M5 - Streptococci
Streptococcus pneumoniae Toxins/Extracellular Products
*Pneumolysin* - Similar to streptolysin O - Epithelial cytotoxin - Inhibits activity of cilia *Neuraminidase* - Cleaves cell surface sialic acid *C3 peptidase* - Degrades C3 and thus prevents opsonization
Streptococcus pneumonia Amplification
*Primary* amplification in lungs *Secondary* amplification in CNS
Streptococcus agalactiae Fetal Infection - Replication and Transmission
*Replication* - Can occur in amniotic fluid and fetal mucosal surfaces (lung, gut, nasopharynx) *Transmission/epidemiology* Found in 25% of pregnant women, 1-2% of these women will produce infant with GBS disease.
Mortality Rates of Sterptococcal vs Staphylococcal Toxic Schock Syndrome
*Staphylococcal TSS:* Mortality rate of 5%. *Streptococcal TSS:* Mortality rate of 30%.
Streptococcus pneumoniae Cell Surface Features
- *Capsular polysaccharide: Primary component of virulence* - Organism is avirulent without its capsule - More than 90 serologic types - Pneumococcal surface proteins (PspA, ChBP, etc.) serve as adhesins - Teichoic acids also participate in attachment - No Lancefield group antigens.
Group A Ag testing (for Streptococcus pyogenes)
- Antibody-mediated detection of Group A Antigen: Precipitin testing, rapid strep detection kits - Immunofluorescence - Agglutination.
Streptococcus pneumonia Evasion
- Capsule - prevents phagocytosis - C3b-cutting enzyme - prevents phagocytosis
Streptococcus pyogenes Cell Surface Structures
- Cell wall with Lancefield Carbohydrate and lipoteichoid acid - Hyaluronic acid-based capsule (nonantigenic) - M Protein - IgG Binding Protein
Streptococcus pyogenes Distinguishing Chatacteristics
- Group A Streptococci - Pyogenic - β-hemolytic (as a result of activity of streptolysin S and/or streptolysin O) - Bacitracin sensitive.
Streptococcus agalactiae Fetal Infection - Treatment/Prevention
- Penicillin and Gentamicin are synergistic - Screening for carriers at 35-37 weeks of pregnancy - Antibiotic therapy for mother at labor or membrane rupture
Streptococcus agalactiae Fetal Infection - Risk Factors
- Previous infant with group B streptococcal disease - UTI involving GBS - Immunologic deficit involving low antibody titer to GBS capsular polysaccharide.
Enterococci Diseases
- UTIs - Abdominal abscesses: 10-25% of all cases - Wounds: 15-50% of all cases - Endocarditis: 10-20% of all cases - Bacteremia: Complicates IV catheters and those with poor GI defense.
Alternative Complement Pathway
- complement pathway that recognizes certain non-specific antigens (eg. endotoxin) on microbial surfaces - An innate component of the immune system's natural defense against infections, one of three complement pathways that opsonize and kill pathogens, triggered when the C3b protein directly binds the microbe.
Streptococcus agalactiae Fetal Infection - Pathogeneis
1.) Attachment - Adherence to rectal or vaginal epithelium, likelihood of binding increases with drop in pH. 2.) Invasion - Ascending penetration of intact or ruptured placental membranes and ultimately fetus - Can enter lung epithelial cells and move to bloodstream.
Streptococcus pneumonia Prevention
1.) Capsule Vaccine 2.) Conjugate capsule vaccine (recently approved) - induces immunity in infants - multiple serotypes covered - effective in elderly
What types of vaccines are available for individuals who are particularly susceptible to Streptococcus pneumoniae infection?
1.) Capsule vaccine 2.) Conjugate capsule vaccine recently approved - Induces immunity in infants - Multiple serotypes covered - Effective in elderly.
