Furunculosis Agar

Principle And Interpretation

Aeromonas are ubiquitous inhabitants of natural waters, both fresh and salt where they infect animals, including amphibians, reptiles and fish. In human, they are most commonly associated with infections of wounds acquired near or in water, or with diarrhoeal diseases. The fish pathogen Aeromonas salmonicida prefers temperature of 23°C for their growth, thus it is least likely to cause human infections. A.salmonicida is the causative agent of furunculosis (1), a disease of major significance in the culture of salmonid fish (2). The disease represents a serious problem to farming of Atlantic salmon and causes extensive economic losses to freshwater hatcheries and sea farms. The absence of an efficient selective medium and the poor plating efficiency of the organism in mixed cultures (3) have hampered the development of an efficient diagnostic test for Aeromonas salmonicida and, consequently, the control of furunculosis in salmonid culture. Furunculosis Agar is formulated as per Griffin et al (4) for detection of Aeromonas salmonicida (salmonids-furunculosis) on the basis of production of brownish red pigment.

The medium contains casein enzymic hydrolysate; tyrosine and yeast extract which are sources of carbon, nitrogen, vitamins and minerals. Sodium chloride provides essential ions. Brownish red pigmentation of the colonies in the medium within two to three days of incubation at 22°C is positive presumptive evidence. For the more rapid presumptive test, 0.5 ml of 1% aqueous solution of paraphenylenediamine can be applied to the colonies of a 24 hours old culture growing on the surface of the agar slants. Contact the reagent with all the growth. After application of the reagent, the tubes should be tipped and rotated to spread the reagent to cover the growth on slant, a deep purple colour is seen within 45 to 90 seconds.