28: Staph Aureus

Question 1

characteristics of staphylococcus aureus

Answer 1

cocci (round)

non-motile
- don’t have a flagellum

non-spore forming

opportunistic pathogen

Question 2

how common is staph aureus?

Answer 2

inhibits nasal passages of 10-40% of humans without causing disease

Question 3

staphylococcus aureus toxins

Answer 3

disease-causing because of toxins

virulence factors released by bacteria to provide better survival for the bacteria in the host

common toxins include hemolysin, leukotoxin, exfoliative toxin, enterotoxin and toxic-shock syndrome toxin 1

Question 4

what else does staph aureus have apart from toxins?

Answer 4

enzymes and surface proteins considered as virulence factors

Question 5

how does staph aureus replicate?

Answer 5

extracellularly, using fast replication and toxins to survive in host

however, it can still invade and survive in human cells
- evasion from the immune system, antibiotic treatment and allows bacterial proliferation

Question 6

invasion of skin and blood

Answer 6

bacteria can get across the skin membrane, then get inside, forming an abscess
- area with inflammation, pus and bacteria

once attached to endothelial/epithelial cells, activation of inflammatory cytokines and interferons

Question 7

diseases caused by staphylococcus aureus

Answer 7

local site of skin infection
- boils, pimples, impetigo
* leading cause of acne alongside strep

diseases from skin infections (toxin-related)
- staphylococcal scalded skin syndrome
- menstrual/non-menstrual toxic shock syndrome
- staphylotoxin-mediated food poisoning

Question 8

diseases caused by staphylococcus aureus in healthcare settings

Answer 8

serious and rare events

bacteremia/sepsis when bacteria gets into the blood
- systemic inflammatory disease

pneumonia
- typically in patients with underlying lung disease or on mechanical ventilators
- bacteria comes in opportunistically after immunosuppression, and then patients die of infection

endocarditis where heart valves are infected
- leads to heart failure or stroke

osteomyelitis where bones get infected

Question 9

local impetigo with staph aureus

Answer 9

relatively harmless skin infection in children

treated with antibiotics

Question 10

staphylococcal scalded skin syndrome

Answer 10

disease mediated by exfoliation toxins

primarily kills skin cells in children

no vaccine

Question 11

history of toxic shock syndrome

Answer 11

first used in 1978 to describe staph outbreaks in children
- bacteria could not be isolated, indicating a toxin might be involved

emerging disease since no one had seen this before and no one recorded systemic toxic shocks

in 1980, appearances of TSS in menstruating women
- common risk factor identified as users of rely tampons

Question 12

toxic shock syndrome symptoms

Answer 12

unexplained acute fever

vomiting

rash

high number of deaths

Question 13

TSS and tampons

Answer 13

rely tampons made with polyester and carboxymethyl cellulose

high absorbency tampons mean lack of liquid access so bacteria grows better and toxin crosses mucosal membrane

Question 14

excessive absorbency leads to altered microbial ecosystem in the vagina

Answer 14

bacteria preventing the viscosity of vaginal fluids, which increased and got thicker

Question 15

deaths from TSS

Answer 15

208 deaths from 5296 cases from 1979-1996
- not all were menstrual TSS

not causing a high number of deaths

Question 16

menstrual TSS

Answer 16

starts within 2 days of beginning or end of menses

associated with high absorbency tampons

TSST-1 isolated from >95% of cases
- bacteria produces toxin and causes disease by leaking into the bloodstream
- bacteremia is not required for TSS

Question 17

non menstrual TSS

Answer 17

similar to menstrual TSS but caused by colonisation of various sites (lung, skin, surgery)

wounds are not inflamed
- can be just a boil

caused by TSST-1 (<50%) or other toxins/superantigens

Question 18

mortality for menstrual and non-menstrual TSS

Answer 18

<5% with proper treatment

complicated with antibiotic resistance

Question 19

superantigens

Answer 19

toxins responsible for TSS and staph-mediated food poisoning

very powerful antigen that activates T cells to make cytokines, and activates macrophages to make more cytokines and inflammation

bind to the side of MHC and T cell receptor, so it will activate T cells to make cytokines as if you were infected with the antigen the T cell normally recognises

Question 20

super antigens that nonspecifically glue the TCR to the MHC, regardless of the peptide present

Answer 20

nonspecific activation of a large percentage of T helper cells results in excessive inflammatory cytokine production by macrophages
- highly toxic

Question 21

staphylotoxin-mediated food poisoning

Answer 21

one of the main causes of food poisoning where super antigens are enterotoxins

viable bacteria not necessarily found in contaminated food

toxins are heat-stable

no fever but severe nausea and vomiting
- no bacteria replicating