Bacterial Identification

Question 1

2 reasons culture is better for bacterial diagnostics than PCR

Answer 1

1. Cost (urine culture $1 vs $15)

2. Sensitivity (culture better than PCR - might not even pick up the bacteria)

Question 2

MALDI-TOF

Answer 2

Matrix assisted laser desorption ionization - time of flight

Move to proteomics and using a mass spec

Question 3

What are protein biomarkers?

Answer 3

Highly expressed proteins responsible for housekeeping functions
Ex: ribosomal (16S) and transcription/translation proteins
These are what are detected in MALDI-TOF

Question 4

Why is MALDI-TOF better than Vitek?

Answer 4

Cheaper**
Faster
Better

Question 5

Bacteremia

Answer 5

The presence of bacteria in the bloodstream

Question 6

2 mechanisms that bacteremia occurs

Answer 6

1. Drainage from the primary focus of infection via the lymphatic system to the vascular system (ex: abscess)
2. Direct entry from needles, contaminated IV devices, or graft material or trauma

Question 7

Transient bacteremia

Answer 7

Minutes to hours
Often occurs following manipulation of infected tissues or instrumentation of contaminated mucosal surfaces (ex: brushing teeth)
Onset of acute bacterial infections such a pneumonia, meningitis and septic arthritis

Question 8

Intermittent bacteremia

Answer 8

Most commonly occurs with un-drained abscesses

Question 9

Continuous bacteremia

Answer 9

Usually reflects an endovascular infection such as endocarditis or an infected aneurysm

Question 10

What are some of the most common primary foci

Answer 10

IV devices
Respiratory tract
Urinary tract
Intra-abdominal infections

Question 11

What 3 bacteria are the most common causes of bacteremia

Answer 11

S. aureus and E. coli the most

Coagulase negative Staph is a close third

Question 12

What are some poor prognosis findings for bacteremia

Answer 12

Advanced age
Nosocomial bacteria (more resistant usually)
Enterococcal, gram -'ve, or fungal etiology (harder to treat)
Underlying cirrhosis or malignancy
Primary focus in the resp tract or skin
Surgical wound of abscess
Septic shock
Lack of a febrile response to sepsis

Question 13

Nosocomial infections

Answer 13

Hospital acquired infections

Usually more resistant to drugs

Question 14

Why do you need to dilute the blood in broth?

Answer 14

Diluting greater than 1:5 increases microbial recovery, probably by diluting antimicrobial agents and natural inhibitory factors in the blood

Question 15

Whats the most common anticoagulant in blood?

Answer 15

SPS

Question 16

Automated blood culture systems

Answer 16

24 hour continuous monitoring
When bacteria grow they make CO2 - will change the colour of the membrane and the detector sees that (fluorescence)
Door lights up and sends an alarm

Question 17

How are
1. SBA
2. CHOC
3. BHI
4. MAC
incubated?

Answer 17

1. Aerobically
2. With 5% CO2
3. Anaerobically
4. For gram negatives

Question 18

What is the most common anaerobes you’re going to grow?

Answer 18

Bacteriodes

Question 19

What 3 bacteria do not usually represent true bacteremia?

Answer 19

Corynebacterium spp
Bacillus spp
Propionibacterium acnes