A 67-year-old smoker with COPD is admitted with fever and purulent sputum. The sputum Gram stain shows fewer than 10 squamous epithelial cells and more than 25 neutrophils per low-power field, with many small, pale, pleomorphic gram-negative coccobacilli. At 24 hours, sheep blood agar has a moderate mix of alpha-hemolytic streptococci and Neisseria species. Chocolate agar has the same flora plus heavy growth of small, gray, moist colonies that are absent from the blood agar. MacConkey agar has no growth. The chocolate-only colony is porphyrin (ALA) test negative. The best report is:

Heavy H. influenzae; do a beta-lactamase test

Poor-quality specimen; request a new sputum

Heavy H. parainfluenzae, part of oral flora

Normal oral flora only; no further workup

A 70-year-old man has been on a ventilator for 6 days and has a new infiltrate with purulent secretions. A bronchoalveolar lavage (BAL) specimen is sent. The cytocentrifuged smear shows many neutrophils, squamous epithelial cells under 1% of cells, and gram-negative rods. Undiluted fluid is plated with a 0.001 mL calibrated loop. At 24 hours the plates show 45 colonies of Pseudomonas aeruginosa, 30 colonies of mixed viridans streptococci and Neisseria species, and 3 colonies of Candida albicans. The laboratory uses 10^4 CFU/mL as the BAL threshold for pneumonia. The correct report is:

P. aeruginosa 4.5 x 10^4 CFU/mL, with susceptibility

P. aeruginosa and C. albicans, both significant

P. aeruginosa 4.5 x 10^3 CFU/mL, below threshold

Mixed flora; quantitative culture not valid

A 68-year-old with lobar pneumonia got one dose of ceftriaxone before sputum was collected. The Gram stain shows many neutrophils and lancet-shaped gram-positive diplococci, but culture grows only oral flora. Which test can still confirm the likely pathogen?

