Base media and selective supplement for the isolation of Aeromonas spp.

Typical formula  g/l

Tryptone	15.00
Soy peptone	5.00
Sodium chloride	5.00
DNA	2.00
Maize starch	10.00
Agar	15.00

pH: 8.0 +/- 0.2

Suspend 18.35g of m-Aeromonas Selective Agar Base or 26g of Aeromonas Starch DNA Agar Base in 500 ml of cold distilled water. Heat to boiling with frequent agitation and sterilise by autoclaving at 121°C for 15 minutes. Cool to approximately 50°C and, under aseptic conditions, add the contents of one vial of Aeromonas Selective Supplement-Ampicillin reconstituted with 5ml of sterile distilled water. Mix well and distribute Aeromonas Selective Agar into sterile 55mm dishes, and Aeromonas Starch DNA Agar into 90 mm Petri dishes.

The significance of Aeromonas species as human pathogens is getting increasing attention (Holmberg and Farmer); many investigators have reported that the aquatic environment can be considered the biggest source of infection, Buchanan and Palumbo implicated Aermonas as potential food-poisoning agent. m-Aeromonas Selective Agar Base supplemented with ampicillin, corresponds to the medium described by Havelaar, During and Versteegh. It is used for the detection of Aeromonas in water and other liquid samples by means of a membrane filtration procedure. Appropriate volumes or decimal dilutions of the samples are filtered using membrane filters 0.45μm pore size, and the filters are transferred onto the plates. After 24 hours of incubation at 30°C in aerobic conditions, Aeromonas colonies show a visible yellow colour (dextrin fermentation). The detection of dextrin fermentation is considered by Havelaar to be highly specific and until now no dextrin negative Aeromonas strains have been found. Confirm the presumptive detection with standard biochemical tests. The use of ampicillin suppresses adequately the background flora without having any decrease in the Aeromonas recovery. Strains sensitive to 10 mg/l of ampicillin appear to occur at a frequency of 1% or less (Havelaar et al.).

Aeromonas Starch DNA Agar is a modification of Palumbo's et al. formulation and consists of Tryptone Soy Agar, starch, DNA and ampicillin. The complete medium allows the selective growth of Aeromonas spp. and the presumptive differentiation of A. hydrophila by means of DNA and starch hydrolysis. Aeromonas Starch DNA Agar is useful for the isolation and enumeration of Aeromonas spp. from food and clinical samples. The undiluted or diluted sample is surface plated and incubated at 30oC _{^{for 24 hours in aerobic conditions. After incubation, check for a clearing halo around the colonies (starch hydrolysis).}}

_{Pick suspected colonies up for further biochemical tests. Flood the plates with HCl 1N solution. If the colonies are DNAse positive, a new clearing halo occurs on an opaque background. Amylase positive and DNAse positive cultures must be subjected to biochemical characterisation for a complete identification.}

_{^{User quality assurance (30°C-24 hrs)}}

_{^{A.hydrophila ATCC 7965: good growth}}

_{^{E.coli ATCC 25922: inhibited}}

_{^{Dehydrated media: 15-30°C}}

_{^{User prepared plates: up to 7 days at 2-8°C}}

_{^{• Buchanan, R.L., Palumbo, S.A. (1985) J. Food Saf. 7, 15-29}}

_{^{• Havelaar, A.H., During, M., Versteegh, J.F.M. (1987) J. App. Bact. 62, 279-287}}

_{^{• Holmberg, S.C., Farmer, J.J. (1984) Rev. Inf. Dis. 6, 633-639}}

_{^{• Palumbo, S.A. et al. (1985) App. Environ. Microbiol. 50, 1027- 1030}}