Micro Spring 2013 Block II Diagnosis – Flashcards
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| How is Hep A detected in serology studies? |
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| Fecal HAV detected 4-6 weks IgM Anti-HAV detected early on but then drops IgG is inclusive because it increases over time, needs to see the trend |
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| What is the best diagnostic measure for HBV detection? |
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| IgM antibody to HBcAg along with or without HBsAg in the serum |
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| How is HCV diagnosed? |
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| Detection of HCV antibody May remain negative for 1-3 weeks after clinical onset May never become positive in up to 20% of patients with acute, resolving disease |
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| How is Hep D diagnosed? |
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| IgM or IgG antibodies or both to the delta antigen in serum IgM antibodies appear within 3 weeks of infection and persist for several weeks IgG antibodies persist for years |
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| The majority of GI pathogenic bacteria grow on what medias? |
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| Majority are gram-neg and grow on MacConkey agar which inhibits gram-pos growth |
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| How is Hektoen agar used to diagnostically distinguish GI pathogenic bacteria? |
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| Inhibits common colon flora Selective to recover Salmonella and Shigella spp. Detects H2S production (black centers to colony) |
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| What does Campylobacter spp. grow on? |
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| Enriched blood agar |
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| What makes distinguishing E. coli so difficult? |
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| Many strains are a part of the normal GI flora and basic diagnostics will not discriminate between normal and pathogenic E. coli |
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| How is Enterotoxigenic E. coli (ETEC) diagnosed? |
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| Characteristic symptoms with ONLY lactose fermenting organisms on differential media ELISA for toxins |
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| How is Enterohemorrhagic E. coli (EHEC) diagnosed? |
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| Cultures that fail to ferment sorbitol MacConkey agar using sorbitol instead of lactose ELISA for toxins MUG assay: Does not produce b-glucoronidase while 92% of other strains do |
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| How is Enteroinvasive E. coli (EIEC) diagnosed? |
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| HE (Hektoen enteric) agar, MacConkey DNA probes are commercially available |
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| What does Yersinia culture on? |
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| Most enteric media except Salmonella-Shigella agar Produces urease |
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| How is Yersinia diagnosed? |
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| Stool culture on enteric media |
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| What media is used to culture Francisella tularensis? |
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| Requires special media for growth that is enriched in cysteine |
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| How is Francisella tularensis diagnosed? |
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| Serology is negative the first week but still the best means for confirmation Diagnosis is usually based on clinical suspicion |
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| How is Brucella melitensis diagnosed? |
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| Culture from blood, bone marrow, or other tissues Grows very slowly so allow extra time in cases of suspicion Serum agglutination test may also be used |
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| What media is used to culture Bacteroides fragilis? |
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| Forms colonies overnight on blood agar |
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| How is H. pylori cultured? |
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| Grows on Skirrow media Requires a microaerophilic atmosphere and is slow (3-5 days) to grow |
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| How is an H. pylori infection diagnosed? |
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| Endoscopic biopsy and culture Detection of urease activity via urease breath test with 13C- or 14C-labeled urea Serology for specific antibody |
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| How is Vibrio cholera cultured? |
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| Oxidase positive and can grow both in aerobic and anaerobic conditions Grown on Thiosulfate Citrate Bile Salt Sucrose (TCBS) medium which inhibits gram pos |
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| How is Virbrio cholera detected by serology? |
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| H and O antigens (especially enterobacteriae) |
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| How is cholera diagnosed? |
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| Isolation of the organism from stool by culture (e.g. blood agar and MacConkey agar) or on a selective medium (thiosulfate-citrate-bile salt-sucrose agar) Latex agglutination test |
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| How is Campylobacter jejuni cultured? |
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| Microaerohilic (requires low oxygen tension), oxidase positive Slow growing (2-4 days, sometimes as long as one week) in selective medium (Campy-blood agar or Skirrow agar) at higher temperature (42C) |
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| How is campylobacter diagnosed? |
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| Stool isolation and culture via Campy-blood agar or Skirrow agar Plates are to be incubated in microaerophilic condition |
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| How is salmonella cultured? |
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| Ferment glucoses with acid and sometimes gas; most of them produce hydrogen sulfide (H2S) not urease Grows on most common bacteriological media, resistant to chemicals such as bile and dyes |
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| How is Salmonella poisoning diagnosed? |
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| Hektoen enteric agar medium Bile salts and the indicator dyes inhibit the Gram-pos Fails to ferment lactose H2S forms black colonies |
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| How do common GI pathogens present on Hektoen enteric agar cultures? |
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| Fermenters produce yellow-pink colonies (e. g. E. coli) H2S producers (salmonella) form colonies with black precipitate Shigella colonies are green or transparent |
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| How is shigella cultured? |
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| Selective Hektoen enteric agar Does not produce urease or H2S, most do not ferment, colonies are green or transparent |
