Lecture 27 - Streptococcus Flashcards
(17 cards)
describe the strep genera
- Lactobacillales
- flori/lacto/streptococcus and lactovum genera with 105 spp in strep
- G+ve cocci in chains/pair, non motile, non spore, 1.6-2.4Mb genome
- catalase -ve
- some only in humans
describe the metabolism of strep
- Facultative/strict anaerobes
- Strict homofermentative = lactic acid byproduct only
- fastidious
- alpha haemolysis = oxidise haemoglobin to methaemoglobin
- beta haemolysis = full lysis
list the 3 strep groups based on pathogenicity
- pyogenic = pus, beta haemolysis, eg pyogenes
- Oral = heterogenous, mouth and upper resp, eg mutans, pneumoniae
- other
describe strep grouping based on serology/Lancefield grouping. provide groups for pyogenes, agalactiae, enterococci
- CW carb antigen = 20 groups A-O
- immunised rabbit reagents -> antiseria for polyclonal antibodies
- now use latex agglutination
- A pyogenes, B agalactiae, D enterococci
list the 2 typing methods for strep
- serology = polysac antigen typing (GBS)
- molecular = PFGE, MLST for emm, PCR, WGS
list the 6 major species groups of strep and the 2 major evolutionary lineages
- spp = pyogenic, mitis, anginosus, bovis, mutans, salivarius
- lineages = pyogenic, mitis
briefly describe the disease patterns noted in the strep pneumoniae transformation mouse study by griffith
- smooth live = death
- rough live = survived
- smooth dead = no effect
- live rough + dead smooth = pneumonia + both strains isolated
how does strep normally exist in the human body? which 2 strep spp are major human pathogens?
- commensal in resp tract, mouth, large intestine, genitourinary
- pathogenic = group A pyogenes and pneumoniae
describe the pathogenesis of strep pyogenes/GAS
- commensal in oropharynx
- pharyngitis = 2-4day incubation, inflammation in throat/tonsils, white and RBC lysis, 50% cases with exudate, self-limiting or complications
describe the 2 complications/post-strep diseases 1-4wks after the acute infection
- glomerulonephritis by strep pyogenic exotoxin B (SpeB) = type 3 hypersensitivity of antigen-antibody complexes dmging glomerular membrane, 90% heal
- Rheumatic fever = children autoimmune, inflammatory lesions in heart/joints/subcutaneous/CNS, requires M proteins triggering autoantibodies against heart
what are the 2 types of VFs in strep (examples do separate bc too many)
- cell associated
- secreted
what antibiotic susceptibilities and resistance patterns are associated with strep?
- penicillin sensitive but higher dose
- macrolide resistant
how does strep mediate antibiotic resistance? what are the issues with possible vaccines?
- intracellular persistence in tonsils or protection from beta lactamases from other bacteria
- vaccines cross reactive with organs and too antigenically variable
describe the pathogenesis of s pneumoniae and who is at risk for infection
- very young/old = pneumonia, meningitis, otitis media
- commensal in upper resp
- resp epithelial dmg from viral infection allows access to alveolar tissue
- risks = dysfunctional airways/immunity
- inflammation reduces lung function = 30% untreated mortality
what are the 4 VFs of s pneumoniae?
- capusle = blocks antimicrobials, prevents mucous entrapment, 90 serotypes
- pneumococcal phosphorylcholine binding proteins PspAC = adhesion, protect from apolactoferrin, reduces opsonisation by C3b
- pneumolysin = DNA dmg = cell cycle arrest
- autolysin = cell lysis
what vaccines are available for s pneumoniae?
- conjugate 12/20 = 13 serotypes, non-toxic diphtheria protein, <5yo
- polysacc 23 = 23 serotypes, >70yo
list some other pathogenic strep spp
- S. agalactiae/GBS = meningitis, bacteraemia, endocarditis
- dental disease = Mutans, sanguis, sobrinus, gordonii, oralis, mitis
