Blood Culture

What sample is needed for Blood Culture?

1. >10 ml of blood from the patient is required; the best time is during fever.
2. This is collected in the culture bottle.

What are the recommendations for the blood culture?

1. Inoculation of Blood <5 ml shows markedly reduced yield.
2. One reference recommends 20 to 30 mL of blood/per culture.
3. Some suspected organisms may need more blood.
4. Take the blood sample immediately after the onset of fever and chills.
5. The best time to take a blood sample is one hour before the fever spike.  This spike time occurs at approximately the same time every day.

6. It is better to get three samples during the fever. These samples may be taken from both arms.
7. Take 2 to 3 cultures per septic episode or per 24-hour period.
8. In continuous bacteremia, such as endocarditis, the timing of the sample is unimportant.
9. In the case of intermittent bacteremia, take a sample at the onset of fever and continue taking samples up to three times in 24 hours.
10. Paired culture,  aerobic and anaerobic samples are taken, ideally from the opposite arms.
11. Clean the site to avoid contamination by 70%  Alcohol. It needs at least 2 minutes to be effective.
    1. Then clean with the 2% iodine.
    2. If the patient is sensitive to iodine, then cleaning with alcohol is enough.
12. For a fever of unknown origin, draw two blood samples.
13. A quantity of less than one ml is insufficient to detect bacterial infection.
14. The culture needs at least 72 hours for the report.
    1. Blood, with or without microorganisms, is collected into bottles for growth in either an aerobic or anaerobic environment.

What are the advantages of more blood samples?

1. More culture samples increase the possibility of a positive blood culture.
2. Positive cultures in 2 or 3 separate samples indicate continuous bacteremia that is typically found in bacterial endocarditis.
3. Positive cultures in 2 or 3 samples indicate that there is no contamination. This is particularly important in prophylactic valve endocarditis, where S. epidermidis is commonly found.

What are the precautions for blood culture?

1. A strict aseptic technique must be observed.
2. Antimicrobial treatment before collecting the blood sample may result in a negative culture report. This may be negative even in bacteremia.
3. Using inappropriate culture media or the container may interfere with aerobic growth.
4. Inadequate time for the culture, temperature, or culture conditions may fail to provide an adequate amount of bacteria for its identification.
5. If there is patient skin contamination for the culture.
6. Don’t draw blood from the I/V catheter unless no veins are found.
7. In infants, blood is taken from an umbilical artery catheter.

What are the indications for blood culture?

1. Blood culture is advised when there is a suspicion of bacteremia or septicemia.
2. Find a bacterial infection that has spread into the blood, such as meningitis, osteomyelitis, pneumonia, a kidney infection, or sepsis.

3. To find the type of bacteria in a culture.
4. Find a fungal infection, such as yeast, in the blood.
5. Check for endocarditis, an infection caused by bacteria that live on the heart’s valves.
   3. Repeated blood cultures are needed in case of endocarditis.
6. Find the best antibiotics to kill the bacteria. This is called sensitivity testing.
7. Find the cause of an unexplained fever or shock.
8. In an unexplained fever (PUO) of several days duration.
   1. In patients with chills.
   2. Infected burn.
   3. Urinary tract infection.
   4. Postoperative wound sepsis.
   5. Indwelling venous or arterial catheter.
9. If bacteria are found in the culture, another test is often performed to determine the most effective antibiotic for killing the bacteria. This is called sensitivity or susceptibility testing.
   1. Sensitivity testing is crucial for treating blood infections effectively. This also helps prevent bacteria from becoming resistant to antibiotics.

What are the factors about Blood culture?

1. Blood culture reports, which often identify microorganisms, typically require at least 24 hours.
   1. 67% of the pathogens are identified in 24 hours.
   2. 90% of the pathogens were identified within 72 hours.
   3. Fungi and mycobacteria may need more time, maybe weeks.
2. Vascular catheter-related infections (bacteremia) account for at least 20% to 40% of all infections in hospitalized patients.
3. After the growth, the organism is tested with various drugs impregnated discs.
   1. Sensitivity will take another 24 hours or more.
4. This test finds the bacteria in the blood (bacteremia).

How will you define Bacteremia?

1. Bacteremia is the presence of bacteria in the blood and various organs. It may be:
   1. Intermittent: These are periodic and often from a localized infection.
   2. Transient: These are short-term and may be seen after teeth brushing.
   3. Persistent: This refers to the continuous presence of bacteria, such as in endocarditis.
2. Except in endocarditis or suppurative thrombophlebitis.

What are the causes of Bacteremia in different procedures?

What are the sources and causative agents of infections?

1. Approximately 50% of cases show growth of gram-negative bacilli, and most of these are E. Coli.
2. Staphylococcus aureus is the second most common organism.
3. The most common site of entry is often associated with previous urinary tract infections.
4. Other portals of entry follow surgery due to the use of instrumentation.
5. Fungal endocarditis is most commonly due to Candida spp, followed by Torulopsis glabrata and Aspergillus spp.
6. The mortality rate in septicemia may be as high as 20% in immunocompromised and debilitated patients.

What are the Clinical signs and symptoms of bacteremia?

1. An episode of bacteremia is followed by:
   1. Chills.
   2. Fever.
2. This is the best time to take the blood sample.
3. S/S are accompanied by high fever and leukocytosis.
4. Septic patients may be afebrile in 10% (4% to 18%) of the cases.
5. These patients exhibit leukocytosis in 60% to 65% (42% to 76%) of cases.
   1. The band form may be increased from 70% to 75% in some cases.
   2. Total WBC count increases in 75% (66% to 92%) of the cases.
6. Some patients may exhibit leukopenia in 10% (4% to 18%) of cases.

