Exam 1: Meningitis I (lecture checkpoint questions)

Question 1

Pneumonia caused by S. pneumoniae is frequently proceeded by a URT infection, usually viral. Why?

Answer 1

Aspiration of the S. pneumonia (which is normal flora of the URT)

Question 2

S. pneumoniae looks very different from other Streptococci upon Gram staining. How?

Answer 2

S. pneumoniae is a lancet shaped gram (+) diplococci

vs

other Streptococci are chain shaped gram (+) diplococci

Question 3

Which major virulence factor is required for invasive disease for S. pneumoniae?

Answer 3

Capsule (anti-phagocytic)

83 serotypes (7 cause 85% of human invasive disease)

antibody to capsule is protective - vaccine target

Question 4

How is the S. pneumoniae vaccine in children (<2-years-old) different from the one used in adults?

Answer 4

the polysaccharide by itself will not generate sufficient immune response in children (<2-years-old)

so the polysaccharide is conjugated to an inactivated diptheria toxin protein to trigger sufficient AB production

*new vaccine is PCV 13 (prevnar 13) which covers 29 polysaccharides (23 old ones + 6 new ones)

Question 5

S. pneumoniae can be either α or β-hemolytic. How?

Answer 5

α-hemolytic in aerobic environments

no toxin action; capsule is the only VF

β-hemolytic in anaerobic environments

β-hemolytis (cytolitic toxin)

BOTH capsule and pneumolysin are VF

Question 6

How can sputum color indicate pneumococcal pneumonia?

Answer 6

pneumococcal pneumonia sputum is copious and “rusty” colored

“rusty” color is due to the pnemolysin lysing red blood cells

Question 7

Which two genera of bacteria are the only medically relevant Gram negative cocci?

Answer 7

The only 2 medically relevant genera of bacteria that are gram-negative cocci:

_Neisseria*_ and Moraxella

*Members of the Neisseria genus are gram-negative diplococci in classic kidney-bean shape

Question 8

What are the oxygen requirements of Neisseria?

Answer 8

obligate aerobes

sensitive to adverse environmental conditions (drying, cold UV light, etc) so it is rarely spread from human to environment to human

Question 9

Which agar is commonly used to grow Neisseria?

Answer 9

Chocolate agar is commonly used to grow Neisseria

Carbohydrate fermentation assays are also used

Neisseria is catalase (+) and oxidase (+)

Question 10

Which trait of Neisseria’s LPS makes it immunoevasive?

Answer 10

Neisseria’s LPS is a LOS (lipooligosaccharide)

It has no O-antigen *→ makes it immunoevasive

* same as N. gonorrhea and H. infleunza

Question 11

Which virulence factor of N. meningitidis is required for invasive diseases?

Answer 11

the major VF is the capsule*

the capsule is not present in N. gonorrhea!

Pili (fimbria) are MINOR VF

Question 12

What are the most commonly isolated capsule serogroups clinically isolated in meningococcal disease?

Answer 12

the most commonly isolated capsule serogroups clinically isolated in meningococcal disease are

A, B*, C, Y, and W

*B is weakly antigenic so it is difficult to make an effective vaccine for

Question 13

Why is IgA protease so important for S. pneumoniae, H. influenzae**, and **N. meningitidis colonization?

Answer 13

IgA protease protects against IgA on mucosal surfaces

aiding in colonization and critical in mucosal immunity

Question 14

Who are the highest at risk groups for meningococcal disease?

Answer 14

Susceptible age groups and populations for meningococcal disease

6–24 month

College students

Military recruits (particularly basic training)

Patient with complement deficiencies

Asplenic* individuals, sickle cell anemia

Elderly

*Asplenic patients are acutely susceptible to disseminated encapsulated bacterial infections! They have a difficult time clearing encapsulated bacteria from the blood stream.

Question 15

What are the most common diseases caused by N. meningitidis?

Answer 15

Asymptomatic colonization is the most common outcome, mild local inflammation. However, N. meningitidis can spread to the bloodstream via local lymph nodes.

leads to:

Meningitis – high mortality, permanent damage common

Meningococcemia – bloodstream invasion, sepsis, DIC

Local infection – nasopharynx, pneumonia (rare)

Question 16

What are the most common diseases caused by S. agalactiae and who are the at-risk groups?

Answer 16

S. agalactiae common diseases:

pneumonia, septicemia, and meningitis*

S. agalactiaeat-risk groups:

newborns

Also causes invasive disease in the elderly (>60) and severely immunocompromised

*In the U.S., S. agalactiae is the leading cause of meningitis in the first week of life.

Question 17

Why does S. agalactiae infect newborns so frequently?

Answer 17

S. agalactiae** is **normal flora in roughly 25% of women in both the vagina and GI tract.

During vaginal births, S. agalactiae is transferred from mother-to-child, potentially leading to severe invasive diseases.

Question 18

How are the majority of S. agalactiae infections prevented?

Answer 18

All women that are 35-37 weeks pregnant should be screened for S. agalactiae (rectal and vaginal swab).

If the mother is a carrier, I.V. antibiotics should be given during labor, usually penicillin.

I.V. antibiotics is the only method proven to reduce the risk of S. agalactiae transmission to newborns.

Question 19

After birth, how long are infants at risk for an S. agalactiae infection?

Answer 19

Infections can manifest in newborns early (first week) or later (within first 3 months) in life

Question 20

Which common characteristics distinguish S. pneumoniae and S. agalactiae?

Answer 20

S. pneumoniae:

• Gram-positive cocci in lancet shapped diplococci
• β-hemolytic in anaerobic environment (Blood agar) due to the stabilization of pneumolysin.

•α-hemolysic in aerobic environment (no toxin action)

S. agalactiae:

• Gram-positive cocci in chains
• β-hemolytic in aerobic environment (Blood agar), Catalase negative

Question 21

2 main species of Neisseria

Answer 21

N. meningitidis and N. gonorrhoeae