Neomycin Blood Agar: Introduction, Principle, Composition, Preparation

Neomycin Blood Agar: Introduction, Principle, Composition, Preparation, Procedure, Colony Morphology, Uses and Keynotes

Introduction of Neomycin Blood Agar

Neomycin Blood Agar is a selective medium used for the isolation of group A ( Streptococcus pyogenes) and B streptococci (Streptococcus agalactiae).

Composition of Neomycin Blood Agar

Typical Formula gm/liter (BBL)

Pancreatic Digest of Casein: 14.5
Papaic Digest of Soybean Meal: 5.0
Sodium Chloride: 5.0
Growth Factors: 1.5
Neomycin: 0.03
Sheep Blood defibrinated: 50 ml
Agar: 14.0 g

Principle of Neomycin Blood Agar

The pancreatic Digest of Casein incorporation of medium supplies nitrogen, vitamins, minerals, and amino acids while the Papaic Digest of Soybean Meal is a rich source of vitamins and carbohydrates of soybean. Sodium Chloride keeps the osmotic balance of the medium. Growth Factors enhance the growth of organisms. Incorporation of neomycin in sheep blood agar enhances the detection of group A (Streptococcus pyogenes)and group B streptococci ( Streptococcus agalactiae) by suppressing the growth of other hemolytic organisms and normal flora. The defibrinated sheep blood provides enrichment for the growth of fastidious organisms. Agar is the solidifying agent.

Preparation of Neomycin Blood Agar

Suspend 30.03 grams in 1 liter of purified/distilled or deionized water.
Heat to boiling to dissolve the medium completely.
Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
After autoclaving, leave for cooling to 45-50°C.
Aseptically add 50 ml of defibrinated sheep blood.
Mix properly it.
Pour medium into each plate and leave plates on the sterile surface until the agar has solidified.
Store the plates in a refrigerator at 2-8°C.

Storage and Shelf life of Yersinia Selective Agar

Store at 2-8ºC and away from direct light.
Media should not be used if there are any signs of deterioration (shrinking, cracking, or discoloration), or contamination.
The product is light and temperature sensitive; protects from light, excessive heat, moisture, and freezing.

Test Requirements

Test specimens ( Clinical sample or growth of bacteria)
Inoculating loop
Bunsen burner
CO₂Incubator
Control strains (Escherichia coli ATCC 25922 and Streptococcus pyogenes ATCC 19615)
Culture Media

Procedure of Neomycin Blood Agar

Allow the plates to warm at 37°C or to room temperature, and the agar surface to dry before inoculating.
Inoculate and streak the specimen as soon as possible after collection.
If the specimen to be cultured is on a swab, roll the swab over a small area of the agar surface.
Streak for isolation with a sterile loop.
Incubate plates aerobically at 35-37ºC for 18-24 hours and 48-72 hours, if necessary.
Examine colonial characteristics.

Colony Morphology of Neomycin Blood Agar

Streptococcus pyogenes– Moderate to heavy growth with translucent or opaque, white to gray, small (1-2 mm) colonies surrounded by a zone of beta hemolysis
Streptococcus agalactiae-Moderate to heavy growth with zones of beta hemolysis
Staphylococcus aureus-Partial inhibition (no growth to fair growth). Maybe beta-hemolytic.
Escherichia coli-Partial inhibition (no growth to trace growth)

Uses of Neomycin Blood Agar

It is used for the isolation of group A streptococci (S. pyogenes) and group B streptococci (S. agalactiae) from clinical samples in which the presence of these organisms is suspected.
Neomycin blood agar is also a selective medium for vancomycin-resistant Enterococcus faecium.

Keynotes on Neomycin Blood Agar

Neomycin inhibits most staphylococci, Enterobacteriaceae, Neisseria , Listeria, and some Pseudomonas species.
Neomycin blood agar is also used as a selective medium for vancomycin-resistant Enterococcus faecium.
Lancefield group A streptococci (Streptococcus pyogenes) and group B streptococci (Streptococcus agalactiae) are medically important gram-positive beta-hemolytic bacteria.
The use of 0.04 units of bacitracin may differentiate S. pyogenes from S. agalactaie.
This Neomycin Blood Agar is less selective than BBL Group A Selective Strep Agar(ssA) for normal throat flora. It is recommended that the ssA medium be used when only group Streptococcus pyogenes is suspected.
Anaerobe Neomycin 5% Sheep Blood Agar is also available for isolation and cultivation of fastidious and slow-growing obligately anaerobic bacteria from a variety of clinical and non-clinical specimens.

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