Bacteremia and Meningitis Quiz

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Questions and Answers

What is the definition of bacteremia?

Bacteria present in urine

Bacterial infection in the lungs

Bacteria in the bloodstream (correct)

Bacteria associated with fever

Which type of bacteremia occurs with no other known infected site?

Occult bacteremia

Secondary bacteremia

Primary bacteremia (correct)

Pseudobacteremia

What characterizes septicemia?

Bacteremia with clinical signs and symptoms (correct)

Signs of an abscess only

Presence of bacteria without symptoms

A viral infection causing fever

What is the most common mortality rate associated with septic shock?

More than 50% Signup and view all the answers

What does pseudobacteremia represent?

False bacteremia due to contaminated blood culture Signup and view all the answers

Which of the following describes intermittent bacteremia?

Bacteria released periodically into the bloodstream Signup and view all the answers

Which bacteremia pattern involves organisms traumatized in the bloodstream from mucous membranes or skin?

Transient bacteremia Signup and view all the answers

What is a source of intravascular bacteremia?

Infected heart valves Signup and view all the answers

What is the recommended blood culture volume for adults?

1 mL Signup and view all the answers

Which culture media is most commonly used for blood cultures?

BAP and CHOC Signup and view all the answers

What type of white blood cells are typically found in bacterial meningitis?

Neutrophils Signup and view all the answers

What is the main purpose of antigen detection tests in diagnosing meningitis?

To supplement cultures and smears Signup and view all the answers

Which organism is likely to be responsible for a brain abscess?

Anaerobic bacteria Signup and view all the answers

In which type of meningitis is Mycobacterium tuberculosis often identified?

Tuberculous meningitis Signup and view all the answers

What is the sensitivity range for Gram stain smears in detecting bacterial organisms?

75-90% Signup and view all the answers

What is the preferred method for collecting blood for culture?

Needle & syringe Signup and view all the answers

What type of white blood cells are typically present in viral meningitis?

Lymphocytes Signup and view all the answers

Which antimicrobial agent is recommended for preventing clotting during blood culture collection?

Sodium polyanethol sulfonate (SPS) Signup and view all the answers

What organism is considered a common cause of nosocomial bacteremia?

Coagulase negative staphylococci Signup and view all the answers

What is a key step in the site preparation before blood collection?

Swab the skin with iodine from inside out Signup and view all the answers

What type of bacteria falls under nonfermenting Gram-negative rods (GNR)?

Pseudomonas aeruginosa Signup and view all the answers

Which of the following is NOT an inappropriate anticoagulant for blood culture specimens?

Sodium polyanethol sulfonate (SPS) Signup and view all the answers

Which step should be taken immediately after blood is collected into a syringe?

Inoculate into blood culture bottles without delay Signup and view all the answers

What should be done to the specimen container tops before collecting blood?

Disinfect with 70% alcohol or iodine 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 and symptoms like fever, chills, hypothermia, hyperventilation, and septic shock.
Exotoxins and/or endotoxins trigger a massive immune response in Septicemia.
Septicemia has a mortality rate greater than 50%.

Types of Bacteremia

Primary bacteremia: Bacteremia with no known infected site.
Secondary bacteremia: Bacteremia associated with an infected body site.
Occult bacteremia: Bacteremia with no known cause, often in children.
Pseudobacteremia: False bacteremia, where contaminants in blood culture media cause a false positive result.

Bacteremia Patterns

Transient: Bacteria are present in the bloodstream for minutes to hours, often due to a traumatized body site (e.g., teeth cleaning, surgery). This can also be an early stage of some diseases (meningitis, osteomyelitis, etc).
Intermittent: Bacteria are periodically released into the bloodstream (e.g., pneumonia, meningitis, abscess).
Continuous: Bacteria are constantly present in the bloodstream due to an infected intravascular site.

Bacteremia Sources

Intravascular: Associated with the vascular system, such as infected heart valves, catheters, or veins.
Extravascular: Occurring outside the vascular system. Lymphatic vessels often carry organisms to the bloodstream from UTIs, RTIs, or abscesses.

