If humans colonised another planet, would harmful bacteria develop?

Question: If humans colonised another planet, would harmful bacteria develop?
- Keywords:
  bacteria,
  colony,
  develop,
  human,
  planet
Asked by Floopy_TOOD to Kevin, Liz, Beccy, Rosie on 20 Jun 2017.
- anon answered on 20 Jun 2017:
  
  We would probably bring some with us. We all have bacteria in our digestive systems (where we need them!). But some bacteria from my digestive system could get onto something and grow in a way that someone else could get ill if infected. That’s why we should all wash our hands after using the toilet!
- Rosie Fok answered on 20 Jun 2017:
  
  We would take our bacteria with us, and they might already be bacteria there.
- Liz Buckingham-Jeffery answered on 21 Jun 2017:
  
  Interesting question! As Rosie and Christl have said, the first exploring humans will almost certainly take bacteria with them.
  
  Scientists already worry about our activities in space contaminating planets and moons where there may be the possibility of life. I was reading recently that Nasa plan to crash their Cassini spacecraft into Saturn so that it was get destroyed in Saturn’s atmosphere… on purpose! This is so it doesn’t accidentally contaminate other places later on when it runs out of fuel. Super interesting!
  
  Here is the news article I was reading that has more details: https://www.theguardian.com/science/2017/apr/04/nasa-cassini-spacecraft-end-20-year-mission-saturn-moons

Question: If humans colonised another planet, would harmful bacteria develop?