Two obstetric patients develop fever, headache and a stiff neck 12 to 24 hours after spinal anesthesia given on different days by the same anesthesiologist. Their anesthetic and other drugs came from different single-dose vials and lots. One patient's CSF: WBC 2,600/µL [2,600 x 10^6/L], 92% neutrophils; glucose 18 mg/dL [1.0 mmol/L] with serum glucose 92 mg/dL [5.1 mmol/L]; protein 260 mg/dL [2,600 mg/L]. Both CSF cultures grow alpha-hemolytic, catalase-negative gram-positive cocci in chains that are optochin resistant, bile insoluble and PYR negative. The most likely source of the organism is:

Oral flora of the anesthesiologist

Pneumococci carried by the patients

Contaminated vials of anesthetic

Skin flora of the patients' backs

A 36-year-old man with untreated HIV infection (CD4 count 30 cells/µL [0.03 x 10^9/L]) has had headache and blurred vision for 3 weeks. Lumbar puncture: opening pressure 34 cm H2O (reference up to 20 cm H2O). CSF: WBC 8/µL [8 x 10^6/L], mostly lymphocytes; glucose 42 mg/dL [2.3 mmol/L] with serum glucose 95 mg/dL [5.3 mmol/L]; protein 68 mg/dL [680 mg/L]. The Gram stain shows no organisms, and an India ink preparation shows no encapsulated yeast. His serum RPR is nonreactive. Which CSF test should be done next?

Cryptococcal antigen lateral flow assay

Acid-fast smear and mycobacterial culture

CSF cultures (meningitis)

