Gram negative pyogenic cocci
Constitute the largest group of human pathogens
-Due in part to the presence of lipid A in the bacterial cell wall
-Triggers fever, inflammation, shock, and
disseminated intravascular coagulation (blood clots within blood vessels)
Almost every Gram-negative bacterium that can
breach the skin or mucous membranes, and evade the immune system can cause disease and death in humans
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
(Glucose fermentation +ve, Maltose +ve)
The gonococcus, N. gonorrhoeae
(Glucose fermentation +ve, Maltose -ve)
Cultural characters
They grow on enriched media (chocolate blood agar) The selective medium is Thayer Martin medium (Chocolate blood agar + VCN)
They require extra CO2 for growth especially upon primary isolation.
Pathogenicity ofNeisseria sp.
Polysaccharide capsules protect the bacteria from phagocytes
Fimbriae to attach to human cells Lipooligosaccharide: (endotoxin)
IgA protease cleaves secretory IgA in mucous Change of it’s surface antigens (especially in N.
Humans are the only natural carrier of N. meningitidis Can be a member of the normal microflora 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
results in death as early as 6 hours after initial symptoms
Initial symptoms include fever, sore throat, headache, stiff neck, vomiting and convulsion
Meningococcal septicemia (Meningococcemia), blood poisoning, can also be life threatening
Can produce blood coagulation and the formation of minute hemorrhagic lesions
Dissemination of the meningococcus from a
nasopharyngeal infection
One clinical sign of meningococcemia
Is acute and potentially life-threatening infection of the bloodstream that commonly leads to:
Clinical Diagnosis
Gram stain CSF (cerebrospinal fluid), blood, or nasopharyngeal sample
Culture for differentiation
(Use of differential and selective media, oxidase test)
Neisseria meningitidis
More than 13 known antigenic types
Types A, B, C, Y & W135 are more commonly associated with human disease
Presence of Gram-negative diplococci in phagocytes of the central nervous system
Treatment
Penicillin, administered intravenously, is the drug of choice
Prevention
Vaccination
Diplococcus Gram-negative
Fimbriae extend several micrometers from cell surface
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
Gonorrhea in men
Usually symptomatic producing inflammation that causes painful urination and purulent discharge
Can cause scarring and infertility
Symptoms (if present)
Males: urethral discharge, severe burning on urination Females: vaginal discharge, yellow or blood-stained, pain on urination
Gonorrhea in women
Often asymptomatic (50%)
Can infect the cervix and other parts of the uterus, including the Fallopian tubes
• Can result in ectopic pregnancy or sterility Gonococcal infection of children
Neisseria gonorrhoeae
Diagnosis of gonorrhoeae disease
Gonorrhea in men can be identified by the presence of Gram-negative diplococci in pus from an inflamed
genital organ, they appear characteristically as gram-negative diplococci intra and extracellular)
-Gram stain -Culture
-Oxidase, and sugar fermentation
Diagnosis
“Gold Standard”
Types of Tests
Treatment of gonorrhoeae
Gonococcal strains resistant to: Penicillins
Tetracyclines Spectinomycin Fluoroquinolones
Presently, ciprofloxacin, ofloxacin , and ceftriaxon recommended for treatment
Vaccine
Hard to develop
No animal model
No immune memory to Neisseria gonorrhoeae Antigenic variation strategy
Difficulty finding target common to all strains
