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Microbio > Catalase negative, Gram positive cocci > Flashcards

Catalase negative, Gram positive cocci Flashcards

Streptococcus, Enterococcus and similar organism

1
Q

What enzyme are Streptococcus and Enterococcus species negative for, which differentiates them from staphylococci?

A

Catalase.

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2
Q

What type of oxygen requirement do Streptococcus and Enterococcus species have?

A

Facultative anaerobes

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3
Q

Name a common pathogen in human infections caused by Group A Streptococcus.

A

Streptococcus pyogenes.

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4
Q

Which Streptococcus species is known for causing neonatal infections?

A

Streptococcus agalactiae (Group B Streptococcus).

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5
Q

Which Enterococcus species are commonly encountered in nosocomial infections?

A

Enterococcus faecalis and Enterococcus faecium.

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6
Q

To which Lancefield group does Streptococcus pyogenes belong?

A

Group A.

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7
Q

What type of hemolysis is exhibited by Streptococcus pyogenes on blood agar?

A

β-hemolysis (complete hemolysis).

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8
Q

Is Streptococcus pyogenes sensitive or resistant to bacitracin?

A

Bacitracin sensitive

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9
Q

What test result helps to differentiate Streptococcus pyogenes from other streptococci?

A

PYR test positive.

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10
Q

What virulence factor is responsible for the β-hemolytic pattern of Streptococcus pyogenes on blood agar plates and is oxygen-labile?

A

Streptolysin O.

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11
Q

Which virulence factor is oxygen-stable and nonimmunogenic, yet capable of lysing erythrocytes in the presence of room air?

A

Streptolysin S.

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12
Q

Which enzyme known as the “spreading factor” helps Streptococcus pyogenes spread through tissues?

A

Hyaluronidase.

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13
Q

What protein enables Streptococcus pyogenes to resist phagocytosis and adhere to mucosal cells?

A

M protein

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14
Q

It causes the red spreading rash seen in scarlet fever.

A

erythrogenic toxin

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15
Q

Which virulence factor of Streptococcus pyogenes can lyse fibrin clots?

A

Streptokinase.

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16
Q

Which virulence factor of Streptococcus pyogenes is antigenic, allowing for detection of antibodies following infection?

A

DNAseB

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17
Q

What is the most common bacterial cause of acute pharyngitis in children aged 5 to 15?

A

Streptococcus pyogenes (Group A).

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18
Q

Which skin infection caused by S. pyogenes is characterized by perioral blistered lesions with honey-colored crusts?

A

Impetigo (Impetigo Contagiosa).

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19
Q

What is a potential complication of impetigo caused by S. pyogenes?

A

Post-streptococcal glomerulonephritis (poststrep GN).

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20
Q

What superficial skin infection caused by S. pyogenes extends into the dermal lymphatics?

A

Erysipelas.

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21
Q

Which deeper skin infection involving subcutaneous or dermal tissues is facilitated by hyaluronidase?

A

Cellulitis

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22
Q

What rapidly progressive infection of deep subcutaneous tissues is facilitated by exotoxin B?

A

Necrotizing Fasciitis.

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23
Q

Which enzyme produced by Streptococcus pyogenes facilitates the spread of cellulitis by breaking down hyaluronic acid in connective tissues?

A

Hyaluronidase.

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24
Q

What condition, often associated with streptococcal pharyngitis, is caused by streptococcal pyrogenic exotoxins and presents with a characteristic sandpaper-like rash and strawberry tongue?

A

Scarlet Fever.

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25
Q

How is the diagnosis of acute pharyngitis (strep throat) confirmed in a clinical setting?

A

Diagnosis is confirmed through a throat culture or a positive rapid strep test.

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26
Q

Acute pharyngitis most common bacterial cause

A

S. pyogenes

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27
Q

What is Streptococcal Toxic Shock Syndrome similar to?

A

Toxic shock syndrome caused by Staphylococcus aureus.

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28
Q

What mediates STSS?

A

Production of potent streptococcal pyrogenic exotoxins (SPEs).

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28
Q

What often tests positive in cases of STSS?

A

Blood cultures for Streptococcus pyogenes.

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29
Q

What protein is associated with Rheumatic Fever?

A

M protein.

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30
Q

What precedes Rheumatic Fever?

A

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

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31
Q

What protein mediates Acute Glomerulonephritis?

A

M protein.

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32
Q

What condition is associated with immune complex deposition in the kidneys?

A

Acute glomerulonephritis.

