Pathogenic analysis of Aeromonas hydrophila septicemia

Aeromonas hydrophila has emerged as a potential pathogen in the immunocompromised host. Various aeromonal infections, including septicemia, have also been reported in apparently healthy individuals. For years, researchers have disagreed over the epidemiologic roles of aeromonads in gastroenteritis. Isolation rates of aeromonads by stool culture among patients with gastroenteritis are not consistently high. Carriers of this bacterium also exist. The septicemic course is, however, often fulminant and fatal, and may lack an obvious focus. Pathogenic mechanisms are complex and largely unresolved. The objective of this study is to report the necropsy findings from a uremic patient who presented with typical aeromonal septicemia of obscure origin asking if such investigation could give insight into some of the questions mentioned previously. Western blot immunostaining for aerolysin (beta-hemolysin of aeromonads) was used to evaluate whether or not such a virulence factor is involved in the process of septic dissemination. The autopsy showed that the skin and liver contained microabscesses. The upper gastrointestinal mucosae and spleen contain patchy putrefactive lesions with adjacent focal hemorrhage. Perimortem blood cultures grew Aeromonas hydrophila. A conventional Western blot analysis of the culture supernatant failed to show aerolysin. A control Aeromonas sobia American Type Culture Collection (ATCC) strain produces readily detectable aerolysin. It is concluded that this isolate may be aerolysin-deficient or one secreting low levels of aerolysin; these would require more sensitive methods of detection. The primary focus of infection might be the upper gastrointestinal tract. Other virulence factors including the bacterial proteases and/or phospholipases might be responsible for the pathogenesis of septic dissemination.