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85 Cards in this Set

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What is Neisseria?
Facultative
Anaerobic
G-
Diplococcus
Wht is the classic morphology of Neisseria on light microscopy?
Kidney bean shaped diplococci
Which environment provides optimal growth for neisseria?
High CO2 concentration
What are two important enzymes that Neisseria possess?
1) Cytochrome C oxidase
2) Catalase
Wht is the function of Neisseria's two important enzymes?
1) Cytochrome C oxidase is an enzyme that is part of electron transport and nitrate metabolism that can acept electrons from other substrates.
2) Catalase is an enzyme that inactivates toxic oxygen species by converting hydrogen peroxide to water and oxygen.
What selective media is used for culturing Neisseria?
Thayer-Martin VCN
What is the composition of Thayer-Martin VCN media?
Chocolate agar with vancomycin, colistin, and nystatin.
What makes Thayer-Martin VCN selective?
1) Vancomycin kills the G+ organisms
2) Colistin kills all G- organisms except Neisseria
3) Nystatin kills fungi
What are two Neisseria species that cause disease in humans?
N. meningitidis
N. gonorrhoeae
How are N. meningitidis and N. gonorrhoeae metabolically differentiated?
N. meningitidis can metabolize maltose and glucose
N. gonorrhoeae can only metabolize glucose.
How are N. meningitidis and N. gonorrhoeae structurally differentiated?
N. meningitidis is encapsulated and will have a positive Quellung reaction
N. gonorrhoeae is unencapsulated and will have a negative Quellung reaction
What is N. meningitidis?
Encapsulated facultative, anaerobic, G- diplococcus capable of fermenting maltose and glucose
What is another name for N. meningitidis?
Meningococcus
What are the virulence factors of meningococcus?
1) Antiphagocytic polysacharide capsule
2) Lipooligosaccharide (LOS) endotoxin
3) Immunoglobulin (Ig) A1 protease
4) Pili-facilitating adherence
5) Transferrin-binding proteins A and B, i.e., proteins that extract iron from human transferrin
What are two ways of classifying N. meningitidis?
Serotype
Serogroup
What is the basis for N. meningitidis serotype differentiation?
Outer membrane proteins and LOSs
How many serotypes exist for N. meningitidis?
>20
What is the basis for N. meningitidis serogroup differentiation?
Polysaccharide capsule
How many N. meningitidis serogroups exist?
>13
Which N. meningitidis serogroups are infectious?
Serogroups A, B, C, W, and Y
Which N. meningitidis serogroup is the predominant cause of meningococcal disease in the United States?
Serogroup B
Which virulence factor is responsible for the petechial rash of meningococcal infections?
LOS
What is the only natural host for N. meningitidis?
Humans
What is the mode of transmission for N. meningitidis?
Inhalation of aerosolized respiratory droplets.
What are two populations at increased risk for meningococcal infections?
1) Infants (6months-2 years)
2) Individuals living in close quarters such as schoold, prisons, and military barracks
Why do infants younger than 6 months of age have a smaller risk of meningococcal infection?
Maternal antibodies (IgG) confer protection.
What are three predisposing risk factors for meningococcal disease?
1) Recent URI
2) Active or passive smoking
3) Deficiencies in the late complement components, e.g., deficiency of C5b-C9 membrane attack complex (MAC)
How does N. meningitidis most commonly affect humans?
Asymptomatic nasopharyngeal colonization.
How does N. meningitidis adversely affect humans?
1) Meningitis
2) Meningococcemia
3) Waterhouse-Friderichsen syndrome (fulminant meningococcemia)
What is a classic sign of N. meningitidis infection?
Petechial rash progressing to purpura.
What is the most common form of meningococcal disease?
Meningitis
What is meningitis?
Inflammation of the protective tissues covering the brain.
What are five symptoms of meningitis?
1) Nucal rigidity
2) Severe headache
3) Altered mental status
4) Photophobia
5) Nonspecific symptoms including fever, vomiting, irritability, and lethargy
What is meningococcemia?
The presence of N. meningitidis in the blood.
What is teh classic skin finding seen with meningococcemia?
Petechial rash
What are the symptoms of meningococcemia?
1) Spiking fevers
2) Chills
3) Arthralgias
4) Myalgias
What is the drug of choice for treating meningococemia in the adult?
Ceftriaoxne
Cefotaxime
What is Waterhouse-Friderichsen syndrome?
Bilateral hemorrhage of the adrenal glands leading to adrenal insufficiency causing hypotension, tachycardia, disseminated intravascular coagulation, coma, and death.
What is used for N. meningitidis prophylaxis?
Rifampin
When is prophylaxis for N. mengitidis indicated?
For individuals who are close-contacts of patients infected with N. meningitidis.
Is there a vaccine available for N. meningitidis?
YES
Who should get vaccinated for N. meningitidis?
College students living in dormitories, military recruits, and travelers visiting endemic areas.
What serogroups does the N. meningitidis vaccine protect against?
