Med Lab Science Review #22: Infectious Agents & Diagnostic Techniques

MEDICAL LABORATORY SCIENCE 9. SUMMATIVE EXAM REVIEW QUESTIONS #22 + ANSWERS & RATIONALIZATIONS 1. 2. 3. 4. 5. 6. 7. 8. Most rapid method for detection of mycobacteria: a. Direct sputum smear microscopy (DSSM) b. Culture c. Molecular diagnosis d. None of these Determines resistance to anti-tuberculosis drugs: a. Direct sputum smear microscopy b. Molecular diagnosis c. Serological tests d. X-ray Acid-fast staining of a smear prepared from digested sputum showed slender, slightly curved, beaded, red mycobacterial rods. Growth on Middlebrook 7H10 slants produced buff-colored microcolonies with a serpentine pattern after 14 days at 37°C. Niacin and nitrate reduction tests were positive. What is the most probable presumptive identification? a. Mycobacterium tuberculosis b. Mycobacterium ulcerans c. Mycobacterium kansasii d. Mycobacterium avium–intracellulare complex The characteristic that is most commonly associated with the presence of strict anaerobic bacteria and can be taken as presumptive evidence of their presence in a clinical specimen is the: a. Presence of a single bacterial species b. Production of gas in a thioglycollate broth culture c. Growth on a blood agar plate incubated in an anaerobic jar d. Presence of a foul, putrid odor from tissue specimens and cultures Which of the following specimens would be best for identifying Bacillus cereus as the cause of an outbreak of food poisoning? a. Blood b. Rectal swabs c. Stool samples d. Food Methods other than packaged microsystems used to identify anaerobes include: a. Antimicrobial susceptibility testing b. Gas–liquid chromatography (GLC) c. Special staining d. Enzyme immunoassay Pre-reduced and vitamin K1-supplemented blood agar plates are recommended isolation media for: a. Mycobacterium marinum and Mycobacterium avium intracellulare b. Bacteroides, Peptostreptococcus, and Clostridium spp. → anaerobes c. Proteus spp. d. Enterococcus spp. Identification of Clostridium tetani is based upon: a. Gram stain of the wound site b. Anaerobic culture of the wound site c. Blood culture results d. Clinical findings 10. 11. 12. 13. 14. 15. The classic form of foodborne botulism is characterized by the ingestion of: a. Spores in food b. Preformed toxin in food c. Toxin H d. All of these option Which mechanism is responsible for botulism in infants caused by Clostridium botulinum? a. Ingestion of spores in food or liquid b. Ingestion of preformed toxin in food c. Virulence of the organism d. Lipase activity of the organism A stool sample is sent to the laboratory for culture to rule out Clostridium difficile. What media should the microbiologist use and what is the appearance of the organisms on this media? a. BBE: colonies turn black b. Brucella agar: red pigmented colonies c. CCFA: yellow, ground glass colonies d. CNA: double zone hemolytic colonies Propionibacterium acnes is most often associated with: a. Normal oral flora b. Post-antibiotic diarrhea c. Tooth decay d. Blood culture contamination A patient has a suspected diagnosis of subacute bacterial endocarditis. His blood cultures grow nonspore-forming pleomorphic gram-positive bacilli only in the anaerobic bottle. What test(s) will give a presumptive identification of this microorganism? a. Beta-hemolysis and oxidase b. Catalase and spot indole → P. acnes c. Esculin hydrolysis d. Hydrolysis of gelatin → Propionibacterium acnes is part of the normal flora on the skin and is a common blood culture contaminant. The gram stain given is typical for P. acnes, and it is catalase and indole positive. Gram stain of a smear taken from the periodontal pockets of a 30-year-old man with poor dental hygiene showed sulfur granules containing gram-positive rods (short diphtheroids and some unbranched filaments). Colonies on blood agar resembled “molar teeth” in formation. The