Microbiology (Endocrine, Skin, Msk)

Question 1

Name the (3) coagulase (-), aka CoNS, Staphylococci

Answer 1

S. epidermis
S. haemolyticus
S. saprophyticus

Question 2

Colony color of Staph aureus v. the CoNS

Answer 2

S. aureus: pale yellow, orange, or golden

All other staph are White!

Question 3

What is one feature of staphylococcus that is important in its transmission

Answer 3

survives drying conditions and can live on surfaces. thus if doc touches bed rail w/ MRSA or MSSA on it, can transfer it on hands to next hospital surface, and so on

Question 4

use of catalase test

Answer 4

useful for differentiating between staphylococci and streptococci.
Staph = catalase +
Strep = catalase (-), b/c they are obligate anaerobes that do NOT use oxygen

Question 5

Name top 3 pathogens in order of most common causes of skin and soft tissue infections

Answer 5

#1 = Staph aureus
#2 = Coagulase-negative Staphylococci (epidermidis, haemolytius, and saphorphyticus)
#3 = GpA (and GpB) Streptococcus

Question 6

Does Staph aureus cause community-acquired pneumonia?

Answer 6

Yes, it’s the 5th most common

#1 = Strep pneumo, #2 = Haemophilus influenzae

Question 7

(3) most common pathogens causing hospital-acquired pneumonia

Answer 7

#1 = Gram-neg enterics (enterobacteriaceae)
#2 = Pseudomonas aeruginosa group
#3 = Staph aureus

Question 8

What age group is most susceptible to bacterial meningitis from staph aureus and staph epidermis?

Answer 8

ANY age group (v. Grp B strep, for ex, which affects neonates)

Question 9

Top 2 pathogens causing endocarditis

Answer 9

#1 = Staph aureus
#2 = Coagulase-negative staphylococci

Question 10

What is typically the compromising event in a Staph epidermidis infection?

Answer 10

A foreign body, e.g. shunt, catheter, joint prostheses. Almost every mucosal surface of the body has staph epidermidis. It can’t get going by itself very well, but if it has a foreign body to stick to like a BIOFILM, it can take off.

Question 11

Reason behind name of S. haemolyticus

Answer 11

S. haemolyticus is the only other staph - besides S. aureus - that can lyse blood. So will occasionally get beta-hemolysis on blood agar w/ S. haemolyticus.

Question 12

Which staph species most commonly causes UTIs? Why?

Answer 12

S. saprophyticus - it esp likes to grow on perineal skin, so it can easily move to colonize the urethra and invade into the bladder. Thus, think of S. saprophyticus w/ young, sexually active females

Question 13

Growth requirements of staphylococci

Answer 13

they are facultative anaerobes, meaning they can grow in healthy tissue (with oxygen: aerobic) OR in pus/abscesses (anaerobic). Dr. Miller says staph grows on everything, including blood agar.

Question 14

What does the beta-hemolysis property of S. aureus and S. haemolyticus mean?

Answer 14

Means they are secreting hemolytic toxins into the agar

Question 15

What is the visual representation of a coagulase test (i.e. how does it work in the lab)? Which staph species is coagulase (+)?

Answer 15

take rabbit plasma and let the strain grow there for a while. If it produces the enzyme, Coagulase, then will get clot at bottom of the tube.
S. aureus is only coagulase (+) of the staphs! However, they are all CATAlase (+)

Question 16

Which (3) parts of staph’s cell wall make it inherently inflammatory in our bodies? Which is the major protein component of the cell wall?

Answer 16

1 and 2) the Peptidoglycan and Techoic Acid of their gram + cell wall are both antigens recognized by our immune system
3) Protein A = major protein component, also antigenic.

Question 17

How does protein A block phagocytosis in s. aureus? What other feature of s. aureus is also anti-phagocytic?

Answer 17

it interacts with the Fc of immunoglobulins, which means it basically grabs them upside down b/c normally the Fc part is what binds to the neutrophil for phagocytosis.
Thus, protein A = anti-phagocytic. It’s capsule is also anti-phagocytic

Question 18

What is the function of the several cytolytic toxins that S. aureus makes?

Answer 18

lyse cells! the most imp cell they lyse are white blood cells (neutrophils), in order to interfere w/ phagocytosis

Question 19

PVL toxin. What is it and who has it?

