Gram (+) Cocci Flashcards
Pharyngitis from GAS
Strep throat
red, erythematous, inflamed throat
Rash from scarlett fever
spares the face
Scarlett Fever
one of the SPE (A, C) caused infections from strep pyogenes.
reddening, swelling of tongue (strawberry tongue)
Pharyngitis
widespread rash that SPARES THE FACE
Pneumonia in staph aureus
XR shows patchy infiltrate
Normally it’s a post-viral bacterial pneumonia. It happens after immune system has been weakened by viral infection.
Scaled skin syndrome
Result of staph aureus
skin peels off
Mediated by exfoliative toxin (a protease)
Post-streptococcal Glomerulonephritis (PSGN)
Damage caused by own immune system after strep pyogenes infection - Type 3 hypersensitivity
Damage is from circulating antigen-antibody immune complexes that deposit in glomerulus
Symptoms: Dark brown, cola colored urine
Facial swelling, puffiness from erythema
Happens 2 weeks after initial strep infection
RF occurs after pharyngitis, but PSGN can happen after pharyngitis OR skin infection like impetigo
Early dx/tx of strep throat does NOT prevent PSGN
What disease process is Strep Sanguines associated with most?
A type of Strep Veridans
Causes subacute endocarditis in damaged heart valves.
Only infects damaged heart valves.
Mitral is most common, bc it’s the most likely to be damaged already (MVP, RF)
After teeth cleaning in person with a damaged valve, the bacteria enter the blood and can adhere to any fibrin-platelet aggregates of damages tissue by creating dextrans.
Staph food poisoning
Toxin-mediated disease of staph aureus
rapid onset from a preformed toxin (1-8 hrs)
More associated with vomit than diarrhea (!!!)
Meats and cream-based food (mayo,custard) left out too long
Describe Staph Aureus appearance on blood agar
Colonies have yellow/gold look on blood agar
Prevention for strep pneumo
2 vaccines:
Adults: 23-valent polysaccharide vaccine (IgM)
No protein so the immune system generates T-cell-independent response and only generates IgM (no long-lasting protection)
Kids: 7-valent, but it’s conjugated to protein (IgG)
Tx for enterococci
Linezolid or Tigecycline
How do Strep viridans adhere to platelets?
Dextrans - it creates this adherent from glucose
How do you prevent GBS infection in newborns?
At 35 wks, mom’s vagina and rectum are swabbed to checl for colonies.
If she is colonized give mom penicillin during delivery (intrapartum)
Heart issue caused by Staph aureus
Acute bacterial endocarditis. This has a fast onset and happens more in IV drug users (this makes it right sided)
Valve most affected = tricuspid
Diseases caused by staph aureus
Inflammatory (Pneumonia, Septic arthritis, Abscesses, Acute bacterial endocarditis, skin issues [impetigo, cellulitis, foruncles, carbuncles, abscesses], osteomyelitis)
Toxin-mediated (Scalded skin syndrome, TSS, food poisoning)
Which Strep species is CAMP (+)?
Agalactiae - when it is plated with S.aureus you see an increased zone of hemolysis
Arrowhead zone of hemolysis
Streptolysin O
Another strep pyogenes virulence factor
Allows GAS to lyse RBCs and be B-hemolytic
We generate antibodies to it. Anti-streptolysin O antibodies (ASO titer) tells us if we have been recently infected by GAS (helpful in diagnosing acute RF or PSGN)
Protein A mechanism
It binds Fc portion of immunoglobulins. This prevents complement from binding that region and prevents opsonization/phagocytosis.
What are the 3 major illnesses caused by enterococcus?
UTI, Endocarditis, Biliary Tree infections
Describe the appearance of Strep species?
They form long chains or pairs instead of clusters
Impetigo from GAS
Skin infection that looks honey crusted
Can also be caused by Staph aureus
What does strep pneumo look like?
Lancet-shaped gram (+) diplococci
Which staph species are urease (+)?
Staph epidermidis and staph saprophyticus
In what population does Strep Agalactiae (GBS) cause the most serious infections?
newborns
What is the #1 cause of meningitis in neonates?
Strep agalactiae (GBS)
What are the 3 infections caused by streptococcal pyrogenic exotoxin (SPE)
Scarlett Fever (SPE A, C) Toxic Shock Like Syndrome (SPE A, C) Necrotizing Fasciitis (SPE B)
Describe the appearance of Staph
Look like bundles of grapes
What is the most common cause of endocarditis affecting artificial heart valves?
Staph epidermidis
MRSA
It becomes resistant to methicillin by altering its penicillin binding proteins (PBPs)
PBPs help build cell walls.
Describe the pneumonia of strep pneumo
1 cause of community acquired pneumonia in adults
Lobar pneumonia that infiltrates lower lobes
Leads to production of rust-colored sputum
How do you differentiate staph epi from staph sapro?
Novobiacin sensitive = epidermidis
Novobiacin resistent = saprophyticus
What do you do if you see staph epi on culture?
NOTHING! It’s normal skin flora. It contaminates a lot of cultures (blood cultures too)
What does staph sapro like to cause?
UTIs in sexually active women.
How do you treat staph epi caused endocarditis?
vancomycin
DNase
Another strep pyogenes virulence factor
Depolymerizes DNA
List the gram (+) cocci (8)
Staph Aureus Staph Epidermidis Staph Saprophyticus Strep Pyogenes Strep Agalactiae Strep Pneumoniae Strep Viridans Enterococcus
Tx for strep pneumo
erythromycin (Macrolide)
OR Ceftriaxone (3rd gen cephalosporin)
In Staph vs Strep, which is catalase (+)?
