Clinical disease spectrum and pathogenic factors associated with Plesiomonas shigelloides infections in humans

Plesiomonas shigelloides is a gram-negative, facultatively anaerobic rod whose appropriate taxonomic position is presently under investigation. The isolation and identification of this microorganism in contaminated specimens (e.g., feces) by a clinical laboratory depend on the screening of gram-negative colonies for oxidase and indole positivity and the appropriate use of selective and differential agars. Plesiomonads have been associated with extraintestinal diseases (bacteremia, meningitis) on rare occasions; they have been recovered sporadically from patients presenting with acute gastroenteritis. Although case reports and epidemiologic data support a role for P. shigelloides in diarrheal disease, laboratory investigations have failed to identify an enteropathogenic mechanism in these bacteria consistently or to reveal an animal model that faithfully reproduces the disease. Moreover, studies with volunteers have failed to establish an etiologic relation between Plesiomonas and bacterial gastroenteritis. An accurate picture of the role of this bacterium in human disease must await future studies.