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BACTERIOLOGY > Gram Positive Bacteria > Flashcards

Gram Positive Bacteria Flashcards

1
Q

3 medically important genus for gram cocci

A

Staphylococcus
Streptococcus

Gram (-)
Neisseria

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2
Q

Gram positive cocci that is positive in catalase testing

A

Family: Micrococcaea
Genus: Micrococcus &
Staphylococcus

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3
Q

Gram positive cocci that is negative in catalase testing

A

Family: Streptococcaceae
Genus: Streptococcus

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4
Q

Gram positive cocci that is oxidation positive for glucose degradation test

A

Micrococcus (asaccharolytic)

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5
Q

Gram positive cocci that is fermentation/ oxidation positive for glucose degradation test

A

Staphylococcus (fermentative)

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6
Q

Glucose degradation test

A

It tests an organism’s ability to ferment the sugar glucose as well as its ability to convert the end product of glycolysis, pyruvic acid into gaseous byproducts.

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7
Q

Catalase test

A

used to detect the presence of cytochrome oxidase enzyme

-differentiates family micrococcaceae/ staphylococcus (catalase +) from streptococcus(catalase -)

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8
Q

Main reagent in Catalase testing

A

Hydrogen Peroxide

  • Agua oxinada
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9
Q

Procedure for catalase testing

A
  • Add drop of 3% H2O2 solution on glass lside

- then add small amount of bacterial growth from culture medium

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10
Q

Positive reaction for Catalase testing

A

Bubbling/ Bubbles

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11
Q

Reaction during catalase testing

A

H2O2 ———> H2O + O2

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12
Q

Test used to differentiate Staphylococcus from Micrococci

A

Oxidative/ Fermentative test

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13
Q

Another test used to differentiate Staphylococcus from Micrococci

A

Microdase (modified oxidase) test

(+) blue

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14
Q

Bacteria that is positive in Microdase testing

A

Micrococcus

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15
Q

Antibiotics that are effective in differentiating Micrococcus and Staphylococcus

A

Bacitracin (most commonly used)
Furazolidone
Lysostaphin

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16
Q

________ is resistant to bacitracin

A

Staphylococcus

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17
Q

________ is susceptible/ sensitive to bacitracin

A

Micrococcus

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18
Q

General characteristics of Staphylococcus species

A
  • gram positive
  • catalase positive
  • grow best in anaerobic conditions
  • facultative anaerobes
  • non-motile
  • non-sporeforming
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19
Q

5 medically important staphylococcus species

A 
S- saprophyticus 
H- haemolyticus 
A- aureus 
L- lugdunensis
E- epidemidis
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20
Q

The most pathogenic Staphylococcus species

A

Staphlycoccus aureus

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21
Q

MRSA

A

Methicillin Resistant Staphylococcus aureus

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22
Q

Mode of transmission for Staphylococcus

A
  • Person to person transmission by fomites, air. etc.

- From infected skin lesions such as impetigo, cellulitis, boils (matagtiki)

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23
Q

Staphylococcus specie responsible for 80% suppurative infection in human

A

Staphylococcus aureus

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24
Q

Dominant site of colonization of Staphylococcus aureus

-site best used to get sample for culture

A

anterior nares, axilla, perineum, and 10-15% human skin

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25
Q

Principal virulence factor for S. aureus

A

Coagulase enzyme

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26
Q

Staphylococcus aureus morphology

A
  • gram-positive cocci
  • grape like or irregular clusters
  • produce lipochrome
  • Beta- hemolytic
  • haloduric
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27
Q

What causes the golden-yellow pigment of S. aureus on BAP

A
  • production of lipochrome

a naturally occurring fat-soluble pigment

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28
Q

3 major components of S. aureus cell wall

PEPTIDOGLYCAN

A
  • elicits production of interleukin 1 (causes fever) and opsonic antibodies
  • provide rigid exoskeleton
  • a chemoattractant (attracts polymorphonuclear cells causing inflammations)
  • activate complement pathway.
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29
Q

3 major components of S. aureus cell wall

TEICHOIC ACID

A
  • polymer of ribitol phosphate
  • regulate the cationic environment of the cell thus control the activity of autolytic enzyme responsible for growth of cell wall
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30
Q

Antiteichoic antibodies are detectable through

A

Gel diffusion

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31
Q

Antiteichoic antibodies are found generally in patients with __________

A
  • active endocarditis due to S. aureus
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32
Q

3 major components of S. aureus cell wall

PROTEIN A

A
  • major protein component of Staphylococcus
  • major antigenic determinant unique to S. aureus
  • antiphagocytic by binding thru FC portions of IgG except for IgG 3.
33
Q

Antiphagocytic

A

preventing the action of phagocytes or the occurrence of phagocytosis.

