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medical microbiology > Streptococci > Flashcards

Streptococci Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What is the most common entry point for respiratory infection?

A

it is your respiratory. there is the upper and the lower.
Upper respiratory - nose, nasal, cavity, sinuses, mouth and throat
Lower - trachea, bronchi, bronchioles and alveoli in the lungs

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2
Q

What are the mechanisms of protection of the lungs?

A

Normal flora alone with nasal hair, nasal turbinates, mucus, involuntary responses, IgA and immune cells

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3
Q

What are characteristics of Streptococci?

A

Gram positive, non, motile and sporing. Catalase negative. Cocci bead like chains, aerobic and anaerobic.
- posses a M protein and LTA (lipoteichoic acid)

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4
Q

What classifies the C-carb

A

Beta hemolysis

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5
Q

What are the forms of the the pathogen

A

A, B,C, F, G

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6
Q

What are the most infectious groups

A

A and B

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7
Q

What does Alpha hemolytic ID

A

S. viridans and S. pneumoniae

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8
Q

What does gamma hemolytic ID

A

Streptococcus and Enterococcus faecalis

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9
Q

What is the overall structure of the cells

A

it has a cytoplasmic membraane, mucopeptide, Groups Carbohydrate, protein antigens, M-protein- antophagocytic and least 80 different M serotypes.
Protein F binds with fibronectin
Protein F and M protein help in attachment wit the host cells in tissues
Protein g binds with the Fc protein of the antibodies
Capsule- composed of hyaluronic acids that protects again phagocytosis.

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10
Q

What are the toxics of Beta-hemolytic Strep. group?

A
  • Strep O is antigenic and used to diagnosis of Rheumatic fever. (ASO Test)
    S- oxygen stable - non-immungoenic, cell bound
    O-oxygen labile - hemolysis under anaerobic conditions only.

Erythrogic toxin - responsible for scarlet fever. screened by Dick test. it is injected intradermally.. localized erythema. DPNase, diphosphopyridine nucleotides play a role in the toxins and exotoxin A is the super antigen that deals with necrotizing fasciitis.

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11
Q

What are the enzymes of Beta- hemolytic Strep, group A?

A

Streptokinase- A and b forms - lyse blood clots
Streptodonase - breaks DNA reducing the viscosity of the pus
Hyaluronidase - spreading factor
C5a peptidase - degrades complemnt component of C5a that attracts phagocytes to the sites of complement deposition and prevents chemotaxis of neutrophils and mononuclear phagocytes

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12
Q

What is SPE

A

Strepococci pyrogenic exotoxins act as super antigen and responislbe for streptococcal TSS.

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13
Q

What are the sources and modes of spread

A

Dried secretion, acute sore throat, acute otitis media and nasal carriers.

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14
Q

How does Group A streptococci cause diseases

A

pyogenic inflammation- cellulitis, impetigo and erysipelas

Exotoxin production - necrotizing fasciitis

immunologic - RF and AGN

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15
Q

What are the indirect pathogenesis

A

rheumatic fever ( Pain in heart and joints) and Glomerulonephritis ( ultimate kidney failure)

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16
Q

What is the pathogenesis of rheumatic fever

A

caused by many M serotypes of S. progenies. probable cross reaction between group A antigen and heart tissue. the genetic factors my play a role along with throat infection.

17
Q

What is the pathogenesis of Glomerulonephritis

A

cause by M serotypes, repeat infections are rare. usually from a previous throat or skin infection. can be a combination of antigen cross reaction between S. pigeons and glomerular basement and autoimmune process

18
Q

What are the lab diagnosis and treatment of S. progenies ?

A

Direct Smear
isolating and culture on blood agar
indirect evidence by antibodies to one or more Strept. enzyme
gram strain
Culture on B/A is a beta hemolysis
Catalase negative
bacitracin senstive- group A strep
High titres of anti-DNasw B
Drug of choice- penicillin, orally or IM
Penicillin allergy - erythromycin

19
Q

What are Group B Streptococci structure

A

you will see the diplococcal pairs in short chains. They have polysaccharide capsules contain sialic acid.

20
Q

What are the types of antigens of group B

A

Ia, Ib,II,III,IV

21
Q

What are one of the most important pathogens in the neonate?

A

Acute fulminating respiratory syndrome and Neonatal meningitis

22
Q

How do you diagnose Group b Streptococci

A

CAMP test
middle streak is S. aureus
Perpendicular streak A- S.agalactiae
Perpendicular streak b- S. pyogenes
CAMP factor makes the steak closer to S. aureus more prominent arrow had hemolysis

23
Q

Group B strepococci is less susceptible to what

A

penicillin. needs to combined with aminoglycosides to be effective

24
Q

What are oral streptococci

A

S. Viridians

25
Q

What are other species fall in s. Viridans

A

S. mutans, sobrinus, salivarius, sanguis and mitis

26
Q

What organisms are involved in dental plaque

A

sanguis, mutans and sobrinus

27
Q

What organisms are involved in Buccal mucosal membrane

A

mitis

medical microbiology (29 decks)

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