1. MLAB 2434 –Microbiology Keri Brophy-Martinez
Bacteremia
MLAB 2434 –Microbiology
Keri Brophy-Martinez

2. Definitions Pseudobacteremia False bacteremia
Contamination of a blood culture during or after collection

3. Definitions Bacteremia – presence of bacteria in blood stream
Some conditions have a period of bacteremia as part of the disease process (ex. Meningitis, endocarditis)
Usually occurs due to a disruption of skin or mucosal barriers to bacterial invasion

4. Classifications of Bacteremia
Classified by Site of Origin
Classified by Causative Agent
Classified by Place of Acquisition
Classified by Duration

5. Classification by Site of Origin
Primary Bacteremia
Blood stream or endovascular bacterial invasion with no preceding or simultaneous site of infection with the same microorganism
Secondary Bacteremia
Isolation of a microorganism from blood as well as other site(s)
Fever of Unknown Origin (FUO)
Source unknown

6. Classification by Causative Agent
Gram positive bacteremia
Gram negative bacteremia
Anaerobic bacteremia
Polymicrobial bacteremia

7. Classification by Place of Acquisition
Community-acquired
Health-care acquired/Nosocomial
Defined as occurring 72 hours post admission

8. Classification by Duration
Transient
Comes and goes
Usually occurs after a procedural manipulation (ex. Dental procedures)
Intermittent
Can occur from abscesses at some body site that is “seeding” the blood
Continuous Bacteremia
Organisms from an intravascular source that are consistently present in bloodstream

9. Sepsis & Septicemia Presence of active bacteria
Results from continuous bacteremia
Clinical signs and symptoms of bacterial invasion and toxin production
Apply the SIRS criteria
Systemic response to bacterial infection

10. Bacteremia Complications
Septic shock
Results from body’s reactions to bacterial bi-products
Endotoxins: lipopolysaccharide
Exotoxins
Disrupts many body functions
Hemodynamic changes, decreased tissue perfusion and compromised organ & tissue function
Mortality 40% to 50%

11. Bacteremia/Septicemia Risk Factors
Immunocompromised patients
Due to decrease in circulating neutrophils
Increased use of invasive procedures & indwelling devices
Disrupts normal flora
Age of patient
Young: defect in humoral immunity
Old: Decreased immune competency
Administration of drug therapy
Broad spectrum antibiotics decrease normal flora
Increase in antimicrobial resistance

12. Sources of Bacteremia Pericarditis and Peritonitis Pneumonias
Pressure sores
Prosthetic medical devices
Total hip replacement
Skeletal system
Skin and soft tissue
Urinary Tract Infections

13. Clinical Signs and Symptoms
Abrupt onset of chills, fever, or hypothermia and hypotension
Prostration (exhaustion/weakness) and diaphoresis (perspiration)
Tachypnea (rapid breathing) is an early sign of bacteremia
Delirium, stupor, agitation
Nausea, vomiting

14. Clinical Signs and Symptoms (cont’d)
Laboratory Values in Bacteremia
Thrombocytopenia
Leukocytosis or leukopenia
Acidosis
Abnormal liver functions
Coagulopathy
DIC
Elevations in CRP, haptoglobin, fibrinogen, ESR, procalcitonin

15. Specimen Collection Positive blood cultures Best Practice
Critical value
Physician correlates finding to clinical picture to verify septicemia
Best Practice
Collect specimen immediately PRIOR to rise in temperature
Collect PRIOR to antibiotic therapy

16. Specimen Collection Aseptic collection procedure is critical
Cleansing agents
Tincture of iodine (1-2%)
Leave on skin for 30 seconds
Povidine-iodine (10%)
Leave on skin 1.5 to 2 minutes
Chlorhexidine/ChloraPrep
2% chlorhexidine gluconate + 70% isopropyl alcohol
Cleansing Technique
In concentric fashion, from inside to out
After cleaning, wait minutes
Acceptable Contamination Rate
1-3%

17. Collection sites Preferred Less common Peripheral venous
Arterial sites
Less common
Central venous catheters
Arterial lines

18. Blood Collection Devices
Traditional set
Aerobic bottle
Selects for aerobic & facultative anaerobes
Anaerobic bottle
Selects for obligate anaerobes
ARD bottle (Antibiotic Removal Device)
Used when patient is on antibiotics prior to blood collection
SPS= Sodium polyanetholsulfonate

