Aeromonas Species in Septicemia: Laboratory Characteristics and Clinical Observations

We retrospectively analyzed clinical and epidemiological data on and laboratory characteristics of 53 cases of aeromonas septicemia. Only four Aeromonas genomospecies (species defined by DNA relatedness) were associated with the 53 cases, with Aeromonas hydrophila (sensu stricto) predominating (47%). Nearly 60% of all Aeromonas isolates from blood fell into one of four somatic groups: serogroups O:11, O:16, O:18, and O:34. Unlike Aeromonas-associated gastroenteritis, septicemia did not peak in frequency during the warmer months but rather was most common in January through March, when approximately 40% of cases occurred. In vitro tests of the pathogenicity of 20 selected blood isolates of Aeromonas indicated that resistance to complement-mediated lysis, elevated levels of protease and hemolysin activity, and the ability to elaborate siderophores correlated with higher virulence. Species and serogroup designations also correlated with the degree of virulence. Susceptibility studies of 50 strains indicated that A. hydrophila was the most drug-resistant species and that Aeromonas veronii was the most susceptible. Susceptibility to first- and second-generation cephalosporins and carbenicillin was species-associated.