Bugs starved of nutrition during infection become resistant to nearly every type of antibiotics, even if they are exposed to some of them for the first time.
http://ummid.com/news/2011/November/20.11.2011/bugs_resistent_to_antibiotics.htm
http://ummid.com/news/2011/November/20.11.2011/bugs_resistent_to_antibiotics.htm