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33
Q

Microscopy: Gram-positive cocci, some in short chains or pairs, round to oval-shaped, occasionally forming elongated cells resembling pleomorphic corynebacteria or lactobacilli.

A

Streptococcus pyogenes

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34
Q

What media is used for cultivating Streptococcus pyogenes?

A

5% sheep blood agar, chocolate agar, and 5% sheep blood agar with trimethoprim-sulfamethoxazole (SXT) for throat swabs.

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35
Q

Blood agar: Small, transparent, smooth colonies with β-hemolysis.

A

Streptococcus pyogene

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36
Q

what test: o presumptively identify and differentiate β-hemolytic group A streptococci (S. pyogenes-susceptible) from other β-hemolytic streptococci.

A

Bacitracin test

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37
Q

What indicates a positive Bacitracin test result?

A

Any ZOI greater than 10 mm indicates susceptibility.

38
Q

What indicates a negative Bacitracin test result?

A

No ZOI indicates resistance.

39
Q

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

40
Q

What indicates a positive PYR test result?

A

Bright red color within 5 minutes.

41
Q

What does the Anti-streptolysin O (ASO) test detect?

A

Antibodies against streptolysin O, a toxin produced by S. pyogenes.

42
Q

What indicates a negative PYR test result?

A

No color change or an orange color.

43
Q

What organism:
Gram-positive cocci in chains
Lancefield group B
β-hemolytic
Bacitracin resistant
CAMP test positive
PYR negative
Hippurate hydrolysis positive
Resistant to SXT

A

Streptococcus agalactiae

44
Q

Where is Streptococcus agalactiae commonly found?

A

Normal microbiota in the female genital tract and lower gastrointestinal tract
Occasional colonizer of the upper respiratory tract

45
Q

What is the most important virulence factor of Streptococcus agalactiae?

46
Q

What other potential virulence factors are associated with Streptococcus agalactiae, though not proven to be factors in infection?

A

DNAse and hyaluronidase

47
Q

Is Streptococcus agalactiae PYR positive or negative?

A

PYR negative.

48
Q

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

A

Pneumonia (0–2 months old)
Meningitis
Sepsis

49
Q

what organism Postpartum infections (e.g., endometritis, pelvic abscesses, septic shock)
Bacteremia
Pneumonia
Endocarditis
Arthritis
Osteomyelitis
Skin and soft tissue infections

A

Streptococcus agalactiae in adults

50
Q

In which group of adults is Streptococcus agalactiae infection more commonly seen?

A

Immunocompromised adults.

51
Q

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

A

Streptococcus agalactiae

52
Q

How is Streptococcus agalactiae detected in vaginal or rectal swabs during pregnancy?

A

Inoculated into Todd-Hewitt broth (containing gentamicin, nalidixic acid, or colistin and nalidixic acid) such as LIM.

53
Q

What is the appearance of Streptococcus agalactiae on CHROMagar StrepB?

A

Mauve colored colonies.

54
Q

How is a positive CAMP test result interpreted?

A

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

55
Q

What does a positive hippurate hydrolysis test indicate for Streptococcus agalactiae?

A

The production of hippuricase, with a purple-colored product formed due to the reaction of end products of ninhydrin oxidation.

56
Q

Hippuric acid is deaminated by the enzyme?

A

hippuricase

57
Q

Principle of hippurate hydrolysis

A

Hippurate acid ->hippuricase> glycine benzoic acid

58
Q

Gram-positive “lancet-shaped” cocci, alpha-hemolytic.

A

Streptococcus pneumoniae

59
Q

Bile solubility sensitive, optochin sensitive, positive Quellung reaction.

A

Streptococcus pneumoniae

59
Q

It is the leading cause of bacterial meningitis in infants, young children, and adults in the US, followed by N. meningitidis and H. influenzae

A

Streptococcus pneumoniae

60
Q

What is the key virulence factor of Streptococcus pneumoniae?

A

Capsule, which inhibits phagocytosis and has 80 antigenic types.

61
Q

It activates the classical complement pathway and suppresses the oxidative burst of phagocytes.

A

pneumolysin

62
Q

It binds to receptors for platelet-activating factor in endothelial cells, leukocytes, platelets, and tissue cells of the lungs and meninges, aiding in entry and spread of the organism.

A

phosphorylcholine

63
Q

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

A

95% of all bacterial pneumonia cases.

64
Q

What are common diseases associated with Streptococcus pneumoniae?

