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Microbiology > Unit 10: Blood Culture > Flashcards

Unit 10: Blood Culture Flashcards

1
Q

What are the differences between bacteremia and septicemia?

A

Both are defined by the presence of bacteria in the blood BUT in septicemia, the bacteria reproduce in the bloodstream and produce an infection. The rates of reproduction often exceed removal by phagocytosis.

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2
Q

What are symptoms of septicemia?

A
  • Fever
    • Chills
    • Malaise
    • Tachycardia
    • Hyperventilation
    • Toxicity
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3
Q

Differentiate the three types of bacteremia

A

a. Transient- organisms of normal flora are introduced into the bloodstream
b. Intermittent- bacteria from an un-drained infected site are released into the bloodstream spasmodically
c. Continuous- organisms are released into the bloodstream at a fairly constant rate; continuously present with or without symptoms

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4
Q

Acute febrile illness: Collection

A

2 separate samples drawn immediately; in tandem from opposite arms
30-45 minutes before temperature spikes

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5
Q

Fever of unknown origin: collection

A

Interval draws
-Initially: interval of 45-60 minutes
Additional: 24-48 hours later
2; then 2 additional sets

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6
Q

Ineffective endocarditis: collection

A

-3 SEPARATE venipunctures; before therapy begins
-Initially: within first 1-2 hours of evaluation; but spaced by at least 30 minutes
If negative: 2 more setson subsequent days

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7
Q

4 important things about general collection

A

1) Must wear universal precautions to maintain low contamination rates
2) Venipuncture site: Cleanse with Chloroprep, apply in concentric fashion, Remain intact on skin for 30 seconds and do not touch skin
3) Bottle: Prep in same manner as venipuncture site
4) Aerobic and anaerobic bottles should be inoculated during time of draw

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8
Q

Which bottle takes priority if necessary?

A

Aerobic bottles take priority if necessary

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9
Q

Recommended volume:

A

8-10 mL per bottle; percentage yield of positive culture decreases if less than 10 mL is obtained

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10
Q

Pediatric bottle:

A

1-5 mL is satisfactory

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11
Q

Ideal recovery and why?

A
  • 1:10 ratio
    -Less blood harder to recover bacteria
    More blood not enough nutrients to support
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12
Q

Incubation and examination:

A

1) Incubated at 35C
2) Examination dependent of system used: macroscopically, radiometrically, fluorometrically
3) Held for 5 days
4) On suspected positive cultures: Gram stain immediately If POS, notify provider immediately

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13
Q

Aerobes: media

A

1) Trypticase Soy Broth/brain Heart Infusion broth
2) Sodium polyanetholsulfonate (SPS)
3) Castaneda double medium
4) Fletchers medium

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14
Q

Trypticase Soy Broth/brain Heart Infusion broth

A
  • Soybean and casein digests

- Can be ok for anaerobic

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15
Q

Sodium polyanetholsulfonate (SPS)

A

-Anticoagulant/prevents clotting
-Does not harm bacteria
-Inactivates neutrophils
-Can inactivate certain antibiotics: aminoglycosides
-May inhibit P. aeruginosa, GC, N. meningitidis, and
G. vaginalis

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16
Q

Castaneda double medium

A

-Biphasic technique: Solid and liquid medium
-For isolation of Brucella (slow growing, fastidious
and intracellular)
-Incubated in 5-10% CO2 at 35-37 for 30 days
-Must be tipped every 48 hours and be subcultured
twice weekly
-NOT IDEAL

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17
Q

Fletchers medium

A
  • Semisolid
    - Contains rabbit serum and SPS
    - For isolation of Leptospira
    - Incubate in the dark, 30C for 28 days
    - Examine weekly by darkfield
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18
Q

Anaerobes: media

A

1) Thioglycollate broth

2) Sodium polyanetholsulfonate (SPS)

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19
Q

Yeast: media

A

SAB media

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20
Q

Septi-Chek System a Biphasic Module

A

Principle: Consists of a conventional blood culture broth bottle with an attached chamber (paddle) containing a slide coated with agar or several types of agar. Must tilt bottle daily to inoculate agar(s). Look for colony growth on agars. Subculture if growth appears for identification.

Disadvantage: Manually tilt every day. May not recover certain types of bacteria (anaerobes).

Advantage: No blind subs or subculturing. Self-contained system, therefore, does not require opening the bottle or uses needles.

21
Q

Bactec FX

A

Tests: bacteria and fungi
Timeframe: continuously tested for five days.

Based upon: non-invasive fluorescent technology. Detection for the system has two components:

1) sensor material, which is the material present in the bottom of each BACTEC bottle
2) the detector which is a light emitting diode (LED) located in each station well of the instrument. The detector activates the sensor material and measures the amount of fluorescence every ten minutes.

