Biology:CNA Agar
Columbia Nalidixic Acid (CNA) agar is a growth medium used for the isolation and cultivation of bacteria from clinical and non-clinical specimens. CNA agar contains antibiotics (nalidixic acid and colistin) that inhibit Gram-negative organisms, aiding in the selective isolation of Gram-positive bacteria.[1] Gram-positive organisms that grow on the media can be differentiated on the basis of hemolysis.
Uses
CNA agar is commonly used in clinical microbiology laboratories to isolate pathogenic Gram-positive bacteria such as Staphylococcus, Enterococcus, Streptococcus, diphtheroids, and Listeria from clinical specimens.[1] A common use for CNA agar is commonly used for the detection of Streptococcus agalactiae carriage in pregnant women.[2] It is also effective for the isolation of Gram-positive anaerobes when incubated under anaerobic conditions.[3]
CNA agar is supplemented with sheep blood to facilitate the growth of more fastidious Gram-positive organisms[4] such as Streptococcus and Enterococcus. 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 and Streptococcus pyogenes will produce colonies surrounded with a clear zone. Alpha hemolytic organisms such as Streptococcus pneumoniae[5] and viridans streptococci will produce colonies surrounded by a light to dark green zone.
Contents
The addition of peptones into the agar provides the growth factors required by the bacteria to grow.[6] Casein also provides a source of amino acids for organisms with fastidious growth requirements such as Lactobacillus brevis.[7] It contains the antibiotics colistin and nalidixic acid which inhibit the growth of many gram-negative bacteria.
Composition
Source:[8]
- Casein peptone - 12.0 g
- Meat peptone - 5.0 g
- Sodium chloride - 5.0 g
- Beef extract - 3.0 g
- Yeast extract 3.0 g
- Corn starch 1.0 g
- Colistin - 10.0 mg
- Nalidixic acid - 10.0 mg
- Sheep blood - 5%
- Agar - 13.5 g
- Demineralized water 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.[9]
References
- ↑ 1.0 1.1 Atlas, R M; Snyder, J W (2011). "Reagents, Stains, and Media: Bacteriology". in Versalovic, James. Manual of clinical microbiology (10th ed.). Washington, DC: ASM Press. ISBN 978-1-55581-463-2. OCLC 657027913. https://www.worldcat.org/title/657027913.
- ↑ El Aila, Nabil A; Tency, Inge; Claeys, Geert; Saerens, Bart; Cools, Piet; Verstraelen, Hans; Temmerman, Marleen; Verhelst, Rita et al. (Dec 2010). "Comparison of different sampling techniques and of different culture methods for detection of group B streptococcus carriage in pregnant women" (in en). BMC Infectious Diseases 10 (1): 285. doi:10.1186/1471-2334-10-285. ISSN 1471-2334. PMID 20920213.
- ↑ Baron, E J; Thomson, R B (2011). "Specimen Collation, Transport, and Processing: Bacteriology". in Versalovic, James. Manual of clinical microbiology (10th ed.). Washington, DC: ASM Press. ISBN 978-1-55581-463-2. OCLC 657027913. https://www.worldcat.org/title/657027913.
- ↑ Golberg, R L; Washington JA, I I (Sep 1976). "Comparison of isolation of Haemophilus vaginalis (Corynebacterium vaginale) from peptone-starch-dextrose agar and Columbia colistin-nalidoxic acid agar" (in en). Journal of Clinical Microbiology 4 (3): 245–247. doi:10.1128/jcm.4.3.245-247.1976. ISSN 0095-1137. PMID 1085777.
- ↑ McDevitt, Erin; Khan, Faidad; Scasny, Anna; Thompson, Courtney D.; Eichenbaum, Zehava; McDaniel, Larry S.; Vidal, Jorge E. (2020-12-23). Johnson, Michael David Leslie. ed. "Hydrogen Peroxide Production by Streptococcus pneumoniae Results in Alpha-hemolysis by Oxidation of Oxy-hemoglobin to Met-hemoglobin" (in en). mSphere 5 (6). doi:10.1128/mSphere.01117-20. ISSN 2379-5042. PMID 33298575.
- ↑ Manual of Microbiological Culture Media (Technical report). Becton, Dickinson, and Company. 2009. 161-2.
- ↑ Bonnet, M.; Lagier, J.C.; Raoult, D.; Khelaifia, S. (Mar 2020). "Bacterial culture through selective and non-selective conditions: the evolution of culture media in clinical microbiology" (in en). New Microbes and New Infections 34. doi:10.1016/j.nmni.2019.100622. PMID 31956419.
- ↑ Remel (Oct 2011). "Columbia CNA Agar w/ 5% Sheep Blood". https://tools.thermofisher.com/content/sfs/manuals/IFU1320.pdf.
- ↑ Ellner, PD; Stoessel, CJ; Drakeford, E; Vasi, F (April 1966). "A new culture medium for medical bacteriology". Am J Clin Pathol 45 (4): 502–4. doi:10.1093/ajcp/45.4_ts.502. PMID 5325709.
 |  |