most likely organism is: a. Actinomyces israelii b. Propionibacterium acnes c. Staphylococcus intermedius d. Peptostreptococcus anaerobius An organism from a peritoneal abscess is isolated on kanamycin-vancomycin laked blood agar and grows black colonies on BBE agar. It is nonpigmented, catalase positive, and indole negative. The genus of this organism is: a. Acidominococcus b. Bacteroides c. Porphyromonas d. Prevotella 1 16. Anaerobic gram-negative rods were recovered from the blood of a patient after gallbladder surgery. The bacteria grew well on agar containing 20% bile, but were resistant to kanamycin and vancomycin. What is the most likely identification? a. Clostridium perfringens b. Bacteroides fragilis group c. Prevotella spp. d. Porphyromonas spp. 17. Epidemic typhus: a. Rickettsia prowazekii → vector: lice b. Rickettsia rickettsia c. Rickettsia akari d. Orientia tsutsugamushi 18. All of the following are true for Candida albicans, EXCEPT: a. True septate hyphae b. Nonseptate hyphae c. Positive for germ tube formation d. Blastoconidia, hyphae, and pseudohyphae are strongly gram positive 19. Specimens collected for virus isolation should be kept at: a. 37 °C b. 20 °C c. 4 °C d. -20 °C 20. At what temperature should clinical specimen suspected of containing viruses be kept for transport that takes days? a. -70 °C b. 37 °C c. 4 °C d. -10 °C 21. Which of the following is the specimen of choice for detecting rotavirus? a. Throat swab b. Urine sample c. Bronchoalveolar wash d. Feces sample 22. Viral transport medium should contain agents that: a. Enable rapid viral growth during transport time b. Inhibit bacterial and fungal growth c. Destroy nonpathogenic viruses d. Inhibit complement-fixing antibodies 23. Specimens for virus culture should be transported in media containing: a. Antibiotics and 5% sheep blood b. Saline and 5% sheep blood c. 22% bovine albumin d. Antibiotics and nutrient → Viral Transport ▪ Delay in the processing of fluid specimens requires dilution in a transport medium (1:2 to 1:5) before storage ▪ Specimens for virus culture should be transported in media containing antibiotics and nutrient 24. More likely to contain trophozoites and should be examined within 30 minutes of passage: a. Liquid stool specimen b. Soft stool specimen c. Formed stool specimen d. Any of these 25. More likely to contain cysts (less likely to contain trophozoites), can be kept up to 1 day with overnight refrigeration: a. Liquid stool specimen b. Diarrheic specimen c. Soft stool specimen d. Formed stool specimen 26. May contain both trophozoites and cysts and should be examined within 1 hour of passage: a. Liquid stool specimen b. Diarrheic specimen c. Soft stool specimen d. Formed stool specimen 27. Ideal temperature at which to hold a fecal specimen for any length of time is: a. Freezer b. Refrigerator c. Room temperature d. Incubator temperature 28. In which of the following sets of nematodes can each organism cause a pneumonia-like syndrome in a person exposed to heavy infection with any of the three parasites? a. Ascaris lumbricoides, Trichuris trichiura, or Onchocerca volvulus b. Enterobius vermicularis, Dracunculus medinensis, or Trichuris trichiura c. Strongyloides stercoralis, Wuchereria bancrofti, or Angiostrongylus costaricensis d. Necator americanus, Ascaris lumbricoides, or Strongyloides stercoralis 29. Ova recovered from the stool are routinely used to diagnose infections caused by all of the following EXCEPT? a. Necator americanus b. Ascaris lubricoides c. Trichuris trichiura d. Strongyloides stercoralis → Rhabditiform larva 30. Characteristics of the rhabditiform (noninfective) larvae of Strongyloides stercoralis include a: a. Short buccal capsule and large genital primordium b. Long buccal capsule and pointed tail c. Short buccal capsule and small genital primordium d. Small genital primordium and