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MTAP FIRST SEM 2024-2025 > MICROBIOLOGY-CATALASE NEGATIVE, GRAM-POSITIVE COCCI (STREPTOCOCCUS, ENTEROCOCCUS, AND SIMILAR ORGANISMS) > Flashcards

MICROBIOLOGY-CATALASE NEGATIVE, GRAM-POSITIVE COCCI (STREPTOCOCCUS, ENTEROCOCCUS, AND SIMILAR ORGANISMS) Flashcards

1
Q

What are the most commonly encountered bacteria in human infections?

A

S. pyogenes, S. agalactiae, S. pneumoniae, E. fecalis, and E. faecium.

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2
Q

iDENTIFY

  • Catalase-negative
  • Gram-positive cocci in pairs or chains
  • Facultative anaerobe
A

STREPTOCOCCUS, ENTEROCOCCUS, AND SIMILAR ORGANISMS

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3
Q

CHARACTERISTIC NI Streptococcus
pyogenes (Group A)

A
  • Gram-positive cocci in
    chains
  • Lancefield group A
  • Group A streptococcus
  • β-hemolytic group A
    streptococcus
  • Bacitracin sensitive
  • PYR test positive
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4
Q

What are common habitats of Streptococcus
pyogenes in the human body?

A
  • Not considered normal microbiota
  • Inhabits skin and upper respiratory tract
    of humans; carried on nasal, pharyngeal,
    and sometimes anal mucosa
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5
Q

What are the modes of transmission for Streptococcus pyogenes

A
  • Direct contact: person to person
  • Indirect contact: aerosolized
    droplets from coughs and sneezes
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6
Q

Virulence factors ni Streptococcus
pyogenes

A

Streptolysin O
Streptolysin S
Streptococcal pyrogenic exotoxins (SPEs)
M protein
Hyaluronidase
C5a peptidase
Erythrogenic toxin
Streptokinase
Protein F
DNASeB
Exotoxin B

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7
Q

IDENTIFY

  • Responsible for the β-hemolytic pattern on blood agar plates
  • Oxygen-labile, immunogenic, capable of lysing erythrocytes, leukocytes, platelets, and cultured cells in the absence of room air
  • Inhibited by cholesterol in skin lipids (no immunity associated with skin
    infections)
A

Streptolysin O

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8
Q
  • Responsible for the β-hemolytic pattern on blood agar plates
  • Oxygen-stable, nonimmunogenic hemolysin, capable of lysing erythrocytes,
    leukocytes, and platelets in the presence of room air
A

Streptolysin S

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9
Q
  • Erythrogenic toxins produced by the lysogenic strains
  • Heat labile
  • Superantigens, activating macrophages, T-helper cells, and immune mediators
A

Streptococcal pyrogenic exotoxins (SPEs)

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10
Q
  • Causes the streptococcal ell to resist phagocytosis
  • Enables the bacterial cell to adhere to mucosal cells
A

M protein

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11
Q
  • Spreading factor
  • Favors the spread of the organism through tissues
A

Hyaluronidase

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12
Q
  • Serine protease capable of inactivating C5a
A

C5a peptidase

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13
Q
  • Causes red spreading rash in scarlet fever
A

Erythrogenic toxin

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14
Q
  • Causes lysis of fibrin clots
A

Streptokinase

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15
Q
  • Fibronectin-binding protein that facilitates adhesion to epithelial cells
A

Protein F

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16
Q
  • Protease that rapidly destroys tissue
A

Exotoxin B

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17
Q

Antigenic and antibodies can be detected following infection

A

DNASeB

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18
Q

What is the most common bacterial cause of strep throat?

A

Streptococcus pyogenes

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19
Q

What age group is most frequently affected by acute pharyngitis?

A

Children between ages 5 and 15 years old.

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20
Q

How is strep throat diagnosed?

A

By throat culture or a positive quick “strep” test.

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21
Q

What are the characteristic lesions of impetigo?

A

Perioral blistered lesions with honey-colored crusts.

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22
Q

What is a complication of impetigo?