Streptococcus agalactiae Fetal Infection - Diagnosis
1.) Culture, Gram Stain 2.) Group B Ag Detection 3.) PCR
Streptococcus agalactiae Cell Surface Features
1.) Lancefield carbohydrate group B 2.) Capsular polysaccharides of nine antigenic types: Ia, Ib, II, III, or VIII required for virulence - All possess sialic acid as a component. - Capsules *block alternative complement pathway*
Evasion of Streptococcus pyogenes
1.) M protein prevents phagocytosis 2.) C5ase makes possible avoidance of PMNs
Enterococci Treatment
1.) Penicillin+Gentamicin, or Ampicillin alone 2.) Vancomycin for Ampicillin-resistant strains - Resistance to Vancomycin displayed by 20-60% of cases 4.) Synercid for completely resistant isolates.
Streptococcus pyogenes Treatment
1.) Penicillin, with erythromycin as an alternative 2.) Clindamycin for serious infections Antibiotics for 10 days prevents rheumatic fever and recurrences, but not acute glomerulonephritis.
Complications of Streptococcal Infections
1.) Rheumatic Fever 2.) Acute Glomerulonephritis
Streptococcus pneumonia Diagnosis
1.) Sputum sample --> gram stain, culture 2.) Blood culture 3.) Antigen detection 4,) Optochin sensitivity (zone of inhibition on culture)
Toxins and Extracellular Enzymes of Streptococcus pyogenes
1.) Streptolysins O and S (Cytotoxins) 2.) Sterptokinase: Fibrnolytic enzyme, converts plasminogen --> protease 3.) DNase 4.) Hylauronidase 5.) Complement-Splitting Enzyme 6.) Surface proteins (e.g. variable M-like proteins, Fibronectin-binding protein, F-protein 7.) Pyrogenic/erythrogenic Exotoxins
Streptococcus pyogenes Transmission/Epidemiology
10% of adults/20% of children are carriers Group A Sterptococci (GAS) responsible for 15-30% of sore throats in children - Spread by droplets - Spread enhanced by crowding, poor hygiene, direct contact, bites.
Necrotizing fasciitis Pathogens
A number of bacteria in isolation or as part of a polymicrobial infection can cause necrotizing fasciitis. - Organisms most closely linked to NF = *group A beta-hemolytic streptococci* (these may cause only a minority of the cases) - Most cases caused by other bacteria or other streptococcal species. CDC estimates ~10,000 to 15,000 severe streptococcal skin infections occur annually in the US, resulting in 2,000 to 3,000 deaths.
NaCl Resistance
Able to grow in high salt environments Mannitol Salt Agar??????
Streptococcus pneumonia Treatment
Antibiotic resistance is emerging ~25% of isolates are penicillin resistant --> Treat with Ceftriaxone, Cefotaxime ~10% resistant to Ceftriazone/Cefotaxime --> Treat with Vancomycin Meningitis is difficult to treat in presence of drug resistance due to location of infection
Streptococcus pneumoniae Pneumonia Antibodies
Anticapsular Antibodies may contribute to phagocytic clearance of microbes --> potential for complete resolution of disease
Invasion by Streptococcus pyogenes
Bacterial growth in tissue fluids and serum. Replication: Toxins and extracellular enzymes allow spread of cocci and continued replication.
Necrotizing fasciitis - Progression of Symptoms
Begins with Fever and Chills. -> After 2-3 days, Erythema is noted, and Supralesional Vesiculation or Bullae formation ensues. - Serosanguineous fluid may drain from the affected area.
Streptococcus agalactiae Fetal Infection - Evasion
Capsule prevents phagocytosis
Strawberry Tongue
Caused by Streptococcal Scarlet Fever - Tongue becomes covered with yellow-white exudate through which red papillae are prominent
Aschoff Body
Characteristic of Rheumatic fever *Involves aggregation of lymphocytes and macrophages around fibrinoid deposits in heart tissue.* area of focal interstitial myocardial inflammation characterized by fragmented collagen and fibrinoid material, by large cells (Anitschkow myocytes) and occasional multinucleated giant cells (Aschoff cells) (Quizlet Definition)
Lancefield Antigens of Pyogenic Streptococci
Classified according to the display of Lancefield Ags: Most common Lancefield groups of streptococci isolated from humans are A, B, C, F, and G. Group D carbohydrate is found in the genus Enterococcus.
