Analytical Procedures for Blood Culture Flashcards
What are the most common sources of blood culture contamination?
insufficient disinfection, improper collection, collection through an indwelling catheter
What are the three most common Continuous Monitoring Blood Culture systems (CMBC)?
BacTec, BacT, VersaTrek
Describe the principle for BacTec.
Positive growth is detected by a change in the concentration of CO2. This change is detected fluorometrically.
Describe the principle for BacT.
Positive growth is detected by a change in the concentration of CO2. This change is detected colormetrically.
Describe the principle for VersaTrek.
Positive growth is detected by a change in pressure. Changes in the concentration of CO2, H2, and O2 are continuously monitored.
The majority of endocarditis infections tend to be this gram reaction:
gram positive
What is the most common intravascular infection?
Endocarditis
What are the most common organisms that cause endocarditis?
Viridans strep of the oral cavity and Staph aureus
Which patients are most at risk for endocarditis?
Ones with endocardial abnormalities or previous valve surgery
What is another word for heart vegetation?
Excrescence
How do most heart vegetations form?
Fibrin-platelet thrombi on the surface of the endocardium “catch” bacteria as they circulate.
What is a septic emboli?
Large vegetations that have broken off from the endocardium and have traveled through the bloodstream. Fungi and gram negative bacilli are likely to do this.
Which side of the heart do most endocarditis infections occur?
The left side (high pressure side)
Which organisms are likely to infect the right side of the heart and why?
Bacillus species, Candida species, or P. aeruginosa. These organisms are commonly seen in contaminated intravenous injection drug use.
What are a few examples of organisms that can cause endocarditis but will not grow in culture? What is the preferred method of detection for these organisms?
C.pneumoniae, Coxiella burnetti, and Bartonella species. Serological or molecular methods.
Which organisms cause early stage intravascular hardware infections?
coagulase negative staph, diptheroids, or organisms that cause wound infections (gnb and yeast)
Which organisms cause late stage intravascular hardware infections?
Viridans strep of the oral cavity and Staph aureus
What are the most serious complications of endocarditis?
Cardiac valve rupture that results in heart failure and metastatic disease caused from septic emboli. Septic emboli can also cause kidney failure and stroke.
What are the clinical characteristics of septicemia?
Fever, chills, malaise, tachycardia, hyperventilation, and toxicity.
Sepsis is traditionally associated with organisms that have this gram reaction:
gram negative
What are the three types of bacteremia?
Transient, intermittent, and continuous
What is transient bacteremia?
Bacteremia that occurs when microorganisms are introduced into the bloodstream by minimal trauma to mucosal membranes such as brushing teeth or straining during a bowel movement.
What is intermittent bacteremia?
Bacteremia that occurs when microorganisms enter the bloodstream from an extravascular site such as a extravascular abscess, cellulitis, or infection of a body cavity.
What is continuous bacteremia?
Bacteremia that occurs when microorganisms enter the bloodstream from an intravascular site such as infected endothelium or hardware.
A bloodstream infection with Clostridium septicum is frequently associated with what?
Neoplastic disease, carcinoma of the colon
A bloodstream infection with Streptococcus bovis is frequently associated with what?
Endocarditis and carcinoma of the colon
Bacteremia that results in sudden, dramatic hemolysis could be due to this organism:
Clostridium perfringens
Which organs play the primary role in clearing bacteria from the bloodstream?
Liver and spleen
What is the most common organism that causes catheter related infections?
coagulase negative Staphylococcus
What is the ideal blood culture contamination rate?
Less than 3%
True or false: Volume is the most important metric for accurately identifying bacteremia.
True
True or false: The number of blood culture bottles is the most important metric for accurately identifying bacteremia.
False
How long does it take to clear bacteria from the bloodstream in a healthy individual?
30-45 minutes
What is the optimal blood to broth ratio in blood culture bottles?
1:5 or 1:10
What is the optimal blood volume for culture? How should this be collected?
30mL. Two sets of 10mL each, collected 15 minutes apart. Each set should have a different collection site.
What is the typical concentration of SPS in blood culture bottles?
0.025-0.05%
What is SPS?
Sodium polyanethole sulfonate. It is primarily used as an anticoagulant.
Other than anticoagulation, what are the other properties of SPS?
Neutrophil inactivation, antibiotic inactivation (gentamicin, streptomycin, kanamycin, and polymixin), and serum complement precipitation.
Which organisms does SPS inhibit?
Peptostreptococcus anaerobius, Neisseria gonorrhoeae, and Neisseria meningitidis.
How can the effects of SPS be neutralized?
Add gelatin to the media to a final concentration of 1%.
Which additional culture will aid in the diagnosis of an intravascular catheter infection? What is the interpretation for a true infection?
Catheter tip culture. >15 colonies
What are quantitative blood cultures used for?
To diagnose an intravascular catheter infection without removing the hardware.
How is a quantitative blood culture collected?
Simultaneous collection through the catheter and venipuncture using Wampole Isolator blood culture collection tubes.
What is the principle of a quantitative blood culture?
If the catheter is the primary source of infection, there should be a higher concentration of bacteria isolated from the catheter collection instead of the venipuncture. If the catheter is a secondary source of infection, there should be a lower concentration of bacteria isolated from the catheter collection, and a higher concentration isolated from venipuncture.
Which organisms cause granulomatous diseases of the bone marrow?
Brucella species, Histoplasma capsulatum, and Mycobacterium species
True or false: when collecting a blood culture from a line, a second blood culture set should be collected by venipuncture.
True
True or false: a blood culture collected from a line is enough culture evidence to prove a line infection.
False
What are a few common aerobic gram positive commensal bacteria that are often considered contaminants?
CNS, Rothia species, Micrococcus, viridans strep, nutrionally variant strep, Bacillus specis, and Corynebacterium species
What are a few common aerobic gram negative commensal bacteria that are often considered contaminants?
None
What are a few common anaerobic gram positive commensal bacteria that are often considered contaminants?
Lactobacillus species and Cutibacterium species
What are a few common anaerobic gram negative commensal bacteria that are often considered contaminants?
None
