What is commensal bacterium?
It’s a bacterium that lives in the body without causing disease during normal conditions. If the host defences are damaged, then an opportunistic infection can occur. This is likely to occur in patients undergoing chemotherapy, using high doese of antibiotics and in those with diseases such as AIDS that damage the immune system. So, it will not usually cause illness in the host, but can act as an opportunistic pathogen. There is some evidence that the presence of commensal bacteria, fungi etc. protects against infection with disease-causing organisms.
