1. Blood Culture

2. Bacteremia: Types  Transient: Disruption of mucosal surfaces (dental or surgical procedures)  Intermittent: Associated with abscesses  Continuous: Infective endocarditis

3. Bacteremia: Pathogens  S. Aureus  S. Pyogenes  S. Pneumoniae  H. Influenzae  Enterobacteriaceae  Bacteroides  Pseudomonas Aeruginosa  Candida species

4. Occurrence of False Positive Blood Cultures (Trash) True (%) Trash (%) Maybe (%) S. aureus8766 Coag negative staph 12826 Enterococcus701614 Diphtheroids2962 C. perfringens2377 C. albicans9010

5. Blood Cultures: Methods  2 blood cultures for separate venipuncture sites is adequate  3 sets of blood cultures for I.E.  At least 10ml/ venipuncture  BLD CX > 5ml blood: 92% yield  BLD CX < 5 ml blood: 69% yield  Diagnostic yield increased by 3% for every 1 ml of blood drawn

6. Blood Cultures: Interpretation  Organisms isolated > 72 hours are often contaminants  (+) BLD cultures not compatible with a clinical syndrome are usually contaminants  A single BLD CX with coagulase (-) staphylococci is often a contaminant  A single (+) BLD CX with S. Aureus, gm (-) bacillie or candida is always a pathogen and requires therapy.

7. Bacteremia: Contaminants  Coagulase (-) Staphylococci  Corynebacterium species  Bacillus species  If multiple isolated from separate sites are obtained, the organisms could be pathogenic  Viridans Streptococci can be a contaminant

8. Aim of the test  Diagnosis of bacteremia by aerobic and anaerobic cultivation of the blood, with identification and susceptibility test of the isolated organism (s).  Blood culture should be made for cases with suspected septicemia, endocarditis, and bacteremia secondary to localized infections (pneumonia, intraabdominal abscesses, pyelonephritis, epiglottitis, meningitis).

9. Aerobic/Anaerobic Blood Culture Bottles

10. Criteria of specimen rejection  Blood collected in tubes or bottles other than aerobic and anaerobic blood culture bottles.  If the information on the label does not match that of the request form.  Specimens for anaerobic blood culture received in aerobic bottles or vice versa.

11. Pathogens

12. Patient preparing  The major difficulty in interpretation of blood cultures is potential contamination by skin flora.  This difficulty can be markedly reduced by careful attention to the details of skin preparation and antisepsis prior to collection of the specimen.

13. Skin preparation

14. Obtaining Blood Culture  Locate the vein  Prep kit Alcohol 5 sec. Dry 30-60 sec Tincture of Iodine-center to periphery. Dry 45- 60 sec  Remove caps, clean with alcohol  Put on gloves  Without palpating, draw 20 ml and put 10 in anaerobic and 10 in aerobic bottle  Dispose of syringe in sharps container  Label bottles and send to lab

15. Quantity of specimen

16. Method  Blood is injected to both aerobic and anaerobic bottles and incubated for up to 10 days at 37 C.  Discard as negative after the 10 days  During the incubation period, a gram stain and subculture onto appropriate media should be done.

18. Interpretation of Positive Blood Cultures  Virtually any organism, including normal flora, can cause bacteremia  A negative culture result does not necessarily rule out bacteremia;  false-negative results occur when pathogens fail to grow  A positive culture result does not necessarily indicate bacteremia;  false-positive results occur when contaminants grow.

19.  Gram-negative bacilli, anaerobes, and fungi should be considered pathogens until proven otherwise.  The most difficult interpretation problem is to determine whether an organism that is usually considered normal skin flora is a true pathogen.

20. Thank you