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Micro 8-Streptococci Flashcards

1
Q

Are streptococci normally colonize mucosal membranes?

A

Yes.
Many normally colonize mucosal membranes (i.e., part of the normal flora/microbiome). The predominant component of the respiratory, gastrointestinal and genital tract

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2
Q

Streptococci mainly have high virulence. True/False

A

False.

Mainly have low virulence. However may also invade normally sterile body sites, causing significant disease

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3
Q

As staphylococci, streptococci also are catalse positive. True/False

A

False. The test is used to differentiate these microbes.

Streptococci are catalase-negative, whereas staphylococci are catalase-positive

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4
Q

Streptococci are able to grow both aerobically and anaerobically. True/False

A

True. Some are strict (obligate) anaerobes

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5
Q

what are the 7 basic features of streptococci?

A

1) May cause hemolysis on blood agar
2) Most are facultative anaerobes
3) Will grow both aerobically and anaerobically
4) Some are strict (obligate) anaerobes
5) Will only grow in the absence of oxygen
6) Catalase negative
7) Used to differentiate streptococci from staphylococci (also a Gram-positive coccus)

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6
Q

The ability of bacteria to reduce hydrogen peroxide into water and oxygen-producing bubbles is determined by what enzyme?

A

Catalase (absent in Streptococci)

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7
Q

Lancefield classification of streptococci is based on:

1) hemolysis
2) antigens contained in their cell walls
3) emm gene

A

antigens contained in their cell walls.
Most commonly used classification systems:
1. Based on their actions on blood-containing agar – (Haemolysis)
2. Based on antigens contained in their cell walls (Lancefield classification)
3. Molecular classification (newer) - based on emm gene (encodes for M protein)

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8
Q

The pattern of hemolysis in which streptococci reduce hemoglobin and cause greenish discoloration on blood agar is referred to as?

A

α-haemolysis

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9
Q

The pattern of hemolysis in which streptococci lyse erythrocytes and cause complete clearing nearby is called?

A

β-haemolysis

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10
Q

What type of change in blood agar produce γ-haemolytic streptococci?

A

no change in blood agar

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11
Q

Based on Lancefield classification, streptococci of groups A-G all are α-haemolytic. True/False

A

False.

All are β-haemolytic except group D

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12
Q

From the Bacteria’s perspective, what are the factors required to cause infection?

A

1) get in-Portal of entry
2) attach to cells (adhesion)
3) defeat/evade the immune system
4) cause damage to host cells
5) get out and spread further

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13
Q

what are the clinically important streptococci?

A

1) Strep. pyogenes (Group A, β haemolytic)
2) Strep. agalactiae (Group B, β haemolytic)
3) Other β haemolytic streptococci
4) α haemolytic streptococci
- “viridans” streptococci
- Strep. pneumoniae (pneumococcus)
5) Enterococci (Group D, β or non-haemolytic)
6) Peptostreptococcus (anaerobic or non-haemolytic)

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14
Q

Streptococcus pyogenes is group A γ hemolytic streptococci. True/False.

A

False.
It is β-haemolytic as well as Streptococcus agalactiae. • One of the most virulent of the streptococci species with a large range of clinical presentations.

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15
Q

Group A streptococci commonly colonize nasopharynx. True/False

A

False.

They commonly colonize oropharynx of children and young adults (vs staphylococci)

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16
Q

Colonization of group A streptococci in the oropharynx is transient or permanent?

A

Colonization is transient, influenced by acquired immunity & competition from other organisms in the oropharynx

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17
Q

Transmission of group A streptococci is via:

1) aerosols
2) large-droplets
3) hematogenous
4) vector-borne

A

Large-droplet transmission

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18
Q

The major cause of bacterial pharyngitis are:

1) group A streptococci
2) group B streptococci
3) group D streptococci

A

group A streptococci, particularly Streptococcus pyogenes

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19
Q

What are the virulence factors of Group A β-hemolytic streptococci?

A

1) Structural components (cell wall, capsule, etc)
2) Cytolysins (cause cell lysis)
3) Pyrogenic (erythrogenic) exotoxins

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20
Q

What structural components of group A β-hemolytic streptococci are involved in its virulence?