16 ASCP MLS practice questions on CSF cultures (meningitis), 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
Two obstetric patients develop fever, headache and a stiff neck 12 to 24 hours after spinal anesthesia given on different days by the same anesthesiologist. Their anesthetic and other drugs came from different single-dose vials and lots. One patient's CSF: WBC 2,600/µL [2,600 x 10^6/L], 92% neutrophils; glucose 18 mg/dL [1.0 mmol/L] with serum glucose 92 mg/dL [5.1 mmol/L]; protein 260 mg/dL [2,600 mg/L]. Both CSF cultures grow alpha-hemolytic, catalase-negative gram-positive cocci in chains that are optochin resistant, bile insoluble and PYR negative. The most likely source of the organism is:
1. APneumococci carried by the patients
2. BContaminated vials of anesthetic
3. CSkin flora of the patients' backs
4. DOral flora of the anesthesiologist
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Answer: D · Oral flora of the anesthesiologist
Alpha-hemolytic, catalase-negative cocci in chains that are optochin resistant, bile insoluble and PYR negative are viridans group streptococci, part of the normal mouth flora. Meningitis after a spinal procedure caused by viridans streptococci, such as S. salivarius, points to droplets from the mouth of the person doing the puncture; the anesthesiologist had worked without a face mask. CDC advises a face mask for anyone placing a catheter or injecting into the spinal or epidural space. Skin flora would be staphylococci, Cutibacterium or corynebacteria, and a contaminated vial is unlikely when the patients received separate single-dose lots. Pneumococci are optochin susceptible and bile soluble. Both cases should be reported to infection prevention at once.
- A: Pneumococci are optochin susceptible and bile soluble; this isolate is neither.
- B: The patients received drugs from separate single-dose vials and lots.
- C: Skin flora would grow staphylococci, Cutibacterium or corynebacteria, not viridans streptococci.
Question 2 · Hard
A 36-year-old man with untreated HIV infection (CD4 count 30 cells/µL [0.03 x 10^9/L]) has had headache and blurred vision for 3 weeks. Lumbar puncture: opening pressure 34 cm H2O (reference up to 20 cm H2O). CSF: WBC 8/µL [8 x 10^6/L], mostly lymphocytes; glucose 42 mg/dL [2.3 mmol/L] with serum glucose 95 mg/dL [5.3 mmol/L]; protein 68 mg/dL [680 mg/L]. The Gram stain shows no organisms, and an India ink preparation shows no encapsulated yeast. His serum RPR is nonreactive. Which CSF test should be done next?
1. AEnterovirus RT-PCR
2. BCryptococcal antigen lateral flow assay
3. CAcid-fast smear and mycobacterial culture
4. DVDRL for neurosyphilis
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Answer: B · Cryptococcal antigen lateral flow assay
Cryptococcus neoformans is the most likely cause of subacute meningitis in a patient with advanced HIV and a CD4 count below 100 cells/µL. These patients often have few CSF white cells, a mildly low glucose, a modestly raised protein and a high opening pressure. India ink misses many cases, so a negative preparation does not exclude infection, while the cryptococcal antigen test detects capsular polysaccharide in nearly all cases. Tuberculous meningitis usually gives a higher cell count and a much higher protein, and the nonreactive RPR makes neurosyphilis less likely. A positive antigen test is followed by fungal culture, and the titer helps judge prognosis.
- A: Enteroviral meningitis is acute, with a normal glucose, and is not linked to a low CD4 count.
- C: Tuberculous meningitis usually gives a higher cell count and a much higher protein.
- D: Neurosyphilis is less likely with a nonreactive RPR and so few CSF cells.
Question 3 · Easy
In the United States, the most common cause of bacterial meningitis in neonates is:
1. AStreptococcus agalactiae
2. BStreptococcus pneumoniae
3. CNeisseria meningitidis
4. DHaemophilus influenzae type b
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Answer: A · Streptococcus agalactiae
Group B streptococcus is acquired from the mother's genital tract during delivery and is the leading cause of neonatal meningitis. Escherichia coli, especially strains with the K1 capsule, is second, and Listeria monocytogenes is less common. Prenatal GBS screening and intrapartum antibiotics reduce early-onset disease but not late-onset disease. Empirical therapy for neonates therefore covers all three.
- B: S. pneumoniae is the leading cause in older children and adults.
- C: N. meningitidis peaks in infants and adolescents, not newborns.
- D: Hib meningitis mainly affected young children before routine vaccination.
Question 4 · Medium
In adults over 50 with suspected bacterial meningitis, ampicillin is added to empirical therapy mainly to cover:
1. AStreptococcus pneumoniae
2. BListeria monocytogenes
3. CHaemophilus influenzae
4. DNeisseria meningitidis
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Answer: B · Listeria monocytogenes
Listeria monocytogenes causes meningitis in neonates, adults over 50, pregnant women and people with weak cell-mediated immunity. It is intrinsically resistant to cephalosporins, so ceftriaxone plus vancomycin would miss it. Ampicillin is therefore added for these groups. On a CSF Gram stain, Listeria can be mistaken for diphtheroids or streptococci.
- A: Pneumococcus is covered by ceftriaxone plus vancomycin.
- C: H. influenzae is covered by ceftriaxone.
- D: Meningococcus is covered by ceftriaxone.
Question 5 · Hard
CSF results: WBC 250/µL [250 x 10^6/L], 85% lymphocytes; glucose 25 mg/dL [1.4 mmol/L] with serum glucose 110 mg/dL [6.1 mmol/L]; protein 350 mg/dL [3,500 mg/L]. A fine web-like clot forms when the tube stands. Which organism is most likely?
1. AHerpes simplex virus
2. BMycobacterium tuberculosis
3. CNeisseria meningitidis
4. DEnterovirus
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Answer: B · Mycobacterium tuberculosis
Lymphocytes, a low glucose (CSF:serum ratio about 0.23) and a very high protein fit tuberculous meningitis, and the high protein, including fibrinogen, forms a pellicle or web clot. Fungal meningitis, such as cryptococcal disease, can give a similar profile. AFB smears are insensitive, so large volumes are sent for culture and nucleic acid amplification. Viral meningitis gives lymphocytes with a normal glucose.
- A: HSV gives lymphocytes, often red cells, and usually a normal glucose.
- C: Meningococcal meningitis gives mainly neutrophils.
- D: Enterovirus gives lymphocytes with a normal glucose and a mildly raised protein.
Question 6 · Hard
A 30-year-old took oral antibiotics for 2 days before lumbar puncture. CSF: WBC 1,800/µL [1,800 x 10^6/L], 90% neutrophils; glucose 20 mg/dL [1.1 mmol/L] (serum 100 mg/dL [5.6 mmol/L]); protein 210 mg/dL [2,100 mg/L]. Gram stain and culture are negative at 48 hours. Which test is most useful next?
1. AEnterovirus PCR as the only test
2. BIndia ink preparation of the CSF
3. CMultiplex PCR meningitis panel on the CSF
4. DAcid-fast stain of the CSF sediment
Answer and explanation in LearnFree account
Question 7 · Easy
A CSF specimen for bacterial culture cannot be plated right away. It should be kept:
1. AFrozen at -20 °C
2. BIn a refrigerator at 2-8 °C
3. COn ice until plated
4. DAt room temperature
Answer and explanation in LearnFree account
Question 8 · Medium
Ten days after a basilar skull fracture, a man with clear fluid dripping from his nose develops meningitis. The CSF Gram stain shows lancet-shaped gram-positive diplococci. Which organism is most likely?
1. AStreptococcus agalactiae
2. BStaphylococcus aureus
3. CStreptococcus pneumoniae
4. DEnterococcus faecalis
Answer and explanation in LearnFree account
Question 9 · Hard
A 4-year-old has fever and shunt malfunction 6 weeks after a ventriculoperitoneal shunt was placed. Shunt-tap CSF: WBC 80/µL [80 x 10^6/L], mostly neutrophils; glucose 45 mg/dL [2.5 mmol/L]; protein 70 mg/dL [700 mg/L]. Catalase-positive, coagulase-negative gram-positive cocci in clusters grow in pure culture. The best interpretation is:
1. ABacterial meningitis spread from the bloodstream
2. BShunt infection with coagulase-negative staphylococci
3. CNormal CSF findings for a child with a shunt
4. DSkin contamination of the shunt tap specimen
Answer and explanation in LearnFree account
Question 10 · Medium
Which processing step most improves the detection of bacteria on a CSF Gram stain?
1. AStaining a drop of uncentrifuged CSF
2. BCytocentrifuging the CSF before staining
3. CStaining the supernatant after centrifuging
4. DRefrigerating the CSF before staining
Answer and explanation in LearnFree account
Question 11 · Hard
Twelve days after a craniotomy, a patient with an external ventricular drain has CSF growing gram-negative coccobacilli. The isolate grows on MacConkey agar, does not ferment glucose, and is oxidase negative, catalase positive and nonmotile. It is resistant to many antibiotics. The most likely organism is:
1. APseudomonas aeruginosa
2. BHaemophilus influenzae
3. CNeisseria meningitidis
4. DAcinetobacter baumannii
Answer and explanation in LearnFree account
Question 12 · Hard
A 9-day-old infant has meningitis. The CSF Gram stain shows gram-negative rods, and the isolate is lactose positive on MacConkey agar, indole positive and oxidase negative. Which surface antigen of this organism is most linked to neonatal meningitis?
1. AO157 somatic antigen
2. BVi capsular antigen
3. CK1 capsular antigen
4. DH7 flagellar antigen
Answer and explanation in LearnFree account
Question 13 · Medium
A CSF Gram stain from an unvaccinated 14-month-old shows small, pleomorphic gram-negative coccobacilli. Which plating medium is essential?
1. AChocolate agar incubated in CO2
2. BMacConkey agar incubated in room air
3. CColistin-nalidixic acid (CNA) agar
4. DSheep blood agar alone in room air
Answer and explanation in LearnFree account
Question 14 · Medium
CSF from a suspected ventriculoperitoneal shunt infection is cultured anaerobically and held for up to 10 days, mainly to recover:
1. ACutibacterium acnes
2. BStreptococcus agalactiae
3. CNeisseria meningitidis
4. DBacteroides fragilis
Answer and explanation in LearnFree account
Question 15 · Medium
A CSF Gram stain shows intracellular gram-negative diplococci. Which precaution is most important while the culture is worked up?
1. AHandle all plates in a biological safety cabinet
2. BPlate the CSF only to MacConkey agar
3. CRefrigerate the CSF until all plating is done
4. DIncubate the plates in an anaerobic jar
Answer and explanation in LearnFree account
Question 16 · Hard
Small gram-positive rods from a newborn's CSF show a narrow zone of beta-hemolysis, are catalase positive, show tumbling motility at room temperature, and are CAMP positive. What is the organism?
1. ACorynebacterium species
2. BListeria monocytogenes
3. CBacillus anthracis
4. DStreptococcus agalactiae
Answer and explanation in LearnFree account

