Stapholococci Flashcards
What’s the division pattern of Staph?
divide along three planes - resulting in grape-like clusters (can also be seen singularly or in pairs, but most often clusters)
How do streptococcus species divide? (different from staph)
divide along a single plane that is perpendicular to long axis of cells - resulting in formation of chains or pairs of cells (diplococci)
What is this?
staph aureus
What is this?
strep pneumoniae
Explain the catalase test.
catalase - breakdown of hydrogen peroxide (H2O2) -> water + O2
take a colony -> drop 3% H2O2 onto colony-> positive test will show bubbling over region (from oxygen!)
staph = positve
strep = neg
Explain the coagulase test.
coagulase converts fibrinogen-> fibrin
plasma inoculated with bacteria -> incubate specimen at 37OC -> positive will see clotting of plasma sample
Explain the mannitol salt agar test.
Positive: changes the pH indicator from red to yellow - meaning mannitol was fermented and acid formed as end product (lowering the pH and causing this change in color)
What is the link between staph aureus and coagulase?
hallmark positive test!
allows staph aureus to wall itself from the immune defenses via promotion of abscess formation (walls off from immune responses AND prevent antibiotics penetration)
What is the siginificance of staph aureus ability to ferment mannitol?
mannitol provides the main carbon source
indication that S. aureus can live happily on the surface of skin despite salt, dry environment containing sebaceous, anti-microbial peptides
test serves as both selective and differential for S. aureus
What is seen on blood agar plate with S. aureus?
gold pigment from production of anti-oxidant pigment staphyloxanthin
(keep in mind is hallmark of the bacteria but not all strains will have this golden pigment)
What is hemolysis?
destruction of RBCs around colony
Where do we find staph aureus?
part of normal/transient flora in human and animals
particularly found on skin (axilla), nasopharynx, nares, groin (perineum)
risk of nosocomial infections!
What is the significance of adherance factors?
helps staph aureus stick to a lot of surfaces
What’s the importance of the antimicrobial resistance factors?
allows staph aureus to bcome resistant to many drugs
How does beta-lactamase work?
cuts off the active part of the antibiotics that allow S. aureus to have immunity
What is the order of virulence factor expressions for S. aureus?
early on we have adherence -> then immuno-evasion and invasiveness -> then exotoxins
makes sense if think about what pathogen needs to invade
Are s. aureus able to make biofilms?
yes! (staph epidermidis can as well)
What is the sigfinicance of biofilms?
makes it hard for antibiotics to get to is - also, hard to eradicate with phagocytes when they’re imbedded in this biofilm
What are the invasins virulence factors of S. aureus?
hyaluronidase, staphylysin, leukocidin, leukotoxin, coagulase, staphylokinase
What do leukotoxin and leukocidin do?
kill WBCs
What are the functions of hyaluronidase and staphylokinase?
spreading factors - promote tissue destruction that allows the bacteria to disseminate throughout the tissue
What are the adherence factors of Staph Aureus?
Fbe (fibrinogen adhesions), AtlE (vitronectin adhesion), GehD (collagen adhesion), Embp (fibronectin adhesion)
aka MSCRAMMs (microbrial surface components recognizing adhesive matrix molecules)
What is significant about the adherence pattern of Staph Aureus?
will bind our own proteins (fibrin, fibronectin) and has predilection for adhering to damaged tissues
gives bacteria ability to adhere to SEVERAL diff surfaces and initiate biofilm formation
What are the exotoxin damage / superantigens of staph aureus?
TSST (toxic shock syndrome toxin), EFT (exfoliative toxins), SE AG (staphylococcal enterotoxin)
What are superantigens?
molecules that can cross-circuit (nonspecific activation) of the T-cell receptors to APCs -> non-specific activation of immune system -> produce hurricane of cytokines with variety of neg consequences
cytokines (IL-1 and TNF) -> fever
capillary permeability -> desquamation
generation of gamma interferon and others (IL-2) -> nausea, vomitting, diarrhea, and shock
What are the biofilm forming virulence factors of S. aureus?
PIA (polysaccharide intercellular adhesion); Aap (accumulated associated protein)
How do biofilms allow for avoidance of antibiotics?
changing the bacteria replication pattern so antibiotics can no longer recognize
How do bacteria conserve energy in regards to virulence factors?
not all virulence factors are produced at once - made as needed
What conditions predisposes to infection with S. aureus?
- breach in skin
- immunological defects (chemotaxis, opsonization, PMNs functional defects i.e. chronic granulomatous disease and leukocyte adhesion deficiency)
- presence of foreign bodies (catheters, prosthetic joints)
- sharing of fomites, contact sports, close quarters, hospital stay, hygiene
- previous tissue damage (scar tissue, endocarditis)
What makes it easy to have Staph Aureus infections?
can survive in environment for substantial periods of times - easy community spread!
