Streptococcus spp

1
Streptococcus spp

• Semmelweis/O.W. Holmes
• mid 1800's (Vienna, Boston)
• independently concluded that spread of childbed
  fever (puerperal sepsis) is by contamination
• hands, clothing of attending obstetrician
• strengthened germ theory of disease

2
Streptococcus spp

• Gram positive, facultatively-anaerobic
• Catalase negative, no spores, nonmotile
• Cell division single plane gt chains
• Lancefield Grouping
• species-specific CHO cell wall antigens
• groups designated A-H, K-V
• some not groupable

3
Bilobar Pneumonia

• Most important cause of community-acquired
  pneumonia in humans
• carrier rate 40-70
• Broad host range (rodents, monkeys, dogs, horses)
• Multidrug resistance increasingly prevalent
• Major effort on vaccine development

4
Virulence

• Polysaccharide capsule resistance to
  phagocytosis
• 80 types, CHO antigen
• nonencapsulated strains avirulent
• occurrence varies with time, geography
• Pneumolysin alveolar necrosis
• O2-labile hemolysin
• slows cilia, reduces clearance
• Neuraminidase decrease mucus viscosity, expose
  receptors

5
Immunity

• Type-specific anticapsular antibodies
• opsonizing, facilitate phagocytosis
• 70 of untreated cases recover
• Recurrence due to infection with different types

6
Streptococcus suisGroups D,R,S,T

• Single genetic type
• Tonsil carrier rate up to 100
• Piglets infected at birth (oral, respiratory)
• Encephalitis, meningitis, arthritis, septicemia,
  abortion, endocarditis in swine

7
Streptococcus agalactiaeGroup B

• Chronic bovine mastitis
• promoted by milking machines
• slowly progressing inflammation, fibrosis
• fibrin plugs in smaller milk ducts loss of
  milk-producing capacity (agalactia)
• Neonatal meningitis in humans
• early onset septicemia ( 15 of all neonatal
  septicemias)
• late onset purulent meningitis (average 4.8
  weeks after birth)
• 5 - 10 of pregnant women are reproductive tract
  carriers

8
Streptococcus equi ss equiGroup C

• Upper respiratory tract infection (strangles) in
  horses
• abscesses in LN develop, enlarge
• pressure on airway causes respiratory difficulty
  (strangles)
• metastasis to lungs, abdomen, brain

9
Virulence

• Nonantigenic hyaluronic acid capsule
• Hyaluronidase
• Streptolysin O (SLO)
• Streptokinase
• IgG Fc-receptor proteins
• Antiphagocytic M protein varying amounts of M
  protein yield variations in virulence
• bind fibrinogen, complement control factor H
• masks bacterial C3b-binding sites
• Opsonizing antibodies formed against N-terminal
  epitopes

10
Streptococcus equi ss zooepidemicus

• Horses
• wound infections, joint ill, lymphatic abscesses
• pneumonia in foals
• mare reproductive tract infections
• Bovine, caprine mastitis
• Lambs wound infections, pneumonia, septicemia
• Pups, chickens, rodents
• Human infections via contaminated dairy products

11
Streptococcus canis

• Canine genital, skin, wound infections
• Canine streptococcal shock emerging problem in
  dogs
• septicemia, toxic shock fatal
• necrotizing fasciitis alone survive with radical
  treatment
• Feline abscesses, metritis, mastitis, kitten
  septicemia

12
Streptococcus pyogenesGroup A

• Pyoderma, lymphadenitis, erysipelas (humans)
• Wounds cellulitis, puerperal fever
• Septic sore throat, scarlet fever
• acute inflammation
• pharyngitis
• pus patches (fibrin, PMNs, mucosal fragments)

13
Streptococcus pyogenesSequelae to strep throat

• Heart valve damage (rheumatic heart disease)
• lt 3 of people with strep throat, weeks after
  sore throat
• migrating arthritis heart valve damage (50),
  some fatal
• recurrences common, lifelong penicillin therapy
• shared antigen M protein, cardiac myosin
• attack by T cells, Ab inflammation, valve damage

14
Streptococcus pyogenesSequelae to strep throat

• Glomemlonephritis
• symptoms 10 days after 1 infection edema
• decreased urination, hematuria, hypertension
• AgAb complexes accumulate, C activated
• provoke inflammatory response, interferes with
  normal kidney function
• young children self-limiting
• teenagers/adults rare permanent kidney damage,
  chronic glomerulonephritis

15
Streptococcus pyogenesScarlet Fever

• Childhood disease, diffuse rash, fever
• Late 1800s highly virulent form, high death rate
• 1900 - 1950 milder form most common
• 1950 - 1980 virtually disappeared
• 1980 appearance of streptococcal toxic
  shock-like syndrome (TSLS after recognition of
  staphylococcal TSS)
• began as skin or wound infection, developed into
  septicemia
• death rate sometimes over 30 ( 2 for TSS),
  some disabled, some healthy

16
Streptococcus pyogenesNecrotizing Fasciitis

• Invasive, nonTSLS disease
• necrotizing fasciitis (flesh-eating bacteria)
• rapid development of shock, multiple organ system
  failure
• high fatality rate

17
Virulence

• Capsule 100X virulence reduction with loss of
  capsule
• C5a peptidase (cleaves C5a)
• Streptokinase dissolves fibrin clots
• M protein 80 serotypes
• antiphagocytic degradation of C3b
• prevents opsonization
• mutants without M protein phagocytosed

18
Virulence Factors

• Streptolysin O thiol-activated toxin (Groups
  A,C,G)
• damages membranes RBCs, myocardial cells, PMNs
• role in intracellular survival
• Erythrogenic toxins rash of scarlet fever
• pyrogenicity, lethal shock
• 105-fold increased sensitivity to endotoxin
• Pyrogenic exotoxin A
• contributes to streptococcal TSLS
• stimulates cytokine production by T cells
• endothelial cell damage, hypotensive shock,
  ischemia-based necrosis