CSF cultures (meningitis)

In the United States, the most common cause of bacterial meningitis in neonates is:

In adults over 50 with suspected bacterial meningitis, ampicillin is added to empirical therapy mainly to cover:

CSF results: WBC 250/µL [250 x 10^6/L], 85% lymphocytes; glucose 25 mg/dL [1.4 mmol/L] with serum glucose 110 mg/dL [6.1 mmol/L]; protein 350 mg/dL [3,500 mg/L]. A fine web-like clot forms when the tube stands. Which organism is most likely?

A 30-year-old took oral antibiotics for 2 days before lumbar puncture. CSF: WBC 1,800/µL [1,800 x 10^6/L], 90% neutrophils; glucose 20 mg/dL [1.1 mmol/L] (serum 100 mg/dL [5.6 mmol/L]); protein 210 mg/dL [2,100 mg/L]. Gram stain and culture are negative at 48 hours. Which test is most useful next?

A CSF specimen for bacterial culture cannot be plated right away. It should be kept:

Ten days after a basilar skull fracture, a man with clear fluid dripping from his nose develops meningitis. The CSF Gram stain shows lancet-shaped gram-positive diplococci. Which organism is most likely?

Which processing step most improves the detection of bacteria on a CSF Gram stain?

A 9-day-old infant has meningitis. The CSF Gram stain shows gram-negative rods, and the isolate is lactose positive on MacConkey agar, indole positive and oxidase negative. Which surface antigen of this organism is most linked to neonatal meningitis?

A CSF Gram stain from an unvaccinated 14-month-old shows small, pleomorphic gram-negative coccobacilli. Which plating medium is essential?

CSF from a suspected ventriculoperitoneal shunt infection is cultured anaerobically and held for up to 10 days, mainly to recover:

A CSF Gram stain shows intracellular gram-negative diplococci. Which precaution is most important while the culture is worked up?

Small gram-positive rods from a newborn's CSF show a narrow zone of beta-hemolysis, are catalase positive, show tumbling motility at room temperature, and are CAMP positive. What is the organism?