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Microbiology 1 > GRAM POSITIVE STREPTOCOCCUS > Flashcards

GRAM POSITIVE STREPTOCOCCUS Flashcards

LECTURE 5

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1
Q

What is the Gram stain result for Streptococcus spp.?

A

Streptococcus spp. are Gram-positive cocci

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2
Q

How do Streptococcus spp. divide?

A

Streptococcus spp. always divide in the same plane and stick together.

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3
Q

What arrangement is commonly observed for Streptococcus spp.?

A

They are found in chains or pairs

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4
Q

What type of anaerobe are Streptococcus spp.

A

Streptococcus spp. are facultative anaerobes

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5
Q

what are the characteristics of streptococcus

A
  1. they are found in chains or pairs
  2. they are facultative anaerobe
  3. they are non-motile
  4. non-sporeforming
  5. they are catalase negative
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6
Q

mention 3 species of

A
  1. S. agalactie
  2. S. pyogenes
  3. S. pneumoniae
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7
Q

What are the three main classification methods for Streptococcus spp.

A
  1. brown’s classification
  2. lancefield grouping
  3. Griffith typing
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8
Q

What does Brown’s classification refer to in the context of Streptococcus spp.?

A

Brown’s classification categorizes Streptococcus spp. based on their hemolytic properties (alpha, beta, or gamma hemolysis).

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9
Q

What is the significance of Lancefield grouping in Streptococcus classification?

A

Lancefield grouping is based on the presence of specific cell wall antigens (group A, B, C, etc.) and helps differentiate different Streptococcus species.

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10
Q

What is Griffith typing used for in Streptococcus identification?

A

Griffith typing involves serological testing to identify specific Streptococcus strains based on their capsular antigens

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11
Q

Which classification method is based on hemolytic properties of Streptococcus spp.?

A

Brown’s classification

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12
Q

What does Lancefield grouping primarily focus on

A

Lancefield grouping focuses on cell wall antigens

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13
Q

What is the primary purpose of Griffith typing

A

Griffith typing is used for serological identification of Streptococcus strains based on capsular antigens

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14
Q

in brown’s classification differentiate between alpha (a) hemolytic, beta (b) hemolytic and gamma (y) hemolytic

A
  1. In alpha hemolytic there is partial hemolysis
  2. In beta hemolytic there is complete hemolysis
  3. In gamma hemolytic there is no hemolysis
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15
Q

which streptococci species will result in alpha hemolytic (partial hemolysis)

A
  1. Pneumoniae
  2. Viridans
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16
Q

which streptococci species will result into complete hemolysis (clear)

A
  1. pyogenes
  2. Agalactiae
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17
Q

which streptococci species will result into no hemolysis

A

Enterococcus ( faecalis and farcium)

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18
Q

What is Lancefield grouping

A

Lancefield grouping is a classification system used for β-hemolytic Streptococcus spp. based on specific carbohydrate antigens in their cell walls.

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19
Q

Which Streptococcus species belong to Group A

A

Group A Streptococcus corresponds to Streptococcus pyogenes.

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20
Q

Which Streptococcus species belong to Group B?

A

Group B Streptococcus corresponds to Streptococcus agalactiae

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21
Q

What is the primary basis for Lancefield grouping

A

The presence of specific carbohydrate antigens in the cell wall determines the Lancefield group to which a Streptococcus species belongs.

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22
Q

how is Group A Streptococcus (GAS) spead

A
  1. Airborne dispersal
  2. Direct contact
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23
Q

mention skin infections caused by skin sepsis due to GAS

A
  1. Impetigo
  2. Erysipelas
  3. Cellulitis
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24
Q

what are characteristics of erysipelas

A
  1. skin is red , swollen and raised
  2. orange- peel texture to skin
  3. acutely unwell with fever
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25
Q

what are characteristics of cellulitis

A
  1. infection of subcutameous tissue
  2. red painful swelling, ussualy of a limb
  3. fever, warmth at swelling
  4. often suffer from recurrent attacks
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26
Q

mention the severe skin sepsis due to GAS and is characteristics

A
  1. necrotising fasciitis
    characteristics: i.acute necrotising cellulitis
    ii. involves the dermis, subcutaneous fat, superficial fascia
    iii. ussually occurss after surgery
    iv. other risk factors include diabetes, age and obesity
    v. rapid deterioration with possible multi organ failure
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27
Q

mention the non-invasive GAS infections

it means that the steptococci does not spread to or damage internal org

A
  1. pharyngitis/ tonsillitis
  2. scarlet fever
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28
Q

what are the characteristics of pharyngitis/tonsillitis

A
  1. Most common infection caused by GAS
  2. Abrupt onset, 2-4 days after exposure
  3. Sore throat, fever, malaise, headache
  4. Pharynx reddened, exudate on tonsils
  5. Clinically indistinguishable from viral sore throat
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29
Q

What is scarlet fever

A

Scarlet fever is an infectious disease caused by certain strains of Streptococcus pyogenes (group A streptococcus). It is characterized by a diffuse erythematous (flushing) rash of the skin and mucous membranes.

