Blood Cultures

List and briefly explain the three categories of bacteremia.

1. Transient: short-lived within the blood 2. Intermittent: bacteria are released into the blood in "showers" 3. Continuous: bacteria are constantly in the blood (always present)

What is the information that should be included in a report of a positive blood culture to a physician?

1. gram stain 2. presumptive testing results (catalase,coagulase...) 3. ID/sensitivity (final report) 4. date/time of notification of (+) BC, and to whom 5. which bottle(s) were positive--aerobic or anaerobic

Why are at least two different sites of blood collection recommended when drawing multiple blood cultures on adult patients?

1. number of bacteria may be low when drawing a set--remember three categories of bacteria. A couple of different drawing sites may increase chances of catching the pathogen 2. At least two BCs are drawn, just in case contamination occurs when drawing a set.

Define the term biphasic media.

2 types of media consistency in one bottle, example: broth and solid agar

Define sepsis/septicemia.

A systematic response to a bacterial infection of the bloodstream

How many blood cultures should be collected from an adult patient? Pediatric patient?

Adults: 2-3 sets from different sights (meaning at least two different veins) Pediatrics: 1 bottle (vent it!)

How much blood should be collected from an adult patient when collecting blood cultures? How much from a pediatric patient?

Adults: 5-10 ml/bottle Pediatrics: (depends on age) 1-5 ml/bottle neonates: 1-2 ml/bottle, 1 month-2 years: 2-3 ml/bottle, children: 3-5 ml/bottle

Define terminal blood culture. What is the purpose of a terminal subculture? (manual method)

After a week of incubation of a BC, a final s/c and gram stain must be performed to ensure the culture is negative before discarding the specimen.

Why is it recommended that blood culture specimens be drawn before administration of antibiotics is started?

Antibiotics can affect the ability of the microbiology lab to ID/sensi the pathogen because the antibiotic affects the pathogen

How often are blood culture bottles examined for growth? (manual method)

BCs are examined everyday--if at anytime any bottle looks suspicious for possible growth, the BC is s/c and gram stained. Any positive BCs must be dealt with ASAP--reported to physician!

What are the most common anaerobic microorganisms found in positive blood cultures?

Bacteroides spp., Peptostreptococcus sp, Clostridium spp.

Why is the aerobic bottle of a blood culture set "vented" after collection? What is "venting"?

Because aerobes need O2 to grow. Venting is the addition of O2 into the blood culture bottle

Why is less blood collected on pediatric patients?

Because pediatric patients don't have much blood volume

Why should blood culture specimens never be drawn above an IV site?

Because the IV fluid will dilute the bacteria/pathogen in the blood

Define blind subculture. What is the purpose of a blind subculture? (manual method)

Even with no growth noted, a s/c and gm stain is performed on a BC. Aerobic blind s/c after 24 hours incubation, anaerobic s/c after 48 hours incubation. The purpose of a blind s/c is to be sure there is no growth happening in a BC at certain times in the BC protocol. This type of s/c can detect pathogens before the naked eye can see them.

How can/do bloodstream infections occur?

Existing illness or compromised immune system allows spread to bloodstream through the capillaries

What is the procedure to follow if a blood culture appears positive? (processing...)

Gram stain--anything positive is reported to physician immediately S/C--after 24 hours incubation, any growth is ID'd/sensi'd--report to physician ASAP

What are the primary clinical signs/symptoms of septicemia?

Hyperventilation, fever, chills

Why should blood culture specimens never be drawn from catheter sites?

It is difficult to properly cleanse the catheter sight and so there is an increased chance for contamination of the blood culture

Before dispensing the blood collected for a blood culture into the blood culture collection set, do the blood culture collection bottles need any kind of preparation?

Manual method: clean the tops of the bottles with iodine Automated method: clean the tops with alcohol

Do all microorganism that gain entry into the bloodstream cause infection? Why or why not?

No--most of the time, in healthy individuals, the immune system is capable of clearing any organisms gaining entrance into the blood without there being any kind of infection

List the normal flora of the bloodstream.

None--the blood is a sterile sight

Usually, how many blood cultures are collected on pediatric patients? How are they processed?

One bottle, vented, incubated at 35-37C, checked daily for one week looking for growth

What and why is SPS added to blood culture bottles?

SPS = sodium polyanetholsulfate, It is an anticoagulant (does not allow blood to clot), an inhibitor of phagocytosis (dos not allow WBCs to phagocytize pathogen), an inhibitor of complement (does not allow complement to be activated to destroy pathogen) and an inhibitor of some antibiotics (does not allow antibiotic to kill pathogen)

What are the clinical signs/symptoms of a complicated, serious septicemia?

Septic shock, bleeding, skin lesions, etc.

What are the most common aerobic microorganisms found in positive blood cultures?

Staph aureus, E. coli, Klebsiella pneumoniae, Pseudomonas spp., Strep pneumoniae, Yeast, CNS

What types of microorganisms contaminate blood cultures? Why does this happen?

Staph epi & other CNS, Strep spp., gram positive bacilli (rods) This happens because of contamination from the skin when drawing the specimen

Define bacteremia.

The presence of viable bacteria in the bloodstream

Define fungemia.

The presence of viable fungi in the bloodstream

When should blood cultures for intermittent bacteremias preferably be drawn? Why?

These BCs should be drawn when the patient spikes a temperature. The rise (spike) in temperature is when the bacteria are being released into the blood (showers)

What type of culture media is commonly used for the cultivation of anaerobic microorganisms in the blood stream?

Thioglycollate Broth (Thio) and BHI

What is the purpose of performing a gram stain on positive blood cultures?

This is a quick and easy test to perform that gives a physician a lot of information to start treatment. It could also serve to determine what media should be set up to be able to grow the organism seen in the gm stain--gm (+) and/or gm (-)...

What are antibiotic-removing resins, and why might they be added to blood culture bottles?

This substance draws the antibiotic out of the patient's blood sample if antibiotic treatment has been started prior to the drawing of the blood culture(s)

What is the purpose of drawing blood cultures?

To find pathogens in the blood--then ID/sensi the pathogen

What type of culture media is commonly used for the cultivation of aerobic microorganisms in the blood stream?

Trypticase Soy Broth (TSB) and Brain Heart Infusion agar (BHI)

What are the visible signs of a positive blood culture?

Turbidity, pellicles (hanging growth within media), gas formation, clotting of blood, hemolysis, "puffballs" within media

How do you properly cleanse the venipuncture site for the collection of blood cultures?

Two step cleaning technique includes an alcohol cleaning and an iodine cleansing.

How long are negative blood culture bottles kept in the incubator? Why? (manual method)

Usually 7 days--depends on the laboratory! This is done this way b/c some organisms are very slow to grow

What do you do if a patient is allergic to iodine, so it cannot be used in the cleansing process?

double alcohol cleansing of the patient's arm.