MT MLO flashcards
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- Blood culture volume
- Adults require 20-30 mL of blood per set, divided 8-10 mL per bottle, to maintain the 1:10 blood-to-broth ratio and maximize recovery of bacteremia.
- Sputum specimen rejection
- Specimens with more than 25 neutrophils and fewer than 10 squamous epithelial cells per low-power field are acceptable; specimens with excess epithelial cells are rejected as saliva.
- CSF transport temperature
- CSF for bacterial culture is transported at room temperature and processed within one hour; refrigeration is avoided because fastidious organisms such as Neisseria meningitidis may die.
- Anaerobic specimen acceptability
- Aspirates, tissue, and blood are acceptable for anaerobic culture; swabs, urine, and sputum are rejected because they are contaminated by normal flora.
- Coagulase test interpretation
- Coagulase-positive, catalase-positive gram-positive cocci in clusters identify Staphylococcus aureus; coagulase-negative staphylococci are typical skin flora and often blood culture contaminants.
- MacConkey lactose reaction
- Lactose-fermenting gram-negative rods such as E. coli and Klebsiella produce pink colonies on MacConkey agar; non-fermenters such as Pseudomonas produce colorless colonies.
- Oxidase-positive organisms
- Pseudomonas, Neisseria, Vibrio, Aeromonas, and Campylobacter are oxidase-positive; Enterobacterales and Acinetobacter are oxidase-negative, aiding preliminary identification.
- D-test purpose
- The D-test detects inducible clindamycin resistance in erythromycin-resistant, clindamycin-susceptible staphylococci; a blunted clindamycin zone indicates resistance and clindamycin should not be reported.
- ESBL confirmation criteria
- A ≥5 mm increase in zone diameter or a ≥3 two-fold dilution decrease in MIC for ceftazidime or cefotaxime combined with clavulanate confirms extended-spectrum beta-lactamase production.
- NALC-NaOH digestion
- Sputum is digested with N-acetyl-L-cysteine and decontaminated with 2-3% NaOH, neutralized, and centrifuged at 3000 × g for 15 minutes to concentrate mycobacteria before inoculation.
- M. tuberculosis biochemical profile
- M. tuberculosis complex is niacin-positive, nitrate reduction-positive, and catalase-negative at 68°C; it is a slow grower requiring 2-6 weeks on solid media.
- Nocardia morphology
- Nocardia appears as gram-positive, weakly acid-fast, branching filamentous rods that grow aerobically on blood and Sabouraud agar, forming chalky colonies in 3-7 days.
- Modified acid-fast stain
- Modified Kinyoun stain uses weaker acid decolorizer to detect partially acid-fast organisms such as Nocardia, Cryptosporidium, Cyclospora, and Cystoisospora.
- Germ tube test
- Candida albicans and Candida dubliniensis form germ tubes within 2-3 hours in serum at 37°C; other Candida species are germ tube-negative.
- Cryptococcus identification
- Cryptococcus neoformans is an encapsulated yeast that is India ink-positive, urease-positive, phenol oxidase-positive on bird seed agar, and grows at 37°C.
- Aspergillus hyphae
- Aspergillus shows septate hyphae with acute-angle (45°) branching; Aspergillus fumigatus grows at 45°C, distinguishing it from many other molds.
- Mucorales hyphae
- Mucorales such as Rhizopus and Mucor show broad, nonseptate or pauciseptate hyphae with right-angle branching and are treated with amphotericin B or posaconazole.
- Candida glabrata resistance
- Candida glabrata is germ tube-negative, lacks pseudohyphae, and has intrinsically high fluconazole MICs; echinocandins are often preferred for treatment.
- Entamoeba histolytica features
- Trophozoites contain ingested red blood cells and a single nucleus with a central karyosome; cysts have 1-4 nuclei and blunt chromatoid bars, distinguishing them from Entamoeba coli.
- Giardia lamblia morphology
- The trophozoite is pear-shaped with two nuclei resembling owl eyes, a ventral sucking disk, and falling-leaf motility; the oval cyst contains four nuclei.
- Modified acid-fast parasites
- Cryptosporidium, Cyclospora, and Cystoisospora oocysts are detected with modified acid-fast stains; UV autofluorescence aids detection of Cyclospora and Cystoisospora.
- Plasmodium falciparum gametocytes
- Falciparum gametocytes are banana-shaped; infected red cells show multiple rings and appliqué forms without enlargement or Schüffner's dots.
- Strongyloides detection
- Routine stool O&P is insensitive for Strongyloides; agar plate culture, Baermann concentration, or serology is recommended for detection.
- Shell vial culture
- Centrifugation-enhanced shell vial culture with monoclonal antibody staining detects viruses such as CMV and HSV within 24-48 hours, faster than conventional tube culture.
- HIV testing algorithm
- A fourth-generation antigen/antibody immunoassay is the screening test; reactive results reflex to HIV-1/HIV-2 antibody differentiation, and nucleic acid testing resolves indeterminate results.
- Hepatitis B serology
- HBsAg indicates current infection, anti-HBs indicates immunity, and anti-HBc IgM indicates acute infection; the combination distinguishes acute, chronic, and resolved states.
- Molecular contamination control
- Unidirectional workflow, separate pre- and post-amplification areas, uracil-N-glycosylase, and negative controls prevent and detect amplicon contamination in PCR laboratories.
- Westgard 1-3s rule
- A control value exceeding the mean by more than three standard deviations is rejected; this rule detects random error and is a rejection rule.
- CLIA daily QC requirement
- Two levels of control, normal and abnormal, are required for quantitative tests each day of testing; qualitative tests require positive and negative controls.
- BSL-3 organisms
- Mycobacterium tuberculosis, Brucella, and Coxiella are handled at BSL-3 with directional airflow, restricted access, and biosafety cabinet work.
- Competency assessment frequency
- CAP requires competency assessment semiannually during the first year of testing and annually thereafter for all testing personnel.
- CLIA high-complexity director
- A high-complexity laboratory director must hold an MD/DO with board certification or a PhD in a relevant science with documented experience in laboratory testing.