New York City (NYC) Medium is primarily designed for isolation of pathogenic Neisseria. It also supports the growth of genital mycoplasmas (Mycoplasma hominis and Ureaplasma urealyticum). New York City (NYC) medium is useful in the diagnosis of gonorrhea and in the recognition of active or asymptomatic mycoplasma infections. It is a transparent medium.
Principle and Interpretation
NYC Agar Base was originally developed by Fauer, Weisburd and Wilson at the New York City Department of Health for selective isolation of pathogenic Neisseria species from clinical specimens.
It consists of primarily a peptone-corn starch agar- base buffered with phosphates and supplemented with horse plasma, horse haemoglobin, dextrose, yeast autolysate and antibiotics. The transparent nature of the medium helps in studying the colonial types.
- Proteose peptone, horse plasma, haemoglobin provide nutrients for the growth of N. gonorrhoeae and N. meningitides.
- Phosphate buffers the medium.
- The selective supplement added contains the antibiotics vancomycin (to inhibit gram positive bacteria), colistin (to inhibit gram negative bacilli), nystatin (to inhibit yeast) and trimethoprim. Colistin inhibits gram negative bacteria, including Pseudomonas species, while Proteus is inhibited by trimethoprim. The combination of trimethoprim and colistin acts synergistically against gram-negative bacilli.
- Starch neutralizes the toxic metabolites produced by Neisseria.
- The yeast autolysate supplement fulfils the CO2 requirements needed to enhance Neisseria growth. Yeast contains oxaloacetic acid which is metabolized by gonococci to produce sufficient CO2 for growth of capnophilic gonococci. Also, presence of yeast autolysate reduces the lag phase of growth of Neisseria, thus enhancing both size and number of colonies.
The specimen can be directly streaked on the medium to obtain maximum isolation.
Composition of New York City Medium Agar Base
|Ingredients||Gms / Litre|
|Dipotassium hydrogen phosphate||4.0|
|Potassium dihydrogen phosphate||1.0|
Final pH ( at 25°C) 7.4±0.2
Procedure for the preparation of New York City Medium
- Suspend 25.50 grams in 320 ml distilled water.
- Heat to boiling to dissolve the medium completely.
- Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Avoid overheating.
- Cool to 45-50°C and add aseptically 100 ml of sedimented horse blood cells and 60 ml of citrated horse plasma along with rehydrated contents of 1 vial of NYC Supplement and 1 vial of Yeast Autolysate Supplement.
- Mix well and pour into sterile Petri plates.
Limitation and recommendation
- Some strains of N. gonorrhoeae are inhibited by the concentration of vancomycin in the selective media, so the addition of nonselective chocolate agar is recommended, especially in suspect cases that are culture negative or for sterile specimens (e.g. joint fluid)