Question

E. coli is a gram negative organism. S. Epidermidis is a gram positive organism. How could that information help explain your results? This is for an osmotic pressure lab.

E.coli showed the most growth (appeared cloudy) in a 0% NaCl nutrient broth tube. S. Epidermidis also showed the most growth in 0% NaCl, though appeared to have almost no change at all from original nutrient broth tube.

Answer 1

E. coli is Gram negative bacteria and has very thin peptidoglycan cell wall which can not withstand much osmotic pressure. When you put the E. coli in the 0% NaCl solution, as the outside solution is hypotonic, the solvent will start to get inside the E. coli cells and the cells will swell up and gradually burst making the media a bit cloudy.

But for the S. aureus, as it is a Gram positive bacteria, it has very thick peptidoglycan layer which can withstand enough osmotic pressure. So, when the bacteria is grown in the 0% NaCl media, though the media is hypotonic and the solvent get inside the cell, the cells do not burst out. So, the culture media is clear.