Streptococci Flashcards
Streptococci Bacteriology
Morphology:
1) Gram(+) Positive
2) Chains of oval cells
(single pair to over 30 cells)
Catalase Negative!!!
Culture:
1) Grow best in Enriched media
2) Facultative Anaerobes (grow in aerobic or anaerobic)
Blood Agar: 1) Beta-Hemolytic (Clear) (Complete hemolysis) _Group A Strept _Group B Strept
2) Alpha-Hemolytic (Green)
(Hazy, partial hemolysis)
_Strept pneumococci
_Viridans Streptococci
Streptococci Classification
Pyogenic Streptococci: _Beta-Hemolytic (Clear) _Most common causes of Serious disease. 1) Group A Strept (Strept pyogenes) 2) Group B Strept (Strept agalactiae)
Pneumococci:
_Alpha-Hemolytic (Green)
_Polysaccharide Capsule
1) Strept pneumoniae (Pneumococcus)
Viridans Streptococci:
_Alpha-Hemolytic (Green)
_Normal Oral Flora
_Rarely Invasive.
Group A Streptococci (GAS)
Cell Surface Virulence Factors
More than 80 immunotypes of M protein, which are the basis of a subtyping system for GAS.
1) Protein F
_Binds to Fibronectin on Host cell
_Mediates Adhesion
2) Lipoteichoic Acid:
_Associated with cell wall and Pili
_Aids in Adhesion
3) M protein:
_Associated with the Pili
_Inhibit Activation of Complement
_Antibodies specific to its epitopes Cross-React with Heart, causing Rheumatic Heart Disease
4) Hyaluronic Acid Capsule:
_Anti-Phagocytic
Group A Strept (GAS)
Extracellular Products
1) Streptolysin O:
Pore-Forming Cytotoxin
_Lyses Leukocytes, Tissue cells, and Platelets
2) Streptococcal SuperAntigens (StrepSAgs):
_Cause Fever and Rash (Scarlet Fever)
_Produced by 10% of GAS
3) Streptokinase:
_Lyses Fibrin Clots
_Thus, Strept is systemic and reaches bloodstream
(whereas Staph is usually localized b/c it triggers clot formation)
4) C5a Peptidase:
_Degrades the C5a Complement protein
_Inhibiting Complement.
5) Hyaluronidase (Spreading Factor)
_Degrades Hyaluronic Acid in Subcutaneous Tissue
_Mediating Rapid spread of Cellulitis (Erysipelas)
Pharyngitis
Group A Strept (GAS)
Epidemiology:
1) GAS are Most Common cause of Bacterial Pharyngitis in School-age children Ages 5-15
Transmission:
1) Respiratory droplets (coughing, sneezing, conversation)
*Very Similar to VIRAL Pharyngitis!!!
Symptoms:
1) Acute Sore Throat
2) Malaise
3) Fever
4) Headache
5) Pharynx:
_Red, Swollen and
_Covered with Yellow-White Exudate
@ Tonsillar pillars, Uvula, Soft Palate
6) Cervical Lymph Nodes may be Swollen and Tender
7) (Rarely) Extensive Spread:
_Meningitis
_Pneumonia
_Bacteremia with Organ involvement
Scarlet Fever
Group A Strept (GAS)
Caused by Strept SuperAntigens
Occurs During Strept Throat
Manifestations:
1) Red @ Buccal mucosa, Temples, Cheeks
2) Pale @ Mouth and Nose
(Circumoral Pallor)
3) Punctate Hemorrhages @ Hard and Soft Palates
4) Yellow-White Exudate through which the Red papillae are prominent
(White Strawberry Tongue) (Day 1)
5) Rash (Day 2),
_Spreads from Upper Chest to Trunk and Extremities
_Punctate, Erythematous, Red “Sandpaper”.
6) Red Strawberry Tongue
(Day 3)
Acute Rheumatic Fever
Group A Strept (GAS)
Epidemiology:
_Follows only Respiratory GAS (Strept Throat)
_Does not follow skin or other non-respiratory GAS infections
Manifestation: = Non-suppurative Autoimmune Disease 1) Fever, 2) Carditis, 3) Subcutaneous Nodules, 4) Chorea, 5) Migratory Polyarthritis
6) Rheumatic Heart Disease:
_Due to Repeated attacks lead to
_Progressive Damage and Scarring to Endocardium and Heart Valves,
_Valvular Stenosis or Regurgitation result.
Erysipelas
Group A Strept (GAS)
Streptococcal infection of primarily the Dermis
*Previous History of Strept Throat is Common
Manifestation: _Rapidly Spreading area of Erythema and Edema (Rapid spread due to Hyaluronidase) _Well-Demarcated edges _Painful _@ Face
Systemic Manifestations:
_Fever
_Lymphadenopathy
Impetigo
Group A Strept (GAS)
Epidemiology:
_Infection of Minor Skin Trauma (e.g. insect bites, acne).