A

–Capsule: resists phagocytosis
–Cell wall: peptidoglycan can activate the alternative complement pathway
–M proteins:
–>80 types, mediate attachment to cells, anti-phagocytic
–Major virulence factors – some types associated with greater severity of the disease
–M like proteins…. Bind IgG/ IgM

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21
Q

Name major cytolysins involved in virulence of group A β hemolytic streptococci?

A 
–Streptolysin O/S exotoxins
      •	ASOT titer
–Hyaluronidase
      •	Can cause tissue destruction, allowing the spread of infection
–Leucocidin
–Haemolysins
–Streptokinase
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22
Q

What are the roles of pyrogenic (erythrogenic) exotoxins of group A β-hemolytic streptococci?

A

–Responsible for rash, fever
–Can be potent activators of the immune system (toxic shock syndrome)
–activation of T cells leads to increased secretion of proinflammatory cytokines produced by both antigen-presenting cells and T lymphocytes

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23
Q

Which structural component of group A β hemolytic streptococci resist phagocytosis?

A

Capsule

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24
Q

Group A β hemolytic streptococci are bacitracin positive or negative?

A

Bacitracin positive (clearing around the bacitracin disk on blood agar)

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25
What are the major clinical manifestations of infection with group A β hemolytic streptococci?
–pharyngitis –scarlet fever –erysipelas, cellulitis, necrotizing fasciitis –toxic shock syndrome, bloodstream infection –pneumonia
26
Infective endocarditis is a common manifestation of group A β hemolytic streptococci infection. True/False
False. | GAS is a very unusual case of infective endocarditis (IE) – but RHD predisposes to IE by other organisms later on
27
Rheumatic fever typically develops after skin infection with group A β hemolytic streptococci. True/False.
False. RF commonly develops after streptococcal pharyngitis, whereas glomerulonephritis typically after skin infection (but also after pharyngitis)
28
What is the predisposing factor for streptococcal pharyngitis
overcrowding, which eases the transmission of bacteria person-to-person spread by droplets of saliva or nasal secretions
29
What is the length of the incubation period of streptococcal pharyngitis 1) several hours to 1 day 2) 2-4 days 3) 7 to 10 days
2-4 days
30
What are the history finding of a patient with streptococcal pharyngitis?
–A patient complains of sore throat –Fever, headache –Nausea and vomiting (especially children)
31
what are the physical examination findings of a patient with streptococcal pharyngitis?
- erythema and edema of the pharynx - lymphadenopathy, especially anterior cervical lymphoid chain (vs infectious mononucleosis which commonly affects posterior cervical chain) - tonsilomegally with exudate, - fever
32
what are the laboratory findings of a patient with streptococcal pharyngitis?
1) Rapid streptococcal antigen test (commonly used in clinical practice, result in 30 minutes, negative result does not rule out diseases) 2) throat culture 3) immunological (antibody) response (anti-streptolysin O titer, ASOT)-important in rheumatic fever and glomerulonephritis
33
what are the complications of streptococcal pharyngitis?
– otitis media – acute mastoiditis –acute glomerulonephritis –acute rheumatic fever (rare in developed countries due to widespread and rapid use of antibiotics)
34
what is the main reason for the antibiotic treatment of streptococcal pharyngitis?
to decrease the risk of autoimmune complications like RF and PSGN
35
widespread activation of T lymphocytes by erythrogenic toxin leading to the release of large quantity cytokines characterize which disease caused by streptococci?
Scarlet fever and Toxic shock syndrome, erythrogenic toxin act as a superantigen
36
what are the clinical manifestations of scarlet fever?
-Pharyngitis + rash (sandpaper rash) -fever -strawberry tongue -can be mistaken with Kawasaki disease –(may also occur following impetigo)
37
what are the types of skin infection with group A β hemolytic streptococci?
1) impetigo (also can be caused by staphylococci) 2) erysipelas 3) cellulitis
38
honey crusted skin lesions characterize?
impetigo
39
what are the predisposing factors for erysipelas and cellulitis?
- disruption to the skin barrier as a result of trauma (e.g. insect bites, abrasions, wounds, injection drug use), - inflammation (e.g. eczema) - preexisting skin infection (e.g. impetigo or tinea pedis) - diabetes mellitus* - varicose veins*
40
