Podcast
Questions and Answers
What is the primary difference between bacteremia and septicemia?
What is the primary difference between bacteremia and septicemia?
Which type of bacteremia is characterized by the bacteria being present constantly in the bloodstream?
Which type of bacteremia is characterized by the bacteria being present constantly in the bloodstream?
What is true regarding primary bacteremia?
What is true regarding primary bacteremia?
Which condition can lead to intermittent bacteremia?
Which condition can lead to intermittent bacteremia?
Signup and view all the answers
What is the typical mortality rate associated with septic shock?
What is the typical mortality rate associated with septic shock?
Signup and view all the answers
Which of the following is an example of extravascular bacteremia?
Which of the following is an example of extravascular bacteremia?
Signup and view all the answers
What characterizes occult bacteremia?
What characterizes occult bacteremia?
Signup and view all the answers
Which bacteria is commonly associated with intravascular bacteremia from catheter use?
Which bacteria is commonly associated with intravascular bacteremia from catheter use?
Signup and view all the answers
What is the preferred method for collecting blood samples for cultures?
What is the preferred method for collecting blood samples for cultures?
Signup and view all the answers
Which anticoagulant is recommended for blood culture sample collection?
Which anticoagulant is recommended for blood culture sample collection?
Signup and view all the answers
What is a crucial step before specimen collection to avoid contamination?
What is a crucial step before specimen collection to avoid contamination?
Signup and view all the answers
What should be done immediately after blood is collected in a syringe for culture?
What should be done immediately after blood is collected in a syringe for culture?
Signup and view all the answers
Which type of bacteria is most commonly associated with nosocomial bacteremia?
Which type of bacteria is most commonly associated with nosocomial bacteremia?
Signup and view all the answers
What is a disadvantage of using indwelling intravascular catheters for blood collection?
What is a disadvantage of using indwelling intravascular catheters for blood collection?
Signup and view all the answers
Which substance can inactivate complement and inhibit phagocytosis in blood culture?
Which substance can inactivate complement and inhibit phagocytosis in blood culture?
Signup and view all the answers
What is the purpose of using a disinfectant on the tops of culture bottles before use?
What is the purpose of using a disinfectant on the tops of culture bottles before use?
Signup and view all the answers
What is the purpose of using Sodium Polyanethol Sulfonate (SPS) in blood culture media?
What is the purpose of using Sodium Polyanethol Sulfonate (SPS) in blood culture media?
Signup and view all the answers
What is the recommended blood volume for children to ensure a higher likelihood of detecting organisms?
What is the recommended blood volume for children to ensure a higher likelihood of detecting organisms?
Signup and view all the answers
Which media is most commonly used for blood cultures?
Which media is most commonly used for blood cultures?
Signup and view all the answers
Which organism is NOT typically associated with bacterial meningitis?
Which organism is NOT typically associated with bacterial meningitis?
Signup and view all the answers
What type of cells typically dominate in the cerebrospinal fluid (CSF) findings of a bacterial meningitis case?
What type of cells typically dominate in the cerebrospinal fluid (CSF) findings of a bacterial meningitis case?
Signup and view all the answers
What is the role of antigen detection tests in diagnosing meningitis?
What is the role of antigen detection tests in diagnosing meningitis?
Signup and view all the answers
Which of the following is a common cause of brain abscesses?
Which of the following is a common cause of brain abscesses?
Signup and view all the answers
Which of the following statements about viral meningitis is incorrect?
Which of the following statements about viral meningitis is incorrect?
Signup and view all the answers
Study Notes
Bacteremia and Sepsis
- Bacteremia is the presence of bacteria in the bloodstream.
- Septicemia is bacteremia with clinical signs/symptoms like fever, chills, hypothermia, hyperventilation, and septic shock.
- Exotoxins and/or endotoxins trigger a massive immune response in septicemia, often resulting in a mortality rate greater than 50%.
Types of Bacteremia
- Primary bacteremia: Bacteremia without a known infection site.
- Secondary bacteremia: Bacteremia associated with an infected body site.
- Occult bacteremia: Bacteremia with no known cause, often found in children.
- Pseudobacteremia: False bacteremia caused by contamination of blood culture media.
Bacteremia Patterns
- Transient: Bacteria present in the bloodstream for minutes to hours, often associated with traumatized body sites (e.g., teeth cleaning, surgery) or early stages of some diseases (e.g., meningitis, osteomyelitis).
- Intermittent: Bacteria are periodically released into the bloodstream (e.g., caused by pneumonia, meningitis, or abscesses).
- Continuous: Bacteria are constantly present in the bloodstream in individuals with infected intravascular sites.
Bacteremia Sources
- Intravascular: Associated with the vascular system, such as infected heart valves, catheters, or veins.
- Extravascular: Outside the vascular system, often originating from lymphatic vessels carrying organisms to the bloodstream (e.g., UTIs, abscesses).
