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Streptococcaceae. Chapter 15: Streptococcus, Enterococcus, and Other Catalase-Negative Gram-Positive Cocci . Streptococcaceae: Genera . Streptococcus – major cause of human infection Enterococcus – frequent cause of human infection

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Chapter 15: Streptococcus, Enterococcus, and Other Catalase-Negative Gram-Positive Cocci

streptococcaceae genera
Streptococcaceae: Genera
  • Streptococcus – major cause of human infection
  • Enterococcus – frequent cause of human infection
  • Aerococcus – occasionally endocarditis, meningitis, urinary tract infection
  • Lactococcus – rare human pathogen
  • Pediococcus – NF of lower GI tract, occasional isolate from abscess
  • Leuconostoc – infrequently isolated from blood, wound, abscess
  • Gemella – rare isolate of upper RT infection
streptococcaceae classification
Streptococcaceae: Classification
  • Medical importance: Streptococcus,Enterococcus
  • Differentiation on CBA – partial, complete, nonhemolytic (, , or none)
  • Serologic classification developed 1930’s by Lancefield
    • CHO (C substance) extracted from cell wall
    • Group A through U
    • Some Strep don’t have this antigen, not ID by this method
    • Lancefield typing used today primarily for betahemolytic Group A, B
  • Physiologic or biochemical characteristics used to differentiate species within Streptococci and Enterococci
  • In future, DNA probes and hybridization, PCR DNA amplification tests will be used (greater sensitivity and specificity)
gram stain
Gram Stain
  • Gram (+) cocci, in pairs or chains (most often seen in broth culture); cell division occurs in 1 plane
  • Strep pneumoniae is lancet shaped diplococcus
  • Strep quickly lose ability to retain crystal violet in Gram stain; appear G (-) in old cultures
strep characteristics
Strep Characteristics
  • Form capsule
  • More fastidious than Staphylococci, require enriched media such as CBA
  • Hemolytic on CBA and source of blood (sheep vs. rabbits) may affect hemolysis, clinical labs use 5% sheep RBCs in CBA
  • Group A Strep two hemolysins:
    • Streptolysin O - oxygen labile; stabbing CBA after inoculation provides lower oxygen tension to identify strains that only produce streptolysin O
    • Streptolysin S – oxygen stable
  • Addition of sulfamethoxazole & trimethoprim (SXT) to CBA may be used to suppress growth of NF and allow better recovery of beta hemolytic Strep
  • Microaerophilic, good growth require reduced oxygen (candle jar or CO2 incubator)
  • Nutritionally deficient Strep may require vitamin B6 or pyridoxal for growth and may be found satelliting Staph aureus
  • Strep pneumoniae is sensitive to cold and may fail to grow if refrigerated
s trep differentiation from other genera
StrepDifferentiation From Other Genera
  • Other Gram(+) cocci:
    • Strep = catalase(-)
    • Staph & Micrococci are catalase(+)
  • Other cocci:
    • Neisseria are Gram(-)
    • May be confused with Strep that lose G(+) as they age
    • However, Neisseria = oxidase(+)
differentiation within strep genus
Differentiation Within Strep Genus
  • Respiratory Tract by CBA hemolysis:
    • Viridans group (Strep mitis, Strep salivarius, Strep sanguis) - partial (α) hemolysis, NF
    • Strep pneumoniae –partial (α) hemolysis
    • Strep pyogenes –complete (β) hemolysis,may be pathogen
  • Differential diagnosis by clinical syndrome:
    • Group A – sore throat
    • Group B – neonatal meningitis
strep pyogenes group a
Strep pyogenes (Group A)
  • Sensitive to Bacitracin (0.04 units, Taxo A disk)
  • Resistant to SXT disk (both Gp. A & B)
  • PYR hydrolysis: Production of pyroglutamyl aminopeptidase; both Gp. A & Enterococcus = (+)
strep agalactae group b
Strep agalactae (Group B)
  • CAMP (Christie, Atkins, Munch-Peterson) test – extracellular protein that enhances Staph aureus hemolysin
  • Hippurate hydrolysis (hippuricase) – hippurc acid to Na benzoate + glycine (amino acid)
  • Growth in 6.5% NaCl (Gp. B & Enterococcus)
  • Resistance to SXT disk (both Gp. A & B)
group d enterococcus streptococcus bovis
Group D: Enterococcus,Streptococcus bovis
