Introduction to Diagnostic Microbiology

Question 1

Some bacteria/fungi are “always” considered pathogens. Two examples of this are

Answer 1

M. Tuberculosis and Vibrio Cholerae

Question 2

How many bacteria must be present to be visible?

Answer 2

10^5/mL

Question 3

hat are three major stains for microscopy?

Answer 3

Gram Stain, Ziehl-Neelson or Kinyoun stain, and immunofluorescent antibody stain

Question 4

The Ziehl-Neelson or Kinyoun stain is used for

Answer 4

Myobacteria

Question 5

A broth culture “back up” in highly enriched medium is required for normally

Answer 5

Sterile specimens

Question 6

What are two rapid bench methods for bacterial identification?

Answer 6

Coagulase tubes and catalase test

Question 7

What are the three advantages of MALDI-TOF for bacterial identification

Answer 7

Accuracy, speed, and cost

Question 8

What are two forms of direct antigen detection?

Answer 8

Enzyme Immunoassays (EIAs) and Latex agglutination

Question 9

What are two examples of EIAs?

Answer 9

Rapid strep and rapid influenza

Question 10

May be used for identification after culture or to directly test specimens

Answer 10

Molecular diagnostics

Question 11

Molecular diagnostics such as nucleic acid amplification tests and DNA sequencing or fingerprinting generally exhibit high

Answer 11

Sensitivity and specificity

Question 12

Has implications for admission decisions, Abx administration, or additional diagnostic testing

Answer 12

Respiratory virus panels

Question 13

Respiratory virus panels have variable numbers/types of targets and can be either

Answer 13

On demand or batched

Question 14

Takes approximately 1-2 hours and can test for 14 target pathogens at once

Answer 14

CNS infection panels

Question 15

Should be interpreted in the context of other laboratory data, i.e. cell count, protein, glucose, and Gram stain

Answer 15

CNS infection testing

Question 16

The main objective of antimicrobial susceptibility testing is to predict the outcome of

Answer 16

Prescribed drug

Question 17

Antimicrobial susceptibility testing can also be used to confirm/refute current

Answer 17

Empiric Rx

Question 18

An infection due to the strain may be appropriately treated with the dosage of anti-microbial agent recommended for that type of infection and species

Answer 18

Susceptible (S)

Question 19

The MIC approaches usually give attainable blood and tissue levels

-response rate may be lower than susceptible isolates

Answer 19

Intermediate (I) Susceptibility

Question 20

Applicable in infection sites where the drug is concentrated (like in urine) or high doses can be used (B-lactams)

Answer 20

Intermediate (I) Susceptibility

Question 21

When strains are not inhibited by usually achievable systemic antimicrobial levels

Answer 21

Resistant (R)

Question 22

In Resistance (R), the MIC falls in the range where specific microbial resistance mechanisms are likely. For example, with

Answer 22

B-lactamases

Question 23

Roughly speaking, is equal to the concentration of antimicrobial at the site of infection

Answer 23

Therapeutic Breakpoint or “Breakpoint”

Question 24

Comparing the MIC to the breakpoint determines

Answer 24

Susceptible-intermediate-resistant interpretation

Question 25

If the MIC is greater than the breakpoint, then the bacteria is

Answer 25

Resistant (R)

Question 26

If the MIC is equal to the breakpoint, then the bacteria is

Answer 26

Intermediate (I)

Question 27

If the MIC is less than the breakpoint, then the bacteria is

Answer 27

Susceptible (S)

Question 28

What is the typical bacteria load in a patient with bacteremia?

Answer 28

1 cfu/mL

Question 29

Most positive blood cultures will show in

Answer 29

2 days

Question 30

If patient has Candida albicans/tropicalis, treat with

Answer 30

Fluconazole

Question 31

If patient has Candida parapsilosis, treat with

Answer 31

Azole (or if higher MIC echinocandins)

Question 32

If patient has Candida krusei/glabrata, treat with

Answer 32

Echinocandin (Azole resistance)

Question 33

If candida is not detected, then consider withholding

Answer 33

Antifungal

Question 34

Most common micro specimen. Received fresh (within 2 hours) or in boric acid

Answer 34

Urine cultures

Question 35

The normal flora of the urethra includes which three bacteria?

