Blood Culture
GROUP MEMBERS:
Aimen Niaz
Rafia Hafeez
Adeena Shafique
Zujaja tul Misbah
Sammia Rehman
Syeda Fatma H. Bukhari
PRESENTED BY:
Adeena Shaique
Sammia Rehman
Syeda Fatma H. Bukhari
WHAT IS BLOOD CULTURE
A blood culture is the laboratory test in which blood
is injected into bottles with media to determine the
presence of microorganism invaded in blood of
patient
PURPOSE OF BLOOD CULTURE
DIAGNOSIS
PROGNOSIS
THERAPY
BACTERAEMIA VS. SEPTICAEMIA


•
•
•
•
The presence of bacteria in the blood is called Bacteraemia
Bacteraemia occurs in
Typhoid fever
Brucellosis
Leptospirosis
Endocarditis.
Severe and life-threatening form of bacteraemia is called
Septicaemia
Septic shock is due to
Gram negative bacilli
PATHOGENS ISOLATED FROM BLOOD
CULTURES

•
•
•
•
•
BACTERIA
E. coli
S. epidermidis
Neisseria meningitidis
Salmonella Typhi
S. aureus
 FUNGI
• Candida albicans
• yeasts
• Histoplasma
capsulatum
NOTE:
Blood does not have a normal microbial flora.
Day 1
Collect blood and inoculate culture media
Collection of blood:
• Blood should be collected before antimicrobial
treatment has started
• Collect the blood as the temperature of patient
begins to rise
• At least two specimens (collected at different times)
should be cultured.
• About 20 ml of blood is taken from adults.
• Blood from neonates should be collected from a peripheral
vein not from the umbilical vein.
• 1–2 ml of blood is enough to detect the presence of bacteria in
children’s blood.
Choice of culture media
• Diphasic blood culture medium
• Columbia agar and broth
• Commercially produced culture media
NOTE: Choice of media depends on the bacterial disease that is
suspected. Some bacteria grow well in a particular medium, others do
not.
Aseptic blood collection and
dispensing
technique
• Wash hands.
• Disinfect the venepuncture site with 70% ethanol and
2% tincture of iodine.
• Decontaminate blood culture bottle tops.
• Using a sterile syringe, withdraw 20ml blood.
• Dispense 10 ml into the culture medium.
• Incubate the inoculated media as soon as possible.
 Incubate upto 4 weeks when brucellosis is suspected
 Incubate upto 14 days for anaerobic infections
Aseptic Technique
Examining the blood culture:
1- CENTRIFUGE:
a sample of EDTA anticoagulated venous blood or heparinized capillary
blood and make smears of the buffy coat layers.
2- STAIN:
• _ Gram smear: for Gram positive and Gram negative bacteria
detection
• _ Ziehl-Neelsen smear: To detect AFB (acid fast bacteria)
• _ Giemsa or rapid Field’s smear: To detect borreliae, or parasites
such as trypanosomes, malaria parasites, and microfilariae.
3- DRY the smears, fix with absolute methanol for 2 minutes and stain
by the appropriate staining technique.
Day 2 and Onwards
3- REPORT
• Diphasic culture (Columbia agar and broth)
Check for microbial growth, indicated by colonies growing on the agar
slope, usually beginning at the agar-broth interface.
• Colonial appearances
Colonies of staphylococci, S. Typhi, brucellae, and most coliforms can usually
be seen easily, whereas colonies of S. pneumoniae, Neisseria species, S.
pyogenes, and Y. pestis are less easily seen.
• Pseudomonas and Proteus species produce a film of growth on the agar.
• When growth is present:
– Subculture on blood agar, chocolate agar, and MacConkey agar.
– Incubate the blood agar and MacConkey agar plates aerobically and the
chocolate agar plate in a carbon dioxide atmosphere (candle jar).
– Examine a Gram stained smear of the colonies.
• Depending on the bacteria seen, test the colonies further (e.g. for
coagulase, catalase, oxidase, urease, and motility).
Large Gram
positiverods
(C. perfringens)
motile, urease and
oxidase negative
Gram negative rods
are isolated
• Subculture on lactose egg
yolk milk agar and
incubate anaerobically
• Subculture the colonies
on Kligler iron agar
catalase
• Suspect Brucella species and
positive,Gram
send for identification.
negative coccobacilli • Mark it as ‘High Risk’.
are isolated
• Examine toluidine blue smear (diphasic
culture)
• Examine thioglycollate culture
• Subculture and examine microscopically
• Incubate subculture anaerobically
NOTE: When there is no growth, wash slope of diphasic
culture. Reincubate cultures and subculture.
Contamination of Blood Culture
Collection of
blood
During
subculturing
Frequent contaminants include:
•Commensal staphylococci, micrococci, and
diphtheroids
•Contaminants from the environment
such as species of Bacillus or Acinetobacter.
Other possibilities
• Occasionally in immunocompromised
patients, organisms usually considered
‘contaminants’ may be pathogenic, especially
fungi.
• Contamination is indicated when an organism
is recovered from only one bottle when it
should have grown in both thioglycollate
broth and the diphasic culture medium or
when a mixed microbial flora is isolated.
Another use…
• Severe and often fatal reactions can be caused
by the transfusion of contaminated blood.
• The bacteriological investigation of a
transfusion reaction is as follows:
Visible signs
• Appearing unusually dark in colour
• Containing small clots
• The plasma appearing red, or unusually turbid
(examine after centrifuging a sample of the blood).
Varied
subculturing
• At room temperature
• At 4°C
Tests
• Motility Test
• Gram stained smear of the plasma