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30
Q

What produces the pyogenic toxin associated with scarlet fever?

A

Certain strains of Streptococcus pyogenes that cause pharyngitis produce the pyogenic toxin responsible for scarlet fever.

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31
Q

When does the rash typically develop in scarlet fever

A

The rash usually develops 1-2 days after the first symptoms of pharyngitis.

32
Q

Where does the rash initially appear in scarlet fever?

A

Initially, the rash appears on the upper chest.

33
Q

How does the rash spread in scarlet fever

A

The rash spreads to the extremities (arms and legs) from the initial chest area.

34
Q

mention the diases caused by GAS and the required sample type

A

Impetigo pus

Erysipelas swab of lesions

Cellulitis swab of lesions

Necrotising: fasciitis exudate, biopsy, tissue fluid

Pharyngitis: throat swab, serum

Scarlet fever: throat swab, serum

35
Q

What are the culture requirements for GAS?

A

Culture GAS on blood agar.

36
Q

Is GAS an obligate aerobe or facultative anaerobe?

A

GAS is a facultative anaerobe

37
Q

Describe the appearance of GAS colonies on blood agar

A

GAS colonies appear transparent, convex, entire, circular, and shiny

38
Q

What type of hemolysis is associated with GAS on blood agar

A

GAS exhibits a wide zone of β-hemolysis

39
Q

How does sensitivity to bacitracin aid in GAS identification

A

A zone of sensitivity to bacitracin allows a presumptive diagnosis of GAS.

40
Q

what will be the result of GAS in catalase test

A

catalase negative

41
Q

What does ASO antibody stand for, and what does it measure?

A

ASO stands for “anti-streptolysin O.” It measures the levels of antibodies produced in response to streptolysin O, a toxin produced by GAS

42
Q

What is the significance of the anti-streptolysin O titre?

A

Elevated anti-streptolysin O titers (>200 IU/ml) indicate recent or ongoing GAS infection.

43
Q

What is the typical detection limit for most ASO antibody tests?

A

Most ASO antibody tests have a detection limit of 200 IU/ml.

44
Q

Describe the principle of the latex agglutination test for GAS.

A

In the latex agglutination test, latex particles coated with streptolysin O are mixed with patient serum. If antibodies (Abs) against streptolysin O are present, agglutination (clumping) occurs.

45
Q

what is the treatment for GAS

A
  1. Penicillin (erythromycin in hypersensitive patients)
  2. Oral or i.v. as appropriate
46
Q

What is the normal habitat of GBS in the human body

A

GBS is a normal faecal commensal, meaning it resides in the gastrointestinal tract.

47
Q

Where does GBS specifically colonize in women?

A

GBS colonizes the genital tract of approximately 20-25% of women

48
Q

What percentage of infants born to colonized mothers become colonized with GBS?

A

Approximately 40-70% of infants born to colonized mothers become colonized with GBS

49
Q

What proportion of colonized infants go on to develop GBS infections?

A

Only about 1% of colonized infants become infected with GBS.

50
Q

mention the diseases caused by group B streptococci (GBS)

A
  1. Neonatal meningitis and sepsis
51
Q

chatacteristics of neonatal meningitis and sepsis

A

early onset: acquired from mother during birth
: Overwhelming general sepsis, meningitis in 30% cases
: High mortality
late onset: Acquired by cross-infection in the hospital
* May be acquired from mother or via cross-infection from other
mothers, neonates or HCWs
* Lower mortality

52
Q

sample from mother from GBS testing

A

high vaginal swab (HVS)

53
Q

Samples from neonate for GBS testing

A

CSF
Blood
ear swab(becomes colonised during delivery)

54
Q

Gram staining results for GBS

A

Gram positive cocci in pairs, chains or singly

55
Q

culture requirements for GBS

A
  1. culture on blood agar
  2. falcutative anaerobe
  3. incubate at 35-37 degree celcius
56
Q

what are the culture appearance for GBS

A

Colonies are larger whitish- grey and smooth
zone of beta-hemolysis is much smaller

57
Q

treatment for GBS

A

Penicillin (it is gentamicin resistance)

58
Q

what result will GBS give in a catalase test

A

catalase negative

59
Q

what test result will GBS give in a lancefield grouping

A

Pure colonies that have been shown to be catalase negative, penicillin sensitive,
gentamicin resistant GPC are mixed with specific Group B antiserum

60
Q

What is the purpose of the CAMP test in the laboratory diagnosis of Group B Streptococcus (GBS)?

A

The CAMP test is used to confirm the presence of GBS when reagents for Lancefield grouping are not available.
It detects an extracellular diffusible protein produced by GBS known as the CAMP factor.
The CAMP factor interacts with the β-lysin produced by Staphylococcus aureus, resulting in enhanced hemolysis on sheep blood agar.

61
Q

What are the essential requirements for performing the CAMP test?

A

A β-lysin strain of Staphylococcus aureus.
A test organism (presumably GBS).
A 10% blood agar (BA) plate.
The test organism should be streaked across the plate, and the β-lysin strain of S. aureus should be inoculated at right angles to it.
The test organism must not physically touch the S. aureus streak.
Enterococcus spp. is inoculated as a negative control.