notch in tail 31. Microfilariae can be detected in the blood throughout the day but are detected at higher levels during the late afternoon or at night: a. Diurnal → L. loa b. Nocturnal → W. bancrofti c. Nonperiodic d. Subperiodic 32. First stage larva liberated from the trematode egg: a. Cercaria b. Metacercaria c. Miracidium d. Redia e. Sporocyst 33. Fluke(s) associated with cholecystitis (inflammation of the gallbladder), and cholangiocarcinoma (cancerous growth in bile duct epithelium): a. F. buski b. P. westermani c. C. sinensis, O. viverrini d. S. japonicum 2 34. Eggs resemble an old-fashioned electric light bulb: a. Fasciola hepatica b. Clonorchis sinensis c. Paragonimus westermani d. Fasciolopsis buski 35. Vector for Paragonimus westermani: a. Copepods b. Fishes c. Water plants d. Crabs 36. The only known human tapeworm with an operculum is: a. Diphyllobothrium latum b. Hymenolepis nana c. Giardia lamblia d. Schistosoma haematobium 37. In infections with Taenia solium, humans can serve as the: a. Definitive host b. Intermediate host c. Either the definitive or the intermediate host d. None of the options 38. When humans have hydatid disease, the causative agent and host classification are: a. Echinococcus granulosus—accidental intermediate host b. Echinococcus granulosus—definitive host c. Taenia solium—accidental intermediate host d. Taenia solium—definitive host → Echinococcus granulosus ▪ Definitive host: dog ▪ Intermediate host: sheep ▪ Man is only an accidental intermediate host and dead-end host 39. Which of the following is the best technique to identify Dientamoeba fragilis in stool? a. Formalin concentrate b. Trichrome-stained smear c. Modified acid-fast–stained smear d. Giemsa’s stain 40. Finely granular, “ground glass” appearance; clear differentiation of ectoplasm and endoplasm; if present, vacuoles are usually small; presence of red blood cells (RBCs) is diagnostic a. E. nana b. E. coli c. E. dispar d. E. histolytica 41. Which of the following is the most important feature in differentiating cysts of Entamoeba histolytica from E. dispar? a. Number of nuclei b. Size of the cyst c. Shape of the karyosome d. Distinguishing surface antigens by immunologic assays 42. Larger, usually eccentric refractile granules may be on one side of karyosome (“basket nucleus”): a. E. histolytica b. E. coli c. E. nana d. I. butschlii 43. Small protozoa that have been missed on wet mounts or concentration methods are often detected with: a. India ink b. Iodine c. Giemsa stain d. Trichrome stain → observed with OIO 44. The preservative to be employed with trichrome stain: a. Formalin b. Alcohol c. PVA d. Iodine 45. Microsporidial infections can be confirmed using: a. Light microscopy and modified trichrome stains b. Phase contrast microscopy and routine trichrome stains c. Electron microscopy and modified acid-fast stains d. Fluorescence microscopy and hematoxylin stains 46. Direct stool specimens stained with iodine make the trophozoite of protozoa: a. A yellow color b. A brown color c. Disappear as they are destroyed by iodine d. Remain the same 47. Bright red pyramidal crystal in a fecal specimen stained with trichrome would be identified as: a. Asbestos body b. Charcot-Leyden crystal → also in sputum, tissues c. Fecalith d. Chromatoid body 48. Use solutions which have higher specific gravity than the organisms: a. Flotation techniques b. Sedimentation techniques c. Both of these d. None of these 49. Use solutions of lower specific gravity than the parasitic organisms: a. Flotation techniques b. Sedimentation techniques → for trematode eggs c. Both of these d. None of these 50. West African sleeping sicknes: The two species of flies responsible for the transmission are Glossina palpalis and Glossina tachinoides: a. Leishmania donovani b. Leishmania tropica c. Trypanosoma brucei gambiense d. Trypanosoma brucei rhodesiense 3