Intravascular Causes

Infections of the endocardium (e.g., viridans streptococci, Enterococci, coagulase-negative staph, and S. aureus).
Catheters and other vascular devices often are a source.

Extravascular Causes

Infections from other localized sites (e.g., Meningitis, enterics like E. coli, Klebsiella, Salmonella, anaerobic bacteria like Bacteroides, Clostridium, skin pathogens, or Pseudomonas).

Detection of Bacteremia

Mortality rates are high. Prompt detection and recovery of the organism are crucial.
Obtain blood via aseptic venipuncture.
Isolate, identify, and test for susceptibilities once growth is detected in blood cultures.

Most Common Causes of Nosocomial Bacteremia

Coagulase-negative staphylococci (S. aureus).
Enterococci spp.
Candida albicans.
Enterics such as E. coli, K. pneumoniae, and Enterobacter spp., Serratia spp.
Non-fermenting Gram-negative rods (GNRs) such as P. aeruginosa and A. baumannii.

Collection Sites and Methods

Venipuncture (preferred): Peripheral aseptic venipuncture is preferred.
Intravascular catheters: Use only if venipuncture is not possible, as intravascular catheters can increase the risk of contamination.
Syringe collection: Preferred method-- transfer to blood culture bottles using same needle.
Butterfly: An alternative method
Tube method (lysis centrifugation): An additional technique.

Collection Procedure

Specimen container preparation
Site preparation
Specimen collection
Site care (removing iodine with alcohol)

Specimen Container Preparation

Disinfect culture bottles and tubes with 70% alcohol or iodine.

Site Preparation

Clean the skin with alcohol to eliminate debris and oil.
Swab the skin with iodine solution in concentric circles.
Allow iodine to dry completely (at least 1 minute) for proper disinfection.

Specimen Collection and Handling

Blood is collected in a syringe, and transferred to blood culture bottles.
Invert bottles to mix broth media and anticoagulant.
Iodine can cause skin irritation. Remove with alcohol.

Anticoagulants

Sodium polyanethol sulfonate (SPS) is the recommended anticoagulant for blood cultures.
SPS prevents clotting and inhibits phagocytosis.
SPS inactivates complement, neutralizes some antimicrobial agents, and inhibits microorganisms such as N. gonorrhoea and N. meningitides.
SPS' 0.025% concentration in blood culture media minimizes its antibacterial effects.
SPS tubes are available but are not commonly used.
Citrate, heparin, oxalate, and EDTA are inappropriate anticoagulants. They are toxic to some organisms.

Blood Volume for Culture

Larger volume is more likely to produce a positive culture result.
The recommended volume varies by patient age.

Blood-to-Broth Ratio

The ratio of blood to broth should be from 1:5–1:10.
This helps to prevent clot formation and dilutes inhibitory factors.

Timing and Number of Cultures Performed

Collect 2 to 3 sets of blood cultures.
1 set detects 80% of bacteremias, while 2 sets identify 90%, and 3 sets can identify 99%.
Samples are taken from separate sites; collections should occur before antimicrobial therapy.

Newer Recommendations for Blood Culture Collection

Collect 3 blood cultures simultaneously or in rapid succession-- 3 venipunctures one directly after another.

Transport

Collect blood for cultures as STAT or as soon as possible, and prioritize transport
If delayed, transport at room temperature (RT) using a 37°C incubator.
Do not refrigerate samples.

Culture Media - Broth

Common broth components include brain heart infusion (BHI), Brucella, Columbia, thioglycollate, and trypticase soy (with variations).
Key components include SPS, nutrients, CO2 headspace, and antibiotic removal devices (ARDs).
These broths also contain osmotic stabilizers (hypertonic).

Culture Media - Agar

Lysis centrifugation, a method, uses agar media.
Biphasic culture bottles combine agar and broth.

Incubation Conditions

Optimal temperature range for incubation is 35-37°C.
Incubation times vary according to the microorganism and range from 5 to 7 days.

