The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, and some are beneficial. However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, and bubonic plague.he word bacteria is the plural of the New Latin bacterium, which is the latinisation of the Greek βακτήριον (bakterion), the diminutive of βακτηρία (bakteria), meaning staff, cane, because the first ones to be discovered were rod-shaped.