How will you perform the blood culture Procedure?

1. Prepare a fresh blood film to rule out parasites, such as malaria, Borrelia, and Trypanosoma.
2. The technique for the collection of blood for culture:
   1. Clean the skin from where the blood is taken.
   2. Can clean the skin with Betadine and then with 70% ethanol.
      1. Let the skin dry.
   3. Clean the top of the culture bottle with Betadine.
   4. This may be followed by 70% alcohol and let it dry.
   5. Take 10 to 15 mL of the blood from different sites.
   6. Discard the needle and attach a new sterile needle to inject the blood into the culture bottle.
      1. Inoculate the anaerobic bottle first, then the aerobic bottle.
      2. Mix gently after the inoculation.

3. Multiple blood samples are taken. Usually, two to three samples are adequate.
4. Take the blood sample when the patient has a high fever or is shivering.
5. If one sample is positive and the other is negative, it will indicate contamination.
6. If both culture media show the same bacterial growth, it indicates bacteremia.
7. If the patient takes antibiotics, it should be reported to the lab.
   1. In this case, take a blood sample in resin, which will inhibit the effect of the antibiotics on bacterial growth.
   2. Take the blood sample before the next dose of antibiotics.
8. Culture from the I/V catheter is always contaminated and should be avoided.
9. If catheter sepsis is suspected, then culture from the IV catheter alone can be performed.
10. Some lab. Prefers multiple sites to collect the blood.
    3. They take blood at various intervals of 0, 30, and 90 minutes.
    4. Multiple sites rule out skin contamination.
    5. The three blood culture samples yield is 99.9%.
    6. A sample of more than 3 does not improve positivity.
11. In adults, take 10 mL of blood per bottle.
    1. Some lab prefers 10 to 15 mL of blood from all sites.
12. Less than a 5 ml blood sample shows a less positive culture yield.
13. Discard the syringe needle and use a new sterile needle to transfer the blood into the blood culture bottle.
14. Culture the blood aerobically and anaerobically.
    1. First, add the blood to the anaerobic media.
15. Gently mix the blood with blood culture media.
16. Subculture these samples for at least 72 hours.
17. After the growth, a sensitivity test determines the sensitive drugs for that growth.
    1. Antibiotic sensitivity tests show zones of inhibition of the growth around the disc impregnated with antibiotics.
18. Resistance is shown by the growth of the organism right up to the disc.

How will you report the Blood culture?

1. Negative culture reports when all cultures, subcultures, and Gram stain smears are negative.
   1. The blood culture report may be reported negative after 5 to 7 days of incubation.
   2. Bacteria need at least 24 hours to grow in the lab.
   3. By then, a preliminary report can be given.
   4. 48 to 72 hours are needed to identify the organism.
   5. Anaerobic organisms take a longer time.
2. The virus can not be detected by blood culture.
3. A definitive diagnosis is made in:
   1. Subacute bacterial endocarditis.
   2. Salmonellosis (Typhoid fever).  The second and third weeks of typhoid fever are the best times for blood culture.
   3. After this period, positivity declines rapidly.
   4. Brucellosis.
      1. Blood culture is positive in 30% to 50% of the cases.
      2. This organism needs CO2, and growth is very slow on ordinary media.
      3. There are special media that assist the growth.
   5. Gonococcal infection (Gonococcemia).
   6. Chronic meningococcemia.
   7. Tularemia.
   8. Form of rat-bite fever.

What is important in blood culture reporting?

1. When the first tube shows growth and the second tube is negative, it is presumed that the first tube may be contaminated.
2. When both tubes show growth, that indicates bacteremia.
3. If the patient is taking antibiotics, then take the blood before the next dose of antibiotics.

What are the possibilities of a positive culture report?

1. Bacteroides.
2. Brucella
3. Enterobacteriaceae.
4. Pseudomonas aeruginosa.
5. H. influenzae.
6. Listeria monocytogenes.
7. Enterococcus.
8. Streptococcal pneumoniae.
9. Candida albicans.
10. Clostridium perfringens.
11. Staphylococcus aureus.
12. Staphylococcus epidermidis.
13. Streptococcus species (Beta-hemolyticus).

When do you need a Positive blood culture for definitive diagnosis?

1. Subacute bacterial endocarditis.
2. Salmonellosis (typhoid fever).
   1. Blood cultures are the best means of diagnosis during the first and second weeks of the infection.
   2. After that, the positivity will decline rapidly.
3. Brucellosis.
4. Chronic meningococcemia.
5. Gonococcal infection (gonococcemia).
6. Tularemia.

What are the causes of false-negative blood cultures?

1. History of recent antibiotic therapy.
2. Insufficient blood is taken for the blood culture.
   1. Most people take a 1:10 ratio of the blood to culture media to be adequate.
3. Use of unsuitable culture media for anaerobes.
4. Slow-growing bacteria may be missed in the first 72 hours.
5. A blood sample was not taken at the appropriate time.

 What percentage will you see a blood culture report in bacteremia (one study)?

What signs and symptoms will you observe in a patient with sepsis?

1. Fever and chills.
2. Less frequent urination.
3. Nausea.
4. There may be rapid breathing and tachycardia.
5. Confusion.
6. There may be a drop in blood pressure.
7. There may be a failure of one or more organs.

Questions and answers: