Behaviour ofAeromonas species in Cary-Blair transport medium at various temperatures

Abstract

Recently, Siitonen and Mattila (1) reported increased isolation of Aeromonas spp. from Patients with traveller's diarrhea after storage of stool specimens in modified Stuart's transport medium for 1 to 5 days at 4 °C. To investigate this phenomenon they compared the influence on culture results of three different transport mediamodified Stuart's medium, Cary-Blair medium and glycerol buffered saline (GBS) -using one single Aeromonassobria strain. They were able to confirm that modified Stuart's medium and Cary-Blair medium (but not GBS) supported growth and multiplication of the Aeromonas strain even at 4 °C, a fact which might lead to overestimation of the role of aeromonads as intestinal pathogens.Using a different approach we chose to study the same question since we recommend that all stool specimens are sent to our laboratory in agar-free Cary-Blair medium, this medium having been shown to be suitable for transport of these specimens (2). In order to simulate the clinical conditions more accurately, we autoclaved a mixture of ten different stool specimens at 120 *C for 15 rain and prepared a 5 % suspension in Cary-Blair medium. Six different fecal Aeromonas strains [two each of A. hydrophila, A. caviae and A. sobria, as identified using a battery of conventional and commercially available tests (3)] were added separately to aliquots of the stool suspension up to a final concentration of approximately 105 cfu/ml (range 1.3-3.5 x 105 cfu/ml). Tubes were incubated at 4 °C, 25 °C and 37 °C, respectively, for 20 days. The number of viable organisms was determined by subculturing serial dilutions on blood agar containing 5 % human blood immediately after inoculation and after 1,3, 6, 14 and 20 days, respectively. All colony counts were adjusted to an initial inoculum of 105 cfu/ml. At both 25 °C and 37 °C all six strains behaved very similarly (data not shown). After incubation for one day, colony counts increased by at least a hundredfold indicating that the conditions were very favourable for growth. This initial increase was followed by a slight decrease in viable organisms, after 20 days the count for each single strain still being at least tenfold higher than just after inoculation.The behaviour of the six strains was very different at 4 °C ( Figure 1). An initial drop in the colony count for all strains during the first 24 hours (by a factor of 10 or more) was followed by a rapid increase only for the two Aeromonas hydrophila strains. The two Aeromonas sobria strains exhibited constant counts for several days followed by a slow increase which, in one strain, resulted in a final number of viable organisms comparable to that of Aeromonas hydrophila (almost 107 or-

Aeromonas allosaccharophila sp. nov., a new mesophilic member of the genus Aeromonas

“…motile aeromonads are ubiquitous inhabitants of freshwater and estuarine environments that have been implicated in the aetiology of a variety of systemic and localized diseases in different mammals, reptiles, fish and humans [1][2][3][4][5][6][7]. motile aeromonads are ubiquitous inhabitants of freshwater and estuarine environments that have been implicated in the aetiology of a variety of systemic and localized diseases in different mammals, reptiles, fish and humans [1][2][3][4][5][6][7].…”

“…motile aeromonads are ubiquitous inhabitants of freshwater and estuarine environments that have been implicated in the aetiology of a variety of systemic and localized diseases in different mammals, reptiles, fish and humans [1][2][3][4][5][6][7]. The taxonomy of motile Aeromonas remains ,.onfused because discordances have been obsereed between groupings obtained by DNA/ DNA hybridization and by phenotypic analysis [6,7,9]. All are facuitative anaerobes and chemoorganotrophs.…”