The effects of Lactobacillus Casei Shirota strain on Escherichia coli through quorum sensing

Escherichia Coli

Lactobacillus Casei

• Gram-negative rod-shaped bacteria

Thus believed to communicate witin its species by means of quorum sensing

• lives in the lower gastrointestinal tract of mammals

And certain strains are known to cause diarrhea

• known to thrive outside living hosts, such as proliferating on the edge of hot springs Thus can easily be cultured in vivo

• can be found in cultured drinks such as Yakult and Vitagen

• Lactobacillus Casein Shirota is capable of:

promotion of phagocytises

enhancement of natural killer (NK) cell cytotoxicity

mediating response of helper T-lymphocytes

INTRODUCTION

• regulation of gene expression in response to fluctuations in cell-population density

• Quorum sensing bacteria produce and release chemical signal molecules called auto inducers that increase in concentration as a function of cell density.

Quorum Sensing

Implication

inhibition of specific Escherichia Coli trans-membrane receptors or enzymatic action on the N-acyl homeserine lactone compound

inhibition of E. Coli communication

Figure 1: Test for contamination of Lactobacillus Casein on MRS agar

Clear colonies of Lactobacillus Casein were observed on the MRS agar on all 4 plates of MRS agar. The colonies were smooth, shiny, convex and opaque in appearance. Only one type of colony was observed thus no contamination was involved in the process of culturing Lactobacillus Casein.

Experiment 1: Yakult was streaked upon the solidified mixture of MRS agar and sodium propionate and lithium chloride. Selectively cultured were inoculated and streaked onto fresh MRS agar plates to observe fro contamination.

Figure 1: Test for contamination of Lactobacillus Casein on MRS agar

Results

Experiment 2: The group hypothesize that Yakult could have contained nutrients that aided Lactobacillus Casein in eliminating Escherichia Coli. Thus Yakult was poured into wells in the agar streaked with Escherichia Coli without the isolation of Lactobacillus Casein from the cultured drinks.

Instead of clearing zones that would imply antibacterial activity, cracks were observed in the agar. The cracks connected at least two wells in Petri-dishes 1, 3 and 4. Wells connected to the crack lines were observed to be larger in diameter than the other two wells. This experiment was inconclusive as no antibacterial activity was observed. The Yakult has entirely evaporated during the incubation period. There was thus a very low concentration of Lactobacillus Casein left in the well, resulting in no visible sites of clearing. Some over spill of Yakult could have evaporated and caused cracks to form. The second experiment on Yakult-Escherichia Coli interaction was equally unsuccessful.

Experiment 3: To increase the concentration of Lactobacillus Casein, Lactobacillus Casein was inoculated into LB broth and placed in similar wells that have be created in a fresh plate of LB agar streaked with Escherichia Coli.

No sites of clearing have been observed and no visible antibacterial activity occurred between Lactobacillus Casein and Escherichia Coli. Mould was observed in Petri-dishes 1 and 3 due to contamination. Petri-dishes 2 and 4 despite not having been contaminated did not provide conclusive results either.

Experiment 4: It was hypothesized that the surface area of contact and agar medium could affect the bacterial interaction. Thus another 2 sets of experiments were carried out. Both sets consisted of Lactobacillus Casein streaked on one half of the agar and Escherichia Coli streaked on the other half of the medium. One set was conducted on LB agar and the other was conducted on MRS agar.

This experiment was just as inconclusive as Lactobacillus Casein and Escherichia Coli streaked on each half of the Petri-dish did not appear in distinct colonies after an incubation period of 2 days. The bacteria cultured separately in MRS and LB agar for Lactobacillus Casein and Escherichia Coli respectively which we inoculated from for these sets of experiments could have been deactivated from a long duration in the refrigerator.