A

Post-streptococcal glomerulonephritis (GN).

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23
Q

A superficial infection that extends into the dermal lymphatics.

A

erysipelas

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24
Q

What enzyme facilitates the spread of cellulitis?

A

Hyaluronidase (spreading factor).

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25
Q

A rapidly progressive infection of deep subcutaneous tissues facilitated by exotoxin B.

A

necrotizing fasciitis

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26
Q

Deeper infection involving subcutaneous or dermal tissues

A

Cellulitis

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27
Q

What toxins are associated with scarlet fever?

A

Streptococcal pyrogenic exotoxins (SPEs)

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28
Q

What are the characteristic symptoms of scarlet fever?

A

Rash of the upper face and trunk (sandpaper-like), and strawberry tongue.

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29
Q

Occurs in association with streptococcal pharyngitis

A

Scarlet fever

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30
Q

Multisystem involvement: renal and respiratory failure, rash, and diarrhea.

A

Streptococcal Toxic Shock Syndrome

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31
Q

What mediates streptococcal toxic shock syndrome?

A

Production of potent SPE.

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32
Q

Are blood cultures often positive in streptococcal toxic shock syndrome?

A

Yes.

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33
Q

What protein mediates rheumatic fever?

A

M protein.

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34
Q

Identify

Symptoms: Fever, endocarditis, subcutaneous nodules, and polyarthritis.

A

Rheumatic Fever

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35
Q

What type of infection typically leads rheumatic fever?

A

A respiratory tract infection believed to be caused by S. pyogenes.

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36
Q

What mediates acute glomerulonephritis?

A

M protein.

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37
Q

What are the symptoms of acute glomerulonephritis?

A

Edema, hypertension, hematuria, and proteinuria.

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38
Q

What causes immune complex deposition on the glomerular basement membrane in acute glomerulonephritis?

A

M protein.

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39
Q

What conditions can lead acute glomerulonephritis?

A

Post-impetigo or postpharyngitic.

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40
Q

What are the microscopic characteristics of Streptococcus pyogenes?

A

-Gram-positive cocci,
-short chains or pairs,
-round to oval-shaped, occasionally forming elongated cells resembling pleomorphic corynebacterial or lactobacilli.

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41
Q

What media are used for the cultivation of Streptococcus pyogenes?

A

-5% sheep blood agar
-chocolate agar.
-Throat swabs use 5% sheep blood agar with trimethoprim-sulfamethoxazole (SXT).

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42
Q

what are the colony characteristics of Streptococcus pyogenes on blood agar?

A

Small, transparent, and smooth colonies with β-hemolysis.

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43
Q

What is the purpose of the bacitracin test?

A

Presumptive identification and differentiation of β-hemolytic group A streptococci (S. pyogenes - susceptible) from other β-hemolytic streptococci.

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44
Q

What indicates a positive bacitracin test?

A

Any ZOI greater than 10 mm (SUSCEPTIBLE).

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45
Q

What indicates a negative bacitracin test?

A

No ZOI (RESISTANT).

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46
Q

What is the name of the disk used in the bacitracin susceptibility test?

A

TaxoA disk.

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47
Q

How many units of bacitracin are in the TaxoA disk used for susceptibility testing?

A

0.04 units.

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48
Q

What is the purpose of the PYR test?

A

Presumptive identification of Group A streptococci (S. pyogenes) and enterococci by the presence of the enzyme L-pyrrolidonyl arylamidase.

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49
Q

What indicates a positive PYR test?

A

Bright red color within 5 minutes.

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50
Q

What indicates a negative PYR test?

A

No color change or an orange color.

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51
Q

What enzyme hydrolyzes the substrate L-pyrrolidonyl-β-naphthylamide?

A

L-pyrrolidonyl arylamidase.

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52
Q

What is the product formed when L-pyrrolidonyl arylamidase hydrolyzes L-pyrrolidonyl-β-naphthylamide?

A

β-naphthylamine.

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53
Q

Which reagent is used to detect β-naphthylamine in the L-pyrrolidonyl arylamidase test?