Pneumococcal urinary antigen test

Legionella urinary antigen test

Lower respiratory tract

16 ASCP MLS practice questions on Lower respiratory tract, part of Microbiology. The first 16 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 67-year-old smoker with COPD is admitted with fever and purulent sputum. The sputum Gram stain shows fewer than 10 squamous epithelial cells and more than 25 neutrophils per low-power field, with many small, pale, pleomorphic gram-negative coccobacilli. At 24 hours, sheep blood agar has a moderate mix of alpha-hemolytic streptococci and Neisseria species. Chocolate agar has the same flora plus heavy growth of small, gray, moist colonies that are absent from the blood agar. MacConkey agar has no growth. The chocolate-only colony is porphyrin (ALA) test negative. The best report is:
1. APoor-quality specimen; request a new sputum
2. BHeavy H. parainfluenzae, part of oral flora
3. CHeavy H. influenzae; do a beta-lactamase test
4. DNormal oral flora only; no further workup
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Answer: C · Heavy H. influenzae; do a beta-lactamase test
The specimen passes the quality screen, and the predominant organism on the Gram stain matches the heavy chocolate-only growth. Haemophilus grows on chocolate agar but not on sheep blood agar, where V factor (NAD) is not available. A negative porphyrin test means the organism cannot make heme from delta-aminolevulinic acid and so needs X factor, which identifies H. influenzae; H. parainfluenzae, a member of the oral flora, is porphyrin positive. H. influenzae is a common cause of pneumonia and exacerbations in COPD, and many isolates produce beta-lactamase, so a beta-lactamase test belongs in the workup.
- A: Fewer than 10 squamous cells and many neutrophils mean a good specimen.
- B: H. parainfluenzae does not need X factor and is porphyrin positive.
- D: The heavy, chocolate-only growth matches the Gram stain and is a pathogen.
Question 2 · Hard
A 70-year-old man has been on a ventilator for 6 days and has a new infiltrate with purulent secretions. A bronchoalveolar lavage (BAL) specimen is sent. The cytocentrifuged smear shows many neutrophils, squamous epithelial cells under 1% of cells, and gram-negative rods. Undiluted fluid is plated with a 0.001 mL calibrated loop. At 24 hours the plates show 45 colonies of Pseudomonas aeruginosa, 30 colonies of mixed viridans streptococci and Neisseria species, and 3 colonies of Candida albicans. The laboratory uses 10^4 CFU/mL as the BAL threshold for pneumonia. The correct report is:
1. AP. aeruginosa 4.5 x 10^4 CFU/mL, with susceptibility
2. BP. aeruginosa and C. albicans, both significant
3. CP. aeruginosa 4.5 x 10^3 CFU/mL, below threshold
4. DMixed flora; quantitative culture not valid
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Answer: A · P. aeruginosa 4.5 x 10^4 CFU/mL, with susceptibility
With a 0.001 mL loop each colony represents 1,000 CFU/mL, so 45 colonies of P. aeruginosa equal 4.5 x 10^4 CFU/mL, above the 10^4 CFU/mL BAL threshold. The specimen is acceptable because squamous cells are under 1% of cells, and the Gram stain matches the culture. The oral streptococci and Neisseria are reported as oral flora, and the yeast, at 3 x 10^3 CFU/mL, is below threshold; Candida in respiratory specimens is rarely a cause of pneumonia. Using the factor for a 0.01 mL loop (x 100) gives the falsely low 4.5 x 10^3 CFU/mL.
- B: C. albicans is at 3 x 10^3 CFU/mL and is rarely a cause of pneumonia.
- C: That count uses a 0.01 mL loop factor; a 0.001 mL loop multiplies by 1,000.
- D: Squamous cells are under 1%, so the specimen is acceptable for quantitation.
Question 3 · Medium
A 19-year-old student has a dry cough, low fever and patchy infiltrates. The sputum Gram stain shows a few neutrophils and no predominant organism. Which test is best for the most likely organism?
1. AMycoplasma pneumoniae NAAT
2. BSputum culture on blood agar
3. CAcid-fast stain of sputum
4. DCold agglutinin titer
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Answer: A · Mycoplasma pneumoniae NAAT
This picture of atypical (walking) pneumonia in a young adult is typical of Mycoplasma pneumoniae. The organism has no cell wall, so it does not stain with the Gram stain and does not grow on routine media. Nucleic acid amplification of a throat, nasopharyngeal or sputum sample is the preferred test because it is rapid and sensitive. Cold agglutinins appear in only about half of patients and are not specific.
- B: Mycoplasma lacks a cell wall and does not grow on blood agar.
- C: Nothing here suggests tuberculosis, and an acid-fast stain would not detect Mycoplasma.
- D: Cold agglutinins are insensitive and nonspecific.
Question 4 · Hard
A 68-year-old with lobar pneumonia got one dose of ceftriaxone before sputum was collected. The Gram stain shows many neutrophils and lancet-shaped gram-positive diplococci, but culture grows only oral flora. Which test can still confirm the likely pathogen?
1. ARepeat sputum culture next day
2. BPneumococcal urinary antigen test
3. CCold agglutinin titer
4. DLegionella urinary antigen test
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Answer: B · Pneumococcal urinary antigen test
Lancet-shaped gram-positive diplococci with many neutrophils point to Streptococcus pneumoniae. Pneumococci are fragile and die quickly after even one antibiotic dose, so culture often fails while the smear is still positive. The urinary antigen test detects pneumococcal cell wall C-polysaccharide and stays positive for days to weeks after treatment starts. A repeat culture after more doses is even less likely to grow the organism.
- A: More antibiotic doses make a repeat culture even less likely to grow pneumococci.
- C: Cold agglutinins relate to Mycoplasma, not pneumococcal infection.
- D: The Legionella antigen detects Legionella, which does not appear as gram-positive diplococci.
Question 5 · Medium
Sputum from a smoker with a COPD flare shows many neutrophils and gram-negative diplococci. Gray-white colonies on blood agar are oxidase positive and slide intact across the agar when pushed with a loop. The most likely organism is:
1. AAcinetobacter baumannii
2. BMoraxella catarrhalis
3. CNeisseria meningitidis
4. DHaemophilus influenzae
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Answer: B · Moraxella catarrhalis
Moraxella catarrhalis is a common cause of flares of chronic obstructive pulmonary disease, as well as otitis media and sinusitis. Its colonies are firm and can be pushed across the agar like a hockey puck. It is oxidase positive and also DNase and butyrate esterase positive, which separates it from Neisseria species. More than 90% of strains make beta-lactamase, so ampicillin is not used.
- A: Acinetobacter baumannii is oxidase negative.
- C: Neisseria meningitidis does not form hockey-puck colonies and is butyrate esterase negative.
- D: Haemophilus influenzae is a coccobacillus and does not grow on sheep blood agar alone.
Question 6 · Hard
Sputum from a patient with severe pneumonia grows colonies on BCYE agar at day 4 that do not grow on blood agar; they are identified as Legionella pneumophila serogroup 6. The urinary antigen test done on admission was negative. What best explains the discrepancy?
1. AUrinary antigen appears only weeks after onset
2. BAntibiotics clear the antigen from urine in hours
3. CThe antigen test detects mainly serogroup 1
4. DThe culture result is probably a contaminant
Answer and explanation in LearnFree account
Question 7 · Medium
A good-quality sputum from an adult with pneumonia grows moderate amounts of four organisms. Which one should be identified and reported rather than included in normal oral flora?
1. AHaemophilus influenzae
2. BCoagulase-negative staphylococci
3. CCorynebacterium species
4. DViridans group streptococci
Answer and explanation in LearnFree account
Question 8 · Medium
Which selective medium is added to cystic fibrosis respiratory cultures to recover Burkholderia cepacia complex?
1. ABurkholderia cepacia selective agar
2. BCetrimide agar
3. CBuffered charcoal yeast extract agar
4. DRegan-Lowe charcoal agar
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Question 9 · Medium
Ten days after influenza, a 34-year-old develops necrotizing pneumonia. The sputum Gram stain shows many neutrophils and many gram-positive cocci in clusters. The most likely cause is:
1. AStaphylococcus epidermidis
2. BStreptococcus pyogenes
3. CStreptococcus pneumoniae
4. DStaphylococcus aureus
Answer and explanation in LearnFree account
Question 10 · Hard
Sputum from a patient with chemotherapy-induced neutropenia (neutrophils 0.2 x 10^3/µL [0.2 x 10^9/L]) shows 2 squamous epithelial cells and 3 white cells per low-power field. How should it be handled for routine bacterial culture?
1. AReject it; too few white cells show it is saliva
2. BAccept it, but report only fungi and yeasts
3. CAccept it; few squamous cells show little saliva
4. DReject it; neutropenic patients need a BAL instead
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Question 11 · Hard
A protected specimen brush sample from a ventilated patient grows Klebsiella pneumoniae at 5 x 10^3 CFU/mL. Using common quantitative thresholds, this result is:
1. ASignificant, above the 10^3 CFU/mL brush threshold
2. BUninterpretable, because brush samples are not quantified
3. CNot significant, below the 10^5 CFU/mL aspirate threshold
4. DNot significant, below the 10^4 CFU/mL BAL threshold
Answer and explanation in LearnFree account
Question 12 · Easy
What is the usual diagnostic threshold for a potential pathogen in a quantitative bronchoalveolar lavage (BAL) culture?
1. A10^4 CFU/mL
2. B10^2 CFU/mL
3. C10^3 CFU/mL
4. D10^6 CFU/mL
Answer and explanation in LearnFree account
Question 13 · Medium
For anaerobic culture in a suspected lung abscess, the acceptable lower respiratory specimen is:
1. AInduced sputum
2. BProtected specimen brush sample
3. CExpectorated sputum
4. DEndotracheal aspirate
Answer and explanation in LearnFree account
Question 14 · Easy
A sputum specimen is judged to be mostly saliva, and unsuitable for routine culture, when the low-power Gram stain fields show many:
1. ANeutrophils
2. BAlveolar macrophages
3. CCiliated columnar cells
4. DSquamous epithelial cells
Answer and explanation in LearnFree account
Question 15 · Hard
BAL fluid is diluted 1:100, and 0.1 mL of the dilution is spread on a plate. It grows 30 colonies of Pseudomonas aeruginosa. What is the count in the original fluid?
1. A3 x 10^2 CFU/mL
2. B3 x 10^4 CFU/mL
3. C3 x 10^3 CFU/mL
4. D3 x 10^5 CFU/mL
Answer and explanation in LearnFree account
Question 16 · Hard
A sputum sent for Legionella culture has 15 squamous epithelial cells and 5 white cells per low-power field. What should the laboratory do?
1. APlate it on blood and chocolate agar only
2. BReject it and request a new specimen
3. CAccept it only for a Gram stain
4. DAccept it and plate it on BCYE agar
Answer and explanation in LearnFree account