62
Q

How is the presence of GBS determined using the CAMP test?

A

After overnight incubation at 35-37°C, observe the area where the S. aureus streak and the test organism meet.
If there is an arrowhead-shaped area of hemolysis, the test organism is presumed to be GBS.

63
Q

diseases caused by streptococcus pneumoniae

A
  1. pneumonia
  2. Bacteremia
  3. Otitis media
  4. Meningitis
  5. Conjunctivitis
64
Q

What is the natural habitat of Streptococcus pneumoniae?

A

Streptococcus pneumoniae is a commensal bacterium commonly found in the upper respiratory tract (URT).

65
Q

How does Streptococcus pneumoniae colonize individuals?

A

Streptococcus pneumoniae can repeatedly colonize the same individual with different strains over time.

66
Q

What are the predisposing factors for disease caused by Streptococcus pneumoniae?

A
  1. Age plays a significant role, with a bimodal distribution (meaning it affects both young and elderly individuals).
  2. Reduced immune response due to aging or other factors.
    Immune deficiency increases susceptibility.
  3. Streptococcus pneumoniae is an important cause of pneumonia in HIV/AIDS patients.
  4. Patients undergoing steroidal treatment are also at risk.
  5. Individuals who have undergone a splenectomy (removal of the spleen) are more susceptible to infections caused by this bacterium
67
Q

explain these diseases caused by streptococcus pneumoniae
1. pneumonia, 2. Bacteremia ,3. Otitis media, 4. Meningitis
5. Conjunctivitis

A

Pneumonia: An infection that causes inflammation in the air sacs of the lungs, leading to symptoms such as cough, fever, and difficulty breathing
2. Bacteremia: The presence of bacteria in the bloodstream, which can lead to severe infections and sepsis
3. Otitis media: Inflammation or infection of the middle ear, often causing ear pain and sometimes fluid accumulation behind the eardrum.
4. Meningitis: Inflammation of the protective membranes covering the brain and spinal cord, resulting in symptoms like severe headache, fever, and neck stiffness.
5. Conjunctivitis: Commonly known as “pink eye,” it is an inflammation of the conjunctiva (the thin membrane covering the white part of the eye and inner eyelids), causing redness, itching, and discharg.

68
Q

epxlain the fram staining characteristics for streptococcus pneumoniae

A
  1. gram positive diplococci (These are round bacteria (cocci) that typically occur in pairs (diplococci))
  2. diplococcus is surrounded by unstained empty are of the capsure
69
Q

characteristics of gram positive diplococci

A
  1. These are round bacteria (cocci) that typically occur in pairs (diplococci).
  2. elongated shape
  3. They stain purple with the Gram stain, indicating a thick peptidoglycan layer in their cell walls.
    Examples include Streptococcus pneumoniae and Enterococcus spp.1
70
Q

culture requirements for streptococcus pneumoniae

A
  1. Culture on blood agar
  2. Facultative anaerobe
  3. Incubate at 35-37oC
71
Q

culture appearance for streptococcus pneumoniae

A
  1. Translucent, mucoid, glistening colonies
  2. Colonies dip down in the centre after increased incubation, due to action of autolysisns
    (‘draughtsmen’ colonies)
  3. α-haemolysis
    * Partial haemolysis around colonies, giving a green decolourisation of the medium
    * A useful test in the presumptive identification of Streptococcus pneumoniae is sensitivity to
    optochin
    * A 5µg disc is placed on the plate before incubation
    * Zone of inhibition should be at least 10mm
    * Most other α-haemolytic Streptococcus spp. are resistant to optoc
72
Q

what is the catalase result for streptococci pneumoniae

A

catalase negative

73
Q

What is the purpose of the bile solubility test in microbiology

A

The bile solubility test helps differentiate Streptococcus pneumoniae from other α-hemolytic streptococci.

74
Q

How is the bile solubility test performed

A

A heavy inoculum of the test organism is emulsified in saline, and bile salt (sodium deoxycholate) is added.
Explanation: If the test organism is Streptococcus pneumoniae, it will dissolve, resulting in a clearing of the turbidity within 1-15 minutes.

75
Q

What is the purpose of the Pneumococcal Ag test in the laboratory diagnosis of Streptococcus pneumoniae?

A
  1. The Pneumococcal Ag test detects the presence of pneumococcal antigens in cerebrospinal fluid (CSF) and serum.
    Explanation: It helps confirm the diagnosis of Streptococcus pneumoniae infections
76
Q

How is the Pneumococcal Ag test performed?

A

Latex particles coated with capsular antibodies (Abs) are mixed with the patient’s sample.
Explanation: If the patient’s sample contains capsular antigen (Ag), agglutination (clumping) occurs, indicating the presence of S. pneumoniae.

77
Q

treatment of treptococcus pneumoniae

A
  • Chloramphenicol
  • Cephalosporins
  • Erythromycin
  • Tetracycline

Microbiology 1 (27 decks)

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