Elastolytic activity among Aeromonas spp. Using a modified bilayer plate assay.
A total of 166 isolates of Aeromonas, representing diverse geographical regions and originating from various sources, were evaluated for the ability to produce elastase by using a bilayer elastin agar medium (BEAM) plate assay. The degree of elastase activity of individual strains was roughly assessed by measuring the clear area beneath or peripheral to the colony and recorded as 1+, 2+, or 3+. Of the 166 aeromonads tested, 53 (32%) were found to produce elastase, of which 26 (49%) were 3+, 21 (40%) were 2+, and 6 (11%) were 1+. All but one A. hydrophila (n = 45) were observed to produce elastase (98%). One of three A. schubertii strains as well as one isolate of Aeromonas group 501 were elastase positive. All 3+ elastolytic activity was associated with A. hydrophila only. Elastase activity was not detected even after prolonged incubation with A. veronii biogroup sobria (n = 26), A. caviae (n = 57), A. veronii biogroup veronii (n = 4), A. media (n = 1), and A. eucrenophila (n = 1). In addition to its value as a reliable indicator of elastase production for eventual use in virulence assays, we have found that the detection of elastase using the BEAM plate serves as a very useful phenotypic marker for the major, clinically important Aeromonas spp.