Oxacillin Resistance Screening Agar Base (ORSAB) is a new medium that uses aniline blue to detect mannitol fermentation in Staphylococci.

Thermo Scientific's development of ORSAB has been founded on the latest published research on growth requirements of Staphylococci. The result is a medium that contains an optimum salt level for growth of strains sensitive to high salt levels with oxacillin and polymixin B added in a supplement to select for resistant strains. Analine blue is added to indicate mannitol fermentation.

The intense blue colour of MRSA colonies on ORSAB allows rapid visual isolation of individual colonies, even if present in only low numbers on the medium. This is of particular significance when a large number of plates are examined as part of an epidemiological screening programme.

In a clinical evaluation conducted jointly by personnel from Thermo Scientific and the Public Health Laboratory at the University Hospital of Wales, ORSAB recovered a greater number of MRSA isolates from clinical samples after 48 hours incubation in a direct comparison with two Mannitol Salt Agar (MSA) media.

ORSAB also isolated more strains after 24 and 48 hours incubation from an MRSA panel, compared with MSA. The results of this evaluation are available as a poster, if you would like to receive a copy please contact Carlene Simmons, details below.