Streptococcus and Enterococcus Flashcards
Lecture 6
What do Streptococcus spp. and Enterococcus look like?
they are gram-positive cocci (oval/round) typically found in chains
Where are Streptococci and Enterococcus found?
they are normal flora of humans in the oral cavity, nasopharynx, and intestinal tract
What are the characteristics of Streptococcus and Enterococcus?
most are facultative anaerobes, catalase negative (but Enterococcus may be weakly positive), non-motile, non-spore forming, group according to appearance of colonies and hemolytic reaction
Alpha streptococci
produce alpha hemolysis, partial destruction of red blood cells around colony, looks green to brown
Beta streptococci
produce beta hemolysis, red blood cells are completely lysed giving a clear colorless zone around the colony; streptolysin O and streptolysin S can be produced
Gamma streptococci
no hemolysis, there is NO gamma hemolysis
Which Streptococcus and Enterococcus are beta hemolytic?
Strep pyogenes, strep agalactiae, strep equisimilis, strep equi, strep anginosus, strep canis, (enterococcus, and streptococcus bovis are rarely beta-hemolytic)
Which Streptococcus and Enterococcus are alpha hemolytic?
strep pneumoniae, strep bovis, enterococcus, viridans streptococcus group
Which Streptococcus and Enterococcus are nonhemolytic?
strep bovis and enterococcus
What are the virulence factors of S. pyogenes (group A)?
M protein - on cell wall surface allows organism to resist phagocytosis
Hyaluronidase - enzyme digests ground substance of CT
Streptokinase - enzyme digests fibrin clots
Streptolysin O - highly immunogenic, triggers auto-immune reaction
What infections does S. pyogenes cause?
Pharyngitis, tonsillitis, swollen lymph nodes (“strep throat), otitis media, scarlet fever, impetigo, cellulitis
Post-streptococcal sequelae
1) rheumatic fever - auto-immune reaction in heart muscle following pharyngitis with S. pyogenes
2) acute glomerulonephritis - auto-immune reaction in renal glomeruli following skin infection or pharyngitis with S. pyogenes
What is the virulence factor of S. agalactiae (group B)?
produces polysaccharide capsules with 5 major antigen types
What infections does S. agalactiae cause?
colonization of female genital tract (10-30%), leading cause of meningitis, septicemia, pneumonia in neonates, urinary tract infections and bacteremia in the elderly and immunocompromised, post-surgical gynecologic infections
What are the virulence factors of S. pneumoniae?
polysaccharide capsule that prevents phagocytosis, pneumolysin that is toxic to pulmonary endothelial cells and can spread to bloodstream
What infections does S. pneumoniae cause?
virulent strains are encapsulated, more frequent cause of otitis media in children, community acquired bacterial pneumonia, meningitis, sinusitis
What vaccines do we have to prevent S. pneumoniae infections?
Pneumococcal conjugate vaccine for infants and children, and 23-valent polysaccharide vaccine (23 PPVSV) for adults 65 +
What does viridans Streptococcus look like?
it is green or alpha-hemolytic
What infection does viridans Streptococcus cause?
most common cause of subacute bacterial endocarditis
What are some characteristics of Enterococcus?
two species responsible for most human infections are E. faecalis and E. faecium, it has relatively low virulence, normal flora of intestinal tract
What infections does the Enterococcus cause?
urinary tract infection, endocarditis, and wound infections
What is Group D Streptococcus?
possible S. bovis group; can cause GI disease (carcinomas)
How do we treat Streptococcus?
we use penicillin, but we can treat resistance with vancomycin or 3rd generation cephalosporin
How do we treat Enterococcus?
it is resistant to penicillins and cephalosporins when given alone, so we use a combination of penicillin and aminoglycoside; if resistant to this combination we treat with vancomycin. If it is STILL resistant, we can use synercid or linezolid
How do we identify Streptococci?
gram-stain: +
catalase: -
it can cause hemolysis, and we can use bacitracin sensitivity tests as well as rapid strep tests
