S. pneumoniae, oral streptococci and cariogenesis

Question 1

General Features and habitat of Streptococcus pneumoniae

Answer 1

Gram +
Diplococci (“Lancet-shaped”)
Habitat- upper respiratory tract

Question 2

Biochemical Properties of Streptococcus pneumoniae

Answer 2

Polysaccharide capsule (94 serotypes)
Optochin sensitive
Bile-soluble (cannot grow on bile)
Catalase negative

Question 3

Pathogenesis of Streptococcus pneumoniae

Answer 3

Sickle cell anemia or splenectomy are susceptible to S. pneumoniae (spleen remove capsulated organs)

IgA protease- used to invade mucosa and thus reduce host defense

Transmitted directly person to person via respiratory droplets

Question 4

Clinical Features of Streptococcus pneumoniae

Answer 4

Lobar pneumonia with “rust-colored” sputum (usually in lower lobe)
#1 cause of CAP (Community Acquired Pneumonia)

If disseminated, can also cause: Peritonitis, endocarditis and bacterial keratitis (corneal ulceration)

Most common cause for: 
−Meningitis
− Otitis media
− Pneumonia
− Sinusitis

Question 5

Diagnosis of Streptococcus pneumoniae

Answer 5

Alpha-hemolytic on Blood agar (5% CO2)

Capsule swelling test or agglutination

Question 6

Treatment of Streptococcus pneumoniae

Answer 6

Macrolides

Ceftriaxone (usually for meningitis)

Question 7

Prevention of Streptococcus pneumoniae

Answer 7

Pneumovax 23 valent polysaccharide capsule- vaccine for adults and teens
Prevnar 13 valent conjugated to toxoid- for children and elderly

Question 8

General Features and habitat of Viridans Streptococci group

Answer 8

Gram +
normal flora of the oral cavity
pairs or chains

Question 9

Biochemical Properties of Viridans Streptococci group

Answer 9

No capsule
Optochin resistant
Bile resistant (insoluble)
Catalase negative

Question 10

Pathogenesis of Viridans Streptococci group

Answer 10

Viridans group enter the blood stream via wound in oral cavity and adheres to platelets, which can later reach the heart valves

Dextran made by Viridans is used for adherence to make plaques on teeth

Question 11

Clinical Features of Viridans Streptococci group

Answer 11

Dental caries- Viridans group (especially S. mutans and S. sanguinis) colonize the oral cavity and breaking down sucrose. By this, the bacteria are forming dextran-mediated plaques, which trap nutrients and bacteria (like Lactobacillus) that further break carbohydrates, producing acid that damages the teeth (by demineralization)

Subacute endocarditis- in predisposed damaged heart valves (usually mitral valve)

Question 12

Diagnosis of Viridans Streptococci group

Answer 12

alpha-hemolytic on Blood agar

Question 13

Treatment of Viridans Streptococci group

Answer 13

Penicillin or Vancomycin combined with

Aminoglycosides (long treatment ~6 weeks)

Question 14

What is the Lancefield classification?

Answer 14

Grouping system based carbohydrate composition of bacterial antigens found in cell wall
Streptococcus pyogenes = A
Streptococcus agalactiae = B
Enterococcus faecalis, Streptococcus bovis = D

Question 15

Dental caries formation

Answer 15

Demineralization of the enamel of teeth due to lactic acid and other organic acids which accumulate in dental plaque

Usual suspect: S. mutans and Lactobacillus spp.

S. mutans produce a low pH that then allows lactobacillus to grow more efficiently

Question 16

Oral Streptococci general characteristics:

Answer 16

The viridans group of streptococci is a heterogeneous collection of α-hemolytic and non-hemolytic streptococci.
They colonize the oropharynx, GI, and genitourinary tract.

Question 17

Viridans streptococci diseases

Answer 17

Endocarditis: S. oralis, S. Sanguis

Dental caries: S. mutans

Malignancies of the GI: S. bovis