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What are the medical applications of the catalase test ANDMannitol Salt Agar? Think of the detection serious pathogens thatcannot be fully differentiated by Gram stain alone.

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Nestor Rutherford
Nestor RutherfordLv2
28 Sep 2019

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Related questions

The most commonly isolated gram-positive cocci are best differentiated by their:

Gram stain morphology.

catalase reaction.

hemolytic reaction.

both a and b.

both b and c.

ANSWER:

(Level 1, Objective 1)

The novobiocin resistance test is used to

determine treatment options for Staphylococcus saprophyticus.

identify S. saprophyticus.

differentiate S. saprophyticus and S. hominis ssp. novobiosepticus.

both a and b.

ANSWER:

(Level 1, Objective 2)

The slide coagulase and the Staphylococcus latex agglutination tests are similar in that both test for the presence of

protein A.

free coagulase.

clumping factor.

thermonuclease.

ANSWER:

(Level 2, Objective 2)

The esculin/PYR disk test can be used to rapidly identify

Enterococcus spp.

Streptococcus pneumoniae.

Streptococcus pyogenes.

both a and b.

both a and c.

ANSWER:

(Level 1, Objective 2)

The optochin disk test is incubated at/in _____________________.

35°C, ambient air.

35°C, CO2.

42°C, CO2.

25°C, a capnophilic atmosphere.

ANSWER:

(Level 1, Objective 2)

A catalase-positive, gram-positive coccus that agglutinates in a slide coagulase test as well as in saline should be

reported as Staphylococcus aureus.

reported as Staphylococcus not S. aureus.

retested using another method.

retested for the catalase reaction.

ANSWER:

(Level 2, Objectives 2 and 3)

A positive rapid esculin test appears

dark.

pink.

red after the addition of the reagent.

blue.

ANSWER:

(Level 1, Objective 3)

Yellow colonies on mannitol salt agar indicate the definitive presence of

methicillin-resistant Staphylococcus aureus.

Staphylococcus aureus.

Staphylococcus not S. aureus.

unable to definitively identify.

ANSWER:

(Level 2, Objective 4)

A catalase-negative, gram-positive coccus that is bile esculin positive and 6.5% NaCl broth positive belongs to the Lancefield antigenic group

D.

C.

B.

A.

ANSWER:

(Level 2, Objective 5)

10. A leg wound isolate presents as a yellow pigmented, beta-hemolytic, catalase-positive, gram-positive cocci in clusters. Which of the following tests would you expect to be positive for this isolate?

Novobiocin resistance

Heat-stable thermonuclease

PYR

b and c

a and b

ANSWER:

(Level 2, Objective 5)

11. A catalase-negative coccus in pairs and short chains that is susceptible to ethyl hydrocupreine will also

a. require CO2 for growth.

b. be alpha hemolytic.

c. be bile soluble.

d. all of the above.

e. b and c.

ANSWER:

(Level 2, Objective 5)

12. The PBP2a latex agglutination test is used to detect catalase-positive, coagulase-positive, gram-positive cocci that are resistant to

a. vancomycin.

b. novobiocin.

c. oxacillin.

d. penicillin.

ANSWER:

(Level 2, Objective 6)

13. A catalase-negative, gram-positive coccus in chains that is positive for esculin and PYR hydrolysis is also vancomycin resistant. What additional antibiotic resistance can this organism exhibit?

a. high level aminoglycosides.

b. ampicillin and penicillin.

c. beta-lactamase production.

d. all of the above.

e. b and c.

ANSWER:

(Level 2, Objective 6)

14. An alpha-hemolytic, catalase-negative, gram-positive coccus that is susceptible to optochin can cause all of the following diseases except

a. pneumonia.

b. sinusitis.

c. meningitis.

d. pharyngitis.

ANSWER:

(Level 2, Objective 7)

15. The catalase-negative, gram-positive coccus that is the most common cause of neonatal sepsis and meningitis

a. has the potential to be vancomycin resistant.

b. hydrolyzes hippurate.

c. is susceptible to bacitracin.

d. is bile soluble.

ANSWER:

(Level 2, Objective 7)

16. Necrotizing fasciitis is caused by a

a. catalase-negative, gram-positive coccus that is susceptible to bacitracin.

b. catalase-negative, gram-positive coccus that produces CAMP factor.

c. catalase-positive, gram-positive coccus that produces coagulase.

d. catalase-positive, gram-positive coccus that is resistant to novobiocin.

ANSWER:

(Level 2, Objective 7)

17. Infections of indwelling devices, such as intravenous catheters, are often caused by catalase-positive, gram-positive cocci that are

a. coagulase positive and thermonuclease negative.

b. coagulase negative and novobiocin resistant.

c. caogulase positive and thermonuclease positive.

d. coagulase negative and novobiocin susceptible.

ANSWER:

(Level 2, Objective 7)

18. Which of the following factors accounts for the virulence of Streptococcus pyogenes?

a. “C” substance

b. Protein A

c. M protein

d. mecA gene

ANSWER:

(Level 1, Objective 7)

19. The virulence factor most often associated with catalase-negative, gram-positive cocci that are bile soluble is

a. capsule production.

b. vancomycin resistance.

c. hyaluronidase.

d. streptolysin S.

