Gram Pos Aerobic Cocci

Question 1

What should the plates be incubated at?

Answer 1

35 degrees C

Question 2

Which Staph species is most virulent?

Answer 2

S. aureus

Question 3

Since staph spp. are apart of normal flora, how do the organisms gain access to atypical?

Answer 3

Cuts, abrasions, and trauma

Question 4

Most human disease are ____ infections.

Answer 4

Endogenous- those caused by a persons microbial flora that spread to sites where they can cause disease.

Question 5

What are exogenous infections?

Answer 5

Diseases caused by organisms from outside sources (influenza virus, Neisseria gonorrhoeae)

Question 6

ID for Staph spp.

Answer 6

Non-motile
Non-spore forming
Facultative anaerobes
Gram +, pairs, tetrads, or grape - like clusters

Question 7

What is Staph spp. resistant to?

Answer 7

Bacitracin

Question 8

What can Staph aureus cause?

Answer 8

Ritter disease
Caused by the release of exfoliative toxins
Blisters- culture neg
No scarring
Most neonates are capable of fighting off disease themselves.

Question 9

Describe Staph Toxic Shock Syndrome

Answer 9

Fever, erythematosus rash, hypotension, multiple organ system involvement, and associated with tampon use.
Treatment is antibiotics and fluids.

Question 10

List and describe the type of pyogenic cutaneous infections from Staph aureus.

Answer 10

Folliculitis- infection of hair follicles.
Stye- infection of hair follicle on eye lid.
Furuncles (boils)- extension of folliculitis; raised, painful, red nodules that now also involve skin surrounding hair follicles.
Carbuncles- occur when furnucles come together.

Question 11

What does Staph aureus also cause?

Answer 11

Food poisoning
Bullous impetigo- blisters are culture pos
Bacteremia- catheters
Endocarditis- can be nosocomial

Question 12

ID for Staph aureus

Answer 12

Creamy yellow colonies
Beta- hemolysis
Opaque
Medium to large

Question 13

What are 3 purposes of bacterial enzymes and toxins?

Answer 13

To convert host tissue into nutrients the bacteria can utilize.
To evade host immune defenses.
Gain entry to sites allowing them to establish infections.

Question 14

What are Staph aureus’s extracellular enzymes and toxins?

Answer 14

Coagulase- converts fibrinogen to fibrin.
Staphylokinase- dissolves fibrin/clot enabling infection to spread.
Leukocidins- lysis of neutrophils and macrophages inhibiting phagocytosis.
Hemolysins- alpha, beta, gamma, delta- all lyse RBCs- alpha, gamma, delta may lyse WBCs.
Hyaluronidases- hydrolyze hyaluronic acid in connective tissue- spreads infection.
Lipase- hydrolyzes plasma and skin lipids- enables organism to colonize certain body areas
Exfoliatins- hydrolyze tissue-staph scalded skin syndrome.
Protein A- binding IgG molecules at the Fc region and Fab region of B cell receptors, impairs opsonization and phagocytosis.
Beta lactamase- inactivates penicillin

Question 15

How do beta-lactamases work?

Answer 15

They’re enzymes produced by some bacteria that bind to beta- lactam rings in antibiotics and make them ineffective.

Question 16

Beta-lactam antibiotics include:

Answer 16

Penicillins, cephalosporins, carbapenems, and monobactams.

Question 17

ID for Staph epidermis

Answer 17

Gram + Catalase + Coagulase -
Colonies are opaque gray-white 
Produces biofilm 
Gamma hemolysis 
Small to medium size

Question 18

ID for Staph saprophyticus

Answer 18

Gram + Catalase + Coagulase -
Bright white, creamy colonies, gamma hemolysis
Associated as 2nd most common cause of UTI’s in young females. behind UPEC

Question 19

How did MRSA develop?

Answer 19

Overuse of antibiotics

Question 20

What organism contains a mecA gene which imparts a wide range of antibiotic resistance?

Answer 20

Methicillin resistant Staph aureus (MRSA)

Question 21

Micrococcus spp. are strictly ____

Answer 21

Aerobic

Question 22

ID for Micrococcus spp.

Answer 22

Gram + Catalase + Coagulase - Microdase +
Tetrads
Rarely a disease; contaminant
Small to medium size
Opaque, convex
Gamma hemolysis
Various colors: white, tan, yellow, orange, to pink.

Question 23

What media is selective and differential for Staph spp?

Answer 23

Mannitol salt agar

Question 24

How is Mannitol salt selective?

Answer 24

Increased NaCl concentration

Also contains sugar alcohol Mannitol and pH indicator phenol red.

Question 25

What media is selective and differential for MRSA?

Answer 25

BBL CHROM agar MRSA II

Question 26

What is in BBL CHROM agar MRSA II that makes the media selective/ differential?

Answer 26

Cefoxitin- makes selective. Inhibits growth of gram neg organisms and yeasts.
Chromagen additives- differentiation
MRSA hydrolyzes chromagen- MAUVE colored colonies are produced.
Growth of mauve colonies within 24 hrs- definitive ID. Growth after 48 hrs with mauve colonies- presumptive. Need additional tests.

Question 27

What organism is resistant to novobiocin? Sensitive?

Answer 27

Resistant: Staph saprophyticus
Sensitive: Staph epidermis

Question 28

What does catalase convert?

Answer 28

H2O2 into water and oxygen (bubbles)

Question 29

What does the Microdase (modified oxidase test) differentiate?

Answer 29

Staph spp from Micrococcus spp.

Question 30

How does the Microdase test work?

Answer 30

Detects presence of oxidase enzyme

If pos, turn blue (Micrococcus). If neg, disk will stay original color (Staph spp.)

Question 31

What does the Coagulase slide test for?

Answer 31

Only bound factor. Can yield false negatives.

Anytime slide test is neg, confirm with a tube test. Tube test contains both free and bound factor, so more sensitive.

Question 32

What does Lysostaphin sensitivity differentiate?

Answer 32

Staph spp. from Micrococcus spp
Micrococcus-resistant
Staph spp.- susceptible

Question 33

What antibiotics are used to treat MRSA?

Answer 33

Macrolides like clindamycin or vancomycin

Question 34

Which antibiotics are tested in MRSA susceptibility testing?

Answer 34

Oxacillin and cefoxitin