'Leaven' in the Bible

Another simile spake he to them: 'The reign of the heavens is like to leaven, which a woman having taken, hid in three measures of meal, till the whole was leavened.'

and Jesus said to them, 'Beware, and take heed of the leaven of the Pharisees and Sadducees;'

how do ye not understand that I did not speak to you of bread -- to take heed of the leaven of the Pharisees and Sadducees?'

Then they understood that he did not say to take heed of the leaven of the bread, but of the teaching, of the Pharisees and Sadducees.