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CLS 753 > Micro - Gram Positive Cocci > Flashcards

Micro - Gram Positive Cocci Flashcards

1
Q

We see gram positive cocci. If the catalase test is positive, the genus is likely… If the catalase test is negative, the two genera are likely…

A

Staphylococcus

Streptococcus or Enterococcus

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2
Q

The most virulent species of Staphylococcus is

A

Staph aureus

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3
Q

Staph aureus can cause these diseases (4)

A

Food poisoning (toxins)

Toxic shock syndrome

Pyogenic diseases (bullous impetigo, boils, abscesses, folliculitis)

Systemic disease (pneumonia, septicemia)

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4
Q

Staph aureus has this in its cell wall that makes it virulent… What does it do?

A

Protein A (antigenic)

Prevents phagocytosis

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5
Q

Can Staph aureus be cultured in high salt conditions?

A

Yes

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6
Q

Staph aureus - screening media (2)

A

MSA
-high salt

CHROMagar Staph

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7
Q

How does S. aureus compare with S. epidermidis on an MSA plate?

A

S. aureus = ferment mannitol, turns plate yellow

S. epidermidis = does not ferment mannitol, plate stays same color

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8
Q

What do S. aureus colonies look like on a blood agar plate and describe their color? Are they hemolytic and if so, what type of hemolysis?

A

Creamy, buttery
Pale to yellow colonies

Yes, beta-hemolytic
-most are hemolytic, but some are not

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9
Q

What do S. aureus look like under the microscope

A

Gram positive cocci, grape-like clusters

-due to multiple planes of division

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10
Q

Staph aureus is coagulase…

A

Positive

-slide, tube, or latex

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11
Q

A common drug resistant stain of Staph aureus is called… How is the resistance gene induced in the lab?

A

MRSA
-certain strains now also vancomycin resistant

Methicillin resistance gene (mecA) induced in a high salt environment

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12
Q

MRSA strains are detected with this plate…

A

MSA with oxacillin salt

  • high salt induces methicillin resistance gene
  • oxacillin inhibits normal Staph aureus
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13
Q

Besides culturing, rapid results for MRSA include (2)

A

PCR - mecA gene

Latex agglutination to detect penicillin binding protein 2a

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14
Q

Catalase positive, coagulase negative organisms (3). What type of hemolysis?

A

Staph epidermidis
Staph saprophyticus
Staph lugdeninsis

None/gamma

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15
Q

S. epidermidis is a normal flora commonly found on ___. S. saprophyticus is a pathogen commonly found in this type of infection…

A

Skin

UTI
-sexual active young females

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16
Q

S. epidermidis and S. lugdeninsis can form ___ on artificial heart valves, leading to…

A

Biofilm

Endocarditis

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17
Q

Coagulase negative Staph colonies have this color on a blood agar plate… Are they hemolytic?

A

White colonies

No

-appear microscopically similar to S. aureus

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18
Q

S. saprophyticus is resistant to this antibiotic. What should the zone size be?

A

Novobiocin

<= 16mm

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19
Q

This genus looks like Staph on a gram stain and is catalase positive and coagulase negative. They have this unique morphology on a gram stain

A

Micrococcus

Tetrad

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20
Q

Streptococcus pyogenes is a part of what Lancefield group? Members of that group are associated with this level of hemolysis

A

Group A

Beta-hemolysis

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21
Q

S. pyogenes infection causes acute ___, which can lead to these 2 other conditions

A

Pharyngitis

Rheumatic fever
Glomerolonephritis

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22
Q

S. pyogenes causes these 2 skin conditions

A

Impetigo
-usually in children

Necrotizing fasciitis

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23
Q

Bullous impetigo and non-bullous impetigo are caused by what organisms (genus/species)?

A

Bullous impetigo = Staph aureus
-flat, crusted with redness

Non-bullous impetigo = Staph aureus or Strep pyogenes
-raised, swollen

24
Q

Is S. pyogenes an aerobic or anaerobic organism? What special culturing condition does it need? How would we mimic this condition on the media?

A

Anaerobe

Increased CO2

Stab the agar

25
Q

A skin specimen contains suspected S. pyogenes. Why must we use culture media that selects for the organism? What culture plate should we use to isolate the organism??

A

Sample may contain many other organisms and normal flora

Blood agar with sulfa (trimethoprim) disc

26
Q

S. pyogenes - what is the definitive confirmation test and the test result?

A

PYR = positive

27
Q

Name an important Group B Streptococcus species. What type of hemolysis does it have?

