Deck 41: Mycobacteria

Question 1

The specimen of choice for detecting mycobacterium in a skin lesion or wound is a:

A)swab placed in Amie's transport medium or Stuart's medium.
B)needle aspiration.
C)skin scraping.
D)swab placed in anaerobic conditions.

Answer 1

B
If attempting to culture a skin lesion or wound,an aspirate is the best type of specimen to collect.If the volume is insufficient for aspiration,then pus and exudates may be obtained on a swab and placed in Amie's transport medium or Stuart's medium.

Question 2

Which of the following species of Mycobacterium causes a chronic disease of the skin,mucous membranes,and nerve tissue but has not yet been cultivated in vitro?

A)M.paratuberculosis
B)M.lepraemurium
C)M.phlei
D)M.leprae

Answer 2

D
Leprosy is both a bacterial and immunologic disease.Based on the host's response,the spectrum of disease caused by M.leprae ranges from subclinical infection to intermediate stages of disease to full-blown and serious clinical manifestations involving the skin,upper respiratory system,testes,and peripheral nerves.The two major forms of the disease are a localized form called tuberculoid leprosy and a more disseminated form called lepromatous leprosy.

Question 3

The most commonly isolated mycobacterium in the United States is:

A)M.tuberculosis.
B)M.bovis.
C)Mycobacterium avium-intracellulare.
D)Mycobacterium paratuberculosis.

Answer 3

C
Mycobacterium avium complex (MAC)is an important pathogen in immunocompromised and immunocompetent populations.This agent is among the most commonly isolated NTM species in the United States,particularly in its potentially pathogenic role in pulmonary infections in patients with acquired immunodeficiency syndrome (AIDS)and patients who are non-HIV infected.

Question 4

Slow-growing NTM whose colonies become pigmented when exposed to light are referred to as:

A)scotochromogens.
B)photochromogens.
C)nonphotochromogens.
D)chromogenicums.

Question 5

The Runyon system of classification is based on:

A)colonial and microscopic morphologic characteristics.
B)biochemical characteristics.
C)growth rate and colonial pigmentation.
D)genotypic characteristics.

Question 6

The primary reservoir of the Mycobacterium responsible for leprosy is:

A)infected humans.
B)infected animals.
C)contaminated food.
D)contaminated objects.

Question 7

A positive tuberculin skin test,or PPD test,is characterized by:

A)erythema and induration.
B)redness and rash.
C)swelling and erythema.
D)edema and rash.

Question 8

The specimens of choice for detecting nontuberculous mycobacterial disease are:

A)spontaneously produced sputa.
B)gastric lavages.
C)transtracheal aspirations.
D)bronchial lavages,washings,and brushings.

Question 9

Mycobacterium fortuitum,Mycobacterium chelonae,and Mycobacterium abscessus are:

A)responsible for approximately 90% of clinical mycobacterial disease.
B)unable to grow on routine bacteriologic media.
C)gram-negative rods resembling Escherichia coli on Gram stain.
D)slow growers requiring a minimum of 14 days to grow.

Question 10

Known to cause an inflammatory bowel disease referred to as Johne's disease in cattle,sheep,and goats,which organism has been isolated from the bowel mucosa of patients with Crohn disease?

A)M.paratuberculosis
B)M.avium-intracellulare
C)Mycobacterium phlei
D)Mycobacterium lepraemurium

Question 11

What quantity of cerebrospinal fluid (CSF)is considered sufficient for the detection of tuberculous meningitis?

A)1 mL
B)5 mL
C)10 mL
D)20 mL

Question 12

The recent emergence of epidemic multidrug-resistant strains of M.tuberculosis,in conjunction with the end of the downward trend of reported cases of tuberculosis in the United States,has been largely attributed to:

A)human immunodeficiency virus (HIV)epidemic.
B)ineffective treatment regimens.
C)political factors.
D)shortened treatment regimens.

Question 13

Slow-growing NTM whose colonies are pigmented when grown in the dark or the light are referred to as:

A)scotochromogens.
B)photochromogens.
C)nonphotochromogens.
D)chromogenicums.

Question 14

The tuberculin skin test,or the purified protein derivative (PPD)test,is based on:

A)delayed hypersensitivity cell-mediated immunity to certain antigenic components of the organism.
B)injection of M.tuberculosis under the skin and subsequent mild cutaneous infection.
C)antigen-antibody reactions occurring at the injection site.
D)humoral-mediated immune response.

