CNS Bacteria - Barbieri

Question 1

Name the four primary pathogens most often affiliated with bacterial meningitis

Answer 1

Group B Strep

S. pneumoniae

N. meningitidis

H. influenza

Question 2

What process drives most of the brain damage associated with bacterial meningitis?

Answer 2

The host’s own inflammatory response (not the bacteria itself!)

Example; S. pneumoniae activates leukocytes that release proteolytic enzymes and ROS, damaging host tissue

Question 3

Which pathogen(s) are most often affiliated with bacterial meningitis in:

Premature babies and newborns?

Older children?

Adults?

Answer 3

Premature babies and newborns: Group B streptococci, E. coli, Listeria

Older children: S. pneumoniae, N. meningitidis, H. influenzae (less of a problem now due to vaccination)

Adults: S. pneumoniae, N. meiningitidis, Listeria (>50 y.o.)

Question 4

Is a conjugate vaccine available for:

Group B strep?

S. pneumoniae?

N. meningitidis?

H. influenzae?

What about a polysaccharide capsule vaccine?

Answer 4

No

Yes

Yes

Yes

All four have an available polysaccharide capsule vaccine.

Question 5

Give the gram stain and morphology of H. influenzae

Answer 5

G-, pleomorphic coccobacilli

Question 6

Virtually all invasive infections of H. influenzae are attributable to what serotype?

Describe the composition of its polysaccharide capsule

What age group is most susceptible to infection?

Answer 6

Serotype B (Hib)

Capsule: ribose and ribitol

Children [3months, 3years]. Maternal antibodies are protective before 3 months, and children over 3 years will have developed humoral immunity to Hib.

Question 7

What protein carrier was added in the second-generation Hib vaccine to give it greater immunogenicity?

Why is this superior?

Answer 7

conjugated PRP-D to Diphtheria toxoid

The carrier protein domain of the conjugated vaccine is internalized and processed by the B cell. It is then presented to a Th cell on MHCII. Actions of the T-cell induce memory.

Question 8

Describe the three virulence factors of Neisseria meningitidis

Answer 8

Lipoligosaccharide: Component of the outer membrane (endotoxin). Stimulates the TLR system to produce fever, septic shock, and hemorrage (destruction of RBCs)

**Polysaccharide capsule: **prevents phagocytosis

**Fimbriae: **attachment to nasopharynx

Question 9

Desribe the gram stain and morphology of N. meningitidis

What is the preferred growth medium for culture?

How else might it be identified?

Answer 9

G-, diplococci

Chocolate agar

Gram stain (gold standard) or PCR

Question 10

Persons infected with N. meningitidis should be tested and treated (admit to hospital) as soon as possible. Why?

Who else should be notified/treated?

Answer 10

Fatality ~15% within 12 hours of infection

All contacts over the previous seven days should be identified/notified and receive antibiotic prophylaxis (especially children)

Question 11

Asplenic children are especially susceptible to what form of bacterial meningitis? Who else is especially vulnerable to this pathogen?

Answer 11

N. meningitidis

Most common in infants <1yr or 16-21 y.o. (college students and military recruits)

Question 12

Name the six serogroups of N. meningitidis that are responsible for virtually all human cases.

Describe the vaccination options

Answer 12

A, B, C, Y, W135

MCV4 (conjugate vaccine) - preferred for people <55y.o.

MPSV4 (polysaccharide vaccine) - preferred for people >55y.o.

Question 13

Describe the hemolytic character of the following:

Group A strep

Group B strep

S. pneumoniae

Answer 13

beta

beta

alpha

Question 14

Give the gram stain and morphology of S. pneumoniae

Describe its virulence factors and their function(s)

Answer 14

G+ cocci in pairs and short chains

Surface adhesion proteins - colonize nasopharynx

pneumolysin - spread into normally sterile tissues

IgA protease - cleave IgA and spread into normally sterile tissues

teichoic acid - stimulate TLR inflammatory response

peptidoglycan fragments - stimulate TLR inflammatory response

polysaccharide capsule - evade phagocytic killing

Question 15

Describe the vaccine options for S. pneumoniae, including their indications

Answer 15

PCV13 (conjugate vaccine): greater memory, but covers fewer serotypes. Indicated for infants <2y.o. and children 6-18y.o. and older (so… adults?).

PPSV23 (polysaccharide capsule): less memory, more serotypes covered. Indicated for adults >65y.o.

Question 16

Is a vaccine available for S. agalactiae?

Give its gram staining, morphology, hemolysis, and Lancefield group

In what population(s) is infection with this organism especially concerning?

What mucosal surfaces usually harbor this bug?

Answer 16

No

G+ cocci, beta-hemolytic, Group B

Full-term infants (2-8% mortality) and pre-term infants (up to 30% mortality)

Commonly inhabits the pharynx and vagina (transmission risk to infants during birth?)

Question 17

What is the preferred therapy for S. agalactiae infection?

Who should be given antibiotics prophylactically against this bug?

Answer 17

Penicillin

Prophylaxis: pre-term infants, pregnant women with early membrane rupture, pregnant women with previous Group B streptococcal disease