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Blood Culture

Blood Culture. Bacteremia: Types. Transient: Disruption of mucosal surfaces (dental or surgical procedures) Intermittent: Associated with abscesses Continuous: Infective endocarditis. Bacteremia: Pathogens. S. Aureus S. Pyogenes S. Pneumoniae H. Influenzae Enterobacteriaceae Bacteroides

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Blood Culture

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  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)

  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.

  17. 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.

  18. 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.

  19. Thank you

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