Answer 35

Lactobacillus, streptococci, and staphylococci

Question 36

You want to discard the first part of the urine unless you are testing for

Answer 36

GC and chlamydia

Question 37

A high volume of urine is required to detect

Answer 37

Myobacteria, cryptococcus, and dimorphic fungi

Question 38

A throat swab only detects

Answer 38

GSA

Question 39

You can perform an NP swab/wash, or OC swab/scraping to test for

Answer 39

Influenza

Question 40

Not useful for diagnosis of sinusitis

Answer 40

NP swabs

Question 41

The most common lower respiratory tract specimens are properly collected

Answer 41

Sputum and trach aspirate

Question 42

Assessed for contamination based on presence of epithelial cells/absence of neutrophils

Answer 42

Sputum

Question 43

What are the only three bacteria types that contaminated sputum specimens are still ok for?

Answer 43

Legionella, nocardia, and myobacterium spp

Question 44

Can be used to test for S. pneumoniae and Legionella -Should be supplemented with Cx

Answer 44

Urine Ag testing

Question 45

Routine Gram stain and Cx, requires how much sterile body fluid per test?

Answer 45

1-2 mL

Question 46

However, to perform Gram stain or Cx on myobacterial or fungal analysis, we need

Answer 46

Greater than 5 mL each

Question 47

Concentrated prior to microscopy -most cultures positive in 1-2 days

Answer 47

CSF

Question 48

Most untreated patients with bacterial meningitis should have a positive

Answer 48

GS (except listeria)

Question 49

Bacterial antigen testing is rarely useful for

Answer 49

CSF

Question 50

When testing CSF, what are the tests of choice for Borrelia and Treponema pallidum?

Answer 50

Serology or NAATs

Question 51

May be inoculated to blood Cx bottle with additional fluid for Gram stain, NAAT, or Ag testing (in sterile container)

Answer 51

Peritoneal/pleural fluid

Question 52

There are no swabs for

Answer 52

Peritoneal/pleural fluid

Question 53

Better than a rectal swab for testing gastrointestinal specimens

Answer 53

Stool

Question 54

We do not perform a bacterial Cx or parasite exam on patients who have been hospitalized for

Answer 54

More than 3 days

Question 55

We test one specimen per day x 3 days for stool for

Answer 55

Cx and OP exam

Question 56

What are the three routine bacteria in gastrointestinal specimens?

Answer 56

Campylobacter, Salmonella, and Shigella

Question 57

Better than testing WBCs to test for inflammatory response because neutrophils may be degraded

Answer 57

Lactoferrin

Question 58

We test for Shiga toxin/SMAC only when there is

Answer 58

Bloody stool

Question 59

On a GI specimen, we can test for C. difficile using

Answer 59

Antigen or DNA detection

Question 60

Antigen testing is also used on GI specimens to test for

Answer 60

H. Pylori

Question 61

With vaginitis, we use direct smears (wet preps) to test for

Answer 61

Candidiasis and Trichomoniasis

Question 62

On GU specimens, Gram stain can be used to test for

Answer 62

Bacterial vaginosus (GNR > GPR)

Question 63

In GU specimens, for a symptomatic man, GC/chlamydia, and trichomoniasis can be tested using

Answer 63

Gram stain

Question 64

In aGU specimen, we test for T. pallidum using

Answer 64

Darkfield, DFA, or Serology

Question 65

An acid fast stain (Kinyoun fluorescent) test is used in

Answer 65

Myobacteriology

Question 66

In myobacteriology, are rapid and require culture confirmation

Answer 66

NAATs

Question 67

What is the incubation period in myobacteriology?

Answer 67

6 week incubation

Question 68

There is a long incubation period in

Answer 68

Mycology

Question 69

In mycology, for yeasts, what kind of agar do we use?

Answer 69

Chromogenic agar (colorimetric species identification)

Question 70

Microscopy is of limited value for

Answer 70

Virology

Question 71

Culturing is slow but sensitive -Shell vial culture improves rates of detection

Answer 71

Virology

Question 72

Useful for viral infections where other diagnostic approaches do not exist or are ineffective (i.e. HIV, Hepatitis)

Answer 72

Serology

Question 73

The vast majority of testing in virology is now

Answer 73

NAAT based

Question 74

Predominantly microscopy based -However there is antigen detection for common GI parasites

Answer 74

Parasitology

Question 75

In parsitology, we use antigen detection for common GI parasites like

Answer 75

Giardia