**4. Diseases with established correlation to the gut microbiota**

Necrotizing enterocolitis (NEC) (Wang et al 2009) and inflammatory bowels disease (IBD) (Frank et al 2007, Nell et al 2010) are two diseases that have a recognized established link to the gut microbiota.

NEC is a severe disease affecting preterm infants with a high mortality. About 10% of infants with a birth weight below 1500 g develop NEC, with mortality rate is as high as 30%. It has been suggested that this disease is associated with a reduced diversity of the gut microbiota (Wang et al 2009). Both due to the impact of the test, and because the preterm infant gut microbiota is relatively simple, NEC is an attractive target for developing a human gut microbiota test.

IBD represents a collection of diseases associated with gut inflammation. It has two main sub forms: Crohn's Disease (CD) and Ulcerative colitis (UC). Disturbance of the normally stable GI microbiota are predicted to adversely affect the health of the host (Frank, et al., 2007). Studies of experimental animal models of IBD reveal that germ-free animals show few signs of inflammation; experimental colitis is exhibited only when the animal is exposed to natural microbial communities. Likewise human studies have shown a response of IBD patients to antibiotic and probiotic treatment (Hecht, 2008). In CD patients inflammation most commonly appears in the gut locations where bacterial concentrations are high. Furthermore, diversion of the fecal stream from the lumen is associated with improvement of the inflammation, indicating a role for bacteria in the IBD pathogenesis (Baker, Love, & Ferguson, 2009). Taken together, there are relatively good evidence for a correlation between IBD and the gut microbiota.
