Lecture 1.1.2 Diagnosing Bacterial Infections: Blood Cultures

A(n) _____ is a single venipuncture with blood inoculated into blood culture bottles.

Blood culture

_____ is the presence of microorganism(s) in the blood.

Bacteremia

_____ is the presence of microorganism(s) in the blood AND clinical symptoms of infection.

Sepsis

True/False:

Both bacteremia and sepsis are associated with high levels of morbidity and mortality.

True

_____ is the infection of the bloodstream without evidence of an infection site.

Primary infection

_____ is the infection of the bloodstream with the isolation of organisms from blood and another site.

Secondary infection

_____ is the infection of the bloodstream in which bacteria had been translocated.

Transient bacteremia

Which of the following are factors that may indicate the presence of infectious cultures?

A) Hyper or hypothermic conditions

B) Low or high WBC count

C) Known site of infection

D) Fever of unknown origin

E) All of the above

E) All of the above

What site is preferred to used for drawing blood?

Peripheral venipuncture (vein)

True/False:

The skin is highly colonized with bacteria.

True

Which of the following catheters are useful for short-term therapy or emergency situations?

A) Non-tunneled

B) Tunneled

C) PICC

D) Midline

A) Non-tunneled

Which of the following catheters are useful for long-term therapy?

A) Non-tunneled

B) Tunneled

C) PICC

D) Midline

B) Tunneled

Which of the following catheters are passed under the skin to a separate exit point?

A) Non-tunneled

B) Tunneled

C) PICC

D) Midline

B) Tunneled

Which of the following catheters are inserted into a large vein and threaded so the tip rests in the superior vena cava?

A) Non-tunneled

B) Tunneled

C) PICC

D) Midline

C) PICC

Which of the following catheters are more common than the others?

A) Non-tunneled

B) Tunneled

C) PICC

D) Midline

C) PICC

True/False:

Catheters are unlikely to become colonized.

False

* Can become colonized in the entry/exit points and in the lumen

When blood cultures are drawn, they are contained in blood culture bottle "sets," including one _____ bottle and one _____ bottle.

Aerobic

Anaerobic

Which of the following number of blood culture bottles is generally preferred (if acceptable for the patient population)?

A) 1 aerobic bottle, 1 anaerobic bottle

B) 2 aerobic bottles, 2 anaerobic bottles

C) 1 aerobic bottle, 2 anaerobic bottles

D) 2 aerobic bottles, 1 anaerobic bottle

B) 2 aerobic bottles, 2 anaerobic bottles

* A single set of blood culture bottles may not be interpretable

* This will vary based on type of patient (e.g body volume)

Aerobic blood culture bottles contain mostly _____.

Anaerobic blood culture bottles contain increased _____ and _____.

Oxygen

Carbon dioxide

Nitrogen

The best time to collect a blood culture is around the time of a(n) _____.

The two sets should be drawn within _____ from two ______.

Fever

Minutes

Distinct sites

Which of the following is correct about drawing blood cultures?

A) Should be drawn before taking antibiotics

B) Should be drawn after taking antibiotics

A) Should be drawn before taking antibiotics

* Blood cultures drawn while on antibiotics will decrease the yield of desired bacteria

What is the correct volume for each of the 4 bottles of blood cultures?

A) 2 mL

B) 5 mL

C) 10 mL

D) 15 mL

C) 10 mL

* This will vary for pediatric patients

Overfilling a blood culture bottle may result in a(n) _____.

False positive

* > 10 mL per bottle

When drawing blood from children, the volume should be ______ based.

It should be roughly _____% of total blood volume.

Weight

2-4

Which of the following could cause blood culture contamination?

A) Improper use of skin antiseptic

B) Improper culture bottle preparation

C) Colonization of catheter

D) All of the above

D) All of the above

Which of the following common contaminates are typically skin colonizers? Select all that apply.

A) Coagulase-negative staphylococci

B) Bacillus spp

C) Micrococcus

A) Coagulase-negative staphylococci

C) Micrococcus

Which of the following common contaminates are typically environmental colonizers?

A) Coagulase-negative staphylococci

B) Bacillus spp

C) Micrococcus

B) Bacillus spp

List the following steps of a microbiology lab workflow in the correct order.

- Incubation

- Blood culture is collected

- Plating onto solid agar

- Organism identification and susceptibility testing

- Gram staining

- Filmarray (PCR)

- Blood culture is collected

- Incubation

- Gram staining

- Filmarray (PCR)

- Plating onto solid agar

- Organism identification and susceptibility testing

During the _____ process, a Bactec machine is used to promote bacterial growth.

This is done but using distinct _____ controls and by gently _____ the bottles.

Incubation

Temperature

Agitating

True/False:

The time to positivity (TTP) in the microbiology lab is typically 3 days in most organisms.

False

* Varies amongst organism

* This process aids in differentiating "true" organisms from contaminants

_____ refers to stopping/reducing in number or spectrum of antibiotic therapy.

Antibiotic de-escalation

Which of the following would affect time to positivity (TTP)?

A) Intrinsic growth rate of organism

B) Inoculum size

C) Presence of antibiotics

D) Liver failure/neutropenia

E) All of the above

E) All of the above

Most aerobic bacteria growth within ______.

48 hours

* Those that take longer than 48 hours typically are considered a contaminant (with exceptions)

Although bacteria that take longer than 48 hours typically are considered contaminants, _____ and _____ are those that are KNOWN to take longer than 48 hours (and are NOT considered contaminants).

Anaerobes

Yeast

Which of the following media is the most common and grows almost all bacteria?

A) Blood agar

B) Chocolate agar

C) MacConkey

D) Mueller-Hinton

A) Blood agar

* Made from sheep's blood

Which of the following media is the made from lysed red blood cells?

A) Blood agar

B) Chocolate agar

C) MacConkey

D) Mueller-Hinton

B) Chocolate agar

* Gives it the brown color

Which of the following media is the best for growing fastidious organisms?

A) Blood agar

B) Chocolate agar

C) MacConkey

D) Mueller-Hinton

B) Chocolate agar

* Fastidious organisms are more challenging to grow

* Chocolate agar has added nutrients for this reason

Which of the following media contains bile salts?

A) Blood agar

B) Chocolate agar

C) MacConkey

D) Mueller-Hinton

C) MacConkey

* Minimizes the growth of gram-positive bacteria

* Considered "selective media"

If growth was shown on a MacConkey medium, which bacteria would most likely be present?

A) Gram-positive

B) Gram-negative

B) Gram-negative

* MacConkey media contain bile salts which minimize the growth of gram-positive bacteria

* So if growth occurred, you would be confident the bacteria was gram-negativee

Which of the following media is used for determining antimicrobial susceptibility?

A) Blood agar

B) Chocolate agar

C) MacConkey

D) Mueller-Hinton

D) Mueller-Hinton