Analytical Procedures for Blood Culture

Question 1

What are the most common sources of blood culture contamination?

Answer 1

insufficient disinfection, improper collection, collection through an indwelling catheter

Question 2

What are the three most common Continuous Monitoring Blood Culture systems (CMBC)?

Answer 2

BacTec, BacT, VersaTrek

Question 3

Describe the principle for BacTec.

Answer 3

Positive growth is detected by a change in the concentration of CO2. This change is detected fluorometrically.

Question 4

Describe the principle for BacT.

Answer 4

Positive growth is detected by a change in the concentration of CO2. This change is detected colormetrically.

Question 5

Describe the principle for VersaTrek.

Answer 5

Positive growth is detected by a change in pressure. Changes in the concentration of CO2, H2, and O2 are continuously monitored.

Question 6

The majority of endocarditis infections tend to be this gram reaction:

Answer 6

gram positive

Question 7

What is the most common intravascular infection?

Answer 7

Endocarditis

Question 8

What are the most common organisms that cause endocarditis?

Answer 8

Viridans strep of the oral cavity and Staph aureus

Question 9

Which patients are most at risk for endocarditis?

Answer 9

Ones with endocardial abnormalities or previous valve surgery

Question 10

What is another word for heart vegetation?

Answer 10

Excrescence

Question 11

How do most heart vegetations form?

Answer 11

Fibrin-platelet thrombi on the surface of the endocardium “catch” bacteria as they circulate.

Question 12

What is a septic emboli?

Answer 12

Large vegetations that have broken off from the endocardium and have traveled through the bloodstream. Fungi and gram negative bacilli are likely to do this.

Question 13

Which side of the heart do most endocarditis infections occur?

Answer 13

The left side (high pressure side)

Question 14

Which organisms are likely to infect the right side of the heart and why?

Answer 14

Bacillus species, Candida species, or P. aeruginosa. These organisms are commonly seen in contaminated intravenous injection drug use.

Question 15

What are a few examples of organisms that can cause endocarditis but will not grow in culture? What is the preferred method of detection for these organisms?

Answer 15

C.pneumoniae, Coxiella burnetti, and Bartonella species. Serological or molecular methods.

Question 16

Which organisms cause early stage intravascular hardware infections?

Answer 16

coagulase negative staph, diptheroids, or organisms that cause wound infections (gnb and yeast)

Question 17

Which organisms cause late stage intravascular hardware infections?

Answer 17

Viridans strep of the oral cavity and Staph aureus

Question 18

What are the most serious complications of endocarditis?

Answer 18

Cardiac valve rupture that results in heart failure and metastatic disease caused from septic emboli. Septic emboli can also cause kidney failure and stroke.

Question 19

What are the clinical characteristics of septicemia?

Answer 19

Fever, chills, malaise, tachycardia, hyperventilation, and toxicity.

Question 20

Sepsis is traditionally associated with organisms that have this gram reaction:

Answer 20

gram negative

Question 21

What are the three types of bacteremia?

Answer 21

Transient, intermittent, and continuous

Question 22

What is transient bacteremia?

Answer 22

Bacteremia that occurs when microorganisms are introduced into the bloodstream by minimal trauma to mucosal membranes such as brushing teeth or straining during a bowel movement.

Question 23

What is intermittent bacteremia?

Answer 23

Bacteremia that occurs when microorganisms enter the bloodstream from an extravascular site such as a extravascular abscess, cellulitis, or infection of a body cavity.

Question 24

What is continuous bacteremia?

Answer 24

Bacteremia that occurs when microorganisms enter the bloodstream from an intravascular site such as infected endothelium or hardware.

Question 25

A bloodstream infection with Clostridium septicum is frequently associated with what?

Answer 25

Neoplastic disease, carcinoma of the colon

Question 26

A bloodstream infection with Streptococcus bovis is frequently associated with what?

Answer 26

Endocarditis and carcinoma of the colon

Question 27

Bacteremia that results in sudden, dramatic hemolysis could be due to this organism:

Answer 27

Clostridium perfringens

Question 28

Which organs play the primary role in clearing bacteria from the bloodstream?

Answer 28

Liver and spleen

Question 29

What is the most common organism that causes catheter related infections?

Answer 29

coagulase negative Staphylococcus

Question 30

What is the ideal blood culture contamination rate?

Answer 30

Less than 3%

Question 31

True or false: Volume is the most important metric for accurately identifying bacteremia.

Answer 31

True

Question 32

True or false: The number of blood culture bottles is the most important metric for accurately identifying bacteremia.

Answer 32

False

Question 33

How long does it take to clear bacteria from the bloodstream in a healthy individual?

Answer 33

30-45 minutes

Question 34

What is the optimal blood to broth ratio in blood culture bottles?

Answer 34

1:5 or 1:10

Question 35

What is the optimal blood volume for culture? How should this be collected?

Answer 35

30mL. Two sets of 10mL each, collected 15 minutes apart. Each set should have a different collection site.

Question 36

What is the typical concentration of SPS in blood culture bottles?

Answer 36

0.025-0.05%

Question 37

What is SPS?

Answer 37

Sodium polyanethole sulfonate. It is primarily used as an anticoagulant.

Question 38

Other than anticoagulation, what are the other properties of SPS?

Answer 38

Neutrophil inactivation, antibiotic inactivation (gentamicin, streptomycin, kanamycin, and polymixin), and serum complement precipitation.

Question 39

Which organisms does SPS inhibit?

Answer 39

Peptostreptococcus anaerobius, Neisseria gonorrhoeae, and Neisseria meningitidis.

Question 40

How can the effects of SPS be neutralized?

Answer 40

Add gelatin to the media to a final concentration of 1%.

Question 41

Which additional culture will aid in the diagnosis of an intravascular catheter infection? What is the interpretation for a true infection?

Answer 41

Catheter tip culture. >15 colonies

Question 42

What are quantitative blood cultures used for?

Answer 42

To diagnose an intravascular catheter infection without removing the hardware.

Question 43

How is a quantitative blood culture collected?

Answer 43

Simultaneous collection through the catheter and venipuncture using Wampole Isolator blood culture collection tubes.

Question 44

What is the principle of a quantitative blood culture?

Answer 44

If the catheter is the primary source of infection, there should be a higher concentration of bacteria isolated from the catheter collection instead of the venipuncture. If the catheter is a secondary source of infection, there should be a lower concentration of bacteria isolated from the catheter collection, and a higher concentration isolated from venipuncture.

Question 45

Which organisms cause granulomatous diseases of the bone marrow?

Answer 45

Brucella species, Histoplasma capsulatum, and Mycobacterium species

Question 46

True or false: when collecting a blood culture from a line, a second blood culture set should be collected by venipuncture.

Answer 46

True

Question 47

True or false: a blood culture collected from a line is enough culture evidence to prove a line infection.

Answer 47

False

Question 48

What are a few common aerobic gram positive commensal bacteria that are often considered contaminants?

Answer 48

CNS, Rothia species, Micrococcus, viridans strep, nutrionally variant strep, Bacillus specis, and Corynebacterium species

Question 49

What are a few common aerobic gram negative commensal bacteria that are often considered contaminants?

Answer 49

None

Question 50

What are a few common anaerobic gram positive commensal bacteria that are often considered contaminants?

Answer 50

Lactobacillus species and Cutibacterium species

Question 51

What are a few common anaerobic gram negative commensal bacteria that are often considered contaminants?

Answer 51

None