  • CBA - may be partial, complete, nonhemolytic (α, β, none)
  • Bile esculin agar - all Group D grow in bile, hydrolyze esculin = growth + blackening on agar
  • 6.5% NaCl–Enterococcuss = (+) growth
  • PYR hydrolysis–Enterococcus= (+)
s pneumo viridans group
S. pneumo & Viridans Group
  • CBA - both partial (α) hemolysis
  • Taxo P disk- Optochin (ethyl hydrocupreine hydrochloride) susceptibility, detergent that activates autolytic enzyme, lyse cell wall of Strep pneumoniae
  • Bile solubility– bile salt (Na desoxycholate) activate autolytic enzyme of Strep pneumoniae (test - 37°, 30 min.) dissolve isolated colonies
  • Most labs do not speciate the Viridans group (Strep mitis, Strep salivarius, Strep sanguis) except for blood isolates or epidemiology
serology tests
Serology Tests
  • Serogroups – Lancefield typing
    • Group A-H, K-V
    • Group A Serotypes - >80; based on M protein of cell wall
  • Quellung test - for Strep pneumoniae
    • 84 serotypes based on specific soluble substance in capsule
    • specific antisera binds to substance, under microscope capsule appears swollen
strep pyogenes virulence extracellular products
Strep pyogenes Virulence: Extracellular products
  • Streptolysin S – alters membrane permeability; lyses RBCs, leukocytes, and other cells containing sterols in membrane
  • Streptolysin O – forms membrane penetrating channels (porin) leading to membrane defects and cell lysis
    • Cytotoxic to RBCs and many tissue cells, particularly cardiotoxic
    • Antigenic - for strep throat infections (but not skin), anti-streptolysin O (ASO) antibody used to diagnose recent infection
strep pyogenes virulence extracellular products1
Strep pyogenes Virulence: Extracellular products
  • Erythrogenic toxin
    • Act as superantigen - fever, cardiotoxic, enhanced susceptibility to endotoxin shock, suppress antibody response
    • Rash seen in scarlet fever; due to delayed hypersensitivity reaction to other streptococcal antigens enhanced by toxin
    • Toxin involved in toxic shock syndrome similar to Staph. aureus
strep pyogenes virulence extracellular products2
Strep pyogenes Virulence: Extracellular products
  • Streptokinase – cleaves plasminogen to plasmin, then acts as protease to lyse fibrin clots
  • Hyaluronidase – spreading factor
  • DNAse – degrades accumulated inflammatory exudate DNA from leukocyte disintegration; antigenic and antibodies used to diagnose recent Strep infection (including skin infections)
strep pyogenes virulence cell associated factors
Strep pyogenes Virulence: Cell Associated Factors
  • M protein
    • Fibrous protein on cell surface
    • MAJORvirulence factor for group A Strep
    • >80 different types
    • Protects MO from opsonization and phagocytosis by binding to fibrinogen
    • Also play role in adherence
    • Some types of M protein act as super antigen causing shock in patient
    • Poorly immunogenic; antibodies, if made, are protective, long lasting, type specific
strep pyogenes virulence cell associated factors1
Strep pyogenes Virulence: Cell Associated Factors
  • Lipoteichoic acid
    • mediates attachment to epithelial cells
  • Capsule
    • hyaluronic acid (note organism also produces a hyaluronidase)
    • antibodies to capsule are not protective against infection
strep agalactiae virulence extracellular products
Strep agalactiae Virulence: Extracellular Products
  • Hemolysin - increase vascular permeability in lungs, leading to respiratory distress
  • Neuraminidase – cleaves sialic acid residues, involved in hyaline membrane disease of lung
  • Hyaluronidase – spreading factor
  • DNAse – spreading factor
  • Protease – spreading factor
strep agalactiae virulence cell associated factors
Strep agalactiae Virulence: Cell associated Factors
  • Capsule – antibodies are type specific and protective
  • Lipoteichoic acid – for attachment
strep pneumoniae virulence extracellular products
Strep pneumoniae Virulence: Extracellular Products
  • Pneumolysin O
    • cytolytic for RBCs and other tissue cells
    • Cytoplasmic rather than extracellular protein, released when bacteria lyse
    • Acts as porin to disrupt host cell membranes
