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These discs are used in qualitative susceptibility testing procedures in culture media. They serve as a convenient method for addition of antimicrobial agents to culture media, especially for qualitative studies of mycobacteria and related organisms.

Certain susceptibility test discs, i.e., streptomycin, 10 µg, kanamycin, 30 µg and rifampin, 5 µg, are also recommended for use in this procedure.^1,2

The discs are added to measured amounts of liquified agar medium, e.g., Middlebrook and Cohn 7H10 Agar or Seven H11 Agar, to prepare recommended concentrations of the antimicrobial agent in solidified agar.²

Falcon™ four compartment X Plate™ Petri dishes may be used with these discs. Three sections may be employed for various agents or differing concentrations of the same agent and the fourth section as a drug-free control.

Since 1882 when Koch showed that the tubercle bacillus was the cause of tuberculosis, a variety of media and methods have been investigated in an effort to reduce the time required for isolation and drug susceptibility testing.

Acid-fast bacilli from human specimens demonstrated by microscopic examination or culture are usually Mycobacterium tuberculosis; however, other pathogenic and possibly nonpathogenic acid-fast organisms may be found. These "atypical" or "unclassified" mycobacteria must be recognized and characterized in the laboratory because the prognosis and response to drug therapy differ greatly for disease caused by these organisms.

This disc susceptibility method employing discs in culture media has been shown to be a valuable and reliable tool for many laboratories.^3-5 The simplicity of preparation of disc medium, the convenience and economy of preparing any number of test plates, the stability of drugs in dry discs, the elimination of possible errors in diluting and measuring drug solutions and the immediate recognition of the drug and concentration present in each medium by means of coded discs make this a desirable technique. Only one medium is prepared; the different drugs and their concentrations are provided by the discs.

Check drug-free medium for performance by inoculation with pure cultures of stable control strains of mycobacteria producing known, desired reactions. A drug-susceptible strain of M. tuberculosis is satisfactory as a control to demonstrate the activity of drugs in the media used.²

Quality control requirements must be performed in accordance with applicable local, state and/or federal regulations or accreditation requirements and your laboratory's standard Quality Control procedures. It is recommended that the user refer to pertinent NCCLS guidance and CLIA regulations for appropriate Quality Control practices.

Sensi-Disc brand discs are prepared by impregnating high quality absorbent paper with accurately determined amounts of antimicrobial agents. Discs are clearly marked on both sides with letters and numbers designating the agent and the drug content. Sensi-Disc agents are furnished in cartridges containing 50 discs each. The last disc in each cartridge is marked "X" and contains the drug as coded. The cartridges are for use in Single Disc Dispensers.

For in vitro Diagnostic Use.

Observe aseptic techniques and established precautions against microbiological hazards throughout all procedures.^1,6 Perform all manipulations in a biological safety cabinet. Sterilize cultures, containers and other contaminated materials after use.

Biosafety Level 2 practices and procedures, containment equipment and facilities are required for non-aerosol-producing manipulations of clinical specimens such as preparation of acid-fast smears. All aerosol-generating activities must be conducted in a Class I or II biological safety cabinet. Biosafety Level 3 practices, containment equipment and facilities are required for laboratory activities in the propagation and manipulation of cultures of M. tuberculosis and M. bovis. Animal studies also require special procedures.⁶