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| How is shigella diagnosed? |
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| Culture on selective Hektoen enteric agar Slide agglutination tests using O group specific antisera (A, B, C, D) |
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| How is rotavirus diagnosed? |
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| Shed in large amounts in the stool (only during an active infection), and a variety of molecular and enzymatic tests can confirm infection |
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| How is Trichuris trichiura (Whipworm) diagnosed? |
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| Eggs in stool |
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| How is Enterobius vermicularis (Pinworm) diagnosed? |
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| Tape test from perianal region reveals eggs |
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| How is Ascaris lumbricoides (Roundworm) diagnosed? |
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| Eggs in stool (negative in early infection) |
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| How is Necator americanus and Ancylostoma duodenale (Hookworm) diagnosed? |
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| Eggs in fresh stool, larvae in old stool |
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| How are Cestode (tapeworms) or Taenias diagnosed? |
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| Detection of eggs or proglottids in stool Cystercerci: plain films reveal calcified “puffed rice” lesions |
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| How is a biliary trematode (fluke) infection diagnosed? |
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| Ova can be identified in stools, dilation of ducts by imaging |
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| How is a liver trematode (fluke) infection diagnosed? |
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| Fever, hepatomegaly or liver pain, proper clinical setting Serology, as ova may not be detected in stool |
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| What types of media are capable of culturing Staph aureus |
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| ?-hemolytic sheep’s blood agar Selective media: Mannitol salt agar Phenylethylalcohol agar (PEA |
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| What types of media are capable of culturing Clostridium perfringens? |
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| EYA (egg yolk agar) with anti-toxin A in ? of the plate: precipitate forms around colonies, indicates lecithinase activity Double-zone of hemolysis on blood agar |
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| How is botulin toxin food poisoning diagnosed? |
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| Presence of organism and/or toxin in vomitus, gastric fluid, or stool |
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| How is Bacillus cereus food poisoning diagnosed? |
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| Samples of contaminated food must be cultured Identification in stool specimens of symptomatic patients is strong evidence Grows rapidly on sheep blood agar |
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| How is Cryptosporidium infections diagnosed? |
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| Modified Ziehl-Nielsen acid-fast stain Microscopic observations of small, acid-fast oocysts in smears of fecal specimens |
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| How is Giardia lamblia diagnosed? |
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| Microscopic identification of cysts or trophozoites in feces |
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| How is Entamoeba histolytica diagnosed? |
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| Microscopic evidence of trophozoites in stool specimens via wet mounts or trichrome-stained smears Sigmoid biopsies ELISA provides evidence of current infection but is not diagnostic |
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| How is a Cylcospora cayetanensis infection diagnosed? |
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| Evidence of oocysts in stool specimens by microscopy Stool specimens should be refrigerated or preserved in 10% formalin Requires 3 or more specimens collected at 2-3 day intervals due to intermittent release of oocysts Modified acid-fast stain |
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| Haemophilus influenza is grown on what type of media? |
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| Chocolate blood agar Requires the 2 erythrocyte growth factors X (hemin) and V (nicotinamide adenine dinucleotide) for growth |
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| Strep pneumonia is cultured on what media? |
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| Blood agar medium results in alpha-hemolysis (partial hemolysis) Can grow very quickly under optimal conditions |
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| How do you differentiate Staph epidermidis from Staph aureus? |
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| Staph epidermidis is coagulase-negative whereas Staph aureus is positive |
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| How is Chlamydia trachomatis diagnosed? |
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| Immunofluorescence |
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| How is Francisella tularensis cultured? |
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| Grown on chocolate agar |
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| How is Toxoplasma gondii diagnosed? |
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| Indirect immunofluorescent assay (IFA) Ring enhancing lesions on imaging is indicative |
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| Hemophagocytic Syndrome can interfere with the diagnosis of what treatable infectious disease? |
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| Visceral leishmaniasis |
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| What initial diagnostic tests should be performed if Hemophagocytic syndrome is suspected? |
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| Blood and urine cultures Chest radiography to screen for tuberculous infections Serological assays for viral infections Throat and rectal swabs for viral culture Fungal antigen testing Determine if an underlying T-cell lymphoma is present |
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| How is Rickettsia diagnosed? |
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| Giemsa stain is preferred |
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| How is malaria diagnosed? |
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| Giemsa or Wright stains are gold standard |
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| What are other forms of malarial diagnosis? |
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| Malarial RDTs (rapid diagnostic test) |
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| How is Babesiosis diagnosed? |
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| Direct blood smears show tetrad formation in RBCs Indirect fluorescent antibody test |
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| How is Bartonellosis diagnosed? |
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| Serologic testing Microscopic examination of Giemsa-stained blood smears |
