Staphylococci and Related Gram + cocci

Question 1

What are the two major groups in the family microccaceae?

Answer 1

1) micrococcus

2) rothia

Question 2

What are the 5 KEY characteristics of staph?

Answer 2

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

Question 3

What is the main way to determine staph from strep?

Answer 3

CATALASE testing

\+ = staph
- = strep

Question 4

What are the 4 main types of staph to know?

Answer 4

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

Question 5

Where is staph aureus normally found?

Answer 5

perineum, axillae, vagina

Question 6

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

Answer 6

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

Question 7

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

Answer 7

TRUE

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

Question 8

Define pyoderma

Answer 8

any skin disease that is pyogenic (pus forming)

Question 9

What is a furuncle?

Answer 9

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

Question 10

What is a carbuncle?

Answer 10

abscesses larger than boils (with one or more openings)

Question 11

What are 3 toxin-mediated infections from staph aureus?

Answer 11

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

Question 12

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

Answer 12

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

Question 13

How do capsules interfere with phagocytosis?

Answer 13

prevent ingestion of organisms by PMNs

Question 14

How does Protein A act as a virulence factor?

Answer 14

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

Question 15

What is PVL and what does it do?

Answer 15

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

Question 16

How does Coagulase work?

Answer 16

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

Question 17

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

Answer 17

PVL+

Question 18

What are the 4 hemolysins in staph aureus?

Answer 18

alpha, beta, gamma, delta

Question 19

What are the hallmarks of alpha hemolysin?

Answer 19

lyses RBCs, dermonecrotic on SubQ injection, leukocyte toxicity

Question 20

What are the hallmarks of beta hemolysin?

Answer 20

shingomyelinase

produces hot-cold lysis

Question 21

What are hallmarks of delta hemolysin?

Answer 21

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

Question 22

What are the hallmarks of gamma hemolysin?

Answer 22

can cause lysis in a variety of cells

Question 23

What toxins are responsible for staphylococcal scalded skin syndrome?

Answer 23

exfoliatins (aka epidermolytic toxins)

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

Question 24

What are enterotoxins?

Answer 24

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

Question 25

What 3 enzymes are produced by staph aureus?

Answer 25

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

Question 26

What are examples of some superantigens associated with staph aureus?

Answer 26

``` toxic shock (TSST-1) streptococcal pyrogenic exotoxins (SPE) ```

Question 27

What 3 biological characteristics are shared by staph aureus supertoxins?

Answer 27

pyrogenicity superantigenicity enhance lethal effects all induce polyclonal T-cell proliferation

Question 28

What virulence factor is used to identify staph aureus?

Answer 28

coagulase if it clots it is staph aureus

Question 29

What is the alternative coagulase test?

Answer 29

latex agglutination agglutination = positive

Question 30

What is the most common coagulase NEGATIVE staph?

Answer 30

staphylococcus epidermidis

Question 31

What particular infections are associated with staph epidermidis?

Answer 31

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

Question 32

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

Answer 32

staph saprophyticus

Question 33

What are 2 HUGE identifiers of staph saprophyticus?

Answer 33

1. Coagulase NEGATIVE 2. Resistant to novobiocin (should be furozolidone susceptible)

Question 34

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

Answer 34

staph lugdunensis

Question 35

Which staph colonizes the human inguinal area?

Answer 35

staph lugdunensis

Question 36

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

Answer 36

true

Question 37

What are common community acquired MRSA sources?

Answer 37

``` MPSM (men play sports men) MSM jails military recruits daycare nurseries ```

Question 38

What is the significance of the mecA gene?

Answer 38

confers methicillin resistance

Question 39

What does mecA gene encode?

Answer 39

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

Question 40

True or false: mecA gene is born on chromosomes

Answer 40

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

Question 41

When should MRSA come up in differential?

Answer 41

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

Question 42

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

Answer 42

FALSE; same frequency

Question 43

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

Answer 43

true

Question 44

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

Answer 44

real time PCR

Question 45

What is the most important reservoir of MRSA in hospitals?

Answer 45

colonized or infected patients