Diagnosis of Streptococcus pyogenes
Clinical picture plus demonstration of organism at infected site. 1.) Culturing may be necessary to distinguish pathogen from normal biota 2.) Bacitracin sensitivity 3.) Group A Antigen testing
Agglutination
Clumping of cells in the presence of an antibody. The antibody or other molecule binds multiple particles and joins them, creating a large complex. Commonly used as a method of identifying specific bacterial antigens, and in turn, the identity of such bacteria. Because the clumping reaction occurs quickly and is easy to produce, agglutination is an important technique in diagnosis.
M Protein of Streptococcus pyogenes
Consists of a coiled coil structure with a carboxy terminus (highly conserved) anchored in cell wall and cytoplasmic membrane Amino end responsible for antigenic diversity of more than 8o- M serotypes
Complement-Splitting Enzyme
Cuts C5a --> decrease in chemotactic response of Polymorphoneutrophils (PMNs) - (enzyme prevents neutrophils from destroying bacteria by keeping it from moving in)
Scarlet Fever Rash (Picture)
Diffuse red rash on second day of illness: Upper chest, trunk, extremities --> Red pinpoint elevations = Sandpaper feel to skin
Streptococcus pneumoniae Distinguishing Features
Diplococci Gram Positive α-hemolytic Autolytic (not necessary for pneumolysin release) Optochin-sensitive
Is rheumatic fever the result of bacteremia? Is it due to the activity of a bacterial exotoxin?
Endocarditis is the result of bacteremia Cross-Reactive antigens cause RF
Streptococcus pneumoniae Colonization
Fondness for mucosal surfaces - Nasopharynx - Middle ear - Lungs Adherence mechanism - Teichoic acids recognize host cell-surface glycoprotein or integrin.
Acute Glomerulonephritis
Found in children and adults, occurs 10 days post-pharyngitis or 3 weeks post-impetigo. *Symptoms* - Edema, hypertension, hematuria, proteinuria - > Proliferative lesions of glomeruli are diagnostic Result of immunological mechanisms: Ag-Ab complexes -->complement activation --> inflammation.
What is the most significant virulence factor of the GBS? Of the GAS?
GBS = Capsular polysaccharides of 9 antigenic types GAS = Hyaluronic acid capsule, M Protein?
Necrotizing fasciitis Cause
May develop after skin biopsy; at needle puncture sites in those using illicit drugs; and after episodes of frostbite, chronic venous leg ulcers, open bone fractures, insect bites, surgical wounds, and skin abscesses. May also occur in the setting of diabetes mellitus, surgery, trauma, or infectious processes.
Growth Media for Streptococci
May have complex nutrient requirements best agar = blood agar or serum-supplemented media
Streptococcus pneumoniae Pneumonia Cause
Most common community-acquired pneumonia - Aspiration of respiratory secretions containing pneumococci (10-30% carriage rate in adults) --> potential for clearing by cough and epiglottic reflexes, mucociliary escalator, macrophages - Impairment of defenses (smoking, intoxication, anesthesia, trauma, etc.) --> alveolar multiplication of bacterial cells --> edema --> growth and spread of pneumococci, interference with gas exchange --> influx of polymorphonuclear leukocytes (PMNs), erythrocytes --> pinkish or rusty sputum *Symptoms* - Chills, high fever, chest pain common
Streptococcus agalactiae Diseases
Neonatal pneumonia, meningitis Osteomyelitis Bacteremia in immunocompressed adults
Rheumatic Fever
Nonsuppurative inflammatory disease Can occur 3 weeks post-pharyngitis and be of 2-3 months duration. *Symptoms* Fever, inflammation of joints, heart, subcutaneous tissue, and CNS *Clinical Manifestations* Carditis (involves connective tissue, endocardium --> cardiac enlargement, valvular murmurs, effusions), subcutaneous nodules, chorea, migratory polyarthritis.
