Loss of any of these determinants may result in reduced virulence, but not necessarily. Mutations which result in avirulence are often pleiotropic in nature, often mapping to a gene involved in the regulation of multiple virulence factors. This has implications for disease eradication. A facultative pathogen is one that can grow or survive in the environment as well as its host. Facultative intracellular pathogens can grow both inside and outside of cells and can be cultured on an agar surface in the laboratory.
Normal flora can protect the host, but in some cases, can also cause disease.
Saprophytes Zoonosis B. Entry 1. However, many pathogens can cause disease without leaving the mucosal surface. The acid pH of the stomach is a very effective disinfectant. The lungs are protected by the action of cilia. The intestine is constantly moving by peristalis.