  • Leukocidan
  • Neuraminidase
  • Hyaluronidase
  • IgA protease
strep pneumoniae virulence cell surface structures
Strep pneumoniae Virulence: Cell Surface Structures
  • Capsule – most important virulence factor
  • > 80 different types capsular polysaccharide
  • Antibodies against capsule type specific and protective (used for vaccine)
streptococcus clinical significance
Streptococcus Clinical Significance
  • A wide variety of diseases:
    • Suppurative - pus producing lesions
    • Toxemia - Clinical symptoms suggesting toxin
  • Infants - more susceptible, with prolonged, low grade infections; rarely nephritis and rheumatic fever follow
  • Older children and adults - more acute and self-limited infections; occasional complication of nephritis and rheumatic fever (with no pus or MO present)
streptococcus clinical significance1
Streptococcus: Clinical Significance
  • Complete (ß) hemolytic:
    • Gp. A, B, and C most virulent
    • Gp. A greatest number infections
  • Partial (α) hemolytic & non hemolytic:
    • Viridans group found as NF in RT and GI tract, most common cause of subacute bacterial endocarditis
    • Step pneumoniae leading cause of death due to bacterial infection throughout the world, particularly in elderly and very young
strep pyogenes infections pyoderma impetigo
Strep pyogenes Infections:Pyoderma (Impetigo)
  • Superficial skin infection characterized by vesicular rash, becomes pustular, in later stages thick crust
  • Staph aureus may be secondary invader
  • Endemic in tropical areas caused by M serotypes different from those that cause pharyngitis
  • Spread by close, direct contact
  • Disease starts with skin colonization, followed by invasion through abrasions
  • Type specific antibodies to M are made, but antibodies to Streptolysin O are uncommon
  • Most serious complication is acute glomerulonephritis, occur 2-3 weeks post infection
strep pyogenes infections erysipelas
Strep pyogenes Infections: Erysipelas
  • Diffuse, erythematous skin infection
  • Most often on face, occurs following pharyngitis
strep pyogenes infections
Strep pyogenes Infections
  • Wound infections - occasionally following trauma, due to simple contamination of wound
  • Cellulitis – subcutaneous tissue, accompanied by lymphangitis and abscess; typically exhibit chills, fever, marked signs of toxicity
  • Necrotizing fasciitis (”flesh eating bacteria”) – fibrous tissue deep in skin; toxin destruction of sheath that covers muscle
strep pyogenes infections myositis
Strep pyogenes Infections: Myositis
  • Invasion of muscle tissue
  • Extensive muscle necrosis, overwhelming sepsis
  • Usually fatal
strep pyogenes infections pharyngitis strep sore throat
Strep pyogenes Infections: Pharyngitis (Strep Sore Throat)
  • Most common disease caused by Strep pyogenes
  • Spread by droplets of respiratory secretions or via food or water
  • Abrupt onset of sore throat, malaise, headache, fever
  • Throat erythematous with grayish-white exudate
  • Tonsils and lymph nodes are enlarged; tonsils may become infected chronically
  • May spread to sinuses and middle ear
  • Usually self-limited, penicillin used to prevent secondary complications such as rheumatic fever
strep pyogenes infections scarlet fever
Strep pyogenes Infections: Scarlet Fever
  • From URT infection
  • Strep lysogenized by phage with gene for erythrogenic toxin
  • Symptoms similar to pharyngitis - erythematous rash upper chest, spreads to rest of body, ~1 week; followed by weeks of extensive desquamation of skin
  • “strawberry tongue” - red spots on yellowish-white tongue
  • “raspberry tongue” - followed by peeling, red beefy tongue
  • Immunity to toxin is demonstrated by Dick test:
    • Inject toxin in skin, produces erythema in absence of antibody
    • If no erythema, indicates antibodies present, patient infected
  • Erythrogenic toxin may also be involved in causing a toxic-shock like syndrome
non suppurative complications strep pyogenes rheumatic fever
Non-suppurative Complications Strep pyogenes: Rheumatic Fever
  • Inflammatory disease; involve heart, joints, subcutaneous tissue, CNS
  • Primarily in children 6-15 yrs.
