LAB 1 - Staphylococcus, Micrococcus & Similar Organisms

Question 1

Staphylococcus aureus causes … (3)

Answer 1

wound infections, boils, and impetigo

Question 2

Staphylococcus lugdunensis produces ______; often resembles …

Answer 2

biofilm; S. aureus

Question 3

S. epidermidis produces ______ and is often associated with…

Answer 3

biofilm; instrumentation procedures, prosthetic devices sp. prosthetic heart valves

cause subacute bacterial endocarditis; if seen in blood culture, think of this!

Question 4

Ss. saprophyticus causes

Answer 4

UTI in young women

holy moly white

Question 5

S. intermedius is a recent concern in … it is also considered _______

Answer 5

wound specimen; zoonotic (

Question 6

T or F. S. intermedius is partial coagulase pos.

Answer 6

T!

Question 7

Micrococcus

Answer 7

• closely resemble CND
• found in environment and as indigenous skin flora

Question 8

sticky staph

Answer 8

Rothia mucilaginosa

Question 9

Rothia mucilaginosa is normal flora of the …. and it is an _______ GPC that tends to form clusters and ______.

Answer 9

oral cavity; encapsulated; tetrads

Question 10

T or F. R. mucilaginosa is rarely an opportunistic pathogen

Answer 10

T!

Question 11

T or F. DNAse is positive for micrococcus

Answer 11

F! it is neg; unlike Staph which is pos

Question 12

T or F. Staph is ox +

Answer 12

F! ox - but micrococcus is ox +

Question 13

Tests that differentiate micrococcus from staphylococcus (4)

Answer 13

Ox (Staph ox-; Micrococcus ox +)
DNAse (Staph +; Mic -)
Bacitracin or TA (Staph R; Mic S >10mm)
OF test (Staph produce acid from glucose ana; Mic are oxidative glucose utilizes)

Question 14

Why could GPC stain as GN?

Answer 14

• overdecol
• antibiotics given; damage cell wall
• old cultures = cell walls degraded
  NEVER stain off plates with antibiotics

Question 15

S. aureus is carried in the _____ of 20-40% of the general population

Answer 15

nose

Question 16

T or F Mic are slower growing than Staph

Answer 16

T! also non-hem and larger cocci

Question 17

Catalase is read within

Answer 17

ten seconds; to avoid false interpretations such as in Enterobacteriaceae

Question 18

RBCs will produce a weakly positive catalase result.. why?

Answer 18

pseudoperoxidase; so sample from tops of colonies

Question 19

catalase is a _______ similar in structure to hemoglobin present in most _______-containing aerobic and facultative anaerobic bacteria

Answer 19

hemoprotein; cytochrome-continuing

Question 20

T or F. Coagulase should be performed off a nonselective agar

Answer 20

T

Question 21

Slide coagulase tests for…

Answer 21

bound coagulase or clumping factor; present on the surface of the cell wall of most strains of S. aureus and acts directly upon fibrinogen in plasma causing rapid clumping or agglutination of the cells

read within 10 secs
if pos = presumptive S. aureus bc could be slide neg but tube pos

Question 22

tube coag test

Answer 22

• free extracellular coagulase
• reacts with coagulase-reacting factor = produce thrombin-like complex that converts fibrinogen to fibrin causing clot formation in plasma

NOTE = FP or FN can occur with non-sterile plasma

Question 23

DNase media

Answer 23

• contains DNA
• either methyl green (colourless around colonies if pos) or toluidine blue O as indicator (pink for pos)

Question 24

This bacteria ferments mannitol

Answer 24

S. aureus
- mannitol salt agar test = selective/differential primary culture medium
- inhibits mixed flora/most bacteria except Staphylococcus sp.
- acid produced lowers pH; phenol red turns yellow
- other Staph and Mc do not ferment mannitol = reddish colonies

Question 25

SEA

Answer 25

Staphylococcal enterotoxin A
- intoxication; performed; not detected in stool bc toxins are absorbed from the gut