Lower respiratory tract

A 19-year-old student has a dry cough, low fever and patchy infiltrates. The sputum Gram stain shows a few neutrophils and no predominant organism. Which test is best for the most likely organism?

A 68-year-old with lobar pneumonia got one dose of ceftriaxone before sputum was collected. The Gram stain shows many neutrophils and lancet-shaped gram-positive diplococci, but culture grows only oral flora. Which test can still confirm the likely pathogen?

Sputum from a smoker with a COPD flare shows many neutrophils and gram-negative diplococci. Gray-white colonies on blood agar are oxidase positive and slide intact across the agar when pushed with a loop. The most likely organism is:

Sputum from a patient with severe pneumonia grows colonies on BCYE agar at day 4 that do not grow on blood agar; they are identified as Legionella pneumophila serogroup 6. The urinary antigen test done on admission was negative. What best explains the discrepancy?

A good-quality sputum from an adult with pneumonia grows moderate amounts of four organisms. Which one should be identified and reported rather than included in normal oral flora?

Which selective medium is added to cystic fibrosis respiratory cultures to recover Burkholderia cepacia complex?

Ten days after influenza, a 34-year-old develops necrotizing pneumonia. The sputum Gram stain shows many neutrophils and many gram-positive cocci in clusters. The most likely cause is:

Sputum from a patient with chemotherapy-induced neutropenia (neutrophils 0.2 x 10^3/µL [0.2 x 10^9/L]) shows 2 squamous epithelial cells and 3 white cells per low-power field. How should it be handled for routine bacterial culture?

A protected specimen brush sample from a ventilated patient grows Klebsiella pneumoniae at 5 x 10^3 CFU/mL. Using common quantitative thresholds, this result is:

What is the usual diagnostic threshold for a potential pathogen in a quantitative bronchoalveolar lavage (BAL) culture?

For anaerobic culture in a suspected lung abscess, the acceptable lower respiratory specimen is:

A sputum specimen is judged to be mostly saliva, and unsuitable for routine culture, when the low-power Gram stain fields show many:

BAL fluid is diluted 1:100, and 0.1 mL of the dilution is spread on a plate. It grows 30 colonies of Pseudomonas aeruginosa. What is the count in the original fluid?

A sputum sent for Legionella culture has 15 squamous epithelial cells and 5 white cells per low-power field. What should the laboratory do?