A

N,N-dimethylaminocinnamaldehyde.

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54
Q

What type of reaction does L-pyrrolidonyl arylamidase catalyze?

A

The hydrolysis of L-pyrrolidonyl-β-naphthylamide.

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55
Q

Which serodiagnostic test is associated with pyoderma and skin infections?

A

Anti-Dnase B

56
Q

What are some serodiagnostic tests for Streptococcus pyogenes infections?

A

Anti-streptolysin O (ASO), Anti-Dnase B, Antistreptokinase, and Antihyaluronidase.

57
Q

What are the characteristics of Streptococcus agalactiae(Group B)

A
  • Gram-positive cocci in chains
  • Lancefield group B
  • Group B streptococcus
  • β-hemolytic group B streptococcus
  • Bacitracin resistant
  • CAMP test positive
  • PYR negative
  • Hippurate hydrolysis positive
  • Resistant to SXT
58
Q

What are common habitats of Streptococcus
agalactiae in the human body?

A
  • Normal microbiota: Female genital tract and lower genital tract
  • Occasional colonizer of upper respiratory tract
59
Q

What are the modes of transmission for Streptococcus agalactiae

A
  • Endogenous strain: gaining access to sterile sites probable
  • Direct contact: person to person from mother in utero or during delivery; nosocomial transmission by unwashed
    hands of mother or health care personnel
60
Q

VIRULENCE FACTORS ni Streptococcus
agalactiae

A

-Capsule
-Others (DNAse, hyaluronidase)

61
Q

Most important virulence factor

A

Capsule

62
Q

Not been shown to be factors in infection

A

Others (DNAse, hyaluronidase)

63
Q

How do neonates typically acquire pneumonia caused by Streptococcus pyogenes?

A

By inhaling organisms as they pass down the birth canal

64
Q

At what age is pneumonia most commonly seen in neonates due to Streptococcus pyogenes?

A

0-2 months old

65
Q

What are the common infections caused by Streptococcus pyogenes in neonates and infants?

A

Pneumonia, meningitis, and sepsis.

66
Q

What postpartum infection can Streptococcus pyogenes cause in adults, and what can it lead to?

A

Endometritis, which can lead to pelvic abscesses and septic shock.

67
Q

What are some of the infections caused by Streptococcus pyogenes in adults?

A

Bacteremia, pneumonia, endocarditis, arthritis, osteomyelitis, and skin and soft tissue infections.

68
Q

Which group of adults is particularly at risk for Streptococcus pyogenes infections?

A

Immunocompromised adults.

69
Q

What are the microscopic characteristics of Streptococcus pyogenes in clinical specimens and culture?

A

Gram-positive cocci that form short chains in clinical specimens and long chains in culture.

70
Q

What are the colony characteristics of Streptococcus pyogenes on blood agar?

A

Grayish-white mucoid colonies surrounded by a small zone of β-hemolysis.

71
Q

What medium is used for genital carriage of GBS during pregnancy?

A

Vaginal or rectal swab inoculated into Todd-Hewitt broth (gentamicin, nalidixic acid, or colistin and nalidixic acid) such as LIM.

72
Q

What color do colonies of GBS appear on CHROMagar StrepB?

A

Mauve colored.

73
Q

What is the purpose of the CAMP test?

A

To differentiate GBS (S. agalactiae - positive) from other streptococcal species.

74
Q

What indicates a positive CAMP test?

A

Enhanced hemolysis is indicated by an arrowhead-shaped zone of beta-hemolysis at the juncture of the two organisms.

75
Q

How does the CAMP factor function?

A

It acts synergistically with the beta-lysin of Staphylococcus aureus to enhance the lysis of red blood cells (RBCs).

76
Q

How is the CAMP test set up on a sheep blood agar plate?

A

Staphylococcus aureus is streaked in a straight line on the agar, and the test organism (such as GBS) is streaked perpendicular to the S. aureus streak.

77
Q

What enzyme is used for the presumptive identification of a variety of organisms in the hippurate hydrolysis test?

A

Hippuricase.