Manual Culture Methods

Conventional broth: Bottles are examined daily for turbidity, gas, or discoloration as indicators of growth.
Blind subcultures: Subcultures are performed to isolate colonies. Alternatively, Biphasic methods: Castaneda bottles with agar are used. Newer versions add blood.
Paddle method: A paddle device attached to a bottle containing specialized media (like CHOC or MAC) that bathes the media. Examination is done daily to test for growth.

Manual Culture - Lysis Centrifugation Method

Blood is collected in a special isolator tube, anticoagulated, and lysed.
Centrifugation is used to isolate the sediment.
The sediment is inoculated onto specialized agar plates.
The agar plates are then incubated and examined daily for the appearance of isolated colonies.
While this method leads to early colony identification, contamination can be a risk.

Instrumentation

BACTEC systems: Measure CO2 production from metabolizing organisms.
Semiautomated systems (e.g., BACTEC 460): Automated or continuous systems to measure growth.

BACTEC 460 System

First automated system.
Uses radioactive carbon. Microorganisms use carbon and produce radioactive CO2. The amount of CO2 produced is measured.

Continuous Monitoring Systems

BacT/Alert, BacT/Alert 9000 systems, and ESP systems monitor the continuous (or real-time) growth of microorganisms.
Unique bottles, incubators, agitators, and detection systems are used to monitor bottles for growth.

BacT/Alert System

A colorimetric system that monitors CO2 production.
Bottles with gas-permeable sensors change from green to yellow as CO2 is generated.

BACTEC 9000

A fluorescent system using a fluorescent sensor. As CO2 is generated, the fluorescence increases.

ESP/VersaTREK System

A system that measures gas pressure inside culture bottles using a manometric system and a pressure transduder.

Positive Blood Cultures

Critical values like turbidity, hemolysis, gas, and colonies on subculture plates indicate growth and require follow up testing. Instrumentation and other testing protocols will be employed.

Gram Stained Smears

A initial step in testing samples suspected to contain pathogens. Morphology and Gram stain reaction aid in pathogen prediction.

Subculture Methods for Colonies

Positive cultures are subcultured onto agar to isolate colonies.
Media selection is based on Gram stain reaction.
In aerobic conditions, BAP (blood agar plate) CHOC (chocolate agar plate) are common choices. When GNR are suspected, MAC and EMB are used.
In anaerobic conditions, certain plates such as anaBAP may be used.
Subcultures in CO2 are incubated and used to re-incubate (to obtain a definitive identification).

Reporting Results

Report critical values immediately.
Notify the physician immediately about the number of positive cultures, Gram-stained smear results, and any other requested procedures
Document the report with the name, date, and time information to aid in tracking the progress.
Preliminary reports are submitted after 48 hours; conclusive results are reported after further analysis.

Probable Contaminant and Isolation

Determine if the isolate is clinically significant.
Clinically insignificant isolates (skin flora, multiple organisms, non-matching sources) suggest contaminants (e.g. Corynebacterium spp, Propionbacterium acnes, S. epidermis, Micrococcus species).
Isolate microbes and identify them.

Special Cultures

Brucella spp: Incubate samples for 30 days.
Nutritionally deficient streptococci: Require overlay cultures to grow. -Suspected if Gram-positive cocci (GPC) are found on the smear but no growth is observed on routine subcultured plates.
Campylobacter: Grow in blood culture but require a microaerophilic environment for subculturing (like CAMPY agar plate).

Antimicrobial Therapy

Start therapy empirically.
Switch to narrow-spectrum therapy after identification and susceptibility testing are completed.

Central Nervous System (CNS) Introduction

The CNS includes the brain, spinal cord, and meninges.

Cerebrospinal Fluid (CSF)

This fluid envelops the brain and spinal cord. Characterized as being clear and colorless. CSF is examined for cultures, cell count, glucose, and protein levels. CSF is a sterile fluid.

Meningitis Types

Purulent meningitis: (also called pyogenic meningitis). This type is caused by bacteria.
Aseptic meningitis: This type is caused by viruses and is characterized by an absence of microbial growth in testing.

