosynthesis (llmg_2148). The higher lysostaphin activity observed in these mutants was found to be due to higher amounts of lysostaphin being secreted. 

The findings of this thesis contribute to the development of this organism as an antimicrobial agent and also to our understanding of L. lactis genetics.

Fundamental principles of bacteriology

The development of Lactococcus lactis as an antimicrobial agent

A spoiled canned fish, imported from Scotland, was examined and the spoilage was found to have been caused by a cocci type of bacterium. The bacterium was brought into pure culture, studied for its morphological, cultural and physiological properties and on the basis identified asStreptococcus thermophilus Orla-Jensen. Its ability to cause spoilage was proved by inoculating it into freshly processed fish cans. The strain was resistant to heat up to 205° F. and it failed to grow at 20° C. On its temperature relationships, explanation has been offered for its spoilage under Indian conditions and its inactivity under the conditions obtaining in the country where it was packed.

Studies on the microbial spoilage of canned food

This study aimed to determine the effect of the addition of wheat flour as a potential prebiotic on growth and acidification rate of probiotic Lactobacillus acidophilus (L. acidophilus) in fermented milk. The study was conducted by adding the flour with concentrations 1, 3 and 5% in the fermentation medium with 15% skim milk. Observed growth parameters including the total number of probiotic bacteria, decreasing pH and increasing acidity during the fermentation process. The results showed that the addition of wheat flour speed up the fermentation time, accelerate the process of decline in pH, increasing the acidity and increase the total number of probiotic bacteria.This study shows that wheat flour supplemented in fermented milk could enhance the growth characteristics of probiotics L. acidophilus.

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PENGARUH SUPLEMENTASI TEPUNG TERIGU TERHADAP PERTUMBUHAN DAN LAJU PENGASAMAN PROBIOTIK Lactobacillus acidophilus EFFECT OF THE WHEAT FLOUR SUPPLEMENTATION ON PROBIOTIC Lactobacillus acidophilus GROWTH AND ACIDIFICATION RATE

6. ISE studies of growth phases of Desulfovibrio species of sulphate-reducing bacteria

The inactivation of Escherichia coli by microalloyed aluminium based composite was studied. The composite is material in form of steel wire, plated by microalloyed aluminium. Its effects are based on spontaneous dissolution in contact with water, with generation of Al(III) and OHions, and finally voluminous insoluble Al(OH)3. Bearing in mind its great efficacy in purification of water from many chemical pollutants, efficient inactivation of microbiological pollutant of water - E. coli, was expected, too. The experiments were carried out with the water model-solutions (WMS) based on adapted natural surface water, inoculated by the E. coli. Treatments were performed in the original semi-flow system (SFS). The results show that approximately at every 10 min, the number of E. coli bacteria was reduced for about one log10 count, with complete inactivation as the outcome of the treatment. At the end of the treatment, the Al(OH)3 precipitate still contained the low amount of coprecipitated E. coli bacteria, which died in relatively short period.

/pdf/the-inactivation-of-escherichia-coli-by-microalloyed-2f2uo8mkey.pdf

Fundamental principles of bacteriology

Citations

The development of Lactococcus lactis as an antimicrobial agent

Studies on the microbial spoilage of canned food

PENGARUH SUPLEMENTASI TEPUNG TERIGU TERHADAP PERTUMBUHAN DAN LAJU PENGASAMAN PROBIOTIK Lactobacillus acidophilus EFFECT OF THE WHEAT FLOUR SUPPLEMENTATION ON PROBIOTIC Lactobacillus acidophilus GROWTH AND ACIDIFICATION RATE

6. ISE studies of growth phases of Desulfovibrio species of sulphate-reducing bacteria

The inactivation of escherichia coli by microalloyed aluminium based composite udc 628.161.3 + 546.62

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