PBL: Blood Cultures Flashcards
Presence of bacteria in the blood
Bacteremia
Bacteria passing through (dental, colonoscopy)
Transient bacteremia
Bacteria seeding from the infected site to another area intermittently (seeding blood); same organisms on and off
Intermittent bacteremia
Bacterial coming from an intravascular source all of the time (endocarditis)
Continuous bacteremia
Sepsis going on inside a site such as an IV catheter or endocarditis
Primary sepsis
Sepsis going on in an external site such as strep from lungs, UTI, dental surgery, tooth accesses
Secondary sepsis
A contaminant in the blood
Pseudobacteremia
Bacteremia w/ organisms multiplying in blood and symptoms showing
Septicemia
Molds and yeast in the blood
Fungemia
Viruses in the blood
Viremia
Systemic inflammatory response syndrome (things must fall in a category?)
SIRS
Inflammation of the cardiac lining
Endocarditis
Sepsis w/ hypotension
Septic shock
When the proteins that control blood clotting become overactive and you get massive bleeding out
Disseminated intravascular coagulation (DIC)
Blood culture system where the instrument checks for positive cultures (24/7)
Continuous monitoring blood culture systems
Bacteria secreting ____ are notorious for septic shock
Endotoxins
Common symptoms and abnormal lab tests that would be associated w/ possible sepsis
- Fever (↑ or ↓)
- Shaking
- Chills
- Tachypnea
- Prostration (laying down)
- Blood pressure (↑ or ↓)
- DIC
- WBC count (↑ or ↓)
- Lactic acidosis
- C-RP (↑)
- Procalcitonin (indicator of inflammation on high levels indicative of septicemia)
Proper method of collecting a blood specimen for bateriologic culture (5 steps)
- Alcohol
- Iodine based
- Make circles going out
- Draw opposite arm that has IV
- Draw below IV if have to draw from arm w/ IV
Correlate the number, timing, and volume of specimens w/ optimal recovery of organisms fro meaningful clinical use
- Number: 1 set = 1 aerobic bottle and 1 anaerobic bottle; no more than 3 sets in 24 hours
- Volume: 8-10mL for adults; 1-3mL for babies
- Timing: take blood before antibiotics or any therapy and right before a fever
Blood to medium ratio when collecting a blood culture
1:5 to 1:10
IV catheter related
- CoNS
- S. aureus
- Enterococcus spp.
UTI
Escherichia coli (coming from GI)
Subacute endocarditis
- CoNS
- Streptococcus viridans
Acute endocarditis
- Staphylococcus aureus
- Streptococcus pneumoniae
Oral surgery/dental procedures
Mouth flora
Most comon contaminants found in blood cultures
Skin flora
Immunocompromised
- Anything really
- Fungi
Preexisting pneumonia is the most common cause of septicemia. This pneumonia is caused by…
- Streptococcus pneumoniae
- Klebsiella pneumoniae
What is the purpose of the BACTEC system?
Measuring CO2 by fluorescence
- Non-radiolabeled CO2 is taken into the sensor, where it reacts w/ dye and produces hydrogen ions
- ↑ in H+ → ↑ fluorescent light to be detected by the detector
What is the purpose of the BacT/Alert system?
Measuring CO2 by pH change, changing the color of the sensor from gray to yellow
What is the purpose of the SeptiCheck?
Agar paddle or slant used to subculture a specimen and you inoculate it by inverting the broth to cover the agar
What is the purpose of the Lysis centrifugation?
System requires the addition of lysis fluid to blood samples followed by several inversions for mixing. Sediment after centrifugation is used to inoculate all media plates.
- This is for: intracellular pathogens and fungi, yeasts, and molds
What is the purpose of sodium polyanetholsulfoante (SPS)?
Anticoagulant that inhibits lysozyme neutralization, phagocytosis, and complement that would otherwise kill the bacteria
What is the purpose of resins (ARD: antimicrobial removal devices) in blood cultures systems?
Neutralizes antibiotics to prevent the killing of bacteria in the sample
Proper blood culture procedure for possible brucellosis
Castanata bottle/biphasic bottle: used when it takes a long time to grow brucellosis (4 weeks)
What approaches could be used to determine whether an isolate is a skin contaminant or a pathogen
Collect multiple specimens (3 sets a day max)
- All positive blood cultures more likely to be a pathogen
What one Gram POSITIVE organisms may be observed on a gram stained smear from a blood culture bottle but would NOT grow on SBA and, w/ some organisms, not on CHOC
- Anaerobes
- Streptococcus abiotrophia (nutrient variant)
What one Gram NEGATIVE organism may be observed on a gram stained smear from a blood culture bottle but would NOT grow on SBA and, with some organisms, not on CHOC
- Haemophilus (only grows on CHOC)
- Capylobacter (charcoal containing media, not blood OR chocolate)
- Anaerobes
What media should be set up on a positive blood culture, based on results of a positive smear
- SBAP
- CHOC
- ABAP
- Do preliminary susceptibilities
- – Do GLC for anaerobes
What test should you set up if you think you have strep? Of these which can you set up directly from the blood?