Routes of CNS Infection

Hematogenous: blood-borne infection from other sites
Contiguous spread: infections enter from adjacent areas (e.g. sinus infections).
Trauma: Injuries such as skull fracture disrupt the CNS' protective barriers and cause entrance to pathogens.
Surgical microbial contamination: Post surgical infections can occur due to microbial contamination.
Shunts: Microbial contamination via shunts occurs if the drainage tubes have contamination introduced to them.

Acute Bacterial Meningitis Symptoms

Flu-like symptoms, headache, fever, nausea, and vomiting.
Stiff neck (nuchal rigidity) and sensitivity to light (photophobia) are observed signs.
Mental status changes sometimes accompany the other symptoms.

Causative Agents of Meningitis

Neonates (within the first 28 days of life): E. coli, Gram-negative rods, S. agalaetie, Listeria monocytogenes.
Infants and young children: H. influenzae b, N. meningitidis, and S. pneumoniae
Older children, adults, and the elderly: Gram-negative rods (GNRs), pneumococci, or meningococci, Listeria monocytogenes.
Immunocompromised adults: The types mentioned above, as well as encapsulated bacteria.

Specimen Collection— Meningitis

Lumbar puncture is performed to collect CSF.
CSF is collected by inserting a spinal needle between the third and fourth lumbar vertebrae.
3-4 tubes are collected for various analyses. (tube one for chemistry (protein and glucose), tube two for microbiology (gram stain and culture), and tube three for hematology (cell count and differential)).

CSF Processing

Samples are transported at room temperature (RT) for 15 minutes.
The samples may be immediately tested (STAT) or held in an incubator at RT.
Do not refrigerate samples, as refrigeration can affect certain microorganisms (e.g., meningococci, pneumococci, Haemophilus influenzae).
The collected sediment is tested for the presence of microbes via procedures including gram stains and cultures.

Microbiology Processing

If the sample volume exceeds 1 ml of CSF, centrifuge the sample.
The sediment is examined for Gram stains and cultures. The analysis is performed with the aim to ascertain the pathogens present, and obtain a sensitivity testing.
Gram stain sensitivity testing will determine the treatment required. Thick smears increase sensitivity.

Culture Media-Meningitis

Media commonly used are BAP, CHOC (or blood agar and chocolate agar), and, if necessary, MAC (MacConkey agar) or EMB (Eosin Methylene Blue).
AnaBAP media and incubation in CO2 are necessary if anaerobic aerobes are to be detected.

Antigen Detection Tests

Antigen detection tests can be used for certain agents like group B streptococci, Hib (Hemophilus influenza type B), meningitis (meningococci), and Pneumococci.

Other Types of Meningitis

Spirochetes (T. palladium and B. burgdorferi): These are rare causes
Viral infections, often the cause of aseptic meningitis. -No growth from bacterial testing, indicating the infection is viral.
Mycobacterial infections ( M. tuberculosis)
Fungal infections are also possible, but rare cases.
Parasitic infections (e.g., Naegleria, Acanthamoeba) are possible causes of meningitis.

CSF Findings

Microbial presence (bacteria, fungi, or parasites).
Typical cell types associated with different etiologies.

Brain Abscesses

Abscesses are caused by non-fast growing and/or anaerobic microbes, including anaerobic bacteria, staphylococci, viridans streptococci,
Collection and transport of aspirates and biopsy materials should be done in an anaerobic environment.
Microscopic and cultural tests are performed.

Encephalitis/Meningoencephalitis

Encephalitis and meningoencephalitis are caused in most common cases by viruses, but in some cases by the microbes listed in the "Causative Agents" section. Parasites such as Naegleria and Acanthamoeba are among the possible causes.

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Test your knowledge on bacteremia and its relationship with meningitis through this comprehensive quiz. Explore definitions, patterns, and diagnostic techniques associated with these critical medical conditions. Perfect for students studying microbiology or infectious diseases.