Strep etc Flashcards
Strep pneumoniae pathogenesis
Oropharynx - small population, no capsular Ig produced
Aspiration - rare, must have compromise (cilia, alveolar macrophage)
Capsule - antiphagocytic, anti-capsule Ig is key for immunity
IgA protease
Pneumolysin - lytic enzyme
Strep pneumoniae bacteriology
Gram + diplococci (short end apposed/"lancet" vs Neisseria) Alpha hemolytic Optochin sensitive (vs Strep viridans) Bile soluble (vs Strep viridans) Large capsule - multiple serotypes, ID via Quellung reaction (visualize capsule)
Strep pneumoniae clinical
Most common cause of bacterial pneumonia -> rusty sputum
-> 10-20% bacteremia, 5-20% fatality of hospitalized
- requires humoral immunity -> anti-capsule Ig
- requires spleen (higher risk if sickle cell)
Rare meningitis (children, elderly), otitis media (children), sinus
Dx: sputum Gram and culture, blood, CSF
- do not usually determine specific type
Tx: frequent multi antibiotic resistance (inc penicillin)
- must get sensitivity
Strep pneumoniae epidemiology
Colonization - 10% adult, higher children, no animal
Pneumovax = 23 serotype capsular polysaccharide
-> T-cell indep (poor booster response)
- recommended >65 or >2 and at risk (sickle cell, spleen, immune)
Prevnar = 13 serotype capsule + diphtheria conjugate
-> T-cell dep (more effective infants, etc)
- recommended for peds, prevents meningitis
Overview of Streptococcus
Gram + cocci in chains
Facultative anaerobes
Catalase (-)
Different carb antigens (Lancefield) -> groups A, B, C, D, non-type
- precipitation tests with anti-serum (rabbit)
- can also distinguish with hemolysis (ex A-O -> beta except D)
Important
- beta hemolytic -> A (pyogenes, oral), B (vagina), D (enterococcus, colon)
- alpha hemolytic -> pneumococcus, viridans (both oral)
Not important - Groups C, D (beta, bacitracin resistant)
Types of hemolysis
Gamma = no hemolysis
Alpha -> green zone (RBCs intact with altered heme pigment)
Beta -> clear zone (RBCs lysed)
- may be cloudy if doesn’t extend through full thickness
Strep pyogenes bacteriology
aka Group A beta-hemolytic Strep
Gram + streptococci, aerotolerant
Subdivide by M protein - extends through hyaluronic capsule from cell wall
-> 90 specific serotypes
Also have pilus, F protein, etc
5-10% carry in nasopharynx - nasal more infectious than oral, skin
Spread respiratory droplet - large inoculum
Strep pyogenes pathogenesis
Extracellular proteins -> invasive disease
- streptolysins -> beta hemolysis
- O = O2 labile, antigenic -> ASO titer (anti-streptolysin O)
- S = O2 stable, not antigenic
- streptokinase - triggers proteolysis of fibrin clots
- DNAse
- Spe A, B, C -> rash of scarlet fever, toxic shock
(both syndrome prevented by specific antibody)
Antiphagocytic
- hyaluronic capsule
- M protein - sticks through capsule -> adherence
- virulence proportional to M protein
- anti-M Ig -> immunity
Strep pyogenes clinical syndromes
Toxin-mediated - pyogenic exotoxins (Spe A, B, C)
- superantigens -> overproduction of cytokines
- Scarlet fever = pharyg-tonsil -> rash
- toxic shock = hypotension + renal, liver, resp, DIC, soft tissue, rash
Invasive disease
- puerperal fever - childbirth -> uterus (mostly developing)
- acute pharyng-tonsil (aka strep throat)
- impetigo - superficial skin lesion -> minor infection
- erysipelas - severe cellulitis of dermis
- necrotizing fasciitis - highly invasive strains -> surgery, life threat
- other: sinus, mastoid, otitis media, meningitis, pneumonia (2t flu)
Strep pyogenes sequelae
Treat all Strep pyogenes (within 8 days) to prevent sequelae!