What’s important about protein A?
since it binds to Fc receptor of IgG molecule -> blocks the binding site of PMNs and macrophages on IgGs for opsonization and prevents phagocytosis of the organism
so microcapsule has an anti-phagocytic disease
Define abscess.
collection of pus usually around a hair follicle
How do we treat abscesses?
incise, drain, and surgically remove foreign body
What gives pus the yellow/green color?
myeloperoxidase found in neutrophils
What are furuncles?
abscess into subcutaneous tissue
PAINFUL (bc sensors are in this layer)
How do we treat furuncles?
incise, drain, doxycycline
(mupirocin to nares + bleach baths)
Define carbuncles.
multiple contiguous abscesses
found commonly in areas where people may not clean much
How do we treat carbuncles?
drainage +/- antibiotic therapy depending on severity
When is antibiotics not needed?
simple abscesses -> simple drainage of all pus pockets then packing the incisied area will suffice
What is this?
abscess
What is this?
furuncle
What is this?
carbuncle
What are hemolysins?
exotoxin virulence factors that lead to tissue damage at site of infection
Name some hemolysins.
alpha-toxin, gamma toxin, phenol-soluble modulins
beta-toxin and delta toxin
all cytotoxins
What’s the most important exotoxin for Staph Aureus?
alpha-toxin
What’s the significance of alpha toxin?
major pore-forming toxin causing the disease of S. aureus infection - cause of hemolysis and skin necrosis
the pore provides an easy entry route for further S. aureus infection - easy dissemination into blood stream
will aos insert into membranes of PMNs and cause lysis
What bacteria likes to adhere to stitches?
staph aureus
How does staph aureus infection lead to cellulitis?
staphylokinase + hyaluronidase aid in the spread along the subcutaneous fascial plane
How do we treat the staph aureus induced cellulitis?
antibiotics
What virulence factors of staph aureus are involved in formation of corneal ulcers?
alpha, beta, delta, gamma toxins; coagulase, nuclease, lipase, and hyaluronidase
What are the host factors involved in corneal ulcer?
influx of PMNs into the infected region
Describe what it clinically seen in patients with corneal ulcers.
ppthalamic emergency!
- moderate to marked stromal cellular infiltration
- moderate to marked anterior chamber reacton (hypopyon)
- well-demarcated infiltrate: yellow-white (pus)
- satellite lesions may be present
“wake up in the morning with eyes glued shut”
What Staph infections cause impetigo?
Staph Aureus and Staph Pyogenes
How do we treat corneal ulcers?
best outcome: topical antibiotics
worst outcome: cornea perforates and transplant necessary
Describe the transmission of impetigo.
very contagious -> spreading quickly through preschools or grade schools
scratching/picking at sores -> contact with others -> SPREAD
Describe the progression seen in impetigo.
small scartch or barely perceptible lesion -> vesicles -> pustules -> crust over to become honey-colored and flakey
What form if impetigo is specific for Scalded Skin Syndrome?
bullous impetigo - burn-like blisters but pus filled (NOT clear liquid seen in real burns)
How do we treat impetigo?
topical and oral antibiotics (bc no single, focal lesion to be excised and drained)
How does staph aureus cause food contamination?
secretes enterotoxins (SEA, SEB, SEC1, etc)
SEA is ____ - encoded
phage
SED is _____ - encoded
plasmid
In food poisoning, super-antigen effects result in excess what?
IL-2
What treatment is needed for Staph Aureus food poisoning?
supportive treatment - symptoms abate within a day or two
What causes Scalded Skin Syndrome?
skin lifted and filled with fluid from destruction of desmoglein-1 via epidermolyitc exotoxins (exfoliatin A and B - both are proteases)
What layers do desmoglein-1 hold together?
granulosum and spinosum
What is clinically seen in Scalded-Skin Syndrome?
fever, large bullae, erythematous macular rash
- skin slough, serous fluid exudes, electrolytic imbalance - possible secondary infections
- hair and nails lost
- recovery usu within 7-10 days
How do we treat SSS?
treat like a burn!
treat open skin with antibiotics to prevent further infection
What toxin is secreted by Staph Aureus to elicit toxic shock syndrome?
TSST-1: toxic shock syndrome toxin-1 (becomes absorbed and acts as super-antigen)
What is seen clinically in toxic shock syndrome?
initially fever, nausea, vomitting, and diarrhea followed by rash and exfoliation
can be deadly: pressure drops, multiple organ system failure
How do we treat toxic shock syndrome?
antibiotics, remove colonized item, supportive care
Describe “trojan horse” method of dissemination.
Staph aureus can hijack neutrophils during phagocytosis - prevents bacteria from being effectively killed by antibiotics
PMN goes on to spread infection systemically
What is one of the causes for chronic infective endocarditis?
coagulase negative staph - bc their virulence factors do not attract the immune system as quickly
What is PVL?
panton-valentine leukocidin: newer toxin related to S. aureus
What’s the link between PVL and pneumonia?
forms pores in cells lining alveolar spaces allowing fluid to accumulate inside the tissues
activates PMNs and macrophages causing IL-8 release (attracting more PMNs)
PMNs destroy the cells lining alveolar space -> hemorrhaging
lungs = hemorrhagic, necrotic pneumonia
Describe the virulence factors associated with Staph Epidermidis.
Not as prominent as S. aureus but have lots of adhesins -> making easy to stick to plastics (like lines in ICU patients)
Who gets infected by Staph Epidermidis?
sickest of the sick (ICU patients), septicemia, endocarditis
What is seen in blood agar with Staph Epidermidis?
small white non-hemolytic colonies
What is seen on the blood agar of Staph saprophyticus?
large white to yellow non-hemolytic colonies
How do we treat staph saprophyticus?
amoxicillin or bactrim/sulfa-trimethoprim (same as community acquired E. coli)
What is seen on blood agar infected with staph aureus?
golden yellow
