GAIRANOD, Princess Jeanne R.
BS Biology, 2011 – 37638
Synthesis Paper: Shigella flexneri
The genus Shigella includes four different species – Shigella boydii, Shigella dysenteriae, Shigella sonnei, and Shigella flexneri. Several serotypes occur for each species based on O - antigen variations (Jennison & Verma, 2004; Morona, et al., 1995). Members of the genus are gram-negative, highly infective facultative intracellular pathogens, recognized as etiological agents of bacillary dysentery (shigellosis) (Kotloff, et al., 1999; Sansonetti, 2001). Shigella ranks third among the most common causes of bacterial gastroenteritis in the United States, following Salmonella, and Campylobacter, respectively (Gupta, et al., 2004).
Taxonomy
Shigella flexneri
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It is estimated that there are about 164.7 million cases of this bacillary dysentery around the world annually. More than half of this number is believed to occur in developing countries. Further, records of occurrences of Shigellosis in these countries found S. flexneri to be the most pre-dominant cause of shigellosis (Kotloff, et al., 1999).
Shigella spp. are obligate human pathogens and do not infect other hosts. Transmission is often by the fecal-oral route. Hence, food and water sources may be contaminated through improper hygiene and sanitary practices (Kotloff, et al., 1999). In fact, dysentery epidemics have been linked with poor housing and sanitary facilities brought about by the displacement of communities due to wars and natural calamities (Gillespie & Hawkey,
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Entry of S. flexneri at the basolateral surface is dependent on the bacteria’s ability to colonize the intestinal epithelium by the exploitation of epithelial-cell functions, and circumvention of the host immune response (Ashida, et al., 2009). Primarily, this is accomplished through the action of invasion plasmid antigens B and C (ipa B and ipaC). IpaC functions to reorganize cellular cytoskeletal elements leading to membrane ruffling upon contact with the epithelial cell. Acting with ipaB, it forms a channel through which T3SS- secreted effector proteins are translocated into the epithelial cell (Blocker, et al., 2001). The reason for the preferential entry of S. flexneri through the basolateral membrane remains unknown (Jennison & Verma,