Pyogenic Bacteria - Staph and Strep Flashcards
Clinical syndromes associated with Staph and Strep
Skin infections/eruptions Wound infections URI (sinusitis/pharyngitis) Pneumonia (debilitated patients) Food poisoning/TSS Septicemia/disseminated infections
What kind of inflammatory response does staph and strep illicit?
suppurative response - accounts for a majority of suppurative infections and abscess formation
The role of what type of immune response is very important with staph and strep?
role of phagocytosis/opsonization very important
Diseases that interfere with what immune function are characterized by increased infections with pyogenic bacteria?
neutrophil function
General forms of disease from staph
- abscess formation (particularly skin); cellulitis
- bacteremia (sepsis): endocarditis, kidneys, bones, joints
- toxin-mediated disease: food poisoning, TSS
Staph virulence factor important in abscess formation
coagulase positive versus coagulase negative
Staph virulence factors
coagulase toxins (enterotoxins, cytolytic, TSST-1, superantigen) penicillinase fibronectin and vitronectin protein A
Pseudomonas causes what in CF patients
bronchiectasis
Primary mode of protection against staph organisms in humans?
non-immune mediated phagocytosis
major cause of infection in burns and surgical wounds
staph
2nd most common cause of nosocomial infections
staph
TSST-1 acts as a superantigen to stimulate
large amounts of IL-1, IL-2, and tumor necrosis factor
TSS results in
systemic inflammation similar to gram-negative sepsis
TSS patients present with
fever, diffuse macular rash, low blood pressure (shock); exfoliation after 10-14 days
Bronchopneumonia is most commonly found in which types of patients?
mostly hospitalized, debilitated patients
Protein A
binds to the Fc portion of immunoglobulins
fibronectin and vitronetin
bind to host cells
penicillinase
plasmid-mediated antibiotic resistance
how are strep infections grouped
by Lancefield antigens
how are strep infections typed
according to their ability to hemolyse blood agar
Strep infections of breaks in skin, wound infections
cellulitis, impetigo, erysipelas
Strep infections of the URT
strep throat, sinusitis, otitis media
Post-streptococcal hypersensitivity disease
rheumatic fever
immune complex glomerulonephritis
erythema nodosum (vasculitis)
Lancefield antigens (subtypes)
Group A
Group B
Group D
alpha-hemolytic/viridans
Group A strep
beta hemolytic
pharyngitis/post streptococcal disease
Group B strep
perinatal sepsis/newborns
UTIs
Group D strep
anaerobic S. faecalis (enterococcus)
endocartitis, UTI
alpha-hemolytic/viridans
subacute bacterial endocarditis
access to blood stream from mouth colonization by dental work
Streptococcus mutans
major cause of dental caries
Streptococcus virulence factors
cell wall polysaccharides/capsules (M proteins)
streptokinase, streptolysin O,S
erythrogenic toxin
M proteins
prevent phagocytosis
streptokinase, streptolysin O,S
help to lyse ECM along tissue plains
what causes rheumatic fever?
host antibodies to group A strep antigens that cross-react with host tissues
what causes acute poststreptococcal glomerulonephritis?
deposition of immune complexes in the kidney following group A infections
group A infections
Strep throat, impetigo, skin infections with GAHS
acute pharyngitis/upper respiratory infections with Strep
redness, edema, pain fever chills
characterized by extreme inflammation and a suppurative exudate on tonsils
punctate abscesses in tonsillar crypts
peritonsillar, retropharyngeal abscess formation
scarlet fever
febrile exanthematous disorder
erythrogenic toxin produced by bacteria; violaceous red rash on trunk, strawberry tongue
desquamation of skin
post-streptococcal sequelae
post-streptococcal glomerulonephritis
rheumatic fever
acute rheumatic fever
antibodies to M proteins cross-react with tissues
fever, joint disease, myocardial and valvular disease
chronic rheumatic heart disease
long-standing damage to mitral and aortic valves
Strep skin infections
cellulitis, pyoderma impetigo erysipelas necrotizing fasciitis subacute bacterial endocarditis puerperal sepsis
Strep cellulitis/pyoderma
extensive spreading redness, swelling, pain
less localized than staph infections
impetigo
contagious, skin infection in kids
may also be due to staph
can lead to post-streptococcal glomerulonephritis
erysipelas (groups A/C)
middle-aged persons, warm climate, erythematous cutaneous involvement without suppuration
GABHS necrotizing fasciitis
uncommon deep-seated soft tissue infection
gangrene
pre-existing immunodeficiency
subcutaneous strep infection with necrosis that is overtaken by anaerobes (gas formation)
mortality 50-70%
subacute bacterial endcarditis
associated with S. viridans; transient bacteremia following dental work
left sided valvular endocarditis
prophylactic Abx for dental worm
puerperal sepsis (perinatal)
Group B; overwhelming sepsis in newborns
Pathologic features of strep infections
skin - suppurative inflammation with cellulitis (small abscess formation)
strep throat
Pathologic features of strep skin infections
diffuse interstitial neutrophilic infiltrates with minimal destruction of host tissues
characteristic redness and pain
erythrogenic/pyrogenic toxins cause fever, rash
less likely to cause discreet abscesses (like staph)
Pathologic features of strep throat
erythematous, painful (erythrogenic toxins)
collections of pus (crypts, peritonsillar abscess)
Diagnosis of strep throat
rapid strep test - Group A streptococcal carbohydrate antigen
confirmatory culture - catalase negative; antibiotic specificity
Diagnosis of rheumatic fever
anti-streptolysin O Ab titers
Impetigo can be caused by
Staph or Strep
Erysipelas caused by
Strep
Paronychia caused by
Staph
Scalded skin syndrome/Ritter disease caused by
Staph
TSS caused by
S. aureus and Strep pyogenes
Cellulitis caused by
Staph and Strep
Necrotizing fasciitis caused by
Strep pyogenes and anaerobes
Food poisoning caused by
Staph aureus
