Neisseria gonorrhoea
Gram-negative cocci that occur in pairs with their adjacent sides flattened, giving them a "coffee bean" appearance, are typical of the genus Neisseria.
- The presence of intracellular gram-negative diplococci on a smear made from a purulent urethral discharge from a male is considered diagnostic for gonorrhea.5 In this case, cultures may not even be needed unless susceptibilities are required.
- If the genital specimen is from a female (cervical specimen), the presence of gram-negative diplococci is not specific enough to confirm the diagnosis; a culture or other confirmatory testing for N. gonorrhoeae must be performed. (Female specimens contain a great deal of mixed flora.) Organisms such as Acinetobacter sp. and Moraxella sp. may mimic the appearance of N. gonorrhoeae and can lead to false-positive results.
- If the genital specimen was obtained from a child, medicolegal considerations are paramount. Always accompany the Gram stain with a culture, for both male and female children.
Direct smears read specifically for the presence of Neisseria gonorrhea should include specific reference to gram-negative intracellular diplococci.
Of note -- bacterial vaginosis (BV)
The Gram stain may be useful in helping diagnose vaginosis among women. The standardized scoring method, known as Nugent's criteria, is a method for evaluation of the Gram stain for BV. The method is indicated only for women in childbearing years and post-menopausal women on estrogen replacement therapy.6 (Many labs have since deemed the Nugent system cumbersome, opting for point-of-care [nucleic acid] probe testing.)
- Gardnerella vaginalis (and other related organisms) appear as gram-negative or gram-variable pleomorphic bacilli (some appear as coccobacilli, longer, with some curved forms) - bacilli will be covered in more detail on the next few pages.
- WBCs and RBCs, clue cells7, and yeasts are enumerated
- Always follow your laboratory's specific scoring method for evaluation of these types of Gram stains.
And regarding vaginitis...
- Candidiasis (recall that yeast may be a part of the normal vaginal flora when in low concentrations, but sometimes shifts to out-of-control). Purulent specimens may yield large numbers of yeast on Gram stain, but the use of the wet mount is still preferable.
- Trichomonas vaginalis, while seen on wet mount, may not be seen on Gram stain.
5. Image: Neisseria gonorrhoeae from male penile discharge. No date. Submitted by author.
6. Leber A, Burnham CD, eds. Clinical Microbiology Procedures Handbook. 5th ed. Washington DC: ASM Press; 2023. 7. CDC/M Rein. Image #14574, "Epithelial cell with its exterior covered by bacteria giving the cell a roughened, stippled appearance known as a clue cell." PHIL public domain image. Created 1978. Accessed October 27, 2023. https://phil.cdc.gov/Details.aspx?pid=14574
