Antibiotic Medium N°1 EP/USP | Gentaur

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100 µg
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Antibiotic Medium N°1 EP/USP




Suspend  30.5  grams  of  the medium  in  one  liter  of  distilled  water.  Mix  well  and  dissolve  by  heating  with  frequent  agitation.  Boil  for  one  minute  until  complete  dissolution.  Sterilize  in  autoclave  at  121ºC  for  15  minutes.  The  prepared  medium should be stored at 8-15°C. The color is amber, slightly opalescent.

The  dehydrated  medium  should  be  homogeneous,  free-flowing  and  beige  in  color.  If  there  are  any  physical  changes,  discard the medium.


ANTIBIOTIC  MEDIUM  Nº  1  is  used  for  testing  the  potency  of  antibiotics  through  their  inhibitory  effects  on microorganisms. The cylinder assay plate is based on the diffusions of the antibiotics under test, measuring the size of the inhibition zones of microorganisms.

Peptones,  Yeast  extract  and  Beef  extract  provide  nitrogen,  vitamins,  minerals  and  amino  acids  essential  for  growth.  Bacteriological Agar is the solidifying agent.


Seed Agar is used as an inoculum substrate. It is cooled to 48°C and inoculated accordingly with the specific antibiotics under test. Use 2 ml of the liquid culture to inoculate 100 ml of the Seed Agar. Agitate the mixture gently to produce ahomogeneous distribution and pour 4 ml on each plate of solidified Base Agar (21 ml).

It  is  very  important  that  the  seed  layer  is  evenly  distributed  over  the  entire  surface  of  the  Base  Agar.  Once  the  seed  layer is solid, the cylinders are placed evenly spaced on a 2.5 - 3 mm radius. The standard sample is added as described above. This method is used for testing the potency of bacitracin and penicillin preparations.

Seed Agar is used for the basic layer as well as the seed layer for the assay of chloramphenicol in plates. A medium with a higher pH and the same formula is used for the assay of erythromycin, carbomycin and neomycin: Neomycin Test Agar (Antibiotic Medium Nº 11, Cat. 1528