- Catalase
- NaCl
- PYR
- Bile Esculin
- CAMP
- Optochin (bile solubility)
- Bacitracin
Set up from blood: Bile Esculin and optochin
If you have a GPC, what should you do first?
- Gram stain
- Plate it out
- Optochin right away
What would you do if your gram stain was clumped (staph)?
Do a coag right away (in 4 hours) FROM BLOOD
What would you do if your gram stain was a GNR?
Vitek or KIA FROM BLOOD
How long do we keep bottles?
5 days
What is the significance if positive on the first day vs. the fifth day
- First day: more likely to be significant
- Fifth day: more likely to be a contaminant
What is teh best way to do a gram stain on a blod?
MeOH fixation b/c it preserves red cells the best
What is the advantage of the lysis centrifugation system?
The sediment (bacteria) is able to be plated immediately after the centrifugation and pressing process has been completed
What does PNA FISH stand for?
Fluorescence In SItu Hybridization using Peptide Nucleic Acid Probes
Principle of PNA FISH
Molecular method that uses fluorescent probes to evaluate genes and DNA sequences on a c’some
Principle of Verigene
Molecular method that rapidly identifies GP organisms
Principle of MALDI-TOF
Mass spectrometry that rapidly identifies microorganisms and bacteria
What does MALDI-TOF stand for?
Matrix-Assisted Laser Desportion Ionization Time-Of-Flight
Principle of Gene Xpert
Rapid molecular test for MRSA
What steps should be taken after the Bactec indicates a blood culture bottle is positive?
- Remove the bottle from the Bactec (only remove the ones marked by the instrument)
- Prepare a Gram stain
2a. Wipe septum w/ 70% isopropyl alcohol, allow to dry, insert syringe into vial and remove medium, make thin prep smear on slide and fix w/ heat or MeOH, then stain - Call doctor and notify them of type of organism(s) noted during gram stain evaluation.
Advantages of MeOH fixation
Help prevents liquid specimens, such as blood, from washing off the slide; preserves cell morphology, and results in an overall background w/ less debris
Disadvantages of heat fixation
Runs risk of overheating the slide, therefore causing morphologic changes to the cells
What biochemical tests and media should be set up for GPC in clusters?
- Biochemicals: Tube coagulase, QuickFISH
- Media: BAP, CHOC, ANA BAP
What biochemical tests and media should be set up for GPC in pairs and/or chains?
- Biochemicals: optochin disk
- Media: BAP, CHOC, ANA BAP
What biochemical tests and media should be set up for GNR?
- Biochemicals: Vitek GNI, 73 cards from pellet (new card should be set up every 2 days)
- Media: BAP, CHOC, ANA BAP, MAC, CNA
What biochemical tests and media should be set up for GNC?
- Biochemicals: None
- Media: BAP, CHOC, ANA BAP, ML
What biochemical tests and media should be set up for GNR?
- Biochemicals: None
- Media: ALL get BAP, CHOC, and ANA BAP (Lactobacillus: add TJ; Bacillus spp: add PEA)
What biochemical tests and media should be set up for yeast (yeast-like fungi)?
- Biochemicals:yesat traffic light PNA FISH (every 14 days)
- Media: BAP, CHOC, ANA BPA, CSAB, CAC
Incubate ____ media for 48 hours in ____ @ 35°C
Aerobic; CO2`
Incubate TJ and ANA BAP in ____ conditions for 48 hours @ 35°C
Anaerobic
Normal skin flora
- Alpha/gamma streptococci (Streptococcus viridans) → GPCs
- Corynebacterium spp (“dipthroids”)
- CoNS → GPC
- Propionibacterium spp (P. acnes) → GPR
- Staphylococcus saccharolyticus → GPC
Intraabdominal infections (perforated GI → abscess) - What is the cause of primary peritonitis?
Cirrhosis
Intraabdominal infections (perforated GI → abscess) - What bacteria cause secondary peritonitis?
- E. coli → GNR
- Anaerobes
- Enterococcus spp → GPC
Normal GI flora
- Anaerobes (Bacteroides fragilis group, Clostridium spp., Bifidobacterium spp., anaerobic cocci, Fusobacterium spp)
- E. coli → GNR
- Enterobacteriaceae → GNR
- Enterococcus spp → GPC
Colon cancer
- Clostridium septicum → GPR
- Streptococcus bovis → GPC
Normal mouth flora
- Alpha/gamma Streptococci → GPC
- Corynebacterium → GPR
- CoNS → GPC
- Non-pathogenic Neisseria spp → GN diplococci
- Prevotella melaninogenica → GNR
- Porphyromonas spp → GNR
- Prevotella spp → GNR
Skin infections
- Staphylococcus aureus → GPC
- Group A Strep (Streptococcus pyogenes) → GPC
- Group B Strep (Streptococcus agalacticae) → GPC
Brucella spp
- Gram stain
Small GNCB
Brucella spp
- Blood culture collection
- Collected as ordinary blood cultures but incubated in BacTec FX for 14 days
- Vial will be cultured in TSA weekly, and plates will be sotred in CO2 incubator for 4 days
Brucella spp
- Isolator tube collection
Will be plated on BAP, CHOC, and TSA and incubated for 14 days