Question 15

Examples of the mycobacterial species that occur in humans and belong to the Mycobacterium tuberculosis complex include:

A)M.tuberculosis,nontuberculous mycobacteria,M.bovis,and M.africanum.
B)M.tuberculosis,M.gordonae,M.bovis BCG,and M.africanum.
C)M.tuberculosis,M.bovis,M.avium,and M.intracellulare.
D)M.tuberculosis,M.bovis,M.bovis BCG,and M.africanum.

Question 16

Characteristics that are found in the bacteria called Mycobacterium are:

A)a cell wall that contains N-glycolylmuramic acid and has a high lipid content.
B)a cell wall that has a low lipid content.
C)sensitive to decolorization by acidified alcohol.
D)rapid-growers,as compared with most other human pathogenic bacteria.

Question 17

The specimen of choice for detecting tuberculous pulmonary mycobacterial disease is:

A)spontaneously produced sputum.
B)gastric lavage.
C)transtracheal aspiration.
D)bronchoscopy.

Question 18

Slow-growing NTM whose colonies produce no pigment,whether they are grown in the dark or the light,are referred to as:

A)scotochromogens.
B)photochromogens.
C)nonphotochromogens.
D)chromogenicums.

Question 19

The term complex as used in the Mycobacterium tuberculosis complex:

A)means that the identification of the organism is complex and is only performed in large reference laboratories.
B)is used to describe two or more species whose distinction is complicated and of little or no medical importance.
C)refers to a set of organisms that are genetically indistinguishable but are phenotypically different.
D)refers to different subtypes of the bacteria M.tuberculosis.

Question 20

The specimens of choice for detecting urinary tract mycobacterial disease are:

A)single clean-catch midstream urine samples.
B)24-hour timed urine samples.
C)three daily clean-catch midstream urine samples.
D)biopsies of the suspected site.

Question 21

Acid-fast smears should be examined carefully by scanning at least ________ oil immersion fields.

A)100
B)200
C)300
D)400

Question 22

The first test that is always performed on organisms growing on solid or liquid mycobacterial media is a(n):

A)niacin test.
B)acid-fast stain.
C)Gram stain.
D)broth test.

Question 23

Quality control is performed to test the validity of catalase production at 68°C.M.fortuitum and M.tuberculosis are used,which yield a positive and negative reaction,respectively.Which one of the following statements explains this discrepancy?

A)Both organisms were most likely incubated at the wrong temperature.
B)Both organisms were most likely incubated on the wrong media before testing.
C)The catalase reagent is most likely expired.
D)No discrepancy is present.M.fortuitum is catalase-positive and M.tuberculosis is catalase-negative at 68°C.

Question 24

The stain that requires heating the slide for better penetration of stain into the mycobacterial cell wall is known as the:

A)Kinyoun's.
B)Ziehl-Neelsen.
C)fluorochrome.
D)carbolfuchsin.

Question 25

The nonpathogenic Mycobacterium commonly found in tap water,which has been a problem when tap water or deionized water has been used in the preparation of smears,is:

A)M.paratuberculosis.
B)M.lepraemurium.
C)M.phlei.
D)M.gordonae.

Question 26

One drawback associated with the fluorochrome stain method for detecting Mycobacterium is that:

A)it is less sensitive than the conventional carbolfuchsin stains.
B)it requires the smear to be initially examined at lower magnifications.
C)many rapid-growers may not appear fluorescent with these reagents.
D)it increases the amount of time needed for examining smears.

Question 27

For reliable results,the niacin test should be performed only from cultures that are at least:

A)2 weeks old and show at least five colonies on Löwenstein-Jensen medium.
B)3 weeks old and show at least 50 colonies on Löwenstein-Jensen medium.
C)3 weeks old and show at least 50 colonies on Middlebrook 7H11 agar.
D)2 weeks old and show at least five colonies on Middlebrook 7H11 agar.

Question 28

Optimal conditions for the recovery of M.haemophilum from specimens include:

A)inoculation to a sheep blood agar plate.
B)incubation at 35°C to 42°C.
C)placement of an X-factor disk on the media.
D)microaerophilic environment with low humidity.

Question 29

The type of specimen collected for mycobacterial studies that must be neutralized with 10% sodium carbonate is:

A)spontaneously produced sputum.
B)gastric lavage.
C)transtracheal aspiration.
D)bronchial lavage.

Question 30

Optimal conditions for most mycobacterial cultures are:

A)25°C to 30°C in the dark in an atmosphere of 2% carbon dioxide (CO₂)and high humidity.
B)35°C in the dark in an atmosphere of 5% to 10% CO₂ and high humidity.
C)35°C in the dark in a microaerophilic atmosphere of 10% CO₂ and high humidity.
D)32°C in the dark in an atmosphere of decreased CO₂ and increased humidity.