Viridians Streptococci Treatment
Penicillin + Gentamicin (synergistic combination)
Colonization of Streptococcus pyogenes
Pili, lipoteichoic acid, and protein F mediate epithelial adherence via fibronectin --> multiplication --> local epithelial damage.
Streptococcus pneumoniae Diseases
Pneumonia Meningitis Sinusitis/Otitis DOES NOT cause pharyngitis or tonsillitis
Streptococcus pneumonia Invasion
Poorly defined, but pneumonia can be used as model 1.) Aspiration of respiratory secretions. 2.) Multiplication in alveoli 3.) Host inflammatory response involving PMNs 4.) Invasion of bloodstream possible 5.) Potential for meningeal penetration
Streptococcal Pharyngitis
Primarily childhood (5-15 years of age) throat infections. Spread by respiratory secretions, or possibly by contaminated food - Carriage rates up to 10% in children. *Symptoms* - Acute sore throat - Malaise - Fever (38.9-40oC) - Headache - Tonsillar pillars, uvula, soft palate may become red, swollen, and covered with yellow-white exudate - Swollen, tender lymph nodes.
Streptococcus pyogenes Wound/Burn Infection
Puts patient at risk for bacteremia and sepsis
Pyogenic vs Pyrogenic
Pyro = fire = fever Pyo = pus
Pyrogenic/Erythrogenic Exotoxins of Streptococcus pyogenes
Related to staphylococcal toxic shock toxin, enterotoxins. - Result of lysogeny - May have superantigen activity - Cause streptococcal toxic shock syndrome (STSS), rash, fever - Rash of scarlet fever may be at least partially the result of direct effect of erythrogenic toxin on skin and delayed-type hypersensitivity to toxin.
Scarlet Fever/Sterptococcal Toxic Shock Syndrome (Symptoms)
Result of production of *erythrogenic toxin* - Superimposition of signs of scarlet fever on streptococcal pharyngitis. - Deep red buccal mucosa, temples, and cheeks, with pale area around mouth and nose (circumoral pallor). - Punctate hemorrhages on hard and soft palate - Strawberry Tongue - Diffuse red rash on second day of illness: Upper chest, trunk, extremities --> Red pinpoint elevations = Sandpaper feel to skin
Viridans streptococci
S. mitis S. mutans S. salivarius S. sanguis S. milleri "Mighty Mutant Millers Salivate over Sangria on the Veranda" (Miti Mutans Milleri Salivarius Sangui = Viridans)
Streptococcus pyogenes Diseases
Streptococcal Pharyngitis Impetigo Erysipelas Infection of wounds/burns (risk of bacteremia, sepsis) Puerperal Infections Necrotizing Fasciitis Scarlet Fever/Streptococcal Toxic Shock Syndrome
Sinusitis/Otitis
Streptococcus pneumonia responsible for 40% of cases
Meningitis
Streptococcus pneumoniae is most common cause now that H. influenzae vaccine is in use.
Impetigo
Streptococcus pyogenes Most common in 2-5 year olds. Minor trauma -> invasion -> development of vesicle surrounded by area of erythema -> vesicle enlarges, becomes pustular, breaks to form a yellow crust. - Secondary colonization by Staphylococcus aureus common (S. aureus can produce its own form: Bullous impetigo). ("AB" (alphabet) Aureus= Bullous impetigo " vs "PP" Pyogenes = Plain Impetigo)
Viridians Streptococci Diseases
Subacute bacterial endocarditis
Necrotizing fasciitis - Virulence Factors
Surface Protein expression and Toxin production. - *M Surface Proteins*, which increase the adherence of the streptococci to the tissues, protect the bacteria against phagocytosis by neutrophils. - Streptococcal *pyrogenic exotoxins* A, B, and C are directly toxic and tend to be produced by strains causing necrotizing fasciitis. --> These pyrogenic exotoxins may also display *superantigen* activity and induce the release of cytokines, leading to clinical signs such as hypotension.