Intravascular Bacteremia Causes
- Viridans streptococci (normal oral flora), Enterococci
- Catheter, VP shunt-associated bacteremia
- Coagulase-negative staphylococci ( S. epidermidis)
- S. aureus
- Corynebacterium (normal skin flora)
Extravascular Bacteremia Causes
- Bacteria from localized infection sites (e.g., meningitis – N. meningitidis, H. influenzae type B, S. pneumoniae).
- Other sites including E. coli, Klebsiella, Salmonella; Bacteroides, Clostridium; Pseudomonas; other Gram-negative rods (GNRs).
Detecting Bacteremia
- Mortality rates are high; prompt detection and recovery of organisms are essential.
- Collect blood via aseptic venipuncture.
- Perform blood cultures.
- Isolate, identify, and test for susceptibilities if positive growth is detected.
Most Common Causes of Nosocomial Bacteremia
- Coagulase-negative staphylococci (S. aureus)
- Enterococcus spp.
- Candida albicans
- Enterics (E. coli, K. pneumoniae, Enterobacter spp., Serratia spp.)
- Nonfermenting GNRs (P. aeruginosa, A. baumannii)
Bacteremia Collection Sites/Methods
- Venipuncture: Peripheral aseptic venipuncture is preferred. Avoid indwelling intravascular catheters due to high risk of contamination.
- Methods: Syringe collection (preferred), transfer to blood culture bottles using the same needle; "butterfly" method; tube method with lysis centrifugation.
- Procedure: Specimen container preparation; Site preparation; Specimen collection; Site care are necessary steps.
Specimen Container Preparation
- Disinfect the tops of culture bottles and tubes with 70% alcohol or iodine.
Site Preparation
- Clean skin with alcohol to remove debris and oil.
- Swab skin with iodine in concentric circles.
- Let iodine dry for at least 1 minute for proper disinfection.
Specimen Collection Procedures
- Collect blood in a syringe.
- Immediately inoculate the blood into blood culture bottles.
- Invert the bottles.
- Mix blood with broth media and anticoagulants.
Specimen Collection Issues
- Difficulty recovering organisms from clotted specimens.
- Sodium polyanethol sulfonate (SPS) is the recommended anticoagulant for bacteremia specimens.
SPS Advantages
- Prevents clotting
- Inactivates complement
- Inhibits phagocytosis
- Neutralizes some antimicrobial agents
- Inhibits some organisms (e.g., N. gonorrhoeae, N. meningitidis)
SPS Disadvantages
- 0.025% concentration in blood culture media.
- Minimizes some antibacterial effects
- SPS blood collection tubes are available, but not recommended for all instances.
Blood Volume
- Larger volume is more likely to yield positive results.
- Recommended volume depends on patient age and condition (infants/children: 1-5 mL, adults: 10 mL minimum).
Blood-to-Broth Ratio
- 1:5 to 1:10 ratio of blood to broth to prevent clot formation and inhibits inhibitory factors.
Timing and Number of Cultures
- Collect 2-3 sets of blood cultures (aerobic and anaerobic) from different sites before antimicrobial therapy.
- This approach increases the likelihood for detecting bacteremia (one set = 80%, two sets ≈ 90%, and three tests ≈ 99%).
- Newer guidelines recommend collecting three blood cultures simultaneously.
Transport
- Transport specimens 'STAT' with high priority.
- If delayed, store at 37 °C (incubator); do not refrigerate (except in special cases).
Culture Media (Broth)
- Includes Brain Heart Infusion (BHI), Brucella, Columbia, Thioglycolate, and Trypticase Soy; special formulations may be present. Key components include SPS, nutrients, CO2, antibiotic removal device (ARD), and osmotic stabilizers.
Culture Media (Agar)
- Lysis-centrifugation method uses agar media.
- Biphasic culture bottles contain both broth and agar.
Incubation Conditions
- Incubate blood cultures at 35-37°C.
- Incubation time varies for different organisms (5-7 days).
- Agitation (shaking) enhances growth by increasing oxygen.
Manual Culture Methods
- Conventional broth: Daily examination for turbidity, gas, or discoloration. Performing blind subcultures.
- Biphasic method: Using castaneda bottles that contain tipped agar; subculturing colonies on to a specified agar. Newer versions include added blood and use of a paddle that bathes the media to promote growth.
Manual Culture - Lysis-Centrifugation Method
- Blood collected in a special isolator tube.
- Blood anticoagulated, lysed, and centrifuged.
- Sediment inoculated onto agar plates.
- Agar plates incubated and examined daily for colonies. Advantage- early detection, disadvantages: contamination
Instrumentation
- BACTEC systems: Measure CO2 production by metabolizing organisms. Semiautomated system (e.g., BACTEC 460).
- Continuous Monitoring Systems: BacT/Alert, BacT/EC 9000, ESP.
BACTEC 460
- First automated system.
- Uses radioactive carbon.
- Microorganisms metabolize carbon and produce radioactive CO2.