ANSWER:

(Level 2, Objective 7)

20. A catalase-negative, alpha-hemolytic, gram-positive coccus that is resistant to ethyl hydrocupriene is usually considered

a. a member of the normal upper respiratory flora.

b. a pathogen in an expectorated sputum specimen.

c. the causative agent of non-suppurative sequelae.

d. a common urinary pathogen.

ANSWER:

(Level 2, Objective 8)

21. A catalase-positive, coagulase-negative, gram-positive coccus in clusters is isolated from the urine of a 24-year-old female. This isolate will require

a. additional testing to identify.

b. no further testing.

c. a screen for vancomycin resistance.

d. Lancefield grouping.

ANSWER:

(Level 2, Objective 10)

22. A blood culture yields yellow-pigmented, beta-hemolytic, catalase-positive, gram-positive cocci in clusters. The department is out of Staphylococcus latex agglutination reagent. The microbiologist sets up a tube coagulase and mannitol salt agar. She incubates both at 35°C in CO2 overnight. The next day the coagulase test is negative and the mannitol salt agar displays yellow colonies. How will you proceed with these results?

a. Report this organism as Staphylococcus aureus

b. Report this organism as Staphylococcus not S. aureus

c. Repeat the tests due to invalid results

d. Test the organism for novobiocin resistance

ANSWER:

(Level 3, Objective 10)

24. A patient, suspected to have bacterial endocarditis, had two sets of blood cultures drawn. All four bottles are positive with gram-positive cocci in pairs and chains. On sheep blood agar, the gray, transparent, alpha-hemolytic colonies are catalase negative, optochin resistant, ESC negative and PYR negative. Which of the following patient histories correlates with the presence of this organism?

a. 78-year-old male with bacterial pneumonia

b. 47-year-old female with a heart murmur and a history of dental surgery

c. 16-year-old female with a history of untreated pharyngitis

d. 3-day-old premature male

ANSWER:

(Level 3, Objective 10)

25. A translucent colony displaying subtle beta hemolysis is isolated from a placenta culture. The Gram stain revealed gram-positive cocci in pairs. The microbiologist drops 3% catalase reagent onto a colony on sheep blood agar, and it produces bubbles. He then performs a Staphyloccocus latex agglutination and the suspension remains smooth. The next step is to

a. report the organism as Staphylococcus not S. aureus.

b. report the organism as Staphylococcus aureus.

c. repeat the catalase test due to an invalid result.

d. perform a thermonuclease test due to an invalid latex agglutination result.

ANSWER:

(Level 3, Objective 10)

2. A76-year-old man with atherosclerosis had been previously admitted for abdominal aneurysm and resection of the perirenal aorta. He had several follow-up admissions over the next year for postoperative wound infections, with accompanying bacteremia, alternating between Pseudomonas aeruginosa, vancomycin-resistant Enterococcus faecium, and Candida glabrata. On his final admission, blood cultures were positive, with numerous gram-positive cocci in pairs and chains in the smear, but subculture of the bottle showed no growth aerobically with increased CO2 on blood agar or chocolate agar or anaerobically on Brucella agar. QUESTIONS a) What is this organism and what would you do to grow it? b) To control infection, screening for vancomycin resistance in enterococci on selected hospitalized patients is important. What is a cost-effective screening method? c) Many genera of gram-positive cocci are catalase negative, but only a few are vancomycin-resistant. Name these genera, and indicate how they can be differentiated from vancomycin-resistant enterococci.

1. An organism, observed on direct Gram stain from a clinical specimen, does not grow on blood or chocolate agars incubated at 35°C in CO2. This can be explained by all of following statements except

a. the organism is an anaerobe.

b. the organism is dead due to previous antibiotic therapy.

c. the organism requires nicotinamide adenine dinucleotide for growth.

d. the organism is fastidious and is not being provided the growth factor it needs.

2. The laboratory should be notified in advance when the physician suspects Francisella tularensis because the organism is

a. fastidious and requires special medium.

b. infectious for laboratory personnel.

c. not culturable.

d. a and b.

e. b and c.

3. The HACEK organisms share all of the following characteristics except

a. gram-negative coccobacilli that are oxidase and catalase positive.

b. slow growing and stimulated by carbon dioxide.

c. part of the normal oral flora.

d. causative agents of bacterial endocarditis.

4. Legionella pneumophila and Francisella tularensis share the characteristic of

a. being easily identified by biochemical testing.

b. a requirement for cysteine to grow in culture.

c. the necessity for the use of Gimenez stain rather than Gram stain to visualize.

d. having an animal reservoir.

5. Legionella pneumophila and Francisella tularensis share all of the following characteristics except

a. poor Gram staining properties.

b. ability to cause pneumonia.

c. ability to diagnose infection with detection of serum antibodies.

d. fluorescence of colonies.

