The NYC (New York City) medium or GC ( Neisseria gonorrhoeae ) medium agar is a type of selective media used for isolating Gonococci and N. meningitidis . [1]
Contents
The NYC (New York City) medium or GC ( Neisseria gonorrhoeae ) medium agar is a type of selective media used for isolating Gonococci and N. meningitidis . [1]
The agar base is composed of: [1]
| Ingredients | Grams per litre |
|---|---|
| Proteose peptone | 15 |
| Corn starch | 1 |
| Glucose | 5 |
| Sodium chloride | 5 |
| Dipotassium hydrogen phosphate | 4 |
| Potassium dihydrogen phosphate | 1 |
| Agar | 20 |
Final pH ( at 25°C) 7.4±0.2
NYC Agar Base was originally developed by Fauer, Weisburd and Wilson [1] [2] [3] 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. [1] [2] This medium is superior to other media generally employed for the isolation of Neisseria species. [1] [4] [5] The transparent nature of the medium helps in studying the colonial types. [6]
Proteose peptone, horse plasma, haemoglobin provide nutrients for the growth of N. gonorrhoeae and N. meningitidis . Phosphate buffers the medium. The selective supplement added contains the antibiotics vancomycin, colistin, nystatin and trimethoprim, to suppress the accompanying flora. Vancomycin is inhibitory for gram-positive bacteria. Colistin inhibits gram negative bacteria, including Pseudomonas species, while Proteus is inhibited by trimethoprim. [7] The combination of trimethoprim and colistin acts synergistically against gram-negative bacilli. [8] 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. [9] 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.
Streak the specimen as soon as possible after it is received in the laboratory. If material is being cultured directly from a swab, proceed as follows: [10]
Typical colonial morphology is as follows: [7]
N. gonorrhoeae may appear as small (0.5–1.0 mm) grayish white to colorless mucoid colonies. N. meningitidis appears as large colorless to bluish-gray mucoid colonies.
Colonies may be selected for Gram-staining, subculturing or other diagnostic procedures.
Neisseria gonorrhoeae, also known as gonococcus (singular) or gonococci (plural), is a species of Gram-negative diplococci bacteria first isolated by Albert Neisser in 1879. An obligate human pathogen, it primarily colonizes the mucosal lining of the urogenital tract; however, it is also capable of adhering to the mucosa of the nose, pharynx, rectum, and conjunctiva. It causes the sexually transmitted genitourinary infection gonorrhea as well as other forms of gonococcal disease including disseminated gonococcemia, septic arthritis, and gonococcal ophthalmia neonatorum.
Neisseria is a large genus of bacteria that colonize the mucosal surfaces of many animals. Of the 11 species that colonize humans, only two are pathogens, N. meningitidis and N. gonorrhoeae.
An agar plate is a Petri dish that contains a growth medium solidified with agar, used to culture microorganisms. Sometimes selective compounds are added to influence growth, such as antibiotics.
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Thayer–Martin agar is a Mueller–Hinton agar with 5% chocolate sheep blood and antibiotics. It is used for culturing and primarily isolating pathogenic Neisseria bacteria, including Neisseria gonorrhoeae and Neisseria meningitidis, as the medium inhibits the growth of most other microorganisms. When growing Neisseria meningitidis, one usually starts with a normally sterile body fluid, so a plain chocolate agar is used. Thayer–Martin agar was initially developed in 1964, with an improved formulation published in 1966.
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Neisseria cinerea is a commensal species grouped with the Gram-negative, oxidase-positive, and catalase-positive diplococci. It was first classified as Micrococcus cinereus by Alexander von Lingelsheim in 1906. Using DNA hybridization, N. cinerea exhibits 50% similarity to Neisseria gonorrhoeae.
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