Name the (3) coagulase (-), aka CoNS, Staphylococci
S. epidermis
S. haemolyticus
S. saprophyticus
Colony color of Staph aureus v. the CoNS
S. aureus: pale yellow, orange, or golden
All other staph are White!
What is one feature of staphylococcus that is important in its transmission
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
use of catalase test
useful for differentiating between staphylococci and streptococci.
Staph = catalase +
Strep = catalase (-), b/c they are obligate anaerobes that do NOT use oxygen
Name top 3 pathogens in order of most common causes of skin and soft tissue infections
#1 = Staph aureus #2 = Coagulase-negative Staphylococci (epidermidis, haemolytius, and saphorphyticus) #3 = GpA (and GpB) Streptococcus
Does Staph aureus cause community-acquired pneumonia?
Yes, it’s the 5th most common
#1 = Strep pneumo, #2 = Haemophilus influenzae
(3) most common pathogens causing hospital-acquired pneumonia
#1 = Gram-neg enterics (enterobacteriaceae) #2 = Pseudomonas aeruginosa group #3 = Staph aureus
What age group is most susceptible to bacterial meningitis from staph aureus and staph epidermis?
ANY age group (v. Grp B strep, for ex, which affects neonates)
Top 2 pathogens causing endocarditis
#1 = Staph aureus #2 = Coagulase-negative staphylococci
What is typically the compromising event in a Staph epidermidis infection?
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.
Reason behind name of S. haemolyticus
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.
Which staph species most commonly causes UTIs? Why?
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
Growth requirements of staphylococci
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.
What does the beta-hemolysis property of S. aureus and S. haemolyticus mean?
Means they are secreting hemolytic toxins into the agar
What is the visual representation of a coagulase test (i.e. how does it work in the lab)? Which staph species is coagulase (+)?
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 (+)
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?
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.
How does protein A block phagocytosis in s. aureus? What other feature of s. aureus is also anti-phagocytic?
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
What is the function of the several cytolytic toxins that S. aureus makes?
lyse cells! the most imp cell they lyse are white blood cells (neutrophils), in order to interfere w/ phagocytosis
PVL toxin. What is it and who has it?
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.
How do the cytolytic exotoxins of S. aureus work?
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.
Which exotoxin allows Staph to cause food-poisoning? What’s the main sx? How does it work?
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
Name (2) of the S. aureus exotoxins that are super antigens. What does super antigen mean?
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.
Which S. aureus exotoxin causes scalded skin syndrome? What’s the MOA of this exotoxin?
Exfoliative toxin, aka Epidermolytic toxin.
MOA = lyses attachment between cells of the granular layer of the epidermis
What does it mean if you are a nasal carrier of MRSA?
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
Which strains cause hospital-acquired (HA) and community-acquired (CA) MRSA?
HA-MRSA = USA-100 CA-MRSA = USA-300
T/F. Development of Impetigo requires a break in the skin
False. No break in the skin is needed to initiate impetigo by staph/strep.
How does staph cause scalded skin syndrome?
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
How does staph cause toxic shock syndrome?
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
Name (4) sx of Toxic Shock Syndrome. What other disease is it similar to?
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)
Pt presents with fever, fast, vomiting/diarrhea that leads to desquamation of feet and hands. Name (2) possible causes
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.
Name 5 illnesses that are local infections with systemic toxemia (as opposed to bacteremia)
scarlet fever diptheria pertussis scalded skin syndrome staph toxic shock syndrome
Differences on imaging of Staph pneumonia (MRSA) v. Streptococcus pneumoniae pneumonia
XR for staph shows multiple abscesses = patchy consolidation v.
big consolidation seen on XR of S. pneumo infection
most common cause of Osteomyelitis
S. aureus. Once it gets into bloodstream, in addition to sepsis, it can cause osteomyelitis.
Which organism is responsible for about 50% of arthritis cases? How does it cause this?
S. aureus. It infects the joint and destroys the cartilage, leaving a permanent joint deformity
use of Penicillin G in staph v. strep
NEVER an appropriate drug for staph aureus, whether MRSA or MSSA
Can use as tx for GrpA strep
Good topical agent to tx gram + skin infection
Bacitracin
How does MRSA infection classically begin?
Looking like a spider bite
Tx for MSSA
Nafcillin and oxacillin
Tx for MRSA
vancomycin and ceftaroline