A

Streptococcus agalactiae

Weakly beta-hemolytic

28
Q

Does Group B Streptococcus have increased or decreased hemolysis when cultured with Staph aureus. Why?

A

Increased

Releases CAMP, which interacts with beta-lysin from S. aureus to enhance hemolysis
-CAMP is definitive test for Group B Strep

29
Q

Group B Strep clinical diseases (3)

A

Neonatal meningitis
Neonatal pneumoniae
Post-partum endometritis

-mnemonic = Group B is Bad for Babies

30
Q

Group B Strep can be confused with this species due to the types of people it targets and the diseases it causes

A

Listeria monocytogenes

  • affects neonates and pregnant women as well
  • small, narrow zones of beta-hemolysis
31
Q

Group B - pregnant woman’s vaginal and rectal swabs should be cultured in this media overnight

A

LIM broth

-culture on sheep blood agar after growth

32
Q

Strep dysgalactiae is considered to be a part of both Lancefield groups… What type of hemolysis?

A

C and G

Beta-hemolysis

33
Q

Strep dysgalactiae show clinical findings and infections similar to this other Strep species

A

Strep pyogenes

34
Q

Strep pneumoniae has what type of hemolysis?

A

Alpha hemolysis

-no Lancefield grouping

35
Q

Strep pneumoniae can show two types of colony morphology

A

Flat, dull/matte

Mucoid, shiny, glistening

36
Q

Strep pneumoniae has these unique microscopic morphologies (2)

A

Diplococcus

Lancet - flat where the 2 cells touch, pointed on adjacent ends

37
Q

Strep pneumoniae clinical findings (4)

A

Pneumoniae

Meningitis

Sinusitis

Otitis media

38
Q

Strep pneumoniae optochin test result

A

Sensitive

39
Q

What will happen if Strep pneumoniae is tested in a bile salt solution? What does the test result indicate?

A

Cells will lyse

Strep pneumoniae is bile soluble

40
Q

The group of Streptococcus that are normal flora in the oral cavity are collectively called…

A

Viridans Streptococci

-biofilm formation = dental caries

41
Q

Streptococcus viridans can cause these clinical findings (3)

A

Dental caries

Bacteremia (after dental work)

Subacute endocarditis

42
Q

What 2 tests do we use to differentiate S. pneumoniae from S. viridans? What are the results?

A

S. pneumoniae = optochin sensitive, bile soluble

S. viridans = optochin resistant, bile insoluble

-opposite results

43
Q

Streptococcus bovis belongs to this group of Streptococcus. It does not generally cause infections except for…

A

viridans
-also Lancefield group D

Endocarditis

44
Q

Can nutritionally variant streptococci (NVS) grow on blood agar? How can we see its growth?

A

No

Co-culture with Staph aureus to see growth as satellite colonies

45
Q

What type of hemolysis do Enterococcus have?

A

Gamma-hemolysis (none)

46
Q

The two important species of Enterococcus are. They are both resistant to this drug…

A

E. faecalis
E. faecium

Vancomycin
-VRE = vanco resistant Entero

47
Q

On the gram stain, Enterococcus can be confused with… Enterococci look like…

A

Streptococcus pneumoniae

Pairs or short chains
-larger, more plump than Strep

48
Q

Enterococcus clinical findings (3)

A

Bacteremia

Urinary tract infections

Subacute endocarditis

-hospital acquired infections

49
Q

What 3 tests should we do for non-hemolytic (gamma) cocci? What genus are we trying to rule in or out?

A

PYR
High salt broth (6.5%)
Bile esculin
-do PYR first; rapid test

Enterococcus

50
Q

Enterococcus - catalase test result

A

Negative, but with weak bubbles

51
Q

Name the 2 important beta-hemolytic Strep species. What two tests should we do to differentiate them and what are the test results?

A

Strep pyogenes = PYR positive, CAMP negative

Strep agalactiae = PYR negative, CAMP positive

-opposite results

52
Q

Name the 2 important alpha-hemolytic Strep species. What two tests should we do to differentiate them and what are the test results?

A

Strep pneumoniae = optochin sensitive, bile soluble

Strep viridans = optochin resistant, bile insoluble

  • opposite results
  • don’t do PYR and CAMP
53
Q

Which Lancefield serotypes are most commonly seen in the lab?

A

A-H

-also K-T, but not common in the lab

54
Q

Streptococcus colony size on an agar plate are usually… Are they bigger or smaller than Staphylococcus?

A

<= 0.5mm

Smaller

55
Q

What two test results should we expect to rule out Enterococcus from Streptococcus?

A

Enterococcus
PYR = positive
Bile esculin = positive

CLS 753 (12 decks)

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