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14 Cards in this Set
- Front
- Back
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For most specimens, a polyester-tipped swab, such as Dacron, is appropriate for collection. For several sexually transmitted diseases, a particular swab is
inappropriate. State which swab should not be used to collect for recovery of: Herpes simplex virus (HSV): Neisseria gonorrhoeae: Chlamydia trachomatis: |
Calcium alginate can inactivate HSV.
Cotton can be toxic to N. gonorrhoeae. Wood can be toxic to C. trachomatis. |
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What are the four functions of sodium polyethanol sulfonate in blood culture bottles?
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Sodium polyanethanol sulfonate inhibits coagulation, phagocytosis, complement activation, and the aminoglycoside antibiotics.
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What white blood cell types are collected for culture of cytomegalovirus?
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Neutrophils are the main cell type that cytomegalovirus infects, but it is also seen in mononuclear cells, so both should be harvested.
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What serologic test is used to diagnose neurosyphilis from a cerebrospinal fluid specimen?
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The Venereal Disease Research Laboratory (VDRL) test is the only one that can detect antibodies. Recall that this is one of the nonspecific tests.
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Give three methods of diagnosing Chlamydia trachomatis from conjunctival scrapings?
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A Giemsa stain directly from the conjunctival swab, a direct fluorescent antibody test (DFA), and a culture are all methods for detecting C. trachomatis.
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Clinical Consultation: A 4-year-old girl is hospitalized with what is suspected to be whooping cough. The clinician wants to perform a nasopharyngeal culture. You ask him to stop by the laboratory before going to her bedside. What do you give him and why?
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The clinician should pick up a Regan- Lowe plate and inoculate it right at the bedside for optimal recovery. Regan- Lowe is recommended currently over the
older Bordet-Gengou potato agar |
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Is a sputum sample with eight epithelial cells and 30 polymorphonuclear leukocytes (PMNs) acceptable for further processing?
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Yes. There are a few different criteria for acceptability of sputum samples, all based on the number of squamous cells from the oral cavity and PMNs from
the pulmonary system. A good rule of thumb is the more PMNs, the better, and a greater number of PMNs than epithelial cells is satisfactory. |
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Compare the utility of sputum vs bronchoalveolar lavage (BAL) to recover Legionella spp?
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Sputum for DFA and culture is preferred for recovery of Legionella. Culture takes up to 1 week. BAL may be too diluted to be fruitful and the anesthetic can inhibit Legionella organisms.
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Clinical Consultation: A 43-year-old nun has mild urinary frequency and provides a midstream clean-catch urine specimen. A standard loop is used to inoculate sheep's blood agar and MacConkey's agar (MAC) plates. After 48 hours of incubation, 125 bright pink colonies are counted on the MAC plate. What is the most likely agent? Is this a significant number of bacteria, indicating infection?
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This is classic for Escherichia coli. Greater than 1 x 10^5 organisms is significant. A standard loop contains 0.001 mL of urine. 125 colonies x 1000= 125 000CFU/
mL, so this is a real infection. Do you remember that the three major lactosefermenting organisms are E.coli, Klebsiella, and Enterobacter? |
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What culture media are used for recovery of Leptospira interrogans in urine specimens?
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L. interrogans should be cultured on Fletcher's or Ellinghausen- McCullough Johnson-Harris medium.
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What transport temperature and culture medium are used to recover Neisseria gonorrhoeae from an endocervical specimen?
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The important fact to remember for N. gonorrhoeae is to maintain it at room temperature. Do not refrigerate. There are a few media for this organism; one is
the modified Thayer-Martin with added C02• |
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What medium is used to recover shiga-toxin-producing enterohemorrhagic Escherichia coli (STEC), and how does culture compare with toxin detection in terms of sensitivity?
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STEC should be plated on, among other standard media such as sheep blood agar, MAC, and sorbitol MAC. STEC does not ferment sorbitol but almost all
other E. coli do. The toxin detection method is actually more sensitive. |
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Outline collection and processing of stool for Clostridium difficile toxin evaluation by the cell culture method.
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This is a cell culture assay. Collect 25- 50mL of liquid stool in a clean container and process within 2 hours of collection. Extracting the toxin involves centrifugation, either at 2000 g for 20 minutes, or 10 000 g for 10 minutes. The stool is then filtered through a 0.45 )..lm membrane filter. Serial dilutions are
prepared on cell monolayers and incubated for 24- 48 hours. The enzymelinked immunosorbent assay (ELISA) method of toxin detection is simpler and faster but may not be as sensitive |
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Compare and contrast the advantages of the saline and iodine methods in wet preps of stool examined for parasites.
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Saline shows movement of trophozoites, its greatest advantage over other techniques, but will also show cysts and ova fairly well. Iodine destroys trophozoites unless the sample was previously fixed. It neatly highlights the features of cyst forms, though. Usually, a wet preparation is performed with side by side saline and iodine mounts.
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