- Amount of radioactive CO2 is measured.
Continuous Monitoring Systems
- Special bottles, incubators, agitators, and detection systems monitor the bottles for growth.
- Use computer for analysis.
BacT/Alert
- Colorimetric method that monitors CO2 production.
- Gas-permeable sensors detect CO2 changes.
- Sensor changes from green to yellow.
BacT/EC 9000
- Fluorescent sensor detects CO2.
- Fluorescence increases as CO2 is generated.
ESP/VersaTREK
- Manometric system.
- Bottles attached to pressure transducers measure gas pressure within the bottle.
Positive Blood Cultures
- Critical values are detected via appearance of broth (turbid, hemolysis, gas production). Colonies on subculture plates are observed; documentation and identification follow.
Gram-Stained Smears
- First step of work-up.
- Morphology and Gram stain reaction are identified.
Subculture
- Positive cultures are subcultured for colony isolation.
- Media selection depends on Gram stain reaction.
- Aerobic: BAP, CHOC, or both in CO2.
- MAC, EMB added for GNR.
- Mixed cultures: PEA, CNA.
- Anaerobic: anaBAP (CDC).
- Subculture into CO2 and incubation.
Reporting
- Notify physician immediately for critical values.
- Document results (name, date, time); preliminary reports after 48 hours and final results with "no growth after 7 days of incubation"
Contaminants
- Determine clinical significance.
- Probable contaminant: skin flora, Corynebacterium, Propionibacterium acnes, S. epidermidis, Micrococcus.
- Growth of multiple organisms from a single culture.
- Growth of same organism in repeated cultures and from a sterile body site.
Special Cultures (e.g., Brucella)
- Prolonged incubation (e.g., Brucella – 30 days).
- Nutritional deficient streptococci (satelliting streptococci) will sometimes appear on the plate after incubation together with Staph. aureus
- Look for suspected growth on the plate that grows with no growth on subcultures; use special overlays. Special considerations for campylobacter are necessary.
Antimicrobial Therapy
- Initial empiric treatment.
- Narrow-spectrum antibiotics after identification and susceptibility testing.
Brain Abscesses
- Caused by non-fastidious (NF) organisms such as anaerobic bacteria.
- Staphylococci, and viridans streptococci can also cause it.
- Aspirate and biopsy materials should be transported in anaerobic conditions.
- Examine samples microscopically and culture aerobically and anaerobically.
Encephalitis/Meningoencephalitis
- Viruses are the most common cause.
- Bacteria: Listeria monocytogenes, Rickettsia, Mycoplasma, B. burgdorferi.
- Parasites: Naegleria, Acanthamoeba.
CSF Collection and Preparation
- Lumbar puncture is the standard method for collecting CSF.
- STAT processing within 15 minutes of collection; do not refrigerate because organisms like meningococci and pneumococci will not survive.
- Use 3-4 tubes to collect CSF, with specific tubes dedicated for different tests (Tube #1: protein, glucose; Tube #2: Gram stain, culture; Tube #3: cell count, differential)
Microbiology CSF Processing
- If more than 1 mL of CSF is collected, centrifuge the sample.
- Perform Gram stain to identify bacterial morphology.
- Culture the CSF to identify the bacteria. Thick smears can improve sensitivity for bacterial detection (75-90%).
Special Culture Media for CSF
- BAP, CHOC commonly used for routine cultures.
- MAC, EMB may be required if GNR are suspected.
- Anaerobes require specialized conditions and media (anaBAP) – less frequently isolated. Incubate at 35-37°C with CO2 for anaerobic conditions.
Antigen Detection
- Antigen detection tests are available for group B streptococci, Hib, meningococci, pneumococci, and some others; this is supplemental to Gram stains and cultures.
Other Types of Meningitis
- Spirochetes: T. pallidum, B. burgdorferi.
- Viral: Aseptic meningitis with no bacterial growth.
- Mycobacterial: M. tuberculosis.
- Fungal and Parasitic: Rarely encountered, though possible, especially with compromised immune systems.
CSF Findings (Summary)
- Bacterial: High neutrophil count; use culture, antigen, and Gram stains for confirmation.
- Fungal: High lymphocytes; use culture, stains for identification.
- TB: High lymphocytes; use culture, PCR, and stains for confirmation.
- Syphilitic: Lymphocytes; screen using VDRL.
- Viral: Lymphocytes, no bacteria identified.
- Parasitic: Mixed cell types (lymphocytes, eosinophils); use serology and possibly biopsy for confirmation.
Brain Abscesses
- Caused by fastidious organisms often.
- Aspirate and biopsy materials; culture aerobically and anaerobically.
- Transport in anaerobic conditions.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your knowledge on the differences and characteristics of bacteremia and septicemia. This quiz covers topics such as types of bacteremia, common bacteria involved, and blood culture collection methods. Perfect for students in microbiology or healthcare fields seeking to reinforce their understanding.