6. A blood culture isolate that stains as pleomorphic gram-negative coccobacillus and only grows on chocolate agar should be

a. identified using the ALA test.

b. identified using the ALA and horse blood agar tests.

c. presumptively identified under BSL 2 conditions.

d. identified using X and V factor disks and horse blood agar.

7. Which of the following organisms requires factor X only on initial isolation but loses the requirement on subculture?

a. Aggregatibacter actinomycetemcomitans

b. Eikenella corrodens

c. Francisella tularensis

d. Aggregatibacter aphrophilus

8. Haemophilus ducreyi is unique among the genus because it requires

a. factors X and V.

b. no factors.

c. heme only.

d. NAD only.

9. Streptobacillus moniliformis is most easily isolated from blood cultures because it requires _____ for growth.

a. heme

b. serum

c. cysteine

d. 1% α-ketoglutarate

10. A 57-year-old male farmer sees his physician complaining of fever, night sweats, and lethargy that come and go over the past three months. The patient’s history reveals that he raises sheep for wool and meat and goats for milk. The physician suspects undulant fever. What is the optimal specimen(s) for culture of this suspected organism?

a. Blood

b. Bone marrow

c. Lymph node biopsy

d. All of the above

e. B and C

11. A microbiologist processes a specimen for culture using a buffered charcoal yeast extract agar plate. What was the original specimen used for inoculation of this agar plate?

a. Blood

b. Lower respiratory specimen

c. Nasopharyngeal

d. Urine

12. A nasopharyngeal swab containing ciliated epithelial cells is the best specimen for the recovery of the organism that causes

a. whooping cough.

b. undulant fever.

c. rat bite fever.

d. legionnaire’s disease.

13. What is the clinical significance of ALA-positive, gram-negative coccobacilli in a sputum culture?

Normal flora

Potential pathogen

Significant if it is hemolytic on horse blood agar

Further testing is needed to assess significance

14. A small, slender, gram-negative rod was recovered from the blood cultures of a patient following root canal surgery. At 48 hours, the following results were observed:

BAP and CHOC agars: small gray colonies that tend to pit the agar

MAC agar: no growth

Odor upon opening the agar plates: bleach-like

This organism will also be

a. catalase and oxidase positive.

b. catalase positive and oxidase negative.

c. catalase and oxidase negative.

d. catalase negative and oxidase positive.

15. A pleomorphic gram-negative coccobacillus is isolated from the blood cultures of 58-year-old male who had recent dental surgery. His history is significant for rheumatic fever as a child. The organism only grows on chocolate agar. It should be tested using

a. ALA.

b. X and V factor disks.

c. ALA and horse blood agar.

d. X and V factors and horse blood agar.

16. The virulence of Bordetella pertussis is related to its

a. toxin’s ability to paralyze ciliated epithelial cells.

b. ability to hide in the reticuloendothelial system.

c. easy dissemination.

d. ability to live inside white blood cells.

17. Infection due to Brucella spp. is often slow to develop, long term, and displaying periodicity. This can be explained by the organism’s ability to

a. colonize the upper respiratory tract prior to infection.

b. travel and hide in the reticuloendothelial system.

c. cause infection as the vaccine wanes in adults.

d. change its surface antigens.

18. A 10-year-old male gave mouth-to-mouth resuscitation to his pet guinea pig, which proceeded to bite him on the lip. The guinea pig did not survive. Two days after the guinea pig’s funeral, the boy became ill with fever, chills, joint pain, and a rash. What organism should the physician suspect based on the patient’s history?

a. Brucella spp.

b. Francisella tularensis

c. Streptobacillus moniliformis

d. Eikenella corrodens

19. You and your best friend get into a fist fight. Your knuckles are torn and bleeding afterwards. What organism are you likely to isolate if your wounds become infected?

a. Kingella kingae

b. Eikenella corrdens

c. Aggregatibacter aphrophilus

d. Cardiobacterium hominis

20. Epiglottitis, a severe life-threatening infection occurring in non-vaccinated infants and children, is most commonly caused by

a. a pleomorphic gram-negative coccobacillus that is ALA positive and horse blood agar positive.

b. a gram-negative coccobacillus that is identified by direct fluorescent antibody and slide agglutination tests.

c. a gram-negative coccobacillus that is best identified by a rise in antibody titer in serum samples drawn two weeks apart.

d. a pleomorphic gram-negative coccobacillus that requires X and V factors and is horse blood agar negative.

21. An organism isolated from the swab of purulent eye drainage shows no fluorescence on the ALA test. The horse blood agar displays no hemolysis. This organism should be reported as

a. Haemophilus influenzae.

b. H. aegyptius.

c. H. influenzae or H. aegyptius, biochemically similar.

d. H. parainfluenzae.

22. Because of the nature of the profession, a veterinarian is at increased risk of acquiring

1. Brucella spp.

2. Aggregatibacter actinomycetemcomitans

3. Francisella tularensis

4. Streptobacillus moniliformis

5. Eikenella corrodens

a. 1, 2, 4, and 5

b. 1, 3, and 4

c. 2, 3, and

d. 3 and 4

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