Mesophilic Aeromonas (Aeromonas hydrophila, Aeromonas sobria, Aeromonas caviae) have recently been considered important aetiological agents of human diseases, mainly gastrointestinal infections. Although several findings have pointed out the significance of this group of microorganisms as enteric pathogens and suggested the presence of virulence factors, epidemiological and clinical studies are limited by the difficulty of correctly identifying mesophilic Aeromonas at the species level. SDS-PAGE of radiolabelled total protein profiles and bacterial enzymatic activities were used to type 31 clinical isolates (6 A. hydrophila, 7 A. sobria and 18 A, caviae) from patients with gastroenteritis and from healthy controls. Analysis of SDS-PAGE protein patterns, reinforced by the UPGMA-grouping system (AMBIS software) provided a good characterization of A. caviae strains as a homogeneous group of microorganisms, possessing significant differences from the other two species of mesophilic Aeromonas, in good agreement with biochemical and enzymatic tests. Data obtained in analyzing A. sobria protein profiles clearly showed two groups, with a correlation coefficient (CC) 0.70, which in our experience is a doubtful value for assigning two strains to the same species. Strains biochemically identified as A. hydrophila showed a CC = 0.64, which is equally not acceptable for species assignment. Inter-species comparisen highlighted this heterogeneity, showing two mixed subgroups, both containing strains that were assigned to A, sobria and A, hydrophila species on the basis of biochemical features. The taxonomy of A. hydrophila and A. sobria species should be further investigated because of their relevance in human pathology: SDS-PAGE and computer assisted numerical analysis of their protein profiles might represent a useful tool when supported by other data on virulence factors, epidemiological and clinical conditions.