Answer 19

A type of cytolytic toxin secreted by S. aureus, particularly in MRSA! It is a leucocidin that specifically attacks white blood cells (meaning it doesn’t contribute to it’s beta-hemolysis). So PVL toxin is imp in killing phagocytic cells.

Question 20

How do the cytolytic exotoxins of S. aureus work?

Answer 20

When S. aureus starts growing in your tissue, it sends out a cloud of toxins around it. As neutrophils move towards the infection, they encounter this cloud of toxins and are killed or inhibited before reaching the organism.

Question 21

Which exotoxin allows Staph to cause food-poisoning? What’s the main sx? How does it work?

Answer 21

Enterotoxins (which are under the category of Exotoxins). Work b/c they are heat-STABLE, so not destroyed by cooking food. Sx = vomit, vomit, vomit

Question 22

Name (2) of the S. aureus exotoxins that are super antigens. What does super antigen mean?

Answer 22

Enterotoxins (food-poisoning) and TSST-1 (toxic shock syndrome).
Super antigens dont interact like regular antigens do with a very specific MHC; they universally interact with all MHCs.

Question 23

Which S. aureus exotoxin causes scalded skin syndrome? What’s the MOA of this exotoxin?

Answer 23

Exfoliative toxin, aka Epidermolytic toxin.

MOA = lyses attachment between cells of the granular layer of the epidermis

Question 24

What does it mean if you are a nasal carrier of MRSA?

Answer 24

it means you don’t just have it in your nares, but have it all over your skin surfaces = at risk for transmission to self and to others

Question 25

Which strains cause hospital-acquired (HA) and community-acquired (CA) MRSA?

Answer 25

HA-MRSA = USA-100
CA-MRSA = USA-300

Question 26

T/F. Development of Impetigo requires a break in the skin

Answer 26

False. No break in the skin is needed to initiate impetigo by staph/strep.

Question 27

How does staph cause scalded skin syndrome?

Answer 27

Exfoliative toxin is required, get:
Local infection with systemic TOXEMIA. Means you do not need to have staph in the bloodstream in order to get scalded skin syndrome; just get the toxin in the bloodstream and bacteria stay at site of local infection

Question 28

How does staph cause toxic shock syndrome?

Answer 28

local infection with systemic TOXEMIA due to the TSST-1 exotoxin. So, just like scalded skin, don’t need infection in blood with staph, just systemic release of the TSST-1 exotoxin

Question 29

Name (4) sx of Toxic Shock Syndrome. What other disease is it similar to?

Answer 29

Fever, rash, vomiting/diarrhea, and hypotension (leads to cardiac and renal failure)
Very similar to scarlet fever (in both presentation and in fact of being local infection with systemic toxemia)

Question 30

Pt presents with fever, fast, vomiting/diarrhea that leads to desquamation of feet and hands. Name (2) possible causes

Answer 30

Scarlet fever or toxic shock syndrome
(super antigens, for whatever reason, cause skin to exfoliate as body is recovering from infection). This is not due to exfoliative toxin of scalded skin syndrome.

Question 31

Name 5 illnesses that are local infections with systemic toxemia (as opposed to bacteremia)

Answer 31

scarlet fever
diptheria
pertussis
scalded skin syndrome
staph toxic shock syndrome

Question 32

Differences on imaging of Staph pneumonia (MRSA) v. Streptococcus pneumoniae pneumonia

Answer 32

XR for staph shows multiple abscesses = patchy consolidation v.
big consolidation seen on XR of S. pneumo infection

Question 33

most common cause of Osteomyelitis

Answer 33

S. aureus. Once it gets into bloodstream, in addition to sepsis, it can cause osteomyelitis.

Question 34

Which organism is responsible for about 50% of arthritis cases? How does it cause this?

Answer 34

S. aureus. It infects the joint and destroys the cartilage, leaving a permanent joint deformity

Question 35

use of Penicillin G in staph v. strep

Answer 35

NEVER an appropriate drug for staph aureus, whether MRSA or MSSA
Can use as tx for GrpA strep

Question 36

Good topical agent to tx gram + skin infection

Answer 36

Bacitracin

Question 37

How does MRSA infection classically begin?

Answer 37

Looking like a spider bite

Question 38

Tx for MSSA

Answer 38

Nafcillin and oxacillin

Question 39

Tx for MRSA

Answer 39

vancomycin and ceftaroline