M8 Cardiovascular Infections Flashcards
How does intravascular infections occur in general?
Intravascular (organisms gain entry from within the cardivascular system)
How can endocarditis develop and what organism is leading cause of it?
endocarditis/subacute endocarditis
1. Is initiated by damage to the endothelium.
2. Platelets deposit to the damaged area.
3. Bacteria transiently enter the bloodstream and attach to the damaged surface.
4. The web of cells, fibrin, and
organism is referred as a vegetation.
Viridans Streptococcus leading
cause.
How does suppurative thrombophlebitis occur?
Intravascular -
Suppurative thrombophlebitis:
Primary site of infection is the vein, and then these organisms go to the bloodstream
What is the mechanism of IV catheter associated bacteremia?
IV Catheter-associated bacteremia:
- May be caused by IV catheters
organisms move from the catheter entry site through skin to the catheter tip (out). - Organisms migrate along the inside of catheter-to-catheter tips (inside).
What typical organisms cause intravascular Suppurative thrombophlebitis and IV catheter associated bacteremia?
Organisms: CNSS (S.epidermidis), S.aureus, GNB,
Candida, Corynebacterium.
What are sources of extravascular infections?
Initial infection at other body site such as wounds, soft tissue, UTI’s, respiratory, meninges, and gastrointestinal tract.
What infectious organisms often cause bacteremia from wounds and soft tissue?
S.aureus,
Strep A,
CNSS,
Pseudo aeruginosa,
ANO2
What is the most likely source of a bacteremia with Enterobacteriaceae organisms? What other organisms could infect from this source?
Urinary tract infections.
Also Candida UTI could cause bacteremia.
What two sources could a Strep. pneumonae bactermia be caused from? What other organisms come from these areas?
Respiratory and meninges.
Resp:
- Str pneumo,
- H. inf,
- Legionella.
Meninges:
- Str pneumo,
- H. inf,
- Listeria,
- Neiss. meningitidis,
- Pseudo,
- GNB
What organisms from a GI tract infection could result in bacteremia?
GI:
- Salmonella Typhi,
- other GNB,
- ANO2
What are the different states of bacteremia?
- Transient - introduced through normal/routine activities or surgery involving non-sterile site
Immune system clears bacteria, short duration - Intermittent - extravascular site involved, symptoms occur when bacteria gets to blood
but they disappear when cleared. - Continuous - continuously released into bloodstream at a constant rate (endocarditis,
Catheters)
What is septicemia?
Septicemia = bacteremia + sepsis (bacteremia causing harm to the host)
What are the symptoms of septicemia?
Symptoms:
Fever or hypothermia, chills, Hyperventilation, Resp alkalosis, change in mental status, diarrhea, septic shock (major organ failure) .
What are the important elements of blood culture samples?
- Volume
- Site preparation
- Number of sites
What is the definition of one blood culture set?
Two venipunctures.
What is the definition of one blood culture?
One venipuncture.
What is the typical blood volume required from an adult for a blood culture?
40 mL
What is the dilution ratio for manual methods verses automated methods?
1:10 for manual
1:5 for automated
What is the distribution of where the 40 mL is taken (what bottles, location).?
One arm: 10 mL anaerobic and 10 mL aerobic.
Other arm: 10 mL anaerobic and 10 mL aerobic.
What is the purpose of using multiple sites for the blood culture?
Multiple sites serve as a control.
What volume of blood is required from pediatrics?
Pediatrics require a much smaller volume.
O.5 mL to 10 mL.
What bottle is inoculated first and why?
When using a syringe the anaerobic bottle is filled first to reduce exposure to air.
When using butterfly, the aerobic bottle is used first to reduce air in line.
What are the two types of broths used in blood culture bottles?
TSB Trypticase Soy broth
BHI Brain Heart Infusion
What media additives are typically used for blood cultures?
SPS (Sodium polyanethol sulfonate)
- anticoagulant that enhances bacteria growth by inhibiting phagocytes, complement, and some antibiotics.
Resin
- inactivates antibiotics
What is the limitation of using SPS broth in blood culture bottles?
May be toxic to N. gonorrhoeae, N. meningitidis, and Propionibacterium anaerobius.
Gelatin added to counteract the effects.
What are the main steps in doing manual bottle systems?
Manual Bottles
1. Incubate immediately
(at least 6-18 hrs after
collection)
2. Requires a “blind subculture”
3. Check daily for gas, bubbles,
hemolysis
4. “shaker” increases recovery
of organisms
What type of blood culture bottle is inverted to seed prepared media slant?
Biphasic Bottles
What type of blood culture bottles/system is used for fungi or hard to grow bacteria?
