Neisseria (Gram-Negative)

Neisseria are diplococci, meaning they appear as round shaped pairs. Neisseria meningitidis causes meningitis, and Neisseria gonorrhoeae causes gonorrhea.

Neisseria meningitidis
These bacteria are transmitted by respiratory secretions (saliva), and can blend into and become part of normal flora of the nasopharynx in 5-15% of adults. They affect infants of 6 months to 2 years due to their weak immune systems, or army recruits and college freshmen who are exposed to a close group environment. 

• Virulence factors:
• Polysaccharide capsule that is antiphagocytic. 
• LPS endotoxin that can destroy blood vessel and causes sepsis if released. The blood vessel hemmorhage causes petechial rash, which is a classic sign of meningococcal infection.
• IgA1 protease, an enzyme that cleaves IgA antibodies. 
• Pili that attach to cells of the nasopharynx.
• Diseases: 
• Meningococcemia - sudden fevers, chills, joint and muscle pains due to multiplication of bacteria in the bloodstream.
• Fulminant meningcoccemia - septic shock with adrenal gland hemorrhage, causing abrupt hypotension, rapid heart rate (tachycardia), worsened petechiae, disseminated intravascular coagulation (DIC) and death. 
• Neonatal meningitis (late-onset) - most common form of meningococcal disease. Causes fever, vomiting and irritability.

Neisseria gonorrhoeae 
The second most common cause of STD. Transmitted as long as there is a transmission of body fluids: sexually, orally or anally.

• Virulence factors:
• Pili that are hypervariable as a protection against antibodies or vaccines. Pili adhere to host cells so strongly that phagocytosis can be prevented.
• Outer membrane protein porins promote invasion into epithelial cells.
• Opa proteins of the outer membrane promote adherence and invasion into epithelial cells. 
• LPS can destroy cilia of cells before the bacterium is taken up by endocytosis. 
• Diseases: 
• Gonococcal bacteremia when a rare invasion of the bloodstream occurs. Fever, joint pains, skin lesions, followed by rare occurrence of heart inflammation (endocarditis and pericarditis) or meningitis after the bacteria spreads.
• Septic arthritis causing acute fever and pain of one or two joints.
• In men: the urethra is the site of infection. Inflammation of the urethra (urethritis) causes painful urination, pus discharge, and possibly epididymitis, prostatitis and urethral strictures (narrowing of the urethra).
• In women: a less symptomatic version of urethritis in males, such as lower abdominal pain or no symptoms at all. Infection of the cervix epithelium can progress to pelvic inflammatory disease (PID).
• In infants: infection during delivery, resulting in eye infection (ophthalmia neonatorum) and possible blindness.