Neisseria meningitidis is a Gram-negative bacterium. It causes meningococcal disease, including severe infections like meningitis and septicemia. It is a spherical bacterium that typically appears in pairs, often described as kidney-bean or coffee-bean shaped under a microscope.
What Gram Staining Is
Gram staining is a common laboratory technique used to categorize bacteria based on the chemical and physical properties of their cell walls. This method differentiates bacteria into Gram-positive and Gram-negative groups through a series of staining and washing steps. Initially, a crystal violet stain is applied, coloring all bacterial cells purple. Iodine is then added to form a complex with the crystal violet, helping to fix the stain within the cells.
The differentiating step uses a decolorizer, typically alcohol or acetone. Gram-negative bacteria have a thinner peptidoglycan layer in their cell wall, located between an inner and an outer membrane. This thin layer and outer membrane allow the crystal violet-iodine complex to be washed away, leaving Gram-negative cells colorless. A counterstain, usually safranin, then stains these colorless cells pink or red.
How Gram-Negative Affects Neisseria meningitidis
Its Gram-negative classification is linked to its unique cell wall structure and disease-causing ability. Its outer membrane contains lipooligosaccharide (LOS), which functions as an endotoxin. This endotoxin contributes to disease severity by triggering a strong inflammatory response. High LOS levels in the bloodstream are associated with septic shock and organ damage.
The cell wall structure also influences laboratory identification. Gram staining samples from infected individuals reveals characteristic pink or red paired cocci, aiding preliminary diagnosis. The Gram-negative nature also impacts treatment strategies. Its outer membrane can act as a barrier to certain antibiotics, requiring specific drug choices like extended-spectrum cephalosporins (e.g., ceftriaxone or cefotaxime) for effective treatment.
Understanding Neisseria meningitidis Disease
Neisseria meningitidis primarily causes two life-threatening conditions: meningococcal meningitis and meningococcal septicemia. Meningitis is inflammation of the brain and spinal cord membranes, causing symptoms like sudden high fever, severe headache, and a stiff neck. Meningococcal septicemia is a bloodstream infection where bacteria multiply and damage blood vessel walls, often causing a distinctive dark purple rash.
Transmission occurs through respiratory droplets from close contact with an infected individual or asymptomatic carrier, such as through coughing, sneezing, or sharing utensils. Many people carry the bacteria in their nose and throat without becoming sick, but it can invade the bloodstream or central nervous system in a small percentage. Prompt diagnosis, often using Gram stain of cerebrospinal fluid or blood, followed by immediate antibiotic treatment, is important due to rapid disease progression. Vaccination offers the best protection against meningococcal disease, with vaccines targeting various serogroups.