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Pathophysiology > Staphylococci and Related Gram + cocci > Flashcards

Staphylococci and Related Gram + cocci Flashcards

1
Q

What are the two major groups in the family microccaceae?

A

1) micrococcus

2) rothia

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2
Q

What are the 5 KEY characteristics of staph?

A

1) Gram + (clusters)
2) non-motile
3) non-spore-forming
4) catalase positive
5) facultative anaerobes

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3
Q

What is the main way to determine staph from strep?

A

CATALASE testing

\+ = staph
- = strep
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4
Q

What are the 4 main types of staph to know?

A

1) aureus
2) epidermidis
3) lugdunensis
4) saprophyticus

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5
Q

Where is staph aureus normally found?

A

perineum, axillae, vagina

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6
Q

What are 5 factors that predispose one to staph aureus infection?

A

1) defects in leukocyte chemotaxis
2) defects in opsonization by antibodies
3) defects in intracellular killing of bacteria following phagocytosis
4) skin injuries
5) presence of foreign bodies

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7
Q

True or false: the usual site of infection is that where the organism is part of the normal flora

A

TRUE

skin, nose + throat, GI tract, urethra, vagina

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8
Q

Define pyoderma

A

any skin disease that is pyogenic (pus forming)

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9
Q

What is a furuncle?

A

skin disease caused by infection of hair follicles resulting in localized accumulation of pus and dead tissue

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10
Q

What is a carbuncle?

A

abscesses larger than boils (with one or more openings)

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11
Q

What are 3 toxin-mediated infections from staph aureus?

A

1) scalded skin syndrome
2) toxic shock syndrome
3) food poisoning

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12
Q

What are 4 components that interfere with phagocytosis? (AKA VIRULENCE FACTORS)

A

1) capsules
2) protein A
3) panton-valentine leukocidin (PVL)
4) coagulase

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13
Q

How do capsules interfere with phagocytosis?

A

prevent ingestion of organisms by PMNs

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14
Q

How does Protein A act as a virulence factor?

A

binds to Fc region of IgG interfering with opsonization and ingestion of organism by PMNs

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15
Q

What is PVL and what does it do?

A

enzyme that alters cation permeability of rabbit and human leukocytes resulting in white cell destruction

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16
Q

How does Coagulase work?

A

binds to prothrombin catalyzing fibronogen to fibrin which then coats cells (with fibrin) rendering them resistant to opsonization and phagocytosis

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17
Q

Which type of staph aureus is more infectious, PVL+ or PVL-?

A

PVL+

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18
Q

What are the 4 hemolysins in staph aureus?

A

alpha, beta, gamma, delta

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19
Q

What are the hallmarks of alpha hemolysin?

A

lyses RBCs, dermonecrotic on SubQ injection, leukocyte toxicity

20
Q

What are the hallmarks of beta hemolysin?

A

shingomyelinase

produces hot-cold lysis

21
Q

What are hallmarks of delta hemolysin?

A

acts as surfactant to disrupt cell membrane (forms channels that result in leakage of cellular contents)
can cause enterocolitis in neonates

22
Q

What are the hallmarks of gamma hemolysin?

A

can cause lysis in a variety of cells

23
Q

What toxins are responsible for staphylococcal scalded skin syndrome?

A

exfoliatins (aka epidermolytic toxins)

works by dissolving mucopolysaccharide matrix of epidermis causing separation of skin layers

24
Q

What are enterotoxins?

A

heat-stable molecules responsible for clinical features of staphylococcal food poisoning, probably most common cause of food poisoning in U.S.

25
Q

What 3 enzymes are produced by staph aureus?

A

1) Fibrinolysins - break down fibrin clots and facilitate spread of infection
2) Hyaluronidase - hydrolyze intercellular matrix of acid mucopolysacch to spread organisms to adjacent tissues
3) Phospholipase C - makes tissues more susceptible to damage by complement

26
Q

What are examples of some superantigens associated with staph aureus?

A 
toxic shock (TSST-1)
streptococcal pyrogenic exotoxins (SPE)
27
Q

What 3 biological characteristics are shared by staph aureus supertoxins?

A

pyrogenicity
superantigenicity
enhance lethal effects

all induce polyclonal T-cell proliferation

28
Q

What virulence factor is used to identify staph aureus?

A

coagulase

if it clots it is staph aureus

29
Q

What is the alternative coagulase test?

A

latex agglutination

agglutination = positive

30
Q

What is the most common coagulase NEGATIVE staph?

A

staphylococcus epidermidis

31
Q

What particular infections are associated with staph epidermidis?

A

infections of indwelling devices (makes extracellular slime that makes biofilm - need to remove entire device)

32
Q

What is the cause of acute urinary tract infection in young women?

A

staph saprophyticus

33
Q

What are 2 HUGE identifiers of staph saprophyticus?

A
  1. Coagulase NEGATIVE
  2. Resistant to novobiocin

(should be furozolidone susceptible)

34
Q

What is the only staph species that is both PYR and Ornithine positive?

A

staph lugdunensis

35
Q

Which staph colonizes the human inguinal area?

A

staph lugdunensis

36
Q

True or false: the majority of MRSA infections occur in hospitals?

A

true

37
Q

What are common community acquired MRSA sources?

A 
MPSM (men play sports men)
MSM
jails
military recruits
daycare
nurseries
38
Q

What is the significance of the mecA gene?

A

confers methicillin resistance

39
Q

What does mecA gene encode?

A

altered penicillin binding protein 2a (PBP2a)

which has decreased binding affinity for beta lactam antibiotics and allows PG synthesis in the presence of betal lactam antibiotics

40
Q

True or false: mecA gene is born on chromosomes

A

FALSE; carried on a mobile element (has to be acquired) called SCCmec

41
Q

When should MRSA come up in differential?

A 
skin and soft tissue infections (SSTIs)
sepsis syndrome
osteomyelitis
necrotizing pneumonia
septic arthritis
necrotizing fasciitis
42
Q

True or false: infected patients contaminate hospital environment better than colonized patients (with MRSA)

A

FALSE; same frequency

43
Q

True or false: MRSA testing in patients has DECREASED bacteremia in ICUs

A

true

44
Q

What is the most effective method of detecting MRSA in patients?

A

real time PCR

45
Q

What is the most important reservoir of MRSA in hospitals?

A

colonized or infected patients

Pathophysiology (26 decks)

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