34
Q

PATHOGENICITY

A

This term refers to the ability of tan organism to induce a local and systemic infection

35
Q

S. aureus pathogenicity

intracellular
PROTEIN RECEPTORS

A
  • allows organism to adhere to tissue surfaces
36
Q

S. aureus pathogenicity

intracellular
POLYSACCHARIDE CAPSULE

A
  • protect organism from complement mediated attack of polymorphonuclear (PMN) macrophages, leukocyte and etc.
37
Q

S. aureus pathogenicity

extracellular
COAGULASE

A
  • this enzyme reacts with blood factor in the plasma to initiate clot formation
  • enhance deposition of fibrin around organism to protect from phagocytosis
38
Q

S. aureus pathogenicity

extracellular
LIPASE

A
  • helps in colonization of organism on oily skin surfaces

- important in survival of organism on sebaceous area of the body

39
Q

S. aureus pathogenicity

extracellular
HYALURONIDASE

A
  • promote invasion of organism by digesting the intracellular ground substance “glue” (hyaluronic acid) that binds connective tissue in host tissue.
40
Q

S. aureus pathogenicity

extracellular
STAPHYLOKINASE

A
  • degradation of fibrin clot
    (dissolution of clot to spread infection further)
  • also known as fibrinolycin
41
Q

S. aureus pathogenicity

extracellular
NUCLEASE (DNAse)

A
  • heat resistant protein
  • degrade nucleic acid (DNA)
  • lowers viscosity of exodates promoting further motility
42
Q

S. aureus pathogenicity

HEMOLYSINS - CYTOTOXINS

A
  • lyse rbc by destroying membrane thus inducing tissue damage
  • chromosomal mediated
  • causes anemia and make iron available for growth of organism
43
Q

S. aureus pathogenicity

Alpha hemolysin

A
  • most powerful toxin that lyses RBC, platelets, and macrophages thus inducing tissue damage.
  • disrupts smooth muscle in blood vessels
44
Q

S. aureus pathogenicity

Beta hemolysin

A
  • degrades sphingomyelin, and is therefore toxic to rbcs around nerves and many kinds of cells.
  • Heat labile
45
Q

S. aureus pathogenicity

Delta toxin

A
  • disrupts biologic membranes and may have a role in S. aureus diarrheal diseases.
  • cytolytic to erythrocytes
46
Q

S. aureus pathogenicity

Gamma toxin

A
  • a leukocidin that lyses white blood cells

- composed of two proteins designated S and F which may interact with two proteins of Panton- Valentin leukocidin.

47
Q

PANTON-VALENTINE LEUKOCIDINE

A
  • composed two protein components that kills white blood cells and incapacitate phagocytic line of defense of the host. (necrosis and severe inflammation)
  • responsible for various skin, wound, and deep tissue infection.
  • encoded on a mobile phage.
48
Q

S. aureus pathogenicity

ENTEROTOXINS

A
  • heat- stable resistant to the action of gut enzymes
  • produced when S. aureus grows in carbohydrate and protein foods.
  • responsible for food poisoning caused by S. aureus
49
Q

Most frequently food poisoning associated enterotoxins

A
  • Enterotoxin A& D
50
Q

Enterotoxin associated with hospital acquired infection

A
  • Enterotoxin B
51
Q

Enterotoxin associated with toxic shock syndrome

A
  • Enterotoxin F
52
Q

S. aureus pathogenicity

EXFOLIATIVE TOXINS

A

Responsible for:

  • Exfoliative dermatitis
  • Bullous Impetigo
  • Staphylococcal Scarlet fever
53
Q

S. aureus pathogenicity

TOXIC SHOCK SYNDROME TOXIN

TSST - 1 (SUPERANTIGEN )

A
  • the same with enterotoxin F
  • binds to MHC class II mol. yielding t-cell stimulation, which promotes manifestations of TOXIC SHOCK SYNDROME
  • associated with: fever, shock, multisystem involvement, including desquamative skin rash.
54
Q

What causes food poisoning in patients with S. aureus infection?

