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’AN-IDENT’ DISCS

Code: DD0006

To provide a rapid and simple method for presumptive identification of anaerobic gram negative bacteria.

Disc Contents
The set consists of one cartridge of each of the antibiotic discs packed with a desiccant sachet in a securitainer. 1 cartridge. containing 50 discs. `An-ident’ discs should be stored according to the instructions on the container.

Antibiotic levels on the discs are as follows:

The set should be arranged in the dispenser in the above order to coincide with the order given in the identification table. It is primarily designed to allow easy identification of Bacteroides fragilis, the anaerobe species most commonly isolated in the routine hospital laboratory.

Description
`An-ident’ discs provide a rapid and simple method for presumptive identification of anaerobic Gram negative bacteria. They are not suitable for antibiotic susceptibility testing to assess the clinical effectiveness of the various antibiotics.
Sutter and Finegold<sup>1</sup> proposed a method for the identification of Gram negative anaerobic bacilli based on differences in response to a number of antibiotics. Using carefully chosen levels of colistin, erythromycin, kanamycin, neomycin, penicillin and rifampicin with disc diffusion sensitivity testing techniques they showed that these bacteria could be placed fairly consistently into five groups. Other simple biochemical tests and cultural characteristics were used for further identification. In later work summarised by Finegold<sup>2</sup> 5 µg vancomycin discs were substituted for neomycin.
The Oxoid `An-ident’ set makes available these discs in a cartridge presentation suitable for use either in the Oxoid Dispenser or with Oxoid Ejectors. Ejectors can be used independently of the dispenser.

Technique
The technique as recommended by Leigh and Simmons³ is as follows:
An actively growing culture in Thioglycollate Medium CM0173 or Schaedler Broth CM0497 is used as an inoculum. Using a sterile swab, spread the organism uniformly across the surface of a blood agar plate. Alternatively a flood-plate may be prepared from a suspension of several colonies in Thioglycollate Broth.
Discs of each antibiotic are then applied and the plate incubated anaerobically at 35°C for 24-48 hours. The Oxoid Gas Generating Kit provides a convenient way of achieving anaerobiosis and ensuring that adequate levels of CO₂ are present in the anaerobic jar. Strains of Bacteriodes fragilis, Fusobacterium nucleatum, Fusobacterium necrophorum and Fusobacterium varium are used as controls. The diameters of inhibition zones are measured in millimetres; less than 10 mm is considered resistant; equal to or greater than 10 mm considered sensitive.

Quality Control
See under Technique.

References
1 Sutter V. L. and Finegold S. M. (1971) Applied Microbiology 21. 13-20.
2 Finegold S. M. (1977) Paper presented at the IMLS meeting, Liverpool, August 1977.
3 Leigh D. A. and Simmons K. (1977) J. Clin. Path. 30. 991-992.