what is the anatomical difference of erysipelas and cellulitis?
erysipelas involves the epidermis and superficial lymphatics whereas cellulitis involves deeper dermis and subcutaneous fat.
41
how to differentiate erysipelas and cellulitis on physical examination?
erysipelas: raised and well-demarcated borders cellulitis: the distinction between involved and non-involved skin is not obvious
42
what are the types of necrotizing fasciitis?
Type 1: polymicrobial infection Type 2: monomicrobial – Group A Streptococci Involve deep subcutaneous tissue with the destruction of muscle and fat • Cellulitis after which bullae form; gangrene & systemic signs ensue • Mortality may exceed 50%
43
Describe Streptococcal toxic shock syndrome.
• soft tissue inflammation followed by pain, fever, chills, multi-organ failure • pyrogenic exotoxin production which acts as a superantigen • Rapidly progressive A rash similar to scarlet fever rash
44
describe post-infectious immune complications following group A β hemolytic streptococci infection?
– in rheumatic fever, the antibodies cross-react with cardiac tissue – in post-streptococcal glomerulonephritis, immune complexes are deposited on the glomerular basement membrane – Molecular mimicry
45
manifestations of rheumatic fever develop during streptococcal pharyngitis. True/False
False. | 2-3 weeks after infection
46
what are the clinical manifestations of rheumatic fever?
Fever, arthralgia, and carditis (pancarditis) May also get neurological involvement (Sydenham’s chorea) myocarditis is the most common cause of death during acute RF
47
what is the Jone's criteria?
Major criteria Polyarthritis: A temporary migrating inflammation of the large joints, usually starting in the legs and migrating upwards. Carditis: Inflammation of the heart muscle (myocarditis) which can manifest as congestive heart failure with shortness of breath, pericarditis with a rub, or a new heart murmur. Subcutaneous nodules: Painless, firm collections of collagen fibers over bones or tendons. They commonly appear on the back of the wrist, the outside elbow, and the front of the knees. Erythema marginatum: A long-lasting reddish rash that begins on the trunk or arms as macules, which spread outward and clear in the middle to form rings, which continue to spread and coalesce with other rings, ultimately taking on a snake-like appearance. This rash typically spares the face and is made worse with heat. Sydenham's chorea (St. Vitus' dance): A characteristic series of involuntary rapid movements of the face and arms. This can occur very late in the disease for at least three months from the onset of infection. Minor criteria Fever of 38.2–38.9 °C (100.8–102.0 °F) Arthralgia: Joint pain without swelling (Cannot be included if polyarthritis is present as a major symptom) Raised erythrocyte sedimentation rate or C reactive protein Leukocytosis ECG showing features of heart block, such as a prolonged PR interval (Cannot be included if carditis is present as a major symptom) The previous episode of rheumatic fever or inactive heart disease
48
what are the clinical manifestations of streptococcal glomerulonephritis?
nephritic syndrome: -edema, puffy face, swollen extremities •due to sodium and water retention -Hypertension, with albumin and blood in the urine -Majority of young patients recover completely, however, it may lead to permanent renal damage and may warrant lifelong dialysis or renal transplantation or may be fatal
49
Streptococcus agalactiae (Group b β hemolytic streptococci) colonize the upper respiratory tract. T/F
False. | It colonizes gastrointestinal and genitourinary tract
50
what is the major clinical significance of Streptococcus agalactiae?
``` neonatal sepsis Risk factors are: –maternal colonization –premature delivery –prolonged rupture of membranes –intrapartum fever ```
51
name 2 most important α-hemolytic streptococci.
Viridans streptococci and St. pneumoniae β-haemolytic--S. agalactiae and pyogenes γ-haemolytic--enterococci and S Bovis
52
what is the main clinical significance of viridans streptococci?
a common cause of infective endocarditis after dental manipulation. Normal flora in the oropharynx, GIT; genitourinary tract
53
what is the clinical significance of St. bovis?
linked to colon cancer, cause endocarditis, bacteremia
54
what is the clinical significance of Streptococcus anginosus (milleri)
Associated with purulent infections - causes brain and liver abscesses
55
S. pneumoniae are α-hemolytic and gram-positive bacteria that commonly under the microscope are seen as>.
cocci in chains or diplococci
56
site of colonization of S pneumoniae?
