Overview of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 22

(a) (b)

Cell membrane
Flagellum

DNA

Cytoplasm

Figure 2.6 Schematic representation of E. coli plus a microscope image. (a) Low-
temperature electron micrograph of a cluster of E. coli bacteria, magnified 10,000 times.
Each individual bacterium is oblong-shaped. Source: http://commons.wikimedia.org/
wiki/File:E_coli_at_10000x,_original.jpg . Photo by Eric Erbe, digital colorization by
Christopher Pooley, both of USDA, ARS, EMU. (b) Schematic showing the major structures
of E. coli . (For color version of this figure, the reader is referred to the online version of
this topic.)

waterborne disease and, following a 1-14 day incubation period, it can
result in the more serious typhoid fever, which can be fatal. There are mil-
lions of cases every year, although typhoid occurrence is generally limited
in areas with good sanitation systems. Additionally, Salmonella are known to
be sensitive to chlorine disinfection.

2.2.4. Shigella
These Gram negative, nonmotile and non-spore-forming rod-like bac-
teria can grow with or without oxygen. There are four species— Shigella
dysenteriae , Shigella exneri , Shigella boydii and Shigella sonnei —all of which
can cause severe disease. However, S. sonnei usually results in mild, self-
limiting diarrhea, whereas infection by S. dysenteriae can lead to ulcer-
ation and bloody diarrhea, for which the production of the Shiga toxin
is implicated.
The infectious dose is low at 10-100 cells and the resulting intestinal dis-
ease can be severe, including bacillary dysentery. Shigellosis usually develops
after 24-72 h, with symptoms including abdominal pain, fever and watery
diarrhea. Humans and other higher primates seem to be the only natural
hosts of these bacteria. Approximately 2 million infections occur annually,
resulting in an estimated 600,000 deaths, the majority of which occur in
children under the age of 10 in developing countries.