Blood Cultures

Question 1

Bacteremia

Answer 1

Presence of bacteria in the blood stream - may be transient

Question 2

Occult bacteremia

Answer 2

Usually seen in children under the age of 2 with no signs & symptoms.
Usually strep pneumoniae is isolated

Question 3

Septicemia

Answer 3

Bacteremia plus physical signs & symptoms in the patient

Question 4

Which variable, timing or volume, has the most significant effect on blood cultures?

Answer 4

Volume. Optimal ratio of blood to culture medium is 1:10. Dilution is necessary to eliminate bactericidal effects of the patient’s own serum. 20 mL draw

Question 5

How many blood culture sets and how often should they be drawn to ensure the highest recovery rate?

Answer 5

80% of bacteremias will be discovered in 1st set; over 90% of bacteremias will be discovered in 2nd set. Both sets should be drawn within the 1st 2 hrs of clinical presentation from two separate venipuncture sites

Question 6

What do aerobic blood culture bottles contain?

Answer 6

Usually contains soybean casein digest broth, tryptic or trypticase soy broth, brain-heart infusion, Brucella agar or Columbia broth base

Question 7

What do anaerobic blood culture bottles contain?

Answer 7

Same media as aerobic but with 0.5% cesteine

Question 8

What organisms may be inhibited if the anaerobic bottle contains thioglycolate or thiol containing broth?

Answer 8

Pseudomonas & yeasts

Question 9

What can be done if the patient is already on antimicrobial agents @ the time the blood cultures are drawn?

Answer 9

1) B lactam antimicrobial agents - such as penicillinase
2) ARD bottle - contain resins that absorb the antibiotics
3) SPS - sodium polyethanol sulfonate

Question 10

What antibiotics will SPS inactivate?

Answer 10

Inactivates streptomycin, kanamycin, gentamicin, polymyxin

Question 11

What bacteria will be inhibited by SPS?

Answer 11

Peptostreptococcus anaerobes, N. gonorrhaeae, N. meningitidis, Gardnerella vaginalis

Question 12

Continuous-monitoring for the Bactec series

Answer 12

If an organism is beginning to grow, it will produce carbon dioxide, which will diffuse into the sensor-generating hydrogen irons
Increase in hydrogen ion concentration increases the amount of fluorescence, which is measure - noninvasive

Question 13

Continuous-monitoring for EAP

Answer 13

Detects head-space pressure changes & measures consumption or production of gas

Question 14

Continuous-monitoring for Bacti-Alert

Answer 14

pH indicator - measured photometrically - non invasive into bottle

Question 15

5 most frequently isolated pathogens from blood

Answer 15

E. coli
Enterococcous
Staph aureus
Strep pneumoniae
Pseudomonas

Question 16

Most common contaminants in blood cultures

Answer 16

Coag neg staph
Hemolytic Strep (alpha/gamma)
Corynebacterium
Propionibacterium acnes

Question 17

Common protocol for the proper collection

Answer 17

1) Cleanse skin with 80-85% ethanol
2) Iodine-based compound scrubbed in concentric fashion around venipuncture site & left on for at least one minute
3) After venipuncture, antiseptic should be removed from alcohol pad

Question 18

Most common cause of infectious endocarditis

Answer 18

Strep viridans