Mod 2 Gram Positive Cocci

Question 1

Where are Staphylococci found?

Answer 1

1. Widely found in nature.
2. Skin and mucous membranes of mammals and birds.
3. Creates normal flora within mouth, mammary glands, intestinal tract, upper respiratory tract, genitourinary tract, skin, etc. (harmless) but some species are extremely dangerous to humans.

Question 2

What are some shared characteristics of Staphylococcus and Micrococcaceae?

Answer 2

1. G+c in clusters, tetrads, and pairs
2. Catalase positive
3. Facultative anaerobes (can grow w/ or w/o O2)
4. Mesophiles (35-37C)
5. Non-fastidious (not fussy; easy to grow in lab)
6. Most ferment glucose
7. Grow in presence of 7.5% NaCL (high level of salt)
8. Non-motile
9. Non-spore forming
10. Transmission is from person to person.

Question 3

Is staphylococcus aureus encountered as normal flora on/in humans?

Answer 3

Yes, on skin, nasopharynx, mucosal surfaces, etc.

Question 4

What virulence factors does Staphylococci have?

Answer 4

1. Polysaccharide capsule that inhibits phagocytosis.
2. Protein A that binds to immune system factors which prevents its removal
3. Alpha toxin which disrupts smooth muscle in blood vessels and is toxic to RBC, WBC, platelets, and hepatocytes.

Question 5

What illnesses can Staphylococcus aureus cause?

Answer 5

1. Systemic deep infections. E.g. bacteremia, meningitis, pneumonia, etc.
2. Skin infections. E.g. boils, cellulitis, necrotizing fasciitis, etc.
3. Toxin-mediated diseases: Toxic Shock Syndrome (TSS), Scalded Skin Syndrome (SSS) and food poisoning (major public health hazard).

Question 6

What is MRSA?

Answer 6

MRSA is Methicillin-resistant Staphylococcus aureus (MRSA). Major threat. People cannot develop immunity to MRSA due to its virulence factors.

MRSA possesses the mecA gene which makes it resistant to Methicilllin as the binding protein is altered.

Question 7

What Staphylococcus spp. is a urinary pathogen?

Answer 7

Staphylococcus saprophyticus. (it is CoNS).

Especially in young sexually active females.

Question 8

What Staphylococcus spp. is a opportunistic pathogen?

Answer 8

Staphylococcus epidermidis (also a Coag Neg Staph, CoNS)

Otherwise it is typical normal skin flora that do not often cause disease unless introduced to a site that is sterile –> hence are Nosocomial, hospital acquired infections when indwelling catheter lines, joints and valves.

Question 9

What makes Staphylococcus epidermidis ready to be an nosocomial (hospital acquired infection)?

Answer 9

S. epidermidis have a exopolysaccharide outer layer that binds strongly to plastic producing a slime or biofilm.

This also prevents the organism’s phagocytosis.

Question 10

What are Staphylococcus aureus’ virulence factors?

Answer 10

1. Enzymes
   - Catalase - destroys cells
   - Fibrinolysins – coagulase or clumping factor
   - Hyaluronidase – breaks down hyaluronic acid which helps healthy tissues stick together therefore allowing invasion
   - Hemolysins – cause cell destruction.
2. Antigens: adhesins (protein A) & capsule → attack & defense
3. Toxins: α-toxin (disrupts smooth muscle in blood vessels), TSST, exfoliative, endotoxin

Question 11

Is Micrococcus spp. a pathogen of concern?

Answer 11

Micrococcus spp. are considered to be harmless microorganisms that inhabit or contaminate the skin, mucosa, and sometimes the oropharynx in healthy people.

Rarely associated with infections, except with immunocompromised patients.