My father has developed bacterial infections. what is it exactly?

Many different ones: Most bacterial infections will respond to antibiotics. But you have asked a very broad questions, bacterial infections can occur any where in our body.

Complicated: Bacteria are microscopic living things which can invade human beings and create inflammation. This is called infection. The types of bacteria involved and the areas of the body affected will vary greatly and if you have more information we can answer your question better.