  • 1-5 weeks after Strep throat
  • Major manifestations - polyarthritis, carditis, chorea, erythema marginatum
  • Carditis can involve all layers of heart, can lead to rheumatic heart disease - chronic, progressive damage to heart, possibly death
rheumatic fever
Rheumatic Fever
  • By autoimmune, cross-reacting antibodies made against Strep that react with self tissues
  • Attracts host reactive cells, Complement gets activated and leads to cellular damage
  • Diagnosis by serum antibody test - ASO assay
  • Prevent by treating Strep throat infection with penicillin
non suppurative complications strep pyogenes acute glomerulonephritis
Non-suppurative Complications Strep pyogenes: Acute Glomerulonephritis
  • Occur 2-3 weeks following pharyngitis or pyoderma
  • Edema, hypertension, headache, malaise, circulatory congestion, hematuria
  • Only associated with specific nephritogenic M serotypes of Gp. A Strep
  • Immune complex disease - deposition of circulating Strep antigens and antibodies complexes in glomeruli of kidney
  • Damage due to host reactive cells and subsequent Complement activation
strep agalactiae infections
Strep agalactiae Infections
  • NF of adult vagina, urethra, rectum, occasionally pharynx
  • Sexually transmitted disease (STD)
  • Adults - rare infections; URT, meningitis, bacteremia, endocarditis
  • Newborn - most serious disease cases
  • Use to be major cause of puerperal fever (postpartum sepsis, child-bed fever)
strep agalactiae infection newborn
Strep agalactiae Infection:Newborn
  • Early onset disease
    • Infected in utero or at birth
    • MO gain access via RT, symptoms of respiratory disease
    • Septicemia, meningitis may occur
    • High mortality rate
  • Late onset disease
    • 7-10 days after birth, MO rarely found in mother prior to birth
    • MO by direct contact with newborn mucosal surfaces
    • Meningitis or osteomyelitis, possibly bacteremia
    • Mortality rate high, but lower than early-onset disease
streptococcal group c d infections
Streptococcal Group C, D Infections
  • Group C – similar to Gp. A, but without non-suppurative sequelae complications
  • Group D – NF of GI tract
    • Common cause of UT infections, subacute bacterial endocarditis, abdominal abscesses, wound infections
    • Strep bovis in blood suggest surface of colon compromised; associated with carcinoma of colon; proposed as early screen for colon cancer
viridans group infections
Viridans Group Infections
  • NF of RT, GI tract, genital tract
  • Most common cause of subacute bacterial endocarditis, colonize damaged heart valves
  • Strep mutans plays a role in dental decay
strep pneumoniae infections
Strep pneumoniae Infections
  • Found as NF in URT in 15% of children and 5% of adults; carrier state is sporadic
  • Probable pathogen when most predominant MO isolated
  • Leading cause of bacterial pneumonia, particularly in very young, elderly, those with immunological deficiencies
  • Mortality rate is 5-7%.
  • Bacteremia is common, meningitis may occur
strep pneumoniae infections1
Strep pneumoniae Infections
  • Meningitis – not as common as other causes of meningitis except in children under 1 year of age where it is second most common cause of meningitis; mortality rate is high ~40%
  • Otitis media – most common cause of middle ear infection in children (1/3 of cases)
  • Also cause purulent sinusitis and peritonitis
antimicrobial susceptibility
Antimicrobial Susceptibility
  • Penicillin for groups A, B, C; erythromycin for individuals allergic to penicillin. Susceptibility testing is not necessary.
  • Enterococcus and other group D – must do sensitivity testing; now strains of Enterococcus faecalis resistant to all antibiotics
  • Viridans group Strep – do sensitivity testing
  • Strep pneumoniae – use penicillin, but now resistant strains, so sensitivity testing is necessary
pneumococcal vaccine
Pneumococcal Vaccine
  • Use of purified polysaccharide
  • Children: heptavalent pneumococcal vaccine (PCV7) – vaccine of 7 serotypes S. pneumoniae
  • Adults: 23 capsular polysaccharides (PS23) - vaccine for 23 strains most likely to cause pneumonia
  • Given to most likely infected - young, old, chronic respiratory problems
class assignment
Class Assignment
  • Textbook Reading: Chapter 15 Streptococcus, Enterococcus, and Other Catalase-Negative Gram-Positive Cocci
  • Key Terms
  • Learning Assessment Questions
case study 2 streptococcus
Case Study 2 - Streptococcus
  • A 62-year-old man with a history of chronic obstructive pulmonary disease (COPD) came to the emergency department because of a fever of 40°C, chills, nausea, vomiting, and hypotension.
  • The patient also produced tenacious, yellowish sputum that had increased in quantity over the preceding 3 days.
  • His respiratory rate was 18 breaths/min, and his blood pressure was 94/52 mmHg.
case study 2
Case Study 2
  • Chest radiographic examination showed extensive infiltrates in the left lower lung that involved both the lower lobe and the lingula.
  • Multiple blood cultures and culture of the sputum yielded S. pneumoniae.
  • The isolate was susceptible to cefazolin, vancomycin, and erythromycin but resistant to penicillin.
case study 2 questions
Case Study 2 - Questions
  • 1. What predisposing condition made this patient more susceptible to pneumonia and bacteremia caused by S. pneumoniae? What other populations of patients are susceptible to these infections? What other infections does this organism cause, and what populations are most susceptible?
  • 2. What infections are caused by S. pyogenes, S. agalactiae, and viridans streptococci?
case study 2 questions1
Case Study 2 –Questions
  • 3. S. pyogenes can cause streptococcal toxic shock syndrome. How does this disease differ from the disease produced by staphylococci?
  • 4. What two non-suppurative diseases can develop after localized S. pyogenes disease?