Indian J Sex Transm Dis Indian J Sex Transm Dis
Official Publication of the Indian Association for the Study of Sexually Transmitted Diseases
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  Table of Contents  
Year : 2020  |  Volume : 41  |  Issue : 2  |  Page : 221-222

Revisiting blood agar for the isolation of Neisseria gonorrhoeae

1 Department of Medical Microbiology, Postgraduate Institute of Medical Education and Research, Chandigarh, India
2 Department of Dermatology, Postgraduate Institute of Medical Education and Research, Chandigarh, India

Date of Submission18-Jul-2018
Date of Decision05-Feb-2019
Date of Acceptance27-Jun-2019
Date of Web Publication11-Nov-2020

Correspondence Address:
Dr. Sunil Sethi
Department of Medical Microbiology, 2nd Floor, Research Block, Postgraduate Institute of Medical Education and Research, Sector 12, Chandigarh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijstd.IJSTD_51_18

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How to cite this article:
Sethi S, Singh S, Banga SS, Jain N, Gupta S, Sharma N, Chaudhry H, Malhotra S, Narang T. Revisiting blood agar for the isolation of Neisseria gonorrhoeae. Indian J Sex Transm Dis 2020;41:221-2

How to cite this URL:
Sethi S, Singh S, Banga SS, Jain N, Gupta S, Sharma N, Chaudhry H, Malhotra S, Narang T. Revisiting blood agar for the isolation of Neisseria gonorrhoeae. Indian J Sex Transm Dis [serial online] 2020 [cited 2021 Apr 14];41:221-2. Available from:


Neisseria gonorrhoeae is an obligate intracellular bacterium infecting humans, causing cervicitis, urethritis, pharyngitis, and proctitis. If untreated, complications such as infertility, ectopic pregnancy, and pelvic inflammatory disease may result in women, while prostatitis, urethral strictures, and epididymitis may result in men.[1] Dissemination occurs in 0.5%–3% of gonococcal infections, typically presenting with fever, dermatological manifestations, polyarthralgia, and tenosynovitis.[2] Conventionally, chocolate agar or selective media containing antimicrobial agents, such as New York City agar or modified Thayer-Martin agar, have been used for the isolation of N. gonorrhoeae from clinical specimens. Since N. gonorrhoeae lacks hemolysin, it can not directly release factor V (nicotinamide adenine dinucleotide) from red blood cells (RBCs) due to which blood agar is not traditionally used for its primary isolation. Lysed RBCs in chocolate agar readily provide this essential coenzyme due to which it is preferred for N. gonorrhoeae isolation. However, some strains of N. gonorrhoeae can grow on commercially available sheep blood agar, although growth is often slower and less prominent compared to chocolate agar.[3] Recently, a case of bacteremia due to N. gonorrhoeae was described from Korea, wherein aerobic culture in the presence of 5% CO2 resulted in bacterial isolation on blood agar and chocolate agar following 2 days of incubation, suggesting a comparable growth rate on both agar types.[4]

We aimed to study the effectiveness of blood agar for the isolation of N. gonorrhoeae compared to chocolate agar. A total of 1405 cervical swabs and 125 urethral swabs were received at our laboratory from October 2015 to October 2017. All samples and two World Health Organization reference strains C and F were inoculated on blood agar and chocolate agar plates in parallel followed by incubation at 37°C with 5% CO2. Eight urethral swabs and two cervical swab samples demonstrated growth after 48 h, revealing 1–2 mm size, opaque, round, smooth with grayish-white colonies on both blood and chocolate agar [Figure 1]. The appearance of colonies was 24 h earlier in blood agar during primary isolation, and the size and number of colonies in both media were comparable. Identification was done using conventional biochemical tests and confirmed by matrix-assisted laser desorption time of flight by Bruker Daltonics, Germany and MALDI Biotyper 3.0 software (Bruker Daltonics, Billerica, MA, USA). All ten clinical isolates and two reference isolates were confirmed to be N. gonorrhoeae. Antimicrobial susceptibility testing was done as per the Clinical and Laboratory Standards Institute, 2014 guidelines.[5] Identical results of susceptibility were obtained from the isolates from blood agar, and chocolate agar indicating that choice of media did not affect the susceptibility pattern.
Figure 1: (1) Blood agar and (2) chocolate agar plates showing colonies of Neisseria gonorrhoeae after 48 h incubation

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Our study highlights the role of blood agar; likely the most commonly used enriched media in clinical microbiology laboratories, for bacterial culture, specifically for the isolation of N. gonorrhoeae. Blood agar is cheap and readily available in most settings making it a good substitute for chocolate agar. In resource limited areas where gonococcal isolation is often not attempted due to the lack of selective media or non-selective enriched media like chocolate agar, using blood agar which is routinely used even for other samples can help in the prompt diagnosis of this infection. The preparation of in-house blood agar necessitates the maintenance of animal house facilities with an adequate number of healthy sheep, which is a difficult endeavor in small establishments. Thus, in laboratories where blood agar is being routinely purchased or where low sample load for N. gonorrhoeae recovery is expected, using blood agar alone may be recommended under appropriate temperature and CO2 conditions. Although the use of selective media or chocolate agar cannot be replaced by blood agar based on this brief report, an evaluation of blood agar in a larger number of samples may provide more conclusive evidence for substitutive value in isolating N. gonorrhoeae. With greater availability of culture isolates, more robust drug susceptibility profiles of N. gonorrhoeae and drug resistance trends can be conducted for our region.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Ng LK, Martin IE. The laboratory diagnosis of Neisseria gonorrhoeae. Can J Infect Dis Med Microbiol 2005;16:15-25.  Back to cited text no. 1
Winn WC Jr., Allen SD, Janda MW, Koneman WE. Neisseria species and Moraxella catarrhalis. In: Koneman's Color Atlas and Textbook of Diagnostic Microbiology. 6th ed. Philadelphia: Lippincott Williams & Wilkins; 2006. p. 574-8.  Back to cited text no. 2
Janda W, Gaydos C. Neisseria. In: Murray PR, Baron EJ, editors. Manual of Clinical Microbiology. 9th ed. Washington, D.C: ASM Press; 2007. p. 608.  Back to cited text no. 3
Won D, An D, Kim MN, Lee YS. A case of bacteremia by Neisseria gonorrhoeae coincident with massive hemorrhage of esophageal varices. Korean J Lab Med 2011;31:118-21.  Back to cited text no. 4
Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing: Twenty-Second Information Supplement. CLSI Document M100-S24. Wayne (PA): Clinical and Laboratory Standards Institute; 2014.  Back to cited text no. 5


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