78
Q

It is used for the presumptive identification of various organisms by detecting the production of the enzyme hippuricase.

A

Hippurate Hydrolysis test

79
Q

CHARACTERISTICS NI Streptococcus
pneumoniae

A
  • Gram-positive “lancet-shaped” cocci
  • Alpha-hemolytic
  • Bile solubility sensitive
  • Optochin sensitive
  • Positive Quellung reaction
80
Q

What is the principle reaction involved in the Hippurate Hydrolysis test?

A

Hippuric acid is broken down into glycine and benzoic acid.

80
Q

What is the visual indicator of a positive Hippurate Hydrolysis test?

A

purple-colored product indicates a positive test result.

80
Q

Which compound is deaminated by ninhydrin in the Hippurate Hydrolysis test?

A

Glycine

81
Q

What are common habitats of Streptococcus
pneumoniae in the human body?

A

Colonizer of the nasopharynx

82
Q
  • Key virulence factor
  • Inhibits phagocytosis
  • 80 antigenic types
A

Capsule

82
Q

VIRULENCE FACTORS NI Streptococcus
pneumoniae

A

CAPSULE
PNEUMOLYSIN
PHOSPHORYCHOLINE

82
Q

MODE OF TRANSMISSION NI Streptococcus
pneumoniae

A

Direct contact: person to person with contaminated respiratory secretions

83
Q
  • Activates the cell the classical complement pathway
  • Mediates the suppression of the oxidative burst of the phagocytes
A

Pneumolysin

84
Q
  • Binds to receptors for platelet-activating factor in endothelial cells, leukocytes,
    platelets, and tissue cells of the lungs and meninges providing for entry and
    spread of the organism
A

Phosphorylcholine

85
Q

What are some common infections caused by Streptococcus pneumoniae?

A

Sinusitis, otitis media, bacteremia, and meningitis.

85
Q

What percentage of bacterial pneumonia cases are caused by Streptococcus pneumoniae?

A

95% of all bacterial pneumonia

86
Q

What is the leading cause of bacterial meningitis in infants, young children, and adults in the US?

A

Streptococcus pneumoniae.

87
Q

Which bacteria follow Streptococcus pneumoniae as common causes of bacterial meningitis in the US?

A

Neisseria meningitidis and Haemophilus influenzae.

88
Q

How does optochin work in the susceptibility test?

A

Optochin interferes with the ATPase and production of ATP in microorganisms, inhibiting the growth of susceptible organisms and creating a zone of inhibition (ZOI) around the disk.

88
Q

What is the purpose of the optochin (P disk) susceptibility test?

A

To determine the effect of optochin on an organism and differentiate Streptococcus pneumoniae (susceptible) from other alpha-streptococci (resistant).

89
Q

What indicates a positive optochin test?

A

A ZOI of at least 14 mm with a 6 mm disk (SUSCEPTIBLE).

90
Q

What indicates a negative optochin test?

A

No ZOI (RESISTANT).

91
Q

What is the purpose of the bile solubility test?

A

To differentiate Streptococcus pneumoniae (positive; soluble) from alpha-hemolytic streptococci (negative; insoluble).

92
Q

How does the bile solubility test work?

A

Bile or a solution of a bile salt (sodium deoxycholate) rapidly lyses pneumococcal colonies, depending on the presence of amidase.

93
Q

What indicates a positive bile solubility test?

A

Colony disintegrates; an imprint of the lysed colony may remain in the zone.

94
Q

What does the Quellung test detect?

A

Capsular subtypes of Streptococcus pneumoniae.

94
Q

What indicates a negative bile solubility test?

A

Intact colonies.

95
Q

How does the Quellung test work?

A

It is a microscopic “precipitin test” in which the capsules surrounding the pneumococci appear to swell.

96
Q

what are the characteristics ni Enterococcus

A
  • Previously classified as Group D
  • PYR positive
  • Posses group D antigen
  • Grows in 6.5% NaCl
  • LAP positive
97
Q

HABITAT ni Enterococcus

A
  • Normal microbiota: humans, animals, and birds
  • E. faecalis and E. faecium are normal
    flora of the human GIT and female GUT
  • Colonizers
98
Q

Mode transmission ni Enterococcus

A
  • Endogenous strain: gains access to sterile sites
  • Direct contact: person to person
  • Contaminated medical equipment
99
Q

Which two Enterococcus species are most commonly encountered as pathogens?