Viridians Streptococci
Gram Negative chains (Pic)
Steptococci Morhphology and Growth Characteristics
Gram Positive Cocci Non-Motile No Spore Formation Arrangement: Individual cells to chains of 30+ Capsules composed of polysaccharides (e.g. hyaluronic acid) Facultative anaerobes Catalse Negative May have complex nutrient requirements Pyogenic streptococci classified according to Lancefield Ags
Erysipelas
Group A Streptococcus pyogenes Most common in elderly patients with underlying disease. Skin infection, primarily affects the dermis but can affect subcutaneous tissue . *Symptoms* - Spreading area of erythema, edema. - Fever, lymphadenopathy - Previous history of streptococcal sore throat is common Immediate therapy (*penicillin*) necessary to avoid systemic toxicity.
Streptococcus agalactiae Neonatal Pneumonia, Meningitis
Group B Streptococci (GBS) is part of gastrointestinal normal biota Organism maintained vaginally by up to 1/3 of healthy women - Can be passed to neonates during birth and cause Neonatal Pneumonia and/or Meningitis - Heavy colonization of the genital tract with GBS increases chance of preterm delivery of a low birthweight infant - Type-specific Ab is protective, so transplacental Ab may provide protection.
Streptococcus pyogenes Puerperal Infection
Infection of the endometrium Now relatively rare
Streptococcus pneumonia Transmission/Epidemiology
Infections usually found in children and adults over 50 y/o URI may predispose patients to infection
Necrotizing fasciitis
Insidiously advancing soft tissue infection characterized by widespread fascial necrosis. Organisms spread from the subQ tissue along the superficial and deep fascial planes, presumably facilitated by bacterial enzymes and toxins. This deep infection causes vascular occlusion, ischemia, and tissue necrosis. Superficial nerves are damaged, producing the characteristic localized anesthesia. Septicemia ensues with systemic toxicity.
Streptococcus agalactiae Bacteremia
Typically immunocompromised (diabetics, chemotherapy) victims - Third most common cause of bacteremia and high mortality.
Enterococci Distinguishing Features
Usually α-hemolytic Bacitracin resistant NaCl resistant Bile/esculin (+) Gram Positive Survives Gut Environment Intrinsically resistant to many antibiotics, may serve as reservoir for resistance genes Virulence traits poorly understood
Lancefield Antigen Grouping
a method of grouping beta haemolytic bacteria based on the carbohydrate composition of bacterial antigens found on their cell wall
Rheumatic Fever Carditis
may be due to: 1.) Antigenic cross-reactivity. - Amino acid sequence homology with cardiac tropomyosin, cardiac muscle sarcolemma, and glomerular basement membrane antigens --> rheumatic heart disease, glomerulonephritis. 2.) Serum sickness: Ag-Ab complexes may be involved. 3.) Residual toxicity of streptococcal products.
Streptococcus pyogenes - Throat Culture on Blood Agar
zone of Inhibition around Bacitracin Beta-Hemolysis
Viridans streptococci - Distinguishing Characteristics
α-hemolytic Lack capsules, antigens, and toxins of other streptococci - Lancefield Ags not present = bacteria must be identified by physiological properties Found in oral cavity and nasopharynx as part of normal biota Low virulence: Usually only a problem in the immunocompromised Gram Negative Usually appear in chains (but not always)
Streptococcus agalactiae Distinguishing Characteristics
β-hemolytic Bacitracin resistant NaCl resistant Negative Bile/Esculin reaction Tolerates gut environment Group B Streptococci
