Microbiology Case Study: 22 Year Old Female with Joint Pain

A 22 year old female with no significant past medical history presented with a fever, joint pain and a petechial rash. She endorsed having cold/flu symptoms for two weeks prior. The patient was admitted to the hospital where blood cultures were drawn and antibiotics were initiated. One set of blood cultures from the patient flagged positive at 14 hours of incubation with the following gram stain and colony morphology.

Gram stain showing Gram negative diplococci.
Gram stain showing Gram negative diplococci.
Chocolate agar plate with small gray, slightly mucoid colonies.  Photo courtesy of pixgood.com
Chocolate agar plate with small gray, slightly mucoid colonies.
Photo courtesy of pixgood.com


Laboratory identification:

The patient’s blood was cultured on aerobic blood agar and chocolate agar plates. The gram stain revealed gram negative diplococci. Medium sized, round, gray to white, slightly mucoid colonies grew on blood and chocolate agars. The organism was definitively identified as Neisseria meningitidis by VITEK-MS. Prior to adoption of mass spectrometry, biochemical tests were performed for further characterization of the organism. Neisseria meningitidis is catalase positive, ferments glucose and maltose but not lactose, is oxidase positive, and does not reduce nitrate.


Neisseria meningitidis asymptomatically colonizes the oropharynx and nasopharynx of humans. It is transmitted by person-to-person spread of contaminated respiratory droplets. Infection causes a spectrum of disease including life-threatening meningitis. Bacteremia causes the characteristic petechial rash, thrombocytopenia, DIC, and shock. The organism may also cause conjunctivitis, pneumonia, and sinusitis. Its virulence factors include surface structures to facilitate attachment to and invasion of epithelial cells. Once the organism gains access to the vascular system, its survival is mediated by the polysaccharide capsule. Endotoxin release mediates many of the systemic manifestations of infection such as shock.

The differential diagnosis for this organism based on the gram stain and colony morphology includes Neisseria gonorrhoeae and Moraxella species. Different Neisseria species can be identified by the sugars they are able to ferment. For example, N. gonorrhoeae ferments only glucose, but N. meningitidis ferments both glucose and maltose.

There is a vaccine that is available for N. meningitidis that includes serogroups A, C, W-135, and Y. There are 12 different serogroups that can be distinguished based on the polysaccharide capsule. Our patient had been fully vaccinated. The isolate was sent to the state public health lab and it was reported back as non-typable and was sent to the CDC.

Treatment of N. meningitidis consists of supportive therapy for shock plus antimicrobial therapy with penicillin, ceftriaxone, or cefotaxime.

***Rare, fatal cases of meningococcal disease have been reported in laboratory staff. Any potential N. meningitidis should be worked with under a class II biological safety cabinet.


-Lauren Pearson, D.O. is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.


-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.


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