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Questions and Answers
What is the effect of using Sodium Polyanethol Sulfonate (SPS) in blood culture media?
What is the effect of using Sodium Polyanethol Sulfonate (SPS) in blood culture media?
What is the recommended blood volume for children in a blood culture collection?
What is the recommended blood volume for children in a blood culture collection?
Which media is most commonly used for culturing bacteria?
Which media is most commonly used for culturing bacteria?
What cell type is typically found in CSF during bacterial meningitis?
What cell type is typically found in CSF during bacterial meningitis?
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Which of the following is an organism often associated with brain abscesses?
Which of the following is an organism often associated with brain abscesses?
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What is a common finding in viral meningitis CSF analysis?
What is a common finding in viral meningitis CSF analysis?
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What should antigen detection tests do in relation to smears and cultures?
What should antigen detection tests do in relation to smears and cultures?
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Which organism is not typically detected in bacterial culture for meningitis?
Which organism is not typically detected in bacterial culture for meningitis?
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What is the preferred method for collecting blood samples for culture?
What is the preferred method for collecting blood samples for culture?
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Which anticoagulant is recommended during blood collection for culture?
Which anticoagulant is recommended during blood collection for culture?
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What is a major cause of contamination when collecting blood via an indwelling intravascular catheter?
What is a major cause of contamination when collecting blood via an indwelling intravascular catheter?
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What should be done after collecting blood from a syringe for culture?
What should be done after collecting blood from a syringe for culture?
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Which of the following is NOT used as an anticoagulant in blood culture specimens?
Which of the following is NOT used as an anticoagulant in blood culture specimens?
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Why should iodine be allowed to dry for at least 1 minute during site preparation?
Why should iodine be allowed to dry for at least 1 minute during site preparation?
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What is a common cause of significant diseases caused by non-fermenting organisms?
What is a common cause of significant diseases caused by non-fermenting organisms?
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Which organism is considered a non-fermenting Gram-negative rod (GNR)?
Which organism is considered a non-fermenting Gram-negative rod (GNR)?
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What characterizes septicemia?
What characterizes septicemia?
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What is the mortality rate associated with septic shock?
What is the mortality rate associated with septic shock?
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Which type of bacteremia is primarily found in children without a known cause?
Which type of bacteremia is primarily found in children without a known cause?
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Which pattern of bacteremia involves organisms being released into the bloodstream periodically?
Which pattern of bacteremia involves organisms being released into the bloodstream periodically?
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What is a likely source of intravascular bacteremia?
What is a likely source of intravascular bacteremia?
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Which organism is commonly associated with intravascular bacteremia due to its presence as normal skin flora?
Which organism is commonly associated with intravascular bacteremia due to its presence as normal skin flora?
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Which of the following is an example of extravascular bacteremia?
Which of the following is an example of extravascular bacteremia?
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Which condition is typically related to transient bacteremia?
Which condition is typically related to transient bacteremia?
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Study Notes
Bacteremia and Sepsis
- Bacteremia is the presence of bacteria in the bloodstream
- Septicemia is bacteremia with clinical signs and symptoms such as fever, chills, hypothermia, hyperventilation, and septic shock.
- Exotoxins and/or endotoxins from bacteria can trigger a massive immune response.
- Mortality rate for septicemia is >50%
Types of Bacteremia
- Primary bacteremia - no known infected site
- Secondary bacteremia - associated with an infected body site
- Occult bacteremia - no known cause, often in children
- Pseudobacteremia - false bacteremia, contaminated materials in blood culture media
Bacteremia Patterns
- Transient - bacteria in bloodstream for minutes to hours, often after a traumatized body site or mucous membranes. Examples include teeth cleaning or surgery.
- Intermittent - bacteria periodically released into bloodstream, examples include pneumonia, meningitis, and abscesses.
- Continuous - bacteria constantly present in bloodstream, often found in individuals with infected intravascular sites.
Bacteremia Sources
- Intravascular - associated with the vascular system, such as infected heart valves, catheters, and veins. Examples include endocarditis.
- Extravascular - outside the vascular system, such as infections from the urinary tract, respiratory tract, or abscesses.
Intravascular Bacteremia Examples
- Viridans streptococci (normal oral flora)
- Enterococci
- Catheter-associated bacteremia
- Coagulase-negative staphylococci (S. epidermidis)
- S. aureus
- Corynebacterium (normal skin flora)
Extravascular Bacteremia Examples
- N. meningitidis, H. influenzae type B, S. pneumoniae (meningitis)
- Enterics: E. coli, Klebsiella, Salmonella
- Anaerobes: Bacteroides, Clostridium
- NFGNR: Pseudomonas
- Other GNR
Detection of Bacteremia
- High mortality rates, quick detection and recovery of organisms is critical.
