The Gram stain is used to differentiate among different types of bacteria based on the biochemical properties of their cell walls.1 The stain is named after Danish scientist Hans Christian Gram (1853–1938) who developed the method to differentiate between two causes of pneumonia (Streptococcus pneumoniae and Klebsiella pneumoniae).2 The demonstration of Gram-negative cocci in sterile sites usually indicates infection due to Neisseria meningitides or N. gonorrhoeae. Gram-negative bacilli may be described as fusiform (e.g., Fusobacterium nucleatum, Capnocytophaga spp.), curved (e.g., Vibrio spp., Campylobacter spp., Helicobacter spp.), coccobacilli (e.g., Haemophilus spp., Brucella spp.), or rods (e.g., Escherichia coli, Klebsiella spp.).
Many of the characteristic cutaneous manifestations of infection with Gram-negative organisms are due to direct microbial invasion of the skin or subcutaneous tissues. In addition, responses of host cytokines, chemokines, receptor molecules (e.g., Toll-like receptors), and other effector cells and factors may contribute to fever, hypotension, and a variety of cutaneous manifestations.3–7
Meningococcus Infections and the Skin at a Glance
- In the United States up to 2,800 cases of meningococcal disease occur annually.
- Skin lesions associated with meningococcemia result from damage to small dermal blood vessels.
- Three clinical syndromes are associated with meningococcal disease: (1) meningitis, (2) meningococcemia, and (3) chronic meningococcemia.
- Purpura and gross hemorrhage correlate with higher numbers of organisms in the bloodstream and indicate a poorer prognosis.
Three clinical syndromes associated with cutaneous involvement occur in meningococcal disease: (1) meningitis, (2) acute meningococcemia, and (3) chronic meningococcemia. Skin lesions are frequently the most dramatic manifestations of these infections. The presence of areas of purpura or gross hemorrhage is associated with higher numbers of organisms in the bloodstream and indicates a poorer prognosis than for a petechial eruption. The epidemiology, pathogenesis, and clinical presentations of these processes have been reviewed.3,5,6,8,9
Bacteriology and Pathogenesis
Neisseria are aerobic, encapsulated, Gram-negative, bean-shaped cocci. Neisseria meningitidis grows well on blood-enriched media in 5%–10% CO2. With potentially mixed bacterial exudates, these organisms should be grown on a selective medium (e.g., modified Thayer-Martin). They can be distinguished from Neisseria gonorrhoeae by their fermentation of both glucose and maltose rather than of glucose alone. Meningococci are separable on the basis of capsular antigens, of which A, B, C, Y, and W-135 are the major human pathogenic groups. Outer membrane proteins that can identify serotypes are helpful in epidemiologic studies.5 In an epidemic of meningococcal disease, a shift of capsular group can occur (e.g., from group B to group C and vice versa), which facilitates evasion of host antibodies.10 Persons with late terminal complement deficiencies are especially prone to systemic infections with N. meningitides.11
Skin lesions associated with meningococcemia result from damage to small dermal blood vessels. Light and electron microscopy reveal bacteria within endothelial and polymorphonuclear ...