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MEDI2003 Module 2 theory > Gram Positive Cocci > Flashcards

Gram Positive Cocci Flashcards

1
Q

What three genera make up 90-99% of GPC clinical isolates?

A

Staphylococcus
Streptococcus
Enterococcus

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2
Q

Which genera of GPC are catalase positive?

A

Staphylococci and Micrococci

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3
Q

Which genera of GPC are catalase negative?

A

Streptococci

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4
Q

What test is conducted to distinguish between Micrococci and Staphylococci?

A

Modified oxidase test

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5
Q

Which genera of catalase positive GPC is Oxidase negative?

A

Staphylococci

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6
Q

Which genera of catalase positive GPC is Oxidase positive?

A

Micrococci

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7
Q

What secondary test can we perform to determine Staphylococci species?

A

Coagulase testing

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8
Q

Which species of Staphylococci is coagulase positive?

A

Staphylococcus aureus

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9
Q

What secondary testing do we perform to determine the species of Coagulase Negative Staphylococci?

A

Novobiocin testing

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10
Q

Which species of Staphylococci is Novobiocin resistent?

A

Staphylococcus saprophyticus

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11
Q

Which species of Staphylococci is Novobiocin sensitive?

A

Staphylococcus epidermidis

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12
Q

Are GPC usually Oxidase pos or neg?

A

Negative

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13
Q

Are GPC usually catalase pos or neg?

A

Positive

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14
Q

When viewing a clinical smear how are GPC usually arranged?

A
  • clusters
  • single cells
  • pairs (diplococci)
  • tetrads
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15
Q

How many species/subspecies of Staphylococci are there?

A

57

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16
Q

Name the usual characteristics of Staphylococci sp.

A
  • non-motile
  • non-spore forming
  • most are facultative
  • attack sugars fermentatively
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17
Q

How do we divide the staphylococci species?

A

Into coagulase pos or neg species

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18
Q

What is the most virulent and clinically significant pathogen among the Staphylococci?

A

Staphylococcus aureus

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19
Q

On a culture plate, what colour is Staphylococcus aureus likely to be?

A

yellow

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20
Q

True or false: Staphylococcus aureus is both slide and tube coagulase positive.

A

true

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21
Q

Staphylococcus aureus is NF when not in an environment where it is overtly pathogenic. Name the areas on the human body where it is normally found

A
  • anterior nares (nostrils)
  • nasopharynx
  • perineal area
  • skin
  • various mucosal surfaces
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22
Q

In a hospital environment what percentage of people are carriers of Staphylococcus aureus?

A

60-70%

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23
Q

What organism (genus and species) is considered a significant cause of nosocomial infections?

A

Staphylococcus aureus

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24
Q

What is MRSA?

A

Methicillin Resistant Staphylococcus aureus.

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25
Q

What are some infections Staphylococcus aureus causes?

A
  • Wound infections
  • Bacteraemia/endocarditis/pericarditis
  • Meningitis
  • Pulmonary infections
  • Osteomyelitis and septic arthritis
  • Food poisoning
  • Scalded skin syndrome
  • Toxic shock syndrome
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26
Q

What virulence factor in Staphylococcus aureus causes food poisoning?

A

heat stable enterotoxins

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27
Q

Name the virulence factors S. aureus contains.

A
  1. Capsular polysaccharides
  2. Protein A
  3. Enzymes
  4. Haemolysins (not on BA)
  5. Toxins
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28
Q

What enzymes can S. aureus produce?

A
  • Catalase
  • Coagulase
  • Fibrinolysins
  • Hyaluronidase
  • Lipases
  • Nuclease
  • Beta-lactamases
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29
Q

What type of toxins does S. aureus produce?

A
  • Epidermolytic toxins

- Enterotoxins

30
Q

What organism (genus and species) is the most common coagulase negative staphylococci (CoNS)?

A

Staphylococcus epidermidis 50-80%

31
Q

What organism (genus and species) makes up 90% of all skin flora??

A

Staphylococcus epidermidis

32
Q

True or false: Almost all truly significant infections with S. epidermidis are of nosocomial origin.

A

True

33
Q

What does S. epidermidis produce on artificial surfaces (i.e. shunts, catheters, metal plates etc) that helps it to survive and become resistant to therapy and the immune response (i.e. phagocytosis)

A

Biofilm

34
Q

What does S. epidermidis readily acquire from other bacteria?

A

resistance to antibiotics

35
Q

When do we consider S. epidermidis to be clinically relevant for reporting?

A
  • Purity of growth is substantial (+++)
  • quantity of growth (+++)
  • Site of the infection (i.e. sterile site such as blood culture, or wound infection oozing puss)
  • Clinical Hx (i.e. recent hospital admission/surgery)
36
Q

Is Staphylococcus epidermidis haemolytic on Blood Agar?

A

not usually

37
Q

On a culture plate, what colour is the colony growth of S. epidermidis?

A

Grey to white colonies

38
Q

Where is Staphylococcus saprophyticus usually found?

A

In the GIT

39
Q

What organism is the most commonly associated with community acquired UTI’s?

A

Staphylococcus saprophyticus

40
Q

What organism is the most common cause of cystitis (after E. coli), urethritis in men and prostatitis (elderly men)?

A

Staphylococcus saprophyticus

41
Q

On a culture plate, what colour is the colony growth of S. saprophyticus?

A

usually very bright white glossy colonies

42
Q

What are the virulence factors of S. saprophyticus?

A
  • adherence to epithelial cells
  • urease production
  • produces slime layer in the presence of urine and urease (very sticky in urinary system)
43
Q

What organism has a virulence factor of adherence specificity to uroepithelial, urethral and periurethral cells?

