gram positive cocci - streptococci

• • streptococci are gram positive cocci that are typically arranged in chains
  • there are over 100 species of streptococci
  • focus on most common ones that cause human infection, specifically:
  • S. pyogenes
  • S. agalactiae
  • S. pneumoniae
  • viridians streptococci
• major point

  • when it comes to classification of streptococci, there are 2 main methods that are commonly used
  • lancefield groups
  • red blood cell hemolysis pattern
• streptococcus agalactiae

  • group B streptococci
  • colonize lower GI and GU tract
  • beta-hemolytic
  • they are typically only of concern if the woman is pregnant as they can be passed on to the newborn during delivery and cause neonatal sepsis and meningitis
  • prevention --> antibiotic prophylaxis (ampicillin or cefazolin) in group B strep positive pregnant women during labor/delivery
• viridans streptococci

  • organisms
  • multiple species that typically colonize the oropharynx
  • ex: S, sanguinis, S. mutans, S. mitis, S. gordonii, S. salivarius, S. anginosus, S. milleri, and S. intermdius
  • infection
  • can cause bacteremia and endocarditis
  • most commonly occur after dental surgery
• streptococcus pneumoniae

  • alpha hemolytic
  • arranged in pairs (diplococci) or short chains
  • polysaccharide capsule --> major virulence factor and is antiphagocytic
  • types of infections
  • community-acquired respiratory infections, commonly-pnuemonia
  • otits media (children)
  • bacteremia
  • meningitis (rare)
  • laboratory diagnosis
  • culture
  • urine antigen test (used for resp infecitons)
  • prevention via vaccination
• streptococcus pyogenes

  • group A streptococci (GAS)
  • cause a variety of different infections ranging from mild to life-threatening
  • can carry a variety of virulence factors and produce toxins
  • identification typically by culture
  • drugs of choice are penicillin or amoxicillin
• strep pharyngitis

  • strep pharyngitis
  • abrupt onset of sore throat, fever, and headache
  • red swollen tonsils and pharynx
  • purulent exudate on tonsils
  • diagnosed by rapid antigen detection test (RADT)
  • throat swab
  • common in children
• scarlet fever

  • S. pyogenes that produce the erythrogenic toxic
  • largely affects children
  • presentation --> strep pharyngitis plus
  • fever
  • scarlet-red bumpy rash (trunk, neck, extremities)
  • strawberry-red tongue
• SSTIs caused by GAS

  • GAS can cause a variety of SSTIs that vary in severity from mild to life-threatening
  • some examples of mild-moderate SSTIs include impetigo, erysipelas, and cellulitis
• life-threatening infections

  • necrotizing fasciitis
  • exotoxin B producing GAS ("flesh-eating" bacteria)
  • affects skin, fascia, fat, and muscle tissue
  • medical emergency
  • toxic shock syndrome
  • exotoxin A producing GAS
  • disseminated infection associated w/ shock and organ failure