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Diagnostic Micro Exam 1 > Streptococcus > Flashcards

Streptococcus Flashcards

0
Q

What are the methods to classify strep?

A

Lancefield Groups
Site of origin, type of infection
Hemolysis
Biochemical characteristics

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1
Q

What are the general characteristics of streptococcus?

A 
Gram positive cocci that divide linearly
Catalase negative
Aerotolerant anaerobes
Small colonies
Grow well on BAP, some need CO2
Several pathogens
Several commensals
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2
Q

What are the types of lancefield groups?

A

A, B, C

Based on C-carbohydrate

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3
Q

What strep does not have the C-carbohydrate?

A

S. viridans

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4
Q

What are the types of hemolysis does strep have?

A

Alpha
Alpha prime
Beta

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5
Q

What is hemolysis?

A

Clearing of blood around colony due to the presence of hemolysins in the bacteria

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6
Q

What is alpha prime hemolysis?

A

Colonies are surrounded by a zone of non-hemolysis & an outer zone of beta hemolysis

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7
Q

What is BAP composed of?

A

5% sheep’s blood in tryptic soy agar
Enriched - helps bacteria grow
Differential - types of hemolysis we see

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8
Q

What are the groups of beta hemolytic strep?

A

Group A
Group B
Group C,F,G

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9
Q

What strep is Group A?

A

Strep pyogenes

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10
Q

What strep is group B?

A

Strep agalatactiae

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11
Q

What are the virulence factors of S. pyogenes used for?

A

Helping in adhesion & eluding the immune system

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12
Q

What are the virulence factors for S. pyogenes?

A

Fibronectin
Capsules
Enzymes

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13
Q

What is fibronectin & what are some types?

A 
Binding protein
Lipoteichoic acid
Hyaluronic acid capsule
Toxins 
Enzymes
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14
Q

What do capsules do?

A

Mask bacterial antigens

Eluding immune recognition

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15
Q

What do enzymes do for S. pyogenes & what are some types?

A 
Produced
Streptolysin O
Streptolysin S
DNAse
Streptokinase hyaluronidase
Eyrthrogenic exotoxins
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16
Q

What are Streptolysin O & Streptolysin S?

A

Hemolysins produced by the bacteria

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17
Q

What is streptolysin O?

A

Antigenic
We produce antibodies against it
ASO test collects blood from the patient to determine ASO antibodies indicating a recent strep infection

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18
Q

What are the air requirements for streptolysin O?

A

Oxygen labile - sensitive & destroyed by
Can be seen anaerobically either by an anaerobic plate by stabbing the agar
Enhanced hemolysis is seen in stab

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19
Q

What do strep O & S lyse?

A

WBC & platelets

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20
Q

What are the air requirements for strep S?

A

Oxygen stable

Accounts for the hemolysis we see on routine BAP plates

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21
Q

Diseases associated with S. pyogenes?

A 
Bacterial pharyngitis
Pyodermal infections
Necrotizing fascitis
Streptococcal toxic shock syndrome
Poststreptococcal squelae
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22
Q

Group A strep are what type of strep?

A

A type of pyogenic strep

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23
Q

What is the C-carbohydrate for strep pyogenes?

A

A

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24
Q

What protein is in strep pyogenes & what does it do?

A 
M protein - more than 80 serotypes of these
Produced by the emm genes
Is attached to the cell wall
Essential for virulence
Makes organism resistant to phagocytosis
25
Q

S. pyogenes colonizes what?

A

Throat & skin

26
Q

What does pharyngitis mean?

A

Strep throat

27
Q

What are the characteristics of pharyngitis & tonsillitis?

A

Most bacterial pharyngitis is S. pyogenes
Ages 5-15
Brief incubation, sore throat, malaise, fever, headache, nausea, vomiting
Spread by droplet
Cervical lymph nodes are enlarged - neck
Symptoms subside within 3-5 days unless sequelae occur

28
Q

What do pyodermal infections cause?

A 
Eyrsipelas
Impetigo
Cellulitis
Arthritis
Wound infection
29
Q

What is impetigo?

A

Found more in small children

Associated with bug bites or abrasions

30
Q

What are erysipelas?

A

Infects skin & subcutaneous tissue

Very red with definite border

31
Q

What is cellulitis?

A

Caused by deeper invasion & can lead to sepsis

Cellulitis in patients with vascular disease or diabetes can lead to gangrene

32
Q

Scarlet fever occurs if what?

A

If the bacteria has the pyrogenic exotoxin
Within 1-2 days of the infection
Causes a diffuse red rash on the upper chest that spreads
As it disappears, the skin desquamates - peels

33
Q

What is necrotizing faciitis?

A

Flesh eating strep

34
Q

What are characteristics of necrotizing nasciitis?

A

Caused by different bacteria
Type 2 NF is caused by S. pyogenes
Invasive, rapid inflammation & necrosis of skin, subcutaneous fat are fscia
Follows trauma, burn, lacerations
Patient who is immunocompromised is at risk
Healthy patients without a portal have also been identified

35
Q

What is a portal?