A

Staphylococcus saprophyticus

44
Q

What two primary test results (systematics) would indicate that you should consider an isolate as belonging to the genus Staphylococcus?

A

Catalase pos and modified oxidase neg

45
Q

What is the difference between plasma and serum?

A

Plasma is the fluid in blood that contains clotting factor (fibrinogen) while serum does not.

46
Q

List 4 virulence factors. How does each virulence factor for S. aureus act to assist in its ability to cause infection?

A
  • Protein A - confuses the binding orientation of Fc portion of the antibody allowing the organism to avoid phagocytosis.
  • Beta - lactamases - confers resistance against penicillin, ampicillin, and other beta lactam antibiotics
  • Haemolysins - lyses RBC to release nutrients therefore allowing the organism to benefit form the lysed nutrients.
  • Toxins - Epidermolytic toxins cause scalded skin syndrome and enterotoxins can cause food poisoning or toxic shock syndrome.
47
Q

Explain the theory behind the oxidase test

A

Detects the presence of the enzyme cytochrome c (enzymes that are involved in the electron transport chain) via a reagent that when oxidised produces a dark violet purple colour indicating the presence of the enzyme which confirms a positive result for oxidase. This helps to differentiate GN bacteria.

48
Q

What type of infections is S. epidermidis normally associated with and why?

A

nosocomial infections

49
Q

What is coagulase?

A

An enzyme which reacts with fibrinogen causing coagulation.

50
Q

What are the two forms of test for coagulase?

A
  • Bound Coagulase (cell wall) via slide coagulase test

- Free coagulase (secreted) detected by the tube coagulase test.

51
Q

What type of plasma causes false positives with the coagulase test?

A

citrated plasma (blood collected in citrate tube instead of edta)

52
Q

What is the rapid test for coagulase?

A

Slide coagulase (also called “clumping factor”)

53
Q

What should all negative test results for coagulase be checked by? Why?

A

tube method since strains deficient in clumping factor may produce free coagulase.

54
Q

What is the scientific name for Group A Streptococcus?

A

Streptococcus pyogenes (beta haemolytic)

55
Q

What is the scientific name for Group B Streptococcus?

A

Streptococcus agalactiae (beta haemolytic)

56
Q

What antibiotic is the drug of choice used to treat suspected streptococcal pharyngitis?

A

Penicillin or erythromycin if the infection does not resolve on its own

57
Q

What is the likely identity of an unknown organism that is a GPC, catalase negative and was Hippurate positive?

A

Streptococcus agalactiae

58
Q

What is the likely identity of an unknown organism that is a GPC, catalase negative and sensitive to Bacitracin?

A

Streptococcus pyogenes

59
Q

How could you easily differentiate between S. pneumoniae and a member of the viridians streptococci?

A

Bile solubility test.

S. pneumonia is bile soluble whereas Viridians streptococci is not.

60
Q

Which species is resistant to vancomycin?

A

Enterococcus faecium

61
Q

Where is Group B Strep. most likely to be found as NF?

A

URT - Throat

62
Q

What is the principle difference in colony morphology between Group A & B strep?

A

Group A has large zones of Beta haemolysis on BA

Group B has small zones of Beta Haemolysis on BA

63
Q

What systemic infection are the viridians streptococci usually associated with?

A

Endocarditis/septicaemia

64
Q

What is the advantage of using the bile solubility test over the optochin test when using these to ID S. pneumoniae?

A

Bile solubility is a rapid (10 min) test which gets results faster in order to report to the doctor in a timely fashion so they can treat the patient faster.

65
Q

What are the main identifying features of S. pneumoniae? (Primary and secondary test results)

A
  • Two colony types (Mucoid is S - form, rough is draughtsman R - form)
  • Alpha haemolytic (narrow) zones on BA
  • Fastiduous (requires BA or CHOC)
  • GP diplococci in a lancet shape
  • Optochin sensitive
  • Bile soluble
66
Q

What immunological property is thought to play an important role in conferring protection against pneumococcal infection?

A

Humoral Immunity

67
Q

What 3 groups of people would most likely be affected by pneumococcal infection?

A
  • very young
  • elderly
  • immunocompromised
68
Q

List four virulence factors of Group A Streptococcus and give an example of how/why each acts to confer pathogenicity?

A
  • M Proteins assist with resisting phagocytosis and adherence to epithelial cells.
  • Haemolysins O and S are toxic to host cells
  • Streptococcal Pyogenic Exotoxins cause toxic shock syndrome and hypotension.
  • Hyaluronic acid capsule - mucoid isolates evade phagocytosis due to being antigenic invisible, also assist with bacteria adhering to host tissue.
69
Q

List four virulence factors of Group A Streptococcus and give an example of how/why each acts to confer pathogenicity?

A
  • Beta haemolysins (o and s type) - destroys various host cells
  • M Proteins (surface antigens) - adhere to epithelial cells
  • Enzyme production -various enzymes help to break down host cell wall/defences.
  • Hyaluronic acid capsule - mucoid isolates - resists phagocytosis by adhering to host tissue as well as having a similar composition to host CT which helps the organism blend into the host environment.
70
Q

Compare between post streptococcal rheumatic fever and glomerular nephritis.

A
  • Post streptococcal rheumatic fever is an infection of the heart as a result of an auto-immune response
  • Glomerular nephritis is an infection of the kidneys specifically an inflammation of the glomeruli (due to agglutination of antibodies being to big to filter out of the nephrons).
71
Q

Give two reasons why the genus Enterococcus are frequently associated with significant nosocomial infections.

A
  • surgeries of the abdominal cavity/GIT

- structural abnormalities or instruments such as catheters

MEDI2003 Module 2 theory (5 decks)

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