19. Blood Collection Devices
Anticoagulants
SPS= Sodium polyanetholsulfonate
Function/Purpose
Anticoagulant
Neutralizes human serum
Prevents phagocytosis
Inactivates certain antimicrobial agents
SAS(sodium amylosulfate)
Similar to SPS, but less effective in neutralizing serum

20. Specimen Collection: Blood Volume
Ideal ratio of blood: broth
1:5 to 1:10
Dilution aids in preventing the bactericidal effect of WBCs & complement
Volume Recommendations by Age
Younger than 10 years- 1 mL of blood for every year of life
Over 10 years- 20 mL
Short draw?
Inoculate anaerobic bottle first

21. Specimen Collection: Frequency of Collection
Depends if bacteremia is transient, intermediate or continuous
General guidelines
Usually x2 from different body sites, when patient is spiking a fever
Endocarditis
3 sets from 3 different sites within 1-2 hours of clinical presentation
Fever of Unknown Origin (FUO)
Initially 2 sets; hours later, obtain 2 more

22. Specimen Collection: Frequency of Collection
If a catheter-related bloodstream infection is suspected:
One set drawn peripherally
One set drawn via catheter

23. Blood Culture Methods Conventional Broth Systems
Aerobic broth contains soybean casein digest broth, tryptic or trypticase soy broth, Brucella agar or Columbia broth base
Anaerobic broth is usually the same as aerobic with addition of 0.5% cysteine in an aerobic environment
Must be subcultured and gram stained manually, at 12, 24 and 48 hours
Method not recommended due to risk of needlestick and contamination; not cost effective

24. Blood Culture Methods (cont’d)
Biphasic Broth-Slide System
Agar “paddles” attached to top of bottle; includes CA, MAC, malt extract agars
Incubate at 35 OC for 7 days
Allows for blind subcultures
Closed system

25. Blood Culture Methods (cont’d)
Lysis-Centrifugation Blood Culture Systems (Isolator)
Used in the recovery of Fungus and AFB
The Isolator is a special tube that contains saponin, a chemical that lyses cells and other anticoagulants
Approximately ml of blood is placed in the tube, then centrifuged to concentrate microorganisms; sediment is subcultured to fungal and/or mycobacterial media

26. Blood Culture Methods (cont’d)
Automatic Blood Culture Systems
BacTec 9000 Series
Fluorescent light is used to detect changes in CO2 levels

27. Bactec 9000 Series

28. Automatic Blood Culture Systems (con’t)
ESP( Extra Sensing Power)
Now VersaTREK
Measures consumption/production of gases; such as CO2 H2, N2 and O2 in the headspace of each bottle
Detects a change in pressure

29. Automatic Blood Culture Systems (con’t)
BacT-Alert
Carbon dioxide production results in a pH change
pH change results in color change detected by system as “positive”

30. Blood Culture Workup Incubation times Reporting results
Routine aerobic/anaerobic
5-7 days
Endocarditis
2 weeks
Brucellosis/Fungemia/HACEK
21-28 days
Reporting results
Initial report is sent out at 24 hours
Final report is sent out at 5-7 days for all no growth specimens

31. Blood Culture Workup Positive Cultures
Gram stain the bottle to determine the morphology of the organism present
Call the results of the gram stain to the physician or nurse, including how many sets etc., so that antibiotic therapy can be initiated
Subculture to appropriate media
Identify organism and perform sensitivity testing

32. Blood Cultures: Pathogens
Staphylococcus aureus
Streptococcus pneumoniae
Haemophilus influenza
Pseudomonas species
Neisseria species
Coagulase negative Staphylococcus species (immunocompromised)
Group B Streptococcus (infants)
Alpha hemolytic Streptococcus viridans group
Gram negative rods
Yeasts and molds
Anaerobes

33. Blood Cultures: Contaminants
Coagulase negative Staphylococcus
Propionibacterium acnes
Alpha hemolytic Streptococcus viridans group
Bacillus species
Diphtheroids
Growth of multiple organism

34. Treatment & Prevention
Empirical treatment, initially, with broad spectrum antibiotic
Antisepsis therapy; physiological support, anticoagulation agents, glucocorticoids
Adjunctive measures; draining fluids, removing catheters
Prevention
Vaccines; S. pneumo, influenza, varicella

35. References
Broyles, M. (2013, June). A Closer Look at Sepsis. ADVANCE for Medical Laboratory Professionals, 25(5),
Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical Laboratory Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education.
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.