- Obtain blood via aseptic venipuncture
- Isolate, identify, and test for susceptibility once growth is detected
Most Common Causes of Nosocomial (hospital-acquired) Bacteremia
- Coagulase-negative staphylococci
- S. aureus
- Enterococcus spp.
- Candida albicans
- Enterics (E. coli, K. pneumoniae, Enterobacter spp., Serratia spp.)
- Nonfermenting GNR (P. aeruginosa, A. baumannii)
Collection Sites and Methods
- Peripheral aseptic venipuncture (preferred over indwelling intravascular catheters unless necessary)
- Collection methods: Needle/syringe (preferred), Butterfly, Tube method (lysis centrifugation)
- Recommended specimens should be processed immediately after collection
Collection Procedure
- Disinfect specimen containers with 70% alcohol or iodine
- Prepare puncture site with alcohol and iodine. Allow to dry
- Collect blood and transfer immediately into blood culture bottles.
- Mix with broth media and anticoagulant.
Specimen Collection and Anticoagulants
- Difficult to recover organisms in clotted specimens
- Sodium polyanethol sulfonate (SPS) is recommended anticoagulant for blood cultures.
- Citrate, heparin, oxalate, and EDTA are not recommended as they can be toxic to some organisms or inhibit recovery.
Sodium Polyanethol Sulfonate (SPS)
- Prevents clotting
- Inactivates complement
- Inhibits phagocytosis
- Neutralizes some antimicrobial agents
- Inhibits N. gonorrhoeae and N. meningitidis
- 0.025% concentration in blood culture media
- SPS blood collection tubes are available, but are not always recommended
Note about blood cultures
- A single venipuncture is considered one blood culture, even if divided into multiple tubes.
- Larger blood volumes correlate with a higher chance of positive results.
- Recommended volumes depend on patient age and condition.
Blood-to-Broth Ratio
- 1:5 to 1:10 ratio is ideal for preventing clot formation and diluting inhibitory factors.
Timing and Number of Cultures
- 2-3 sets (aerobic and anaerobic) of blood cultures are recommended.
- 1 set usually detects 80% of bacteremias, 2 sets 90%, and 3 sets 99%.
- Ideally, collected from separate sites and before any antimicrobial therapy.
Newer Recommendations
- Three blood cultures collected simultaneously, or three venipunctures, one right after the other.
Transport
- Collection should be prioritized as STAT, and transported quickly.
- Maintain at 37°C if delayed transport is necessary
- Do not refrigerate.
Culture Media - Broth and Agar
- Commonly used broth media: BHI, Brucella, Columbia, Thioglycollate, and Trypticase Soy (with potential special formulations)
- Key components include nutrients, SPS, headspace with CO2 and antibiotic removal devices (ARDs) and osmotic stabilizers.
- Lysis centrifugation method agar is used.
- Biphasic culture bottles (agar and broth) are used as well.
Incubation Conditions
- Temperature range of 35-37°C
- Incubation time varies, typically 5-7 days for most organisms.
- Longer incubation may be necessary for certain organisms.
- Agitation or shaking during incubation can increase oxygen supply to enhance organism growth.
Manual Culture Methods
- Conventional broth: Bottles examined daily for turbidity, gas, and discoloration. Blind subcultures may be necessary.
- Biphasic methods: Commonly use Castaneda bottles. Blood added to the bottle and incubated.
- Lysis-centrifugation method: Blood collected and processed using a special tube and centrifugation to isolate the sediment. Incubation and examination of agar plates is carried out daily.
Instrumentation
- BACTEC systems: measure CO2 production by metabolizing organisms. (BACTEC 460, BacT/Alert, Bactec 9000, ESP)
- BACTEC 460: First automated system uses radioactive carbon. Microorganisms metabolize carbon and produce radioactive CO2. Amount of radioactive CO2 in headspace is determined.
- Continuous monitoring systems: specialized bottles, incubators, agitators, detection systems, and computers aid in growth monitoring.
- BacT/Alert: Colorimetric system monitors CO2 production. Gas-permeable sensors change from green to yellow as gas is generated.
- Bactec 9000: Fluorescent sensors detect generated CO2 increase.
- ESP/VersaTREK: Manometric system measuring gas pressure inside bottles.
Positive Blood Cultures
- Critical values: appearance of turbidity, hemolysis, gas production of colonies or turbidity in broth media, or colonies on culture plates.
