Streptococci Flashcards
What are the characteristics of Streptococci?
Catalase Negative Cocci in pairs/chains Complex Media requirements Prefers Anaerobic Gram Positive Cocci
Describe streptococci relative to staph when plated on agar?
Staph: white/cream opaque colonies in grape like clusters
Strep: clear colonies in chans or pairs
What happens if you put in a drop of H2O2 on Staphylococci or Streptococci?
Staph: Catalase + -> bubbles of O2 formed
Strept: Catalase - -> no bubbles
How are the subspecies of streptococci classified?
Hemolytic properties: B (complete hemolysis), A (incomplete hemolysis), Gamma(No hemolosys)
What are hte key species of streptococci?
B-hemolytic: Strep Pyogenes (Group A), Strep Agalactiae (Group B) Strep Viridans (alpha hemolytic) Strep Pneumo (alpha hemolytic)
What are the diseases caused by S.Pyogenes?
Acute Pharyngitis: self limiting; respiratory droplet transmission
Impetigo: mostly children; associated with trauma/insect bites; Pustules with yellow crust
Erysipelas:spreading erythema wiht well demarcated edge on face
Scarlet Fever
Necrotizing FAscitis
Toxic Shock Like syndrome
Puerperal SEpsis
Rheumatic Fever
Acute Glomerulonephritis
What is scarlet fever?
Caused by erythrogenic exotoxin with complication of streptococcal pharyngitis
Rash of tiny red bumps on chest and abdomen with blanching on pressure => 12-48 hrs after fever
Spares the face Sore throat Fever Strawberry Tongue Desquamation as rash fades
What causes necrotizing fascitis?
Strep infection that occurs deep in subcutaneous tissues and spreads along fascial planes leading ot destrcution of muscle and fat
What is a key characteristic of a patient with necrotizing fascitis and how is it treated?
Pain is significantly disproportionate to how it looks
Surgery -> debride dead tissue
What causes toxic shock like syndrome with S.pyogenes infections?
SPE toxins (similar to TSST-1 of staph aureus)
What is puerperal sepsis?
Seen in women when they get sick following delivery/abortion
how does puerperal sepsis occur?
Organisms in genital tract or OB personnel invade upper genital tract -> bacteremia, endometritis, necrotizing fascitis, streptococcal toxic shock syndrome
What is Rheumatic Fever?
Nonsuppurative Inflammatory Disease 1-5 weeks after strep pharyngitis (can occur in pts sometimes if you dont treat for strep throat)
Characteristic cardiac lesions -> valvular damage-> possible future endocarditis
How does strep cause acute glomerulonephritis?
Antigen from strep -> forms Ab-antigen complex with complement -> complex goes to glomeruli -> damage tissue-> glomerulonephritis
What are the virulence factors of S.Pyogenes?
Capsules Lipoteichoic Acid Hemolysin(S: oxygen stable, non antigenic; O: oxygen labile, ASO Abs) Streptokinase Nucleauses
What are SPE?
Streptococcal Pyrogenic Exotoxins (A, B , C)
Can act as superantigens to stimulate cytokine response -> shock/organ failure
Causes the rash in scarlet fever
What is the M protein in S.Pyogenes?
Strains w/out M protein are AVIRULENT
Promote antiphagocytic characteristics by degrading Complement C3b and also adherence to epidermal cells
How is S.pyogenes treated?
Penicllin/Ampicillin/Amoxacillin
Cephalosporin
Pt is allergic: use erythromycin (macrolide)
What is GBS?
Group B Strep: Strep Agalactiae
How does GBS infections occur?
Kids get it if mothers are carriers as it is normal flora in throat, vagina, GI tract
What does GBS cause?
Early Onset Neonatal Disease: 1st week of life -> bacteremia, pneumonia, meningitis
Late Onset Neonatla Disase: 1 wk -3 mo -> bacteremia w/ meningitis
Pregnant Women: UTI, carrier
Describe the pathogenesis of GBS
Maternal colonizaiton in vagina or rectum -> baby exposed during birht -> lacks protective maternal Ab -> can disseminate
How do hospitals prevent perinatal GBS disease?
Women are cultured vaginally/rectally with swabs at 35-37 weeks gestation
If woman comes in with no prenatal history -> treat as if they are positive for GBS by starting Abx at delivery and then treating baby as well
How do we treat S.Agalactiae/GBS?
Penicllin/Ampicillin + Gentamicin (enhance killing)
Prophylaxis: Culture + pregnant women -> penicllin/ampicillin to prevent neonatal disease
Peniciillin allergy: Clindamycin
What are the characteristics of Strep Viridans?
Alpha/Gamma hemolytic Causes dental caries Bile REsistant Optochin resistant Adhere to fibrin platelet aggregates in damaged heart valves -> endocarditis
Normal flora in upper resp tract
Opportunistic pathogen
What is S.Bovis?
Non-enterococcal group D streptococci
What is the key fact about S.Bovis
Isolation of S.Bovis from blood is associated with colon carcinoma
Pt shoudl get worked up for this if positive for S.bovis
What is the Strep Milleri Group?
Produce pinpoint colonies
Require CO2 for isolation
Butterscotch odor when cultured on agar plates
Where are S.Milleri group found and what do they cause?
Commensals in mouth, oropharynx, GI , vagina
Cause deep seated pyogenic infections in cardiac, abdominal, skin, CNS tissues
Seen in brain abscesses
What do nutritionally deficient strep require to grow on plates?
VitB6 deficient -> needs to be grown with organism producing VitB6 for them
A 7-year-old child presents with a fever, pain in his ankles,
knees and wrist, and a new heart murmur. His mother said
that he complained of a “sore throat” last month, but the
symptoms resolved without taking him to the pediatrician. A
rapid screening test for strep throat is negative. His most
likely diagnosis is:
A. Toxic shock-like syndrome
B. Rheumatic fever
C. Scarlet fever
D. Puerperal fever
E. Acute glomerulonephritis
B
What does strep pneumo cause?
Most common cause of meningitis Pneumonia Sinusitis Otitis Media Endocarditis, osteomyelitis, septic arthritis, etc
What are the characteristics of Strep Pneumo?
Gram Positive Cocci: lancet shaped diplococci Capsulated Alpha Hemolytic Catalase Negative Bile Soluble Optochin Sensitive Many serotypes -> makes vaccination hard
What are the virulence factors for S.Pneumo?
Pneumolysin: damage ciliated cells and activate alt complement path
SIgA Protease = prevent IgA binding of cells to mucus
Teichoic Acid/Peptidoglycan = activate complement alternative path -> inflammation -> C- reactive protein precipitation
Neuraminidase
Phosphorylcholine
What can predispose someone to S.Pneumo?
Alcoholism
DM
Chronic lung, renal diseases
Malignancies
What is S.pneumo the most common cause of?
Most common cause of bacterial meningitis in US
Highest rate of meningitis in children
What are the treatment options for S.Penumo?
Penicillin if susceptible
Cefotaxime/Ceftriaxone if susceptible
*Breakpoints differ for meningeal and nonmeningeal cases
Alternatves: Macrolides (Erythromycin, Clarithromycin, Azithromycin) => MOST COMMON
Fluoroquinolones: Levofloxacin, Moxifloxacin
