Biology of T whipplei
T. whipplei is a rod-shaped bacterium that has an unusual trilaminar plasma membrane surrounded by a cell wall. It is Gram-variable (often Gram-positive, but at times can be Gram-negative) and periodic acid–Schiff (PAS)-positive and is in the order of Actinomycetales. It is very slow-growing with a generation time of approximately 18 days and can take 30 days to detect in cultures. It is considered as an obligate parasite as it lacks several essential biosynthetic pathways (16 amino acids pathways are missing or impaired and the genes for tricarboxylic acid cycle are absent); however, some recent evidence indicates that it might actually be a commensal organism. The genome of T. whipplei has several repeated sequences that may be involved in recombination events in regions encoding surface proteins. It is postulated that these surface proteins are important for T. whipplei to evade the immune system. T. whipplei is thought to be transmitted via feces and saliva and is found in wastewaters. T. whipplei has been found in various samples of healthy individuals, including duodenal biopsies, stool samples, dental plaque, and saliva. Though incidence of classic Whipple’s disease is low, carriage of T. whipplei has been found to be widespread in the human population. Varying with the population and environment, 48% to 72% of general populations have antibodies to T. whipplei . T. whipplei has been found in fecal samples of asymptomatic individuals (1.5%–4%) and at-risk populations, such as sewage workers, homeless, and HIV-infected (12%–25%). When saliva samples are positive, stool samples are generally positive also, indicating a higher bacterial load in stool samples, and that the gut is the preferred niche.