Question 31

Negative mycobacterial cultures are reported final and the cultures are discarded after what period?

A)7 days
B)2 weeks
C)4 weeks
D)8 weeks

Question 32

Sodium hydroxide (NaOH),Zephiran-trisodium phosphate,N-acetyl-L-cysteine-NaOH (NALC-NaOH),and oxalic acid are associated with:

A)methods of cultivating Mycobacterium in vitro.
B)digestion and decontamination of specimens for mycobacterial studies.
C)identification of clinically significant Mycobacterium.
D)antimicrobial susceptibility testing of mycobacterial species.

Question 33

Fluorescent staining is more sensitive than conventional carbolfuchsin stains.What counterstain is used during the procedure?

A)Methylene blue
B)Crystal violet
C)Potassium permanganate
D)Auramine-rhodamine

Question 34

The fluorochrome method of staining Mycobacterium:

A)is less sensitive than the conventional carbolfuchsin stains.
B)enables the smear to be initially examined at lower magnifications.
C)results in a lower yield of positive smears.
D)increases the amount of time needed for examining smears.

Question 35

In the identification of mycobacterial isolates,the niacin test involves the:

A)accumulation of niacin in the medium in which the organism is growing.
B)metabolism of niacin to nicotinic acid by enzymatic action.
C)testing of the isolate for susceptibility to niacin.
D)utilization of niacin in metabolic pathways to produce nicotinic acid.

Question 36

When culturing for Mycobacterium,rapid-growers usually produce colonies within how many days after subculture?

A)At least 7 days
B)Longer than 7 days
C)3 to 4 days
D)2 to 3 days

Question 37

Under what circumstance might slow-growing mycobacteria appear to produce colonies in a few days?

A)When the inoculum is too heavy
B)When subcultured to an enriched medium
C)When incubated at slightly warmer temperatures
D)When kept in the light

Question 38

Specimens for Mycobacterium studies that require concentration,decontamination,or liquefaction include:

A)CSF and other body fluids.
B)sputum.
C)urine.
D)swabs and wound aspirates.

Question 39

On Gram stain,mycobacteria appear as:

A)slender,well-stained gram-positive bacilli.
B)poorly stained,beaded,gram-positive bacilli.
C)gram-variable to gram-positive bacilli.
D)partially invisible gram-negative bacilli.

Question 40

The stain that does not require heating the slide for better penetration of stain into the mycobacterial cell wall is known as the:

A)Kinyoun's.
B)Ziehl-Neelsen.
C)immunofluorochrome.
D)carbolfuchsin.

Question 41

In the identification of mycobacterial isolates,the Tween 80 test involves:

A)an enzyme that is able to produce Tween 80 from certain ingredients found in the medium.
B)a lipase that is able to hydrolyze polyoxyethylene sorbitan monooleate into oleic acid and polyoxyethylated sorbitol.
C)the metabolism of niacin to nicotinic acid by enzymatic action.
D)testing the isolate for susceptibility to Tween 80.

Question 42

A fisherman who cut himself on a fishing hook later develops a cutaneous disease at the inoculation site.The exudate is aspirated and set up on a routine AFB medium for culture.It is incubated at 37°C,but no growth is observed after 8 weeks;however,a slide of the exudate was AFB-positive.Which one of the following statements explains these findings?

A)The infection is most likely the result of a viral infection.
B)The organism should have been incubated at 30°C.
C)The organism should have been incubated at 42°C.
D)The infection is most likely fungal in nature.

Question 43

In the identification of mycobacterial isolates,the catalase test involves the:

A)breakdown of phenolphthalein disulfate into phenolphthalein and other salts.
B)measurement of the height of a column of bubbles of oxygen.
C)production of a lipase that is able to hydrolyze the catalase.
D)development of a pink-to-red color,indicating a positive result.

Question 44

The 3-day test that is useful for identifying the rapid-growers,M.fortuitum and M.chelonae,and that measures the rate by which this enzyme breaks down phenolphthalein disulfate into phenolphthalein and other salts is the ____________ test.

A)niacin.
B)phenolphthalein.
C)arylsulfatase.
D)Tween 80.

Question 45

Which continuous growth system uses a CO₂ sensor to monitor mycobacterial growth?

A)BACTEC 9000 MB
B)BACTEC MGIT 960
C)MGIT System
D)BacT/Alert