Gram’s Staining Name:_________

Bacterial cell wall

• Determine …………………. of bacteria

• Strength prevents ………………….………………….

• ………………….of bacteria

• Unique to ………………….

• Some antibiotics effect directly e.g. ………………….

• ………………….…………………. polymer

-amino acids + sugar

• Amino acids cross link sugars

What is Gram’s staining?

The characteristic compound found in all true bacterial cell walls is peptidoglycan.

The ………………….of ………………….…………………. is among one of the differences between the ………………….………………….and ………………….………………….cell walls.

Gram Positive Cell Walls Gram Negative Cell Walls

Salmonella Toxins

Enterotoxin:

• released by microorganism in the lower ………………….………………….

• alters ………………….…………………. of intestinal wall

• water leaks into intestinal tract causing ………………….………………….

Endotoxin:

• Salmonella enters intestinal cells through

………………….………………….

• ………………….…………………. damage the cells from the inside

• cause fever and ………………….…………………. in large amounts

Making Yoghurt Practical Investigation

Background

Yoghurt is produced by curdling milk. The milk is curdled by the addition of lactic acid. Lactic acid can be produced by special strains of bacteria which are added to the milk for this purpose. These bacteria produce lactic acid through fermentation.

The bacteria used in yoghurt making are Streptococcus thermophilus and Lactobacillus bulgaris. S. thermophilus is added first to lower the pH for the acid-loving L. bulgaris to grow. Together the bacteria produce enough acid to curdle the milk.

Method

1. Take a clean pot and label with your name and the date

2. Fill 2/3 of the pot with UHT

3. Dissolve 1 teaspoon of milk powder into the milk

4. Add 1 teaspoon of yoghurt to the milk

5. Test the pH and make a note of it

6. Put the lid on and place in the water bath at 35 degrees C

Results

pH of the milk + starter culture:______________

pH of the yoghurt: ______________

Conclusion:

Using the information above, explain why the pH is different at the beginning of the experiment to the pH at the end of the experiment?