Under certain circumstances these bacteria are dangerous, because infections are difficult to treat with antibiotics. Two major problems are posed by methicillin resistant Staphylococcus aureus (MRSA), and certain intestinal bacteria which produce extended-spectrum beta-lactamases (ESBL). Even the strictest precautions against these bacteria are often not 100 percent successful, because these pathogens are found not only in humans and animals but also on walls and even in the air of the stable. In a previous study, researchers at the University of Bonn found MRSA on every fifth pig, and an ESBL rate of 30 percent.