nasopharynx
57
what is the predisposing factor of invasive infection with S. penumoniae?
Splenectomy
58
indication fo vaccination against S. pneumoniae?
children age>65 some chronic diseases, splenectomy, sickle cell disease
59
S. pneumonia is optochin sensitive or resistant?
Sensitive. | Viridans streptococci are optochin resistant
60
colonization of nasopharynx is mediated by
adhesins
61
invasion of the cell is mediated by?
cell wall, pneumolysin, adhesins
62
cell damage by S penumoniae is caused by?
pneumolysin and cell wall which activates the complement system and cytokine release
63
what is the range of diseases caused by St. pneumoniae?
* Pneumonia * Sinusitis and otitis media * Meningitis * Bloodstream infection
64
what are the clinical manifestations of pneumococcal pneumonia?
* Pleuritic chest pain, shortness of breath * Purulent sputum (rust-colored is typical) * Classically “lobar” pneumonia but may cause bronchopneumonia especially in the elderly
65
what is the major predisposing factor for pneumococcal pneumonia?
Influenza infection a major predisposing factor
66
what are the common complications of pneumococcal pneumonia?
Parapneumonic effusion, empyema, lung abscess, bacteraemia
67
what is the predisposing factor for pneumococcal otitis media and sinusitis?
upper respiratory tract infection
68
which bacteria is the most common cause of bacterial meningitis in adults?
S. pneumoniae
69
How does S pneumoniae get to the central nervous system?:
* During a bacteremia * Chronic ear infection * Sinus infections * After head trauma
70
what are the most common species of enterococci (γ hemolytic)
E. faecium and E. faecalis
71
what are the common features of enterococci?
* Bowel flora – usually low virulence * Facultative anaerobes * The hemolytic pattern varies….. mainly γ * Grow in presence of bile salts, i.e grow on MacConkey agar
72
how enterococci are transmitted?
hands environment contaminated food or water
73
what are the risk factors for enterococcal infection?
``` • Recent surgery • Underlying disease –malignancy –burns or trauma –Recent antibiotics –cephalosporins or aminoglycosides –Prolonged hospitalization especially in ICU ```
74
what type of infections causes enterococci?
A. Urinary tract infection: Particularly urinary catheter-related B. Endocarditis C. Bloodstream infection D. Wound infections & intra-abdominal infections Important nosocomial pathogen, particularly vancomycin resistant enterococci (VRE)
75
peptostreptococcus is aerobic or anaerobic?
anaerobic
76
site of colonization of peptostreptococci
the oral cavity, gastrointestinal tract, genitourinary tract and skin
77
range of infections caused by peptostreptococci?
–Aspiration pneumonia –Sinusitis and brain abscess –Intra-abdominal abscesses –Pelvic infections
78
what are the aspects to diagnose the infection?
1)clinical suspicion 2)Appropriate samples sent to the laboratory-based on site of infection –Blood (if invasive disease suspected) –CSF (meningitis) –Urine –Throat swab (pharyngitis) 3)In the laboratory: –Gram stain performed on sterile site sample (blood, CSF, pus) –Culture: takes 24 – 48 hours –Samples incubated aerobically and anaerobically –Blood agar (hemolysis) –MacConkey agar (enterococci)
79
name streptococci that are 1) bacitracin sensitive 2) optochin sensitive 3) bile soluble
1) GAS 2) pneumococcus 3) enterococci
80
urinary antigens detection is used for what streptococcal infection diagnosis
pneumococcal infection
81
what is the most common mechanism of antibiotic resistance of pneumococci?
can alter the structure of penicillin-binding proteins (PBPs) that are found on their surface –β lactam antibiotics (e.g., penicillin) cannot bind to pneumococci and destroy their cell wall (GAS are never resistant to penicillin)
82
common antibiotics used in the treatment of streptococcal infections?
Penicillins –Nearly all β hemolytic streptococci susceptible Cephalosporins –For penicillin-resistant pneumococci –Used for treatment of meningitis – cefOTAXime (3rd gen) –Used if rash with penicillin –Do not use for enterococci (are intrinsically resistant) Vancomycin – If β lactam anaphylaxis – If resistance to β-lactams suspected
83
what antibiotics are used in the treatment of enterococci?
ENTEROCOCCI •First-line treatment for enterococci = amoxicillin •If resistant to this (many E. faecium are) then vancomycin However VRE problematic - (ie cant use vancomycin) •Patients may become colonized, +/- develop a significant infection due to VRE •Limited treatment options, with significant potential side effects and interactions – linezolid

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