Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint ® Lecture Slides for M ICROBIOLOGY Pathogenic Gram-Negative Cocci (Neisseria)

Constitute the largest group of human pathogens Due in part to the presence of lipid A in the bacterial cell wall Triggers fever, vasodilatation, inflammation, shock, and disseminated intravascular coagulation (blood clots within blood vessels) Almost every Gram-negative bacterium that can breach the skin or mucous membranes, grow at 37  C, and evade the immune system can cause disease and death in humans Gram-Negative Bacteria

Only genus of Gram-negative cocci that regularly causes diseases in humans Nonmotile, aerobic bacteria often arranged as diplococci Distinguished from many other Gram-negative pathogens by being oxidase positive 2 species are pathogenic to humans The meningococcus, N. meningitidis The gonococcus, N. gonorrhoeae Neisseria

Non-pathogenic Neisseria Non-capsulated Can grow on ordinary media Can grow at room temperature Do not require extra CO 2 Have different fermentation reactions

Cultural characters They grow on enriched media (chocolate blood agar) They are exacting in their nutritional requirements, Neisseria gonorrhea being more exacting than Neisseria meningitidis) The selective medium is Thayer Martin medium (Chocolate blood agar + VCN) They require extra CO2 for growth especially upon primary isolation.

Pathogenicity Polysaccharide capsules protect the bacteria from the lytic enzymes within phagocytes Fimbriae enable them to attach to human cells Lipooligosaccharide: composed of lipid A (endotoxin) and sugar molecules IgA protease produced by the bacteria cleaves secretory IgA in mucous Can easily change its surface antigens leading to evasion of the immune response and multiple infections especially in Neisseria gonorrhoea

Humans are the only natural carrier of N. meningitidis Can be a member of the normal microbiota of the upper respiratory tract Causes life-threatening disease when the bacteria invade the blood or cerebrospinal fluid Most common cause of meningitis in individuals under 20 Respiratory droplets transmit the bacteria among people living in close contact, especially students living in dormitories, soldiers, prisoners &household contacts Neisseria meningitidis

More than 13 known antigenic types Types A, B, C, Y & W135 are more commonly associated with human disease Polysaccharide capsules resist lytic enzymes inside phagocytes

Meningococcal meningitis can result in death as early as 6 hours after initial symptoms Initial symptoms include fever, sore throat, headache, stiff neck, vomiting and convulsions, photophobia Meningococcal septicemia, blood poisoning, can also be life threatening Can produce blood coagulation and the formation of minute hemorrhagic lesions Neisseria meningitidis

Presence of Gram-negative diplococci in phagocytes of the central nervous system Diagnosis

Treatment Penicillin, administered intravenously, is the drug of choice Prevention Eradication is unlikely due to the presence of asymptomatic carriers Vaccination Chemoprophylaxis for close contacts eg, rifampicin, sulfonamides, tetracycline Treatment, and Prevention

Causes gonorrhea, a sexually transmitted disease Gonococci adhere to epithelial cells of the mucous membranes lining the genital, urinary, and digestive tracts of humans spreading to deeper tissue as they multiply As few as 100 pairs of cells are enough to cause disease Gonorrhea in men Usually symptomatic producing inflammation that causes painful urination and purulent discharge Can cause scarring and infertility if prostate and epididymis are involved Neisseria gonorrhoeae

Gonorrhea in women Often asymptomatic (50%) Can infect the cervix and other parts of the uterus, including the Fallopian tubes Can result in pelvic inflammatory disease (PID) Can result in ectopic pregnancy or sterility Gonococcal infection of children can occur during childbirth producing inflammation of the cornea (ophthalmmia neonatorum) and sometimes blindness. Infection of the respiratory tracts can also occur Neisseria gonorrhoeae

Pathogenesis

Diagnosis Gonorrhea in men can be identified by the presence of Gram-negative diplococci in pus from an inflamed penis, they appear characteristically as gram-negative diplococci intra and extracellular) Asymptomatic cases can be identified with commercially available genetic probes Treatment Complicated due to resistant gonococcal strains Broad-spectrum antimicrobial drugs are often used (ceftriaxone, ciprofloxacin) Diagnosis and Treatment

Prevention Most effective prevention is sexual abstinence No vaccine is available Chemical prophylaxis is ineffective Routine administration of antimicrobial agents to the eyes of newborns successfully prevents ophthalmic disease