Lysis –centrifugation:
1. draw into sterile tubes & transported to lab, processed and inoculated onto culture media-used for filamentous fungi or hard to grow bacteria
2. SPS (anticoagulant), saponin (to lyse blood cells), EDTA: lysis cells so organisms become available, then a high speed centrifugation to concentrate, and the precipitate is planted to appropriate media.
Note: Not sure why EDTA is mentioned, read p962 in textbook. It is not noted as part of system.
Name two commercially available automated blood culture bottle/systems and how they are used in general
Automated Systems
1. BAC-T-Alert
-continuous monitoring
system
- incubator, shaker,
detector
- non-invasive
- patient bottles are accessioned and loaded into assigned wells within the instrument
- BACTEC (BD)
No need for “blind subs”, as the machine tells you when the bottle is positive.
How does the BAC-T Alert blood culture bottle system work?
- Compartment sensor in bottom of bottles is separated by a semi-permeable membrane (permeable to CO2)
- Compartment sensor has a pH indicator dissolved in water that is initially pale green
growing microorganisms release CO2 - CO2 diffuses into the compartment combining with H2O and releases H+ ions
- H+ ions react with the “sensor
- As H+ ion conc. increases, the sensor turn to a “pale green” and eventually “yellow”
- Light emitted from sensor is detected by photodiode
- These bottles are removed for identification purposes
How does the BACTEC system detect bacteria growth in blood culture bottles?
BACTEC:
1. CO2 diffuses into sensor solution, H+ ions are released decreasing pH.
2. pH decrease excites a fluorescent output in sensor solution.
3. Instrument reads every 10 min to detect fluorescence. 4. Instrument alerts when measurable amount of fluorescence is detected.
Compare the two principles of detection of BAC-T/Alert versus BACTEC?
BACTEC detects growth fluorometrically
BAC-T-Alert detects growth colormetrically
How long are blood cultures incubated for before calling no growth?
Routine culture
incubate for 5 days before calling as “no growth”
What blood culture bottles need a macroscopic examination?
Macroscopic examination
Manual (conventional) need blind subcultures if visually inspected as positive.
Macroscopic examination
BAC-T-Alert evaluate bottles upon receipt (because the bacteria may growth during transport).
What is the general analysis (testing) procedure for positive blood culture bottles?
- Prepare gram stain from primary media (the broth)!
- Direct tests and direct AST are highly presumptive and not recommended
- Subculture to CA, BA, Mac (if gram negative bacilli) or other media as needed. (SAB for yeasts). Use gram stain to direct choice of plates.
When is Acridine orange (AO) stain used for blood cultures?
AO stain is performed when NO organisms are seen on Gram on a specimen flagged as positive.
Note: Tuberculosis doesn’t show up on a gram stain.
Campylobacter is typically hard to see on a gram stain. And once you know, it is important to incubate it in a microaerobic
atmosphere.
How is an Acridine orange (AO) stain performed?
- Blood culture smears are stained with a fluorochrome that binds to nucleic acid. It can be stained on top of the Gram stain.
- Smears are examined with a fluorescent microscope
bacteria if present will fluoresce orange against a dark background - Red blood cells do not have DNA so do not fluoresce. WBC’s will but there are not so many so they won’t mask bacteria. (They look cool!)
How is reporting done for positive blood cultures?
- Phone and document report ASAP (first Gram). Give as much information as possible ie. if arrangement is seen in gram stain report. [Note she said culture results will then get sent electronically).
- Report how many bottles are “positive”
- Quantitation of isolate not required (from liquid media)
- Keep sending preliminary reports electronically every day, or new information
What is the concern if only one bottle out of 2 or 3 is positive? Does it matter with what organisms?
Contamination.
If only one bottle is positive for certain organisms such as Bacillus spp. (not anthracis), Cornyebacterium spp., Coagulase negative Staph, Viridans Streptococci (except for some species) and Micrococcus spp. contamination is suspected
What if Coagulase neg Staph is present in more than one site? (or Micrococcus, Corynebacterium, etc.)
If these organisms are present in more than one site:
- Bacillus spp. (not anthracis),
- Cornyebacterium spp.,
- Coagulase negative Staph,
- Viridans Streptococci (except for some species) and
- Micrococcus spp.
They are considered the cause of the infection and full work up done.
How is a positive blood culture believed to be contamination reported to the Dr.?
Organism ID is reported without AST with a note saying “This organism is a possible contaminant. Please call … if clinically indicated and further work up is needed.”
What are two possible causes of false positive blood culture bottles?
- Bottles that are growing an organism that is not the cause of the infection: inadequate disinfection-site and or bottle septum (see type of org and amount of sites +)
- Bottles that are flagged as positive by the instrument and do not grow bacteria (true false POS): high WBC in blood?
What are two possible causes of false negative blood culture bottles?
False negative
1. Inadequate volume of blood
2. Overfilling culture bottles (lesser extent), if antibiotics started, additives may be in a ratio too low to neutralize.
