Maximum growth temperature ranges of Aeromonas Spp. isolated from clinical or environmental sources

Only a limited number of phenotypic tests are available for the differentiation of all 13 known hybridization groups (HG) of Aeromonas spp. These organisms have a wide spectrum of warm-blooded and cold-blooded hosts. In the present study, the maximum growth temperatures (tmax) of the most common HGs of Aeromonas spp. originating from human fecal samples, food, water, and healthy and diseased fish were determined with a plate-type continuous temperature-gradient incubator. We observed that determination of the tmax can be applied for differentiation of HG 1 from HG 2 and 3 (phenospecies A. hydrophila); HG 6 from HG 4, 5A, and 5B (phenospecies A. caviae); HG 7 from HG 8/10 (phenospecies A. sobria); and HG 11 from HG 8/10 (phenospecies A. veronii). HG 1, 4, 8/10, and 13 strains occurring also in human clinical samples had a high tmax, about 40°C or higher. Hybridization group 2, 3, 5A, and 5B strains, which in most cases originated from water or food, had tmax values in the range of about 36-39°C, while HG 6, 7, and 11 had tmax values in the range of about 33-37°C. Fish pathogenic strains of A. salmonicida subsp. salmonicida and subsp. achromogenes had the lowest tmax values from about 30 to 35°C.