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Micro Specialty > Analytical Procedures for Blood Culture > Flashcards

Analytical Procedures for Blood Culture Flashcards

1
Q

What are the most common sources of blood culture contamination?

A

insufficient disinfection, improper collection, collection through an indwelling catheter

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2
Q

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

A

BacTec, BacT, VersaTrek

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3
Q

Describe the principle for BacTec.

A

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

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4
Q

Describe the principle for BacT.

A

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

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5
Q

Describe the principle for VersaTrek.

A

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

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6
Q

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

A

gram positive

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7
Q

What is the most common intravascular infection?

A

Endocarditis

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8
Q

What are the most common organisms that cause endocarditis?

A

Viridans strep of the oral cavity and Staph aureus

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9
Q

Which patients are most at risk for endocarditis?

A

Ones with endocardial abnormalities or previous valve surgery

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10
Q

What is another word for heart vegetation?

A

Excrescence

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11
Q

How do most heart vegetations form?

A

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

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12
Q

What is a septic emboli?

A

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.

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13
Q

Which side of the heart do most endocarditis infections occur?

A

The left side (high pressure side)

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14
Q

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

A

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

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15
Q

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?

A

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

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16
Q

Which organisms cause early stage intravascular hardware infections?

A

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

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17
Q

Which organisms cause late stage intravascular hardware infections?

A

Viridans strep of the oral cavity and Staph aureus

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18
Q

What are the most serious complications of endocarditis?

A

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

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19
Q

What are the clinical characteristics of septicemia?

A

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

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20
Q

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

A

gram negative

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21
Q

What are the three types of bacteremia?

A

Transient, intermittent, and continuous

22
Q

What is transient bacteremia?

A

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.

23
Q

What is intermittent bacteremia?

A

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

24
Q

What is continuous bacteremia?

A

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

25
Q

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

A

Neoplastic disease, carcinoma of the colon

26
Q

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

A

Endocarditis and carcinoma of the colon

27
Q

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

A

Clostridium perfringens

28
Q

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

A

Liver and spleen

29
Q

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

A

coagulase negative Staphylococcus

30
Q

What is the ideal blood culture contamination rate?

A

Less than 3%

31
Q

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

A

True

32
Q

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

A

False

33
Q

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

A

30-45 minutes

34
Q

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

A

1:5 or 1:10

35
Q

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

A

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

36
Q

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

A

0.025-0.05%

37
Q

What is SPS?

A

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

38
Q

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

A

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

39
Q

Which organisms does SPS inhibit?

A

Peptostreptococcus anaerobius, Neisseria gonorrhoeae, and Neisseria meningitidis.

40
Q

How can the effects of SPS be neutralized?

A

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

41
Q

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

A

Catheter tip culture. >15 colonies

42
Q

What are quantitative blood cultures used for?

A

To diagnose an intravascular catheter infection without removing the hardware.

43
Q

How is a quantitative blood culture collected?

A

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

44
Q

What is the principle of a quantitative blood culture?

A

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.

45
Q

Which organisms cause granulomatous diseases of the bone marrow?

A

Brucella species, Histoplasma capsulatum, and Mycobacterium species

46
Q

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

A

True

47
Q

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

A

False

48
Q

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

A

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

49
Q

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

A

None

50
Q

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

A

Lactobacillus species and Cutibacterium species

51
Q

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

A

None

Micro Specialty (20 decks)

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