_@ Face and Lower Extremities (exposed body surfaces) in Children Ages 2-5.
_Scratching causes Local Spread
_Spread to other ppl via Direct Contact or Shared Fomites (e.g. Towels)
Manifestation:
1) Primary Lesion: Small (up to 1 cm) vesicle surrounded by an area of Erythema
2) The vesicle enlarges over period of days, becomes Pustular, with Yellow Crust
3) Multiple lesions may coalesce to form Deeper, Ulcerated areas.
Streptococcal
Toxic Shock Syndrome (STSS)
Group A Strept (GAS)
Flesh-Eating Bacteria
(usually GAS)
** Caused by Strept SuperAntigen
** May begin @ Site of Any GAS infection, including at site of seemingly minor trauma
__Most commonly:
@ Skin and Soft Tissues
Manifestation:
1) Vague Myalgia
2) Chills
3) Severe Pain @ infected site
4) Leads to Necrotizing Fasciitis, and
5) Myonecrosis
Continues with
6) Nausea,
7) Vomiting,
8) Diarrhea
Followed by
9) Hypotension,
10) Shock
11) Organ Failure
Amputation may be necessary.
Post-Streptococcal Glomerulonephritis
Group A Strept (GAS)
Epidemiology:
1) Primarily in childhood.
2) May follow either Respiratory or Cutaneous GAS infection
_Involves only certain nephritogenic GAS strains.
Manifestation:
1) Edema,
2) Hypertension,
3) Hematuria,
4) Proteinuria
Pathogenesis:
_Renal injury Caused by Deposition @ Glomerulus of Antigen-Antibody Complexes and Complement Activation with consequential inflammation
(Type III Hypersensitivity)
Wound and Puerperal Infections
Group A Strept (GAS)
Infection @ Endometrium
At or Near Delivery
Transmission:
_Patient-to-patient via hands of medical staff who don’t wash hands.
Life-Threatening
Rare now.
Diagnosis of GAS Infections
1) Culture @ Posterior Pharynx and Tonsils
_Required for diagnosis. Gold Standard.
(Takes 24-48 hrs though)
** Blood Agar, incubated Anaerobically:
Beta-Hemolysis (Clear):
(1) Group A Strept (Strept pyogenes)
(2) Group B Strept (Strept agalactiae)
2) Rapid Antigen Detection Test (RADT) Kit
@ Posterior Pharynx and Tonsils
_Faster than culture
_Less Sensitive
3) Inhibited by Bacitracin
_Inhibits Growth of Group A Strept
Don’t Gram Stain:
_Not helpful B/c there are other Streptococci in Normal Pharyngeal Flora.
Do not sample the oral cavity b/c of normal flora contamination!
Treatment and Prevention of GAS
1) Penicillin G
(drug of choice)
2) Erythromycin
(or Azithromycin)
_For Impetigo to cover prospect of Staph aureus involvement
_For patients allergic to Penicillin
Strept Pharyngitis:
_Treatment within 10 days of onset Prevents Rheumatic Fever by removing the antigenic stimulus.
_Acute Glomerulonephritis cannot be prevented, however.
Prevention:
_Antimicrobial Prophylaxis during Dental extraction for patients with a History of Rheumatic Fever
Group B Strept (GBS)
Streptococcus agalactiae
Epidemiology:
_Normal Flora @ lower GI and Vagina of 10-40% Women
_GBS are Leading Cause of Sepsis and Meningitis in Neonates’ First Few Days of Life
Neonatal Sepsis is acquired from Mother’s Vaginal Flora.
_GBS produces disease in 2% of these encounters.
_Ruptured Membranes and Prematurity increase Risk of Disease.
_GBS infections in adults are uncommon.
Nonspecific Symptoms:
1) Poor Feeding
2) Irritability
3) Lethargy
4) Jaundice
5) Respiratory Distress
6) Hypotension
Other Symptoms:
7) Fever is sometimes absent; may even be Hypothermic.
8) Pneumonia: Common
9) Meningitis: 5-10% cases
GBS in Bloodstream in most cases
10% Mortality rate.
_________________
Diagnosis:
*Culture of Blood, CSF, etc.
Treatment:
_Penicillin (drug of choice)
_GBS are susceptible to same drugs as GAS.
Prevention:
_IV Antimicrobial Prophylaxis @ Intrapartum (During Labor)
_Prophylaxis for all Newborns at Risk
_Risk = Presence of Vaginal or Rectal GBS in Culture taken during 3rd Trimester (35-37 weeks)
_Thus, all Expectant Mothers must be Screened by Selective Culture and Intrapartum Prophylaxis administered to all found Culture-Positive.