A

E. faecalis and E. faecium.

100
Q

From which body sites are Enterococcus species commonly isolated?

A

The respiratory tract and myocardium.

101
Q

Which Enterococcus species is most commonly encountered?

A

E. faecalis.

102
Q

Which Enterococcus species is more frequently resistant to vancomycin?

A

E.faecium

103
Q

Give at least 3 Virulence Factors ni Enterococcus

A
  • Aggregation substance
  • Capsular polysaccharides
  • Surface carbohydrates
  • Ability to translocate across intact intestinal mucosa
  • Hemolysis
  • Lipoteichoic acid
  • Gelatinase
  • Superoxide production
  • Peptide inhibitors
  • Ability to adhere to extracellular
    matrix proteins
104
Q

What are some common infections caused by Enterococcus species?

A

Urinary tract infections, bacteremia, endocarditis, intraabdominal, pelvic, wound, and soft tissue infections.

105
Q

What test can be used to differentiate enterococci from non enterococci based on salt tolerance?

A

The salt tolerance test.

105
Q

What indicates a positive result in the salt tolerance test?

A

Visible turbidity in the broth, with or without a color change from purple to yellow.

105
Q

What indicates a negative result in the salt tolerance test?

A

No turbidity or color change.

106
Q

What concentration of NaCl is used in the broth for the High Salt Tolerance Test?

A

6.5% NaCl is used in the heart infusion broth.

107
Q

What enzyme is detected in the Leucine Aminopeptidase (LAP) test?

A

Leucine aminopeptidase.

108
Q

What are the components of the test medium used in the High Salt Tolerance Test?

A

The test medium contains 6.5% NaCl, heart infusion broth, glucose, and bromcresol purple as an indicator.

109
Q

What indicates a positive LAP test?

A

Development of a red color within 1 minute after adding cinnamaldehyde reagent.

110
Q

Which antibiotics are Enterococcus species intrinsically resistant to?

A

Cephalosporins and aminoglycosides.

111
Q

What indicates a negative LAP test?

A

No color change or development of a slight yellow color.

112
Q

What is VRE?

A

Vancomycin-resistant Enterococcus.

113
Q

What substrate is used in the Leucine Aminopeptidase Test?

A

Leucine-beta-naphthylamide.

114
Q

Are viridans streptococci groupable by Lancefield serology?

A

No, they are not groupable by Lancefield serology.

115
Q

They are fastidious, some strains require increased carbon dioxide for growth, and they produce alpha-hemolysis or no hemolysis (greening) on sheep blood agar.

A

viridans streptococci

116
Q

What smell is associated with viridans streptococci on chocolate agar?

A

Butterscotch smell.

117
Q

What are the groups of viridans streptococci?

A

Mutans group, salivarius group, bovis group, anginosus group (previously S. milleri group), and mitis group.

118
Q

Where is the S. anginosus group normally found?

A

In the oral cavity, oropharynx, gastrointestinal tract (GIT), and vagina.

119
Q
A
120
Q
A
121
Q

How do viridans streptococci typically enter tissues?

A

During dental or surgical procedures.

122
Q

What infections can viridans streptococci cause?

A

Tooth abscess, abdominal infections, and late onset prosthetic valve endocarditis.

123
Q

What is the most common infection caused by viridans streptococci?

A

Subacute bacterial endocarditis, especially in previously damaged heart valves.

124
Q

What condition can viridans streptococci cause following trauma or defects?

A

Meningitis.

125
Q

Which viridans streptococci group plays a key role in the development of dental caries?

A

S. mutans.

126
Q

What other conditions can viridans streptococci cause in immunocompromised patients?

A

Bacteremia and infection in other sterile sites.

MTAP FIRST SEM 2024-2025 (15 decks)

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