staph

Question 1

Staphylococci: gram + or -?
catalase + or -?
arrangement?
motile or non-motile?
spore-forming or non-spore-forming?
aerobic or anaerobic?

Answer 1

gram+ cocci that arrange in clusters (look like grape clusters)
catalase +
non-motile
non-spore-forming
facultative anaerobes (because catalase +) (except S aureus anaerobius and S saccharolyticus which are catalase neg and grow in strictly anaerobic conditions)

Question 2

staph appearance when plated?

Answer 2

off-white/cream colored

has beta-hemolysis (so clear zone around colonies)

Question 3

predisposing factors to staph infection?

Answer 3

defect in leukocyte chemotaxis
defect in opsonization by ABs (secondary to hypogammaglobinemia)
defect in intracellular killing via phagocytosis
skin injury
presence of foreign body
using antibiotics that staph is resistant to
secondary infections to viruses (flu doesn’t kill, but secondary staph pneumo infection does)
chronic diseases

Question 4

Common sites of Staph infection?

Answer 4

Usual sites of infection are those in which the organism is part of normal flora
Skin, throat, nose, urethra, vagina, GI tract

Question 5

Staph aureus toxin-mediated infections?

Answer 5

Scalded-skin syndrome
toxic-shock syndrome
food poisoning

Question 6

Disseminated infections of Staph aureus?

Answer 6

pneumonia, bacteremia, endocarditis

osteomyelitis, septic arthritis, septic embolization

Question 7

Staph virulence factors and their functions?

Answer 7

capsule (prevents phagocytosis)
Protein A (binds Fc region IgG, interfering with opsonization)
PVL (causes WBC destruction)
coagulase (binds+activates prothrombin, which converts fibrinogen to fibrin that coats bacteria and prevents opsonization)
Hemolysins, toxins, and enzymes

Question 8

Staph aureus hemolysins and actions?

Answer 8

alpha-lyses RBCs
beta-sphingomyelinase which destroys RBCs (reason for clear zone on blood agar plate)
delta-makes surfactant that forms channels in cell membrane that increase in size over time
gamma-causes cell lysis (not found in all strands)

Question 9

Staph aureus toxins?

Answer 9

Exfoliatins/epidermolytic toxins-scalded skin syndrome (dissolves the mucopolysaccharide matrix of epidermis, causing separation of skin layers )
Enterotoxins- most common cause of food poisoning, causes effects hours after ingestion (fastest form of food poisoning)

Question 10

Staph aureus enzymes?

Answer 10

fibrinolysins-break down clot to spread bacteria
hyaluronidase-spreads bacteria to adjacent tissue
PLC-more and damage and destruction during complement activation

Question 11

what are the 3 biological characteristics that all superantigens possess?

Answer 11

pyrogenicity (produce fever)
superantigenicity
enhance effects of endotoxins

Question 12

Is staph aureus coagulase pos or neg?

Latex slide pos or neg?

Answer 12

coagulase pos!!!!!
coagulase pos staph=staph aureus
latex slide pos

Question 13

staph epidermidis: coagulase neg or pos?

Main virulence factor and what does it mainly affect?

Answer 13

coagulase neg

adheres to indwelling devices via its biofilm

Question 14

Staph saprophyticus: coagulase pos or neg?
How does the lab differentiate it?
What does it cause?

Answer 14

coagulase neg
IDed via its resistance to novobiocin
UTIs/Cystitis

Question 15

Staph lugdunensis: coagulase pos or neg?
what does it cause?
What is unique about it?

Answer 15

coagulase neg
causes the same diseases as staph aureus
Only species that’s PYR and Ornithine pos as well as coagulase neg

Question 16

Who/What is the most important reservoir for MRSA?

How is it most commonly transmitted?

Answer 16

Already colonized or infected patients

Via hands

Question 17

6 settings associated with CA-MRSA?

Answer 17

1. Sports/MPSM (especially football)
2. Prison/Jail
3. Military (especially recruits)
4. Daycare or other institutions
5. Newborn nurseries or other healthcare settings
6. Men having sex with men (MSM)

Question 18

What does the mecA gene convey to MRSA?

Does MRSA start with mecA gene?

Answer 18

mecA leads to altered penicillin binding proteins (PBP 2a), this decreases the affinity of B-lactams for PBP
mecA must be acquired, staph don’t start with it

Question 19

What does MRSA first present as?

what is the most important characteristic?

Answer 19

Starts off like a spider bite, so reddish, swollen and painful.
The most important characteristic is the pain
If there’s pain in skin and soft tissue infection (SSTI’s), need to consider MRSA

Question 20

5 disease syndromes when MRSA should be in differential diagnosis?

Answer 20

Sepsis syndrome
Osteomyelitis
Necrotizing pneumonia
Septic arthritis
Necrotizing fasciitis