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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
What protein is in strep pyogenes & what does it do?
``` 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
S. pyogenes colonizes what?
Throat & skin
26
What does pharyngitis mean?
Strep throat
27
What are the characteristics of pharyngitis & tonsillitis?
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
What do pyodermal infections cause?
``` Eyrsipelas Impetigo Cellulitis Arthritis Wound infection ```
29
What is impetigo?
Found more in small children | Associated with bug bites or abrasions
30
What are erysipelas?
Infects skin & subcutaneous tissue | Very red with definite border
31
What is cellulitis?
Caused by deeper invasion & can lead to sepsis | Cellulitis in patients with vascular disease or diabetes can lead to gangrene
32
Scarlet fever occurs if what?
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
What is necrotizing faciitis?
Flesh eating strep
34
What are characteristics of necrotizing nasciitis?
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
What is a portal?
Way to get in | Lesion where bacteria is introduced
36
What are characteristics of streptococcal toxic shock syndrome?
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
What are some post streptococcal infection squelae?
Rheumatic fever Glomerulonephritis Psoriasis
38
What are the characteristics of rheumatic fever?
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
What are characteristics of glomerulonephritis?
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
What are types of ways group A strep is diagnosed by laboratory?
Rapid strep test for pharyngitis | Growth on BAP in ambient air & subsequent testing
41
How does the rapid strep test for pharyngitis work?
Direct sample is chemically extracted & tested with immunoassay Negatives should follow up with culture
42
If there is growth of group A on a BAP in ambient air, what subsequent testing should occur?
Microbiologist suspicion of GAS leads to serotyping | GAS is PYR+ & sensitive to bacitracin
43
How is group A strep treated?
Susceptible to penicillin | Erythromycin for patients allergic to penicillin
44
What is group B strep?
Streptococcus agalactiae
45
What are the two syndromes that group B strep causes?
Early onset <7 days | Late onset 7 days - 3 months
46
What does early onset of group B strep cause?
The majority of cases | Due to vertical transmission from a colonized mother
47
What is the percentage of women that are colonized with group B strep vaginally/rectally?
10-30%
48
What are the characteristics of early onset GBS?
Associated with prolonged ruptured membranes & obstetric complications & premature birth Baby has pneumonia &/or sepsis High mortality rate Mother colonized with GBS
49
What are the characteristics of late onset GBS in the newborn?
Meningitis & sepsis Lower mortality rate Mother not colonized with GBS
50
What are the steps to screen pregnant women for GBS?
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
What does selective media do?
Inhibits growth of some bacteria while promoting others
52
What does colistin do?
Kills gram negative bacteria
53
What are the characteristics of GBS infection in adults?
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
How is GBS confirmed in adults?
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
What are characteristics of group C & G strep?
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
What are the characteristics of the PYR test?
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
What are the characteristics of hippurate hydrolysis?
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
What are the characteristics of the SXT plate?
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
What is childbed fever associated with?
Group A strep
60
What does childbed fever cause?
Death or infection of a woman who just had a baby
61
What did Semmelweis do?
Drastically cut childbed fever (peurperal fever) in half by washing hands with bleach

Diagnostic Micro Exam 1 (6 decks)

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