Lecture 26 - Staphylococcus Flashcards
(21 cards)
describe the staphylococcus genera
- Firmicutes, 70 species, 30 subspecies, most non-pathogenic
- G+ve cocci, non motile, non spores, facultative anaerobe, mesophile, 2.5-2.9 Mb
- catalase +ve, oxidase -ve, high salt tolerance, high drying tolerance
- cocci bc divide in multiple planes
- mammal reservoir
list some species in the coagulase +ve staph group incl the most problematic sp
- pseudo/intermedius, delphini, hyicus, lutrae, schleiferi coagulans
- s aureus = 40% carried incl MRSA in nose/armpit/groin/perineum
- 90% s aureus cartenoid = gold (aureus)
what are the 3 diseases caused by s aureus? give examples of each
- Skin and soft tissue infections eg impetigo, boils, scalded skin
- Food poisoning = ingest enterotoxin
- Life threatening eg osteomyelitis, septic arthritis, sepsis, acute endocarditis, pneumonia, toxic shock syndrome
what are the 2 types of s aureus virulence factors? give examples/subclasses of each
- cell associated = adhesins, microcapsule/slime, CW teichoic acids
- excreted = exotoxins, enzymes = coagulase, protease, lipase, hyaluronidase
describe the 3 step process of blood plasma clotting by coagulase
- Reacts with prothrombin = staphylothrombin complex
- cleaves soluble fibrinogen to insoluble fibrin
- Fibrin self-assembles and polymerises = clot
what are the 2 types of s aureus coagulase?
- bound to CW as clumping factor = direct reaction with fibrinogen = fibrin coat on S aureus
- Free = extracellular
what toxins do most strains of s aureus possess?
cytotoxins = haemolysins (alpha, beta, gamma, delta) = damage cell membranes = invasion
what toxins to only some strains of s aureus possess?
exfoliative toxins A and B, toxic shock syndrome toxin (TSST), enterotoxins, panton valentine leucocidin (PVL)
list the 4 different types of haemolysins and their result in sheep BA
- Alpha = beta-barrel transmembrane pore
- Beta = hydrolyses sphingomyelin in PM
- Gamma = beta barrel TM pore
- Delta = phenol soluble modulins (PSMs), non-specific membrane dmg or short lived pores
describe s aureus enterotoxins
- ingestion = vomiting
- 20+ types, A-E = 80% food poisoning
- heat and acid stable
- genes on MGEs = staphylococcal cassette chromosome (SCC), prophage, PAI, plasmid
which s aureus toxins are superantigens and what do they do?
- enteroxins SEA and SEB
- Non-specific T cell activation = bind MHC-2 directly
- 0.001% T cells -> 20-30% = shock
what is toxic shock syndrome associated with and how does it work? how many strains possess the toxin and how is it introduced/carried?
- Vaginal products promoting s aureus in genital tract
- release superantigen TSST into blood = shock and organ failure
- 30-70% mortality
- <10% strains TSST on PAI
how is s aureus acquired and what are the risks for septicaemia, septic arthritis and impetigo?
- hospital by health workers/commensal/community
- septicaemia = young/old
- septic arthritis = joint disease, old, diabetes
- impetigo = school kids
describe the history of antibiotic use for s aureus and subsequent resistance patterns. which antibiotics are still effective?
- pre-1950s penicillin = beta lactamases
- 1950s methicillin = MRSA by mecA on SCCmec (PBP)
- 2000 vanco = VISA/VRSA by vanAB on Tn1546 from enterococci
- Linezolid and clindamycin still effective
describe how vancomycin resistance works
- VANC binds D-ala-D-ala
- disrupts PG assembly
- alters CW intermediates to D-ala and D-ala-d-lac
describe the coagulase -ve group of staph
- Diverse and heterogenous
- Commensal in skin and mucous membranes of mammals
- non pathogenic = Accidental/opportunistic or contamination
list 4 species of coagulase -ve staph and their VFs/disease
- epidermidis = slime, biofilms, PSMs
- haemolyticus = reduced vanco suscep
- lugdunensis = clumping factor, von willebrand clotting factor
- saprophyticus = UTis in females
how is epidermidis transmitted and what diseases does it occur?
- nosocomial in indwelling devices
- endocarditis, bacteraemia
- unlikely in healthy, less invasive
what are the 3 main VFs of epidermidis?
- PSMs = pro-inflammatory, cytolytic, less active than aureus’ version
- slime = adhesion to smooth, inhibits neutrophil mvmt, reduces antibiotic effectiveness
- biofilm = cells in polysacc intercellular adhesin (PIA)/poly-N-acetylglucosamine (PNAG) with extracellular eDNA and small basic protein (Sbp)
decribe antibiotic patterns for epidermidis
- suscep to vanco, some VISA
- methicillin resistant by mecA on SCCmec (PBP2a)
- other plasmid encoded resistance genes
how is mecA on SCCmec related between epidermidis and aureus
- epidermidis = 10 SCCmecs frequently lost/acquired
- aureus version from epidermidis bc commensal = more exposure
- CRISPR only in epidermidis = aureus without CRISPR collects toxins/resistance
