Bugs: Staphylococcus Flashcards
Staphylococcus: Bacteriology -
- Gram?
- shape on micropscopy?
- Distinct biochemical test?
Gram positive
Facultative Anaerobe
Cocci in clusters (grapes)
All Staph is Catalase positive
what is the clinical and biochemical division in the staph species?
what is the difference in apperance on agar culture?
Coagulase positive : staph aureus
golden on culture
Coagulase negative: All other Staph
white on culture
What are the structural properties of Staphylococcus?
Poly saccharide Capusle:
Attached to cell wall; Inhibits phagocytosis
Slime layer:
Loosely attached to cell wall;
Important for adherence; formation of biofilms
What virulence factors does S. aureus have to evade the immune system?
Capsule – inhibits phagocytosis
Protein A – Fc IgG receptor; prevents neutrophils from binding Fc; inhibits phagocytosis
How adherence factors does S. Aureus have to bind to host tissues?
MSCRAMM proteins – any number of the microbial surface proteins that bind to host proteins
(including protein A)
what virulence factors of S. Aureus promote bacterial survival and tissue destruction?
The enzymes:
Catalase
Coagulase, Hyaluronidase
Fibrolysin, lipase, nucleases
What toxins does S. Aureus produce? what diseases do they cause ?
Exfoliative Toxin: Scalded Skin Syndrome
Enterotoxin: Food poisoning; superantigen – cuase of acute gastroenteritis
Toxic Shock Syndrome Toxin 1 (TSST1); which causes TSS (sepsis)
How does S aureus evade abx?(resistance mechanisms)
PCN resistance – PCNases
Methicillin Resistnace – mecA gene (new PBP2a binding site)
Vanc resistnace (very rare!!) – VanA gene alteres D ala ala to D ala lac
Clinical Manifestations of S. Aureus
Cutaneous disease (Impetigo, folliculitis, furuncles, carbuncles; wound infections)
Systemic disease (PNA, osteomyelitis, endocarditis)
Toxin mediated disease (TSS, SSSS, food poisoning)
Describe the cutaneous pyogenic infections:
Staph is common skin colonizer:
Impetigo – contagious infection of superficial skin layers; characteristic honey colored crusting
Folliculits (stye)
Furuncle: boils; extended folliculitis
Carbuncle: coalescence of infected hair follicules; deeper in SubQ
Wound infections: esp after trauma, surgery, foreign body
Describe the systemic disease manifestations of S. aureus
how do they arise
via Direct innoculation or cuteanous infection leading to bacteremia
PNA –
Osteomyelitis –
Endocarditis –
What are the toxin mediated disease of the S. Aureus
briefly describe some their therapies
SSSS – exfoliative toxins
sterile blistering, peeling skin (stratum granulosum)
Self Limiting
No scarring
Boullus Impetigo – localized form of SSSS
Food Poisoning – Enterotoxins
superantigen
Supportive therapy
STTS –
Toxin 1 -
eliminate the infection; surgical intervention/drainage of tissues
Virulence factors of coagulase negative staph
- Slime: biofilm formation
- Enzymes: catalaase, PCNase,
NO (few) TOXINS
ABX resistance
Coagulase negative staph:
the bugs and their Clinical manifestations
S. Epidermidis et al - Infection of foreign bodies, prosthetic materials (central caths, prosthetic joints, heart valves, shunts)
S. saprophyticus: UTIs / pyelonephritis
S. lugdenensis – native valve endocarditis
Management of Staph;
- when do you treat? when do you repeat cultures?
If coagulase negative staph – repeated cultures bc these could easily be contaminant
If coagulase positive staph – assume MRSA and begin treatment