Principle: Microorganisms release carbon dioxide into the medium when they metabolize the nutrients in the culture medium; in turn, a dye in the sensor material reacts with the carbon dioxide, modulating the amount of light absorbed by the fluorescent material in the sensor. Photodetectors within the instrument then measure the level of fluorescence, which corresponds to the amount of carbon dioxide released by the microorganism. This measurement is then interpreted by the system according to preprogrammed positivity parameters, which will determine if the culture is positive.

Resins are present in the Bactec blood culture bottles throughout the entire incubation period. These resins absorb and neutralize antimicrobics in the blood culture medium. Therefore, the resins provide an enhanced surface are to which drugs can bind. This helps create an environment that promotes the growth of certain sensitive microorganisms.

22
Q

The Isolator System

A

Tests: yeast, fungi and mycobacterium

Principle: The isolator tube is a special tube that contains saponin (plus SPS & EDTA), a chemical that lyses both RBCs and WBCs to release INTRACELLULAR organisms.

Process: Approximately 7.5-10 mL of blood is added to the tube, which is mixed well by inversion. The tube is then centrifuged for 30 minutes at 3000RPMs to concentrate any microorganisms that may be present. After centrifugation the supernatant is aspirated and discarded. The sediment is vortexed, aspirated, and sub-cultured to the appropriate media.

Disadvantage: High Rate of plate contamination. Fails to detect certain bacteria (H.fluenzae, Listeria, S.pneumoniae, Anaerobes)

Advantage: Less blood is needed and there is improved recovery of filamentous fungi.

23
Q

Macroscopic appearance: gram negative rods

A

Usually enterics, medium above red cell layer becomes turbid, gas bubbles form

24
Q

Macroscopic appearance: pneumococcus

A
  • turbidity, greenish tint in medium
25
Q

Macroscopic appearance: Streptococcus

A
  • In thioglycolate medium, appears as cotton ball colonies on top of sedimented red cells
26
Q

Macroscopic appearance: Staphylococcus

A

-frequently produces large, jelly-like coagulum; turbid

27
Q

Macroscopic appearance: Bacillus

A

-hemolyzes broth, thick film on surface

28
Q

Macroscopic appearance: Clostridium

A

-produces large head of gas, hemolysis of RBCs

29
Q

Macroscopic appearance: Bacteroides

A
  • less gas than Clostridium, foul odor
30
Q

Macroscopic appearance: Haemophilus influenzae

A

-Little or no change in medium; gram stain EXTRA important!

31
Q

Gram negative bacilli AEROBIC

A

BAP, MAC, CHOC, CDC

32
Q

Gram negative bacilli ANAEROBIC

A

BAP, MAC, CHOC, CDC, CDC-KV, BBE

33
Q

Gram negative cocci AEROBIC

A

BAP, MAC, CHOC, CDC

34
Q

Gram negative cocci ANAEROBIC

A

BAP, MAC, CHOC, CDC

35
Q

Gram positive cocci clusters AEROBIC

A

BAP, CDC

36
Q

Gram positive cocci clusters ANAEROBIC

A

BAP, CDC

37
Q

Gram positive cocci chains AEROBIC

A

BAP with ‘A’ and ‘P’ discs

38
Q

Gram positive cocci chains ANAEROBIC

A

BAP, CDC

39
Q

Gram positive bacilli AEROBIC

A

BAP, CDC

40
Q

Gram positive bacilli ANAEROBIC

A

BAP, CDC

41
Q

Yeast AEROBIC

A

BAP, CHOC, SAB

42
Q

Accurately evaluate the need for antibiotic susceptibility testing.

A

Important for GPC in chains (P and A disk)

GPB wimpy P10 disk

43
Q

select the appropriate test(s) for identification of a. S. aureus

A

GPC grows better aerobically, verify B hemolytic on blood, catalase test and coagulase test

44
Q

select the appropriate test(s) for identification of b. Coag neg staph

A

GPC grows better anaerobically, catalase test POS, coagulase NEG

45
Q

select the appropriate test(s) for identification of S. pneumoniae

A

GPC in chains, drop P disk (SS)

46
Q

select the appropriate test(s) for identification of Beta strep

A

GPC in chains, Beta hemolytic

47
Q

select the appropriate test(s) for identification of Gamma strep

A

GPC in chains, gamma hemolytic

48
Q

Causes of Infective Endocarditis (5)

A
  • Viridans streps: normal oral flora which gain entrance to bloodstream via gingivitis, periodontitis, and dental manipulation
  • Nutritionally Variant streps
  • HACEK group
  • Enterococcus
  • S. aureus
49
Q

Causes of IV Catheter Associated Bacteremia (4)

A
  • S. epidermidis: produces biofilm
  • other Coag-Neg staphs
  • S. aureus
  • Enterobacteriaceae

Microbiology (11 decks)

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