A

Bacterial pneumonia, sinusitis, otitis media, bacteremia, and meningitis.

65
Q

It is the leading cause of bacterial meningitis in infants, young children, and adults in the US.

A

Streptococcus pneumoniae

66
Q

Which other bacteria follow Streptococcus pneumoniae in causing bacterial meningitis?

A

Neisseria meningitidis and Haemophilus influenzae

67
Q

Microscopy: Leukocytosis and numerous lancet-shaped cocci occurring singly, in pairs, or in short chains.

A

Streptococcus pneumoniae

68
Q

On which types of media can Streptococcus pneumoniae be cultivated?

A

Brain heart infusion agar, trypticase soy agar with 5% sheep blood, or chocolate agar. It may require increased CO2 for optimal growth.

69
Q

Blood agar: Round, glistening, wet, mucoid, dome-shaped colonies with alpha-hemolysis.

A

Streptococcus pneumoniae

70
Q

What does a positive Optochin (P disk) susceptibility test indicate?

A

A positive test indicates that the organism is susceptible to optochin, which is characteristic of Streptococcus pneumoniae. A zone of inhibition (ZOI) of at least 14 mm around the disk is considered positive.

71
Q

How does the Bile solubility test differentiate Streptococcus pneumoniae from other alpha-hemolytic streptococci?

A

Streptococcus pneumoniae is bile soluble, meaning its colonies disintegrate when exposed to bile or bile salts, while other alpha-hemolytic streptococci are bile insoluble and remain intact.

72
Q

detects capsular subtypes of Streptococcus pneumoniae by causing the capsule to swell, which is visible under the microscope.

A

Quellung test

73
Q

Species: PYR positive, possess group D antigen, grow in 6.5% NaCl, and are LAP positive.

A

Enterococcus species

74
Q

Which Enterococcus species are most commonly encountered as pathogens?

A

E. faecalis and E. faecium are the pathogenic species most commonly encountered

75
Q

Enterococcus: most commonly encountered

A

E. faecalis

76
Q

Enterococcus: more frequent vancomycin resistance

A

E. faecium

77
Q

What are key virulence factors of Enterococcus species?

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

78
Q

What are common infections caused by Enterococcus species?

A

Urinary tract infections (UTIs)
Bacteremia
Endocarditis
Intra-abdominal, pelvic, wound, and soft tissue infections

79
Q

How is Enterococcus identified using the PYR test?

A

Enterococcus species hydrolyze PYR, leading to a positive result in the PYR test.

80
Q

How does the 6.5% NaCl broth test help in identifying Enterococcus?

A

Enterococcus species can grow in 6.5% NaCl broth, which is used to differentiate them from non-enterococci. Positive result shows visible turbidity and possible color change from purple to yellow.

81
Q

Enterococci is resistant or sensitive to high salt concentration

82
Q

It is used as the test medium for enterococcus

A

HEart infusion broth containing 6.5% NaCl

83
Q

What test helps in the presumptive identification of catalase-negative gram-positive cocci by detecting the enzyme leucine aminopeptidase.

A

Leucine Aminopeptidase (LAP) test for Enterococcus

84
Q

How does a positive Leucine Aminopeptidase (LAP) test result appear?

A

A positive LAP test will show the development of a red color within 1 minute after adding cinnamaldehyde reagent.

85
Q

What are the antibiotic resistance characteristics of Enterococcus?

A

Enterococcus species are intrinsically more resistant to antimicrobials, including cephalosporins and aminoglycosides. Vancomycin-resistant Enterococcus (VRE) is also a notable concern in healthcare settings.

86
Q

Not groupable by Lancefield serology

A

Viridans streptococci

87
Q

Butterscotch smell, especially on chocolate agar

A

Viridans streptococci

88
Q

Fastidious and some strains require increased carbon dioxide for growth
Alpha-hemolysis or no hemolysis (greening) on sheep blood agar
Butterscotch smell, especially on chocolate agar

A

Viridans streptococci

89
Q

Where are Viridans streptococci normally found?

A

Normal microbiota in the oral cavity, oropharynx, gastrointestinal tract (GIT), and vagina.

90
Q

part of the normal microbiota in the oral cavity, oropharynx, GIT, and vagina, and is involved in infections after dental or surgical procedures

A

S. anginosis group

91
Q

What kind of odor might you notice with Viridans streptococci on chocolate agar?

A

A butterscotch smell.

92
Q

Key role in development of dental carries

A

S. mutants

Microbio (5 decks)

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