Staph
How do you tell the difference between Strep Pneumoniae and Strep Viridans?
Strep pneumo = Optochin sensitive, bile soluble (cannot grow in bile)
Strep viridans = Optochin resistant, bile resistant/insoluble
What are the 2 subspecies of Strep Veridans?
Strep Mutans and Strep Sanguines
Cellulitis from GAS
erythema of skin
Also Erysipelas: very superficial cellulitis with well-demarcated borders. GAS is most common cause.
What does staph epidermidis commonly infect?
artificial joints and implanted hardware (the enemy of orthopedic surgeons!)
Also indwelling catheters and lines (it covers our skin… when you penetrate the skin, it is ready to enter)
What makes staph epi so good at sticking to sleek metal/plastic surfaces?
It produces a lot of adherent biofilms
Biofilms are a bunch of polysaccharides that help it stick and form coatings to protect against antibiotics and immune cells.
Since staph epi produces a lot of biofilms, it is resistant to a lot of antibiotics
What disease process is Strep Mutans associated with most?
A type of Strep Veridans
Causes dental carries
M Protein
Main virulence factor in Rheumatic Fever
Highly antigenic protein in strep pyogenes cell wall. Causes Type 2 hypersensitivity.
Interferes with opsonization (anti-phagocytic) and is extremely antigenic. It elicits strong humoral response. There is a very high chance that you will make antibodies against a very similar self-antigen (the myosin in cardiac muscle) in a process called molecular mimicry
Mitral valve is most affected leading to mitral stenosis
Why is a splenectomy relevant?
Pts who have no spleen or who have sickle cell disease are at higher risk of infection from encapsulated organisms.
Tx for strep throat
penicillin
Which Strep species is Hippurate (+)?
Agalactiae - It hydrolyzes sodium hippurate
Where does staph aureus like to colonize?
nares
Tx for staph aureus
MRSA = vancomycin
MSSA = nafcillin (use a penicillin bc it’s more effective than vancomycin)
Septic arthritis and Staph Aureus
Staph aureus is #1 cause in adults
What is the Strep pyogenes capsule made out of?
Hyaluronic acid
We have hyaluronic acid in our own joints, therefore the capsule is not immunogenic
Which Staph species is coagulase (+)?
Staph aureus only. Coagulase converts fibrinogen to fibrin.
Strep Pneumo and Strep Viridans hemolysis
Alpha-hemolytic (partial hemolysis so surrounding zone of hemolysis is a green hue - green from oxidation of hemoglobin)
Staph aureus on Mannitol salt agar
Staph aureus ferments mannitol - turns agar yellow
If organism does not ferment mannitol - it stays pink
Rheumatic Fever course
Starts after strep pharyngitis, but NOT SKIN INFECTIONS and also NOT if the strep throat has been treated right away.
See RF mostly in young children without access to healthcare
Staph aureus hemolysis
B-hemolytic
Main virulence factor of staph aureus
Protein A
Symptoms of Rheumatic Fever
JONES criteria
J = Joints (polyarthritis) O = Heart issues (valvular damage leading to new murmurs, myocarditis, pericarditis) N = Nodules (subQ nodules on extensor surfaces of forearms or elbows/knees) E = Erythema marginarum (rash with thick, red borders) S = Sydenham's chorea (rapid involuntary movements, esp of the hands and face)
Toxic Shock Syndrome
Toxin-mediated disease of staph aureus
Toxin = TSST (toxic shock syndrome toxin)
From leaving foreign packing in too long (tampons, gauze after rhinoplasty)
Non specific binding of MHC II and T cell receptors leads to overactivation and eventual cytokine storm
Could be fatal
Toxic Shock Like Syndrome (TSLS)
one of the SPE (A, C) caused infections from strep pyogenes
superantigen mediated
What makes E. faecium Tx so hard?
It is resistant to a lot of things, even vancomycin
Vancomycin Resistent Enterococcus (VRE)
What are the 2 virulence factors of strep pneumo?
1) It’s capsule
2) IgA Protease - cleaves IgA which lets it colonize and invade our mucosa
Necrotizing Fasciitis
one of the SPE (B) caused infections from strep pyogenes
invades fascia and spreads fast
surgical emergency with amputation possible
What is the #1 cause of osteomyelitis in adults?
staph aureus
What diseases can GBS cause in neonates?
meningitis, sepsis, pneumonia
How do you treat an infected prosthesis?
Prob have to replace it
How can you differentiate GAS from GBS?
GAS = bacitracin sensitive GBS = bacitracin resistant
Special general features about enterococci
Formerly called Group D Strep
Infects the intestinal tract
E. faecalis is most common
E. faecium is less common, but worse.
Bile resistant (can grow in bile)
Can both grow in mediums up to 65% NaCl
What are the 3 main pyrogenic infections caused by Group A Strep (pyogenes)?
Impetigo, Pharyngitis, and Cellulitis
How does a baby get GBS?
As it passes through vaginal canal during delivery
Strep pyogenes (GAS) hemolysis
B-hemolytic (due to streptolysin-O)
What is the function of catalase?
It converts H2O2 to water.
Streptokinase
Another strep pyogenes virulence factor
Converts plasminogen to plasmin
Plasmin is fibrinolytic. We can actually give streptokinase during MI/stroke to lyse clots.
What are the 4 diseases that Strep pneumo is the #1 bacterial cause of?
MOPS
M = Meningitis O = Otitis media P = Pneumonia S = Sinusitis