A

Enterotoxins produced by the organism not by the organism itself.

55
Q

Incubation period for food poisoning caused S. aureus

A

2-6 hrs. followed by abdominal cramps, nausea, vomiting, and diarrhea.

56
Q

Food poisoning caused by S. aureus

A
  • self-limiting

- rapid recovery which takes place within 24hrs.

57
Q

Toxic shock syndrome is characterized by

A

Fever, hypotension, scarlatiniform rashes particularly in the palm and sole which desquamate.

  • common among women using vaginal tampoons.
58
Q

Also referred as pyrogenic Exotoxin C

A

Toxic shock syndrome

59
Q

A skin condition caused by exfoliative toxins produced by S. aureus that is common in babies/ neonates.

A

Staphylococcal Scalded Skin syndrome / Ritter’s Disease

60
Q

Staphylococcal Scalded Skin Syndrome is characterized by

A
  • diffuse erythematous skin rashes involving the entire body with sloughing off the epidermal layer of the skin.
61
Q

Skin infections caused by S. aureus

A

FOLLICULITIS - inflammation in hair follicle
FURUNCLE - spreads to the tissue causing boils
CARBUNCLE - if there is multiple foci and tissue involvement
IMPETIGO - most common manif. in newborn and young children less than 5 yrs. old that is highly communicable.

62
Q

S. aureus Diagnosis

Gram Stain (presumptive)

A

Gram positive cocci in clusters

63
Q

S. aureus Diagnosis

Culture and Isolation
BAP

A
  • beta hemolytic pattern

- golden-yellow pigment

64
Q

S. aureus Diagnosis

Culture and Isolation
Mannitol Salt Agar

A
  • contains 7.5 % to 10% NaCl
  • only S. aureus grow
  • pH indicator is phenol red
  • turns medium from pink to yellow
65
Q

Staphylococcus spp. Diagnosis

Culture and Isolation

Phenyl Ethyl Alcohol
Colistin Nalidix Acid agar (CNA)

A
  • inhibits gram negative organism
66
Q

S. aureus Diagnosis

Culture and Isolation

Chrom Agar

A
  • selective and differential for isolation of MRSA

- (+) mauve/ pink colonies

67
Q

CONS

coagulase negative staphylococci

A

S. saprophyticus

S. epidermidis

68
Q

Coagulase

A

is an enzyme that converts soluble fibrinogen into soluble fibrin.

69
Q

The only significant human pathogen that possesses the coagulase enzyme

A

S. aureus

70
Q

Two types of coagulase

A

Cell bound and free coagulase

71
Q

Two methods for coagulase testing

A

Method:
Tube - free coagulase (Confirmatory)
slide - cell bound coagulase

72
Q

Positive reaction for coagulation testing

A

(+) White fibrin clots

(-) smooth suspension

73
Q

For tube method in coagulase testing, for how many hrs. will you incubate the tube?

A

4hrs - check reaction every 30 mins.

-do not extend beyond 4hrs.

74
Q

Factors that may contribute to coagulase testing of Staphylococcus spp.

A
  • presence of STAPHYLOKINASE enzyme which may lyse the fibrin clot thus may cause a false negative result.
75
Q

In coagulase testing what type of Plasma is used

A

Rabbit Plasma/ (Anticoagulated with EDTA)

76
Q

S. aureus Diagnosis

Biochemical: THERMONUCLEASE TEST

A
  • Staphylococcus contains heat-stable thermonuclease and coagulase negative staphylococcus does not
77
Q

Positive reaction for Thermonuclease test

A

(+) Pink zone of clearing at the edge of the well with a darker blue ring at the outer periphery zone.

78
Q

The only Staphylococci spp. that ferments mannitol

A

S. aureus

BACTERIOLOGY (15 decks)

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