Columbia Nalidixic Acid (CNA) agar is a

growth medium A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation or small plants like the moss ''Physcomitrella patens''. Differe ...

used for the isolation and cultivation of

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

from clinical and non-clinical specimens. CNA agar contains antibiotics (

nalidixic acid Nalidixic acid (tradenames Nevigramon, NegGram, Wintomylon and WIN 18,320) is the first of the synthetic quinolone antibiotics. In a technical sense, it is a naphthyridone, not a quinolone: its ring structure is a 1,8-naphthyridine nucleus that ...

and

colistin Colistin, also known as polymyxin E, is an antibiotic medication used as a last-resort treatment for multidrug-resistant Gram-negative infections including pneumonia. These may involve bacteria such as ''Pseudomonas aeruginosa'', ''Klebsiella ...

) that inhibit Gram-negative organisms, aiding in the selective isolation of

Gram-positive bacteria In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain ...

. Gram-positive organisms that grow on the media can be differentiated on the basis of

hemolysis Hemolysis or haemolysis (), also known by #Nomenclature, several other names, is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may ...

Uses

CNA agar is commonly used in clinical microbiology laboratories to isolate pathogenic Gram-positive bacteria such as ''

Staphylococcus ''Staphylococcus'', from Ancient Greek σταφυλή (''staphulḗ''), meaning "bunch of grapes", and (''kókkos''), meaning "kernel" or " Kermes", is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillale ...

'', ''

Enterococcus ''Enterococcus'' is a large genus of lactic acid bacteria of the phylum Bacillota. Enterococci are Gram-positive cocci that often occur in pairs ( diplococci) or short chains, and are difficult to distinguish from streptococci on physical ch ...

'', ''

Streptococcus ''Streptococcus'' is a genus of gram-positive spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs along a sing ...

'', ''diphtheroids'', and ''

Listeria ''Listeria'' is a genus of bacteria that acts as an intracellular parasite in mammals. As of 2024, 28 species have been identified. The genus is named in honour of the British pioneer of sterile surgery Joseph Lister. ''Listeria'' species ...

'' from clinical specimens. A common use for CNA agar is commonly used for the detection of ''

Streptococcus agalactiae ''Streptococcus agalactiae'' (also known as group B streptococcus or GBS) is a gram-positive coccus (round bacterium) with a tendency to form chains (as reflected by the genus name ''Streptococcus''). It is a beta-hemolytic, catalase-negative, an ...

'' carriage in pregnant women. It is also effective for the isolation of Gram-positive anaerobes when incubated under anaerobic conditions. CNA agar is supplemented with sheep blood to facilitate the growth of more fastidious Gram-positive organisms such as

and

. The sheep blood allows for the presumptive identification of some species of bacteria on the basis of hemolysis. Beta hemolytic organisms such as ''

Staphylococcus aureus ''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often posi ...

'' and ''

Streptococcus pyogenes ''Streptococcus pyogenes'' is a species of Gram-positive, aerotolerant bacteria in the genus '' Streptococcus''. These bacteria are extracellular, and made up of non-motile and non-sporing cocci (round cells) that tend to link in chains. They ...

'' will produce colonies surrounded with a clear zone. Alpha hemolytic organisms such as ''

Streptococcus pneumoniae ''Streptococcus pneumoniae'', or pneumococcus, is a Gram-positive, spherical bacteria, hemolysis (microbiology), alpha-hemolytic member of the genus ''Streptococcus''. ''S. pneumoniae'' cells are usually found in pairs (diplococci) and do not f ...

'' and viridans streptococci will produce colonies surrounded by a light to dark green zone. Although CNA agar is formulated to select for Gram-positive bacteria, microbiologists working with this media should be aware of its limitations. Gram-negative rods that are resistant to

quinolones Quinolone may refer to: * 2-Quinolone * 4-Quinolone * Quinolone antibiotic Quinolone antibiotics constitute a large group of broad-spectrum bacteriocidals that share a bicyclic core structure related to the substance 4-quinolone. They ar ...

and polymyxins may grow on the media. Additionally, ''Candida'' and other molds are not inhibited by the antibiotics. Gram-positive aerobic spore forming bacteria such as ''

Bacillus ''Bacillus'', from Latin "bacillus", meaning "little staff, wand", is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum ''Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-sh ...

'' are also usually inhibited by the media.

The addition of peptones into the agar provides the growth factors required by the bacteria to grow. Casein also provides a source of amino acids for organisms with fastidious growth requirements such as ''Lactobacillus brevis''. It contains the antibiotics colistin and nalidixic acid which inhibit the growth of many gram-negative bacteria.

Composition

Source: * Casein peptone - 12.0 g * Meat peptone - 5.0 g *

Sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...

- 5.0 g *

Beef extract Meat extract is highly concentrated meat stock, usually made from beef or chicken. It is used to add meat flavor in cooking, and to make broth for soups and other liquid-based foods. Meat extract was invented by Baron Justus von Liebig, a Germa ...

- 3.0 g *

Yeast extract Yeast extracts consist of the cell contents of yeast without the cell walls; they are used as food additives or flavorings, or as nutrients for bacterial culture Growing media, media. They are often used to create savoury flavors and umami tast ...

3.0 g *

Corn starch Cornflour, cornstarch, maize starch, or corn starch (American English) is the starch derived from corn (maize) grain. The starch is obtained from the endosperm of the seed, kernel. Corn starch is a common food ingredient, often used to thick ...

1.0 g *

Colistin Colistin, also known as polymyxin E, is an antibiotic medication used as a last-resort treatment for multidrug-resistant Gram-negative infections including pneumonia. These may involve bacteria such as ''Pseudomonas aeruginosa'', ''Klebsiella ...

- 10.0 mg *

Nalidixic acid Nalidixic acid (tradenames Nevigramon, NegGram, Wintomylon and WIN 18,320) is the first of the synthetic quinolone antibiotics. In a technical sense, it is a naphthyridone, not a quinolone: its ring structure is a 1,8-naphthyridine nucleus that ...

- 10.0 mg * Sheep blood - 5% *

Agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from " ogonori" and " tengusa". As found in nature, agar is a mixture of two components, t ...

- 13.5 g *

Demineralized water Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...

1000.0 ml

History

CNA agar was developed by Ellner et al. at Columbia university in 1965 while trying to develop an agar base that would enhance the hemolysis of ''Streptococcus pyogenes''.

References

{{reflist Microbiological media Bacteriology Medical microbiology Gram-positive bacteria

Uses

Contents

Composition

History

References