Streptococci Flashcards
3 main gram positive cocci that cause disease
Streptococcus, Enterococcus, and Staphylococcus
What is main host defense of GPC (gram positive cocci)?
Phagocytosis (mainly) and neutrophils
Empyema
Collection of pus in a body cavity, especially pleural cavity
General characteristics of streptococci Gram Catalase? Morphology Oxygen environment
Gram positive
Catalase negative
Chains
Mostly facultative
Reservoir for pneumococcus
Nasopharynx / throat
Transmission of pneumococcus
Airborne
Strep pneumoniae morphology
Lancet-shaped (elliptical) diplococci
Hemolysis for strep pneumoniae
Alpha
O2 conditions for pneumoniae
Grow better w/ 10% CO2 (capnophile)
How do you differentiate pneumococcus from Strep Viridans?
Both are Gram positive and alpha hemolytic. Pneumococcus is highly susceptible to Optochin disk (Cu compound). Strep viridans is NOT.
What is most common childhood illness?
Acute otitis media from Strep pneumoniae
Major host defense against pneumococcus
Phagocytosis, augmented by IgG
Effect of capsule in pneumococcus
Antiphagocytic by inhibiting complement opsonization (C3b)
Stimulates intense inflammatory response
Main immunogen (Ab detection)
Conjugated vaccine uses capsule
Hypogammaglobulinemia
Can’t make Abs to opsonize / phagocytose organisms; includes myeloma, lymphoma, leukemia, and nephritic syndrome
Who gets pneumococcal vaccine?
Children (> age 2), elderly, immunocompromised.
Which diseases caused by pneumococcus are resistant to penicillin?
Meningitis and bacteremia
Tx for otitis media
Amoxicillin or erythromycin
Tx for sinusitis
Amoxicillin-clavulinate or FQ
Tx for Meningitis
Ceftriaxone + Vancomycin
Risk factors for acquiring penicillin-resistant pneumococcal infection
Prior becta-lactam AB therapy (amoxicillin / oral cephalosporins)
Contact w/ kids in daycare
Exposure to healthcare setting
Recent respiratory infection
Beta hemolytic strains
Group A, B, C, or G
Based on C-polysaccharide (in cell wall)
What test is used to rule out GAS?
Bacitracin
Alpha hemolytic strains
How do you differentiate?
Strep viridans and Strep pneumoniae Optochin testing (pneumococcus is vulnerable)
What test is used to rule out Group D strep?
Bile esculin test
What determines Lancefield groupings?
C Polysaccharide
What determines Lancefield typings?
M Protein
Group A Strep Other Name Hemolysis Reservoir Transmission
Strep Pyogenes
Beta-hemolytic
5-10% of people are carriers in throat, skin, anus, and vagina
Transmitted via air or direct contact
Susceptible hosts to GAS
College students, military recruits, neonates, post-partum women, damaged skin (burns, measles, chickenpox, impetigo), surgery
Function of Lipoteichoic acid and Protein F
Mediate attachment to epithelial cells by binding to fibronectin
Cause of scarlet fever
GAS erythrogenic toxin (exotoxin) is produced after virulence factor is added by lysogenic phage.
Erysipelas Caused by? Characteristics Population Location of rash
Caused by GAS
Erythema / edema w/ well-demarcated edges
Most common in kids and elderly
More common on legs than face
Scarlet Fever
Caused by
Characteristics
Caused by GAS
Erythroderma, strawberry tongue, skin desquamation
What 2 strains cause Toxic Shock Syndrome and which is worse?
GAS is worse than Staph aureus
GAS Toxic Shock Syndrome Initial site of infection? Cytokine Complications (4 things) Tx
Most often due to soft tissue infection or bacteremia
TNF
May cause necrotizing fasciitis, strep gangrene, bacteremia, or shock
Tx w/ penicillin and surgical debridement
Rheumatic Fever Due to which strain? Diagnostic criteria Location of prior infection Tx Prophylaxis for RHD
Due to GAS
Jones Criteria: 2 major or 1 major + 1 minor + lab evidence of GAS
Due to prior pharyngitis (not skin)
Tx w/ aspirin, steroids, or penicillin
Prophylaxis w/ penicillin or sulfadiazine
Post-streptococcal glomerulonephritis Strain Location of prior infection Population Sxs Prevention Tx
GAS
Typically skin infection (sometimes pharyngitis)
Most common in kids
Sxs: oliguria (due to renal failure), dark urine, hematuria, proteinuria, seizures, HTN, edema.
Not preventable
Only supportive tx
Which AB is GAS highly susceptible to?
Penicillin
Group B Strep Other Name Reservoir Diseases Antigen Tx
Strep agalactiae
Asymptomatic colonization of genital tract and lower GI tract. 30% of women are carriers in vagina.
Diseases: #1 cause of bacterial sepsis in newborns. Can also cause puerperal sepsis (in pregnant mother). SSTIs / UTIs in diabetics.
Capsule interferes w/ phagocytosis and complement activation
Tx w/ pencillin. Vancomycin if allergic.
2 main types of Group D Strep
Enterococci and Non-Enterocci (Strep bovis)
Enterococci 2 types Characteristics Catalase? Reservoir Transmission Risk factors Antigens Diseases Tx
E. Faecalis and E Faecium
Major cause of nosocomial infections. Grow in bile and salt. Catalase negative
Catalase negative
Reservoir: soil, food, water, animals. Normal microbiota of GI and Gyn tracts.
Transmission: endogenous, contact, surfaces
Risk factors: invasive devices, broad spectrum AB’s, surgery, >60 y/o
Antigens – adhesins and bacteriocins inhibit competing flora
Diseases: catheter-associated UTI’s, endocarditis, surgical infections (especially after colonic / vaginal surgery).
Does NOT cause pneumonia
Tx w/ ampicillin or vancomycin (however resistance is growing). Linezolid / Daptomycin if VRE.
Strep bovis
2 other names
Association
Tx
Non-enterococci, Strep gallolyticus
Associated w/ colon cancer
Penicillin is tx of choice. Erythromycin / vancomycin if allergic.
Viridans Strep
Hemolysis
Normal microbiota of where?
Diseases
Alpha hemolytic
Normal microbiota of mouth, GI, and GU
Causes dental carries, bacteremia, and SBE
Tx for GAS endocarditis
Penicillin + gentamicin (aminoglycoside)
Importance of spleen
Protects against encapsulated bacteria that immune system has not seen before. Most important in kids