Do not involve Strep bacteria at site -> immunological
Can test ASO titer, ESR (inflammation)
Rheumatic fever: throat -> 2-3 wks
- > rash (erythema marginatum), nodules, heart lesions, joint pain
- cross-reactive antibodies - some strains/M proteins more likely
- short term except for heart (esp mitral, aortic valves)
- prior rheumatic -> penicillin prophylaxis
- still common in developing world
Glomerulonephritis: skin -> 1 week -> edema, hematuria
- immune complex deposition (with Strep antigen)
- only few M-protein serotypes (usu skin, sometimes throat)
Strep pyogenes clinical
Dx:
- do not routinely subtype
- Gram stain -> Gram + streptococci
- beta-hemolysis
- bacitracin sensitive -> Group A (other betas are resistant)
- rapid - beads with anti-A antibody -> agglutination
- “reasonably specific, not as sensitive as culture”
- ASO titer (vs streptolysin O) - >160 or 4x increase
TREAT ALL WITH PENICILLIN to prevent sequelae
(no resistance!)
- erythromycin second line
- ampicillin prophylaxis for prior rheumatic
Group B strep overview
Beta hemolytic (smaller zone than group A)
Bacitracin resistant
Hippurate hydrolysis
cAMP test - more beta hemolysis next to Staph
Most imp species - Strep agalactiae
Can be part of normal colonic/vaginal flora -> neonatal, etc
Sensitive to penicillin
Group B strep clinical
Up to 1/3 neonatal infections -> pneu, meningitis, septicemia, death
Early onset (within 1 week) - from vaginal flora
- prevent with vaginal + colonic cultures -> intrapartum penicillin, ampicillin
- highest risk if no maternal Ig - screen 36 weeks for new infection
- higher risk if premature, long rupture of membranes
Later onset - infant-infant, nosocomial
- less fulminant, lower mortality
Also endometriosis (postpartum), infections in older (>65), etc
Enterococci
aka Group D strep
- Enterococcus faecalis, faecium
Variable hemolysis
Can grow in high salt, bile (hydrolyzes esculin)
Common in GI -> UTI, abdominal, wound, sepsis (esp elderly)
Lots of antibiotic resistance -> vanco + aminoglycoside (some resistance)
- prophylaxis for heart patients (GI,GU procedures) - amp + gent
Strep viridans
S mutans, S sanguis, S mitis
Alpha or gamma hemolysis
Not lysed by bile, resists optochin (vs Strep pneumo)
Normal oral/pharyngeal -> minor oral trauma -> transient bacteremia -> adhere to pre-existing endocardial lesion (valve)
- > infective endocarditis -> subacute with intermittent bacteremia -> death
- detect vegetation on echo
Tx: penicillin (+ aminoglycoside if endocarditis)
Listeria bacteriology and patho
Small Gram + rod
Beta-hemolytic
Motile (tumbling)
Grows at cold temperatures
Invades phagocytes -> intracellular growth
-> direct cell-cell movement by propelling host actin
(evades antibodies!)
-> listeriolysin O (cytolysin) -> escape phagosome -> cytosol
Listeria epidemiology
Common in soil, water, animals -> meat, dairy
- grows at cold temperatures (even refrigerator)
Pregnant women - bacteremia -> transplacental
- early term -> abortion, stillbirth
- late term -> neonatal septicemia, meningitis
- more susceptible if missing cell-mediated immunity
Adults -> septicemia, meningitis, gastroenteritis
- 20% fatality of hospitalized
Prevention - esp pregnant and immune (cellular) compromised
- pasteurization
- avoid soft cheese, raw milk
Tx: amp +/- gent, bactrim
Bacillus anthracis bacteriology and pathogenesis
Aerobic, Gram + bacillus
Forms central spores -> transmission
Pathogenesis:
- “protective factor” - entry of exotoxins into host cell
(antibody is protective)
- exotoxins -
- edema factor - adenylate cyclase - enters and activated by calmodulin
- lethal factor - disrupt cell division signals
Tx:
Ciprofloxacin, tetracycline, penicillin
Bacillus anthracis transmission
Zoonotic - animal-animal common
- human = accidental host, very rare human-human
All transmission from spores
Cutaneous:
- existing lesion -> necrosis, eschar -> bacteremia if untreated
- most common, least serious
Inhalation: ex occupational wool or animal hides
- macrophages -> geminate in lymph nodes -> enlargement
- rapidly fatal if untreated
Intestinal: ingestion of meat, very rare
Vaccine - crude, proteins - more research underway
- safe, effective, used for at-risk
Strep bovis
Group D strep but NOT enterococcus
Variable alpha or gamma hemolysis
Grows in bile salt (hydrolyzes esculin), high salt
Normal colonic flora
Endocarditis
Bacteremia (linked to colon CA)
Sensitive to penicillin (vs Enterococcus resistance)