- Identification and antimicrobial susceptibility testing needs to follow.
Gram-Stained Smears
- First step in workup.
- Determine morphology and Gram stain reaction.
Subculture
- Positive cultures are subcultured to isolate colonies of organisms.
- Media selection depends on Gram stain reaction (aerobic: BAP, CHOC; anaerobic: BAP, CHOC, or other in CO2; MAC, EMB used for identification of GNR; Mixed cultures utilize PEA, or CNA)
- Additional testing needed depending on growth type (anaerobic or aerobic)
Reporting Results
- Notify physician immediately for critical values.
- Document tests and results (eg. Number of positive cultures, Gram stained smear results, other tests).
- Provide preliminary reports (within 48 hours). Final reports follow.
- "No growth after 7 days of incubation" is an important result to report.
Contaminant Determination
- Gram-positive or gram-negative organisms present in multiple cultures
- Growth in repeated cultures
- Growth in blood and a non-sterile body site.
- Examples include bacteria commonly found on the skin.
Special Cultures
- Brucella spp.: prolonged incubation (30 days) required.
- Nutritionally deficient (satelliting) streptococci: subculture/overlay with S. aureus necessary
- Campylobacter: Requires special conditions for growth
Antimicrobial Therapy
- Initial treatment using empiric antimicrobial therapy.
- Switch to narrow-spectrum therapy after identification and susceptibility testing.
Central Nervous System
- The CNS includes the brain, spinal cord, and meninges.
- These structures are considered sterile.
Cerebrospinal Fluid (CSF)
- CSF bathes the brain and spinal cord.
- CSF is clear and colorless.
- CSF is tested by culture, cell count, glucose levels, and protein levels.
- Tests to check possible infection are performed on the CSF.
Meningitis Types
- Purulent (pyogenic) meningitis: caused by bacteria
- Aseptic meningitis: caused by viruses (non-pyogenic).
Meningitis Routes of Infection
- Hematogenous: most common route. Bacteria from a colonized site enter the bloodstream and travel to the meninges.
- Contiguous spread: infections from adjacent sites spread to the meninges
- Trauma: breach of CNS protective barrier, e.g., skull fracture
- Surgery: Microbial contamination.
- Shunt: Portals of entry
Acute Bacterial Meningitis Symptoms
- Flu-like symptoms
- Headache
- Fever
- Nausea
- Vomiting
- Nuchal rigidity (stiff neck)
- Photophobia (sensitivity to light)
- Mental status changes
Causative Agents of Meningitis
- Neonates (through birth canal): E. coli, other gram-negative rods (GNRs), S. agalactiae
- Infants (6–5 years): H. influenzae type b, N. meningitidis, S. pneumoniae
- Older children and adults: N. meningitidis and S. pneumoniae
- Elderly Individuals: similar to older children/adults, but with possible GNRs, L monocytogenes likely also considered
- Immunocompromised: L. monocytogenes and encapsulated bacteria; CN staphylococcus and S aureus in cases of shunt infections.
Specimen Collection - CSF
- Lumbar puncture is used to collect CSF.
- Spinal needle is inserted between the 3rd and 4th lumbar vertebrae.
- CSF specimen should be transported promptly to the lab at room temperature within 15 minutes, and not refrigerated.
- Three to four collection tubes are collected.
- Tube 1 for biochemistry (protein and glucose).
- Tube 2 for microbiology (Gram stain and culture).
- Tube 3 for hematology (cell count).
Microbiology CSF Processing
- STAT (immediately) processing
- If >1 mL of CSF, centrifuge the specimen to obtain sediment for smear and culture.
- Gram stain smears of sediment have 75-90% sensitivity.
- Thick smears may also be used to detect organisms in specimens.
Brain Abscess Culture
- Commonly caused by non-fastidious organisms (NF), such as anaerobic bacteria, staphylococci, viridans streptococci, and other streptococci.
- Aspirate and biopsy the abscess material.
- Transport is in anaerobic conditions. Examine material microscopically.
- Culture material in aerobic and anaerobic conditions.
Encephalitis/Meningoencephalitis causative agents
- Viruses: Most common
- Bacteria: L monocytogenes, Rickettsia, Mycoplasma, and B burgdorferi
- Parasites: Naegleria and Acanthamoeba
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Description
This quiz covers the definitions, types, and patterns of bacteremia and sepsis. It explores the clinical implications, symptoms, and mortality rates associated with these conditions. Test your knowledge on primary, secondary, and other forms of bacteremia.