Serogroups A, C, W, and Y
Unfortunately serogroup B is not effectively covered by this vaccine because it has a capsule containing polysialic acid, which does not elicit an adequate immune response.
What is N. gonorrhoeae?
Unencapsulated, facultative, anaerobic G- diplococcus capable of fermenting glucose.
How is N. gonorrhoeae spread?
1) Sexually
2) During parturition with an infected mother.
What are the virulence factors of gonococcus?
1) Pili
2) IgA1 Protease
3) Outer membane proteins (OMPI and OMPII)
What are three functions of pili?
1) Adherence to host cells
2) Prevention of phagocytosis from macrophages and neutrophils
3) Highly variable antigens protecting against antibodies.
What two mechanisms allow gonococcus to avoid the host's immune system?
Gene conversion
Phase variation
What is gene conversion?
Process by which N. gonorrhoeae produces pilin molecules with different antigens by recombining pilin genes.
What is phase variation?
Reversible lack of pilin expression
How does phase variation occur?
When a pilin gene is moved.
What is the clinical significance of gene conversion and phase variation?
1) Inability to create an effective vaccine because of highly variable bacterial antigens.
2) Reinfection may occur after first infection because initial infection does not confer immunity to gonococci with different antigens.
What are common symptoms of gonococcal infection in males?
Dysuria and purulent discharge from urethra.
What are complications of gonococcal disease in males?
1) Epididymitis
2) Prostatitis
3) Urethral strictures
4) Gonococcal bacteremia
5) Septic arthritis
What are common symptoms of gonococcal infection in females?
Dysuria, purulent vaginal discharge, and pain with sexual intercourse (dyspareunia).
Gonorrhea is more frequently asymptomatic in women than in men.
What are complications of gonococcal disease in females?
1) PID
2) Septic arthritis
3) Endometriosis
4) Gonococcal bacteremia
5) Infertility
6) Increased rate of ectopic pregnancy.
Who is most likely to contract gonococcal septic arthritis?
Sexually active individuals
Why is gonococcal bacteremia less frequent than meningococcal bacteremia?
Unlike encapsulated meningococci, unencapsulated gonococci have a limited ability to multiply in the blood stream.
What are complications of gonococcal bacteriemia?
1) Pericarditis
2) Endocarditis
3) Meningitis
What are less common sites of N. gonorrhoeae infection in sexually active individuals?
Anorectal area and throat.
How is N. gonorrhoeae diagnosed?
Gram stain and culture of infected fluid or discharge.
Culture of infected fluid or discharge is the gold standard for diagnosis because Gram stain is often negative.
What do you look for on Gram stain?
G- diplococci within polymorphonuclear neutrophils (PMNs).
What are two rapid tests for detection of gonorrhea?
1) Enzyme-linked immunoabsorbent assay for detection of gonococcal antigens
2) DNA probe assay for detection of gonococcal ribosomal genes.
What is teh drug of choice for the treatment of gonococcal infections?
Ceftriaxone
Why is doxycycline often added to the treatment regimen for gonorrhea?
Patients with gonorrhea are also aften coinfected with Chlamydia trachomatis.
What clinical manifestation occurs with N. gonorrhoeae infection during parturition?
Ophthalmia neonatorum
What organism besides N. gonorrhoeae causes ophthalmia neonatorum?
C. trachomatis
What type of damage results from Ophthalmia neonatorum?
Damage to the cornea may cause blindness.
How is Ophthalmia neonatorum prevented?
Newborn prophylaxis with erythromycin eye drops.
How is Ophthalmia neonatorum treated?
Systemically with ceftriaxone.
What is Moraxella?
Nonmotile, aerobic, G- coccus usuallly found in pairs that resemble Neisseria.
Is Moraxella oxidase positive or negative?
Oxidase positive.
Does Moraxella ferment glucose?
NO
It does not ferment any carbohydrates.
Which species of Moraxella is the most important human pathogen?
M. catarrhalis
What infection does M. catarrhalis cause?
1) Otitis media
2) Sinusitis
3) Bronchitis
4) Pneumonia
How is M. catarrhalis treated?
Because most strains are resistant to penicillins, trimethoprim-sufamethoxazole is often used.
Whch species of Moraxella is a common cause of blepharitis (infection of the eyelid)?
M. nonliquefaciens
What is another common cause of blepharitis?
Staphylococcus aureus
What is Acinetobacter?
Encapsulated, nonmotile, obligately aerobic coccobacillus that resembles Neisseria.
Is Acinetobacter oxidase positive or negative?
Oxidase negative
Does Acinetobacter ferment glucose?
NO
It does not ferment any carbohydrates
Where is Acinetobacter found?
Widely distributed in soil and water, but also part of normal skin flora.
Which species of Acinetobacter usually causes human infection?
A. calcoaceticus
What infections does A. calcoaceticus cause?
1) Sepsis
2) Pneumonia
3) UTI
Which two patient populations are at higher risk for infection?
1) Immunocompromised patients
2) Hospitalized patients wiht indwelling catheters or who are using respiratory ventilation