Enterococcus Confirmatory HiCynth™ Agar

Principle And Interpretation

Enterococcus Confirmatory Agar formulated by Sandholzer and Winter (5) is used for the detection of Enterococci in water supplies, swimming pools, sewage etc. Enterococci are found as normal flora in the gastrointestinal tracts of humans and animals. They are becoming increasingly important agents of human diseases largely because of their resistance to antimicrobial agents to which other Streptococci are generally susceptible (2). The Enterococcus is a subgroup of the fecal Streptococci group that includes Enterococcus faecalis, Enterococcus faecium, Enterococcus gallinarum, and Enterococcus avium (1). Enterococci are differentiated from other Streptococci by their ability to grow in 6.5% sodium chloride, at pH 9.6 and at 10°C and 45°C (1).

The ability of organisms to grow in the presence of variable amounts of sodium chloride is a test that has been used to characterize several bacteria, including the viridans Streptococci. It is useful for presumptive identification of the Entercoccal group D organisms which have the specific ability to grow in the presence of 6.5% NaCl incorporated into the medium. A positive test is the presence of bacterial growth in the medium. If the organism is bile esculin positive and grows in 6.5% NaCl broth, the organism is an Enterococcus species and if the organism is bile esculin positive and fails to grow in the 6.5%NaCl broth, the organism belongs to a group D Streptococci. The enterococcal portion of the faecal Streptococcus group is a valuable bacterial indicator for determining the extent of faecal contamination of recreational surface waters (1).

Enterococcus Confirmatory HiCynth™ Agar is prepared by replacing animal and vegetable peptones with chemically defined peptones to avoid BSE/TSE risks associated with animal peptones.

HiCynth™ Peptone No.4, HiCynth™ Peptone No.5, dextrose providecarbonaceous, nitrogenous compounds, long chain amino acids, vitamins and other essential growth nutrients for the growth of Enterococci. Sodium azide inhibits other contaminating flora. The positive presumptive tests are confirmed by inoculating from Enterococcus Presumptive Broth (M419) to Enterococcus Confirmatory slant-broth combination prepared with an Azide Agar medium (Enterococcus Confirmatory HiCynth™ Agar, MCD392) overlaid with a Salt Azide Penicillin Broth (Enterococcus Confirmatory Broth, M394). A negative catalase test is considered confirmed positive evidence of the presence of Enterococci. Single strength medium can be used for small inoculum. Production of acid and turbidity in an azide presumptive broth when incubated at 45°C is considered positive presumptive evidence for the presence of Enterococci, which is confirmed by inoculating on Confirmatory Agar (MCD392).