A

Way to get in

Lesion where bacteria is introduced

36
Q

What are characteristics of streptococcal toxic shock syndrome?

A

May follow a severe strep infection & symptoms mimic Staph toxic shock
Patients can have necrotizing fasciitis, organ failure, & death
Group A strep in this condition produce & exotoxin - SpeA
SpeA acts as a super antigen, over-activating the immune system
Young children, especially with chicken pox & elderly are most at risk

37
Q

What are some post streptococcal infection squelae?

A

Rheumatic fever
Glomerulonephritis
Psoriasis

38
Q

What are the characteristics of rheumatic fever?

A

Fever & inflammation of heart, joints, blood vessels, & subcutaneous tissues
Begins about 1 month after the infection
No longer common in the US
Cross reactivity of antibodies to heart tissue -> heart damage

39
Q

What are characteristics of glomerulonephritis?

A

Group A strep
Periorbital edema
More common in children
Follows sore throat or skin infection
Circulating immune complexes may deposit in the glomeruli, leading to inflammation & glomerulonephritis
Usually self limiting
RBC casts seen in urine - blood & protein

40
Q

What are types of ways group A strep is diagnosed by laboratory?

A

Rapid strep test for pharyngitis

Growth on BAP in ambient air & subsequent testing

41
Q

How does the rapid strep test for pharyngitis work?

A

Direct sample is chemically extracted & tested with immunoassay
Negatives should follow up with culture

42
Q

If there is growth of group A on a BAP in ambient air, what subsequent testing should occur?

A

Microbiologist suspicion of GAS leads to serotyping

GAS is PYR+ & sensitive to bacitracin

43
Q

How is group A strep treated?

A

Susceptible to penicillin

Erythromycin for patients allergic to penicillin

44
Q

What is group B strep?

A

Streptococcus agalactiae

45
Q

What are the two syndromes that group B strep causes?

A

Early onset <7 days

Late onset 7 days - 3 months

46
Q

What does early onset of group B strep cause?

A

The majority of cases

Due to vertical transmission from a colonized mother

47
Q

What is the percentage of women that are colonized with group B strep vaginally/rectally?

A

10-30%

48
Q

What are the characteristics of early onset GBS?

A

Associated with prolonged ruptured membranes & obstetric complications & premature birth
Baby has pneumonia &/or sepsis
High mortality rate
Mother colonized with GBS

49
Q

What are the characteristics of late onset GBS in the newborn?

A

Meningitis & sepsis
Lower mortality rate
Mother not colonized with GBS

50
Q

What are the steps to screen pregnant women for GBS?

A

Do urine culture & look for GBS
At 35-37 weeks gestation, vaginal & rectal swabs are collected, & inoculated into todd-hewitt, trans-vag, or lim broth
Broths contain colistin & nalidixic acid, or gentamicin & nalidixic acid; they are selective
Incubate 18-24 hours & subculture to BAP or chromagar in CO2 incubator - differential
Read plates 24 hours later

51
Q

What does selective media do?

A

Inhibits growth of some bacteria while promoting others

52
Q

What does colistin do?

A

Kills gram negative bacteria

53
Q

What are the characteristics of GBS infection in adults?

A

May follow pregnancy or abortion, causing endometritis or wound infections, & endocarditis
Elderly that are immunocompromised are more at risk
Treatment of choice is penicillin, or penicillin & an aminoglycoside

54
Q

How is GBS confirmed in adults?

A

Types of cultures: CSF, blood vag, rectal
Grown to pure culture, on blood - will be beta hemolytic in most cases
Lancefield typing can be done - type B
Bacteria are positive for hippurate hydrolysis & for CAMP factor

55
Q

What are characteristics of group C & G strep?

A

Divided into large & small colony forms
Large colony forming units of beta hemolysis with C or G carbohydrates belong to Streptococcus dysgalactiae subspecies equisimilis - infections are uncommon, but similar to group A strep
Small colony forming units of beta hemolysis with C & G antigens belong to the S. anginosis

56
Q

What are the characteristics of the PYR test?

A

Detects activity of the pyrrolidonyl aminopeptidase
PYR impregnated disks are moistened & 1-2 colonies are rubbed on the paper
Incubated at room temp for 2 minutes & add color developer
Read within 5 minutes
Red - positive = group A strep

57
Q

What are the characteristics of hippurate hydrolysis?

A

Detects the presences of hippuricase
Hippuricase hydrolyzes the substrate sodium hippurate to sodium benzoate & glycine
Bacteria is added to liquid substrate & incubated for 2 hours at 35C
Glycine is detected by the addition of ninhydrin making a purple color

58
Q

What are the characteristics of the SXT plate?

A

Selective with antibiotics suflamethoxazole & trimethoprim used to set up throat cultures
Group A strep will grow, but group C & G are sensitive & won’t grow

59
Q

What is childbed fever associated with?

A

Group A strep

60
Q

What does childbed fever cause?

A

Death or infection of a woman who just had a baby

61
Q

What did Semmelweis do?

A

Drastically cut childbed fever (peurperal fever) in half by washing hands with bleach

Diagnostic Micro Exam 1 (6 decks)

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