Structural and pathogenic properties of Aeromonas schubertii

We investigated the phenotypic, structural, and pathogenic properties of 11 Aeromonas schubertii strains recovered from extraintestinal sites. Most A. schubertii strains were autoagglutination positive, possessed a high surface charge but low hydrophobicity, and fell into one or two biogroups on the basis of carbon substrate utilization patterns. Fatty acid methyl ester analysis of A. schubertii revealed this species to contain a relatively high percentage of branched fatty acids (i-13:0, i-15:0, i-17:1, i-17:0) compared with A. hydrophila. Immunologic and biochemical analysis of the lipopolysaccharides of A. schubertii strains allowed for two groups to be distinguished, namely, (i) a collection of six strains belonging to serogroup O:11 that possessed a characteristic homogeneous O polysaccharide side chain profile by silver staining and immunoblotting techniques and (ii) a second antigenically diverse group (five strains) that either exhibited a heterogeneous side chain profile or were side chain deficient. A, schubertii O:11 strains were all found to contain a 55-kDa major protein associated with the outer membrane fraction which was glycine-hydrochloride extractable; non-O:11 strains did not harbor a similar protein molecule. Screening of A. schubertii strains for reputed virulence factors indicated (i) that slightly more than half of the isolates produce an apparent contact-dependent hemolysin that is not cell associated or released extracellularly, (ii) a potent cytotoxin active against HEp-2 cells that is devoid of hemolytic activity, and (iii) lack of enterotoxigeniclike activity as determined by suckling mouse assays. All A. schubertii strains were pathogenic for mice as determined by 50% lethal dose assays, although no single factor correlated with mouse pathogenicity.