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Micro Spring 2013 Block II Diagnosis
n/a
58
Microbiology
Graduate
04/06/2013

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Cards

Term
How is Hep A detected in serology studies?
Definition
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
Term
What is the best diagnostic measure for HBV detection?
Definition
IgM antibody to HBcAg along with or without HBsAg in the serum
Term
How is HCV diagnosed?
Definition
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
Term
How is Hep D diagnosed?
Definition
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
Term
The majority of GI pathogenic bacteria grow on what medias?
Definition
Majority are gram-neg and grow on MacConkey agar which inhibits gram-pos growth
Term
How is Hektoen agar used to diagnostically distinguish GI pathogenic bacteria?
Definition
Inhibits common colon flora
Selective to recover Salmonella and Shigella spp.
Detects H2S production (black centers to colony)
Term
What does Campylobacter spp. grow on?
Definition
Enriched blood agar
Term
What makes distinguishing E. coli so difficult?
Definition
Many strains are a part of the normal GI flora and basic diagnostics will not discriminate between normal and pathogenic E. coli
Term
How is Enterotoxigenic E. coli (ETEC) diagnosed?
Definition
Characteristic symptoms with ONLY lactose fermenting organisms on differential media
ELISA for toxins
Term
How is Enterohemorrhagic E. coli (EHEC) diagnosed?
Definition
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
Term
How is Enteroinvasive E. coli (EIEC) diagnosed?
Definition
HE (Hektoen enteric) agar, MacConkey
DNA probes are commercially available
Term
What does Yersinia culture on?
Definition
Most enteric media except Salmonella-Shigella agar
Produces urease
Term
How is Yersinia diagnosed?
Definition
Stool culture on enteric media
Term
What media is used to culture Francisella tularensis?
Definition
Requires special media for growth that is enriched in cysteine
Term
How is Francisella tularensis diagnosed?
Definition
Serology is negative the first week but still the best means for confirmation
Diagnosis is usually based on clinical suspicion
Term
How is Brucella melitensis diagnosed?
Definition
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
Term
What media is used to culture Bacteroides fragilis?
Definition
Forms colonies overnight on blood agar
Term
How is H. pylori cultured?
Definition
Grows on Skirrow media
Requires a microaerophilic atmosphere and is slow (3-5 days) to grow
Term
How is an H. pylori infection diagnosed?
Definition
Endoscopic biopsy and culture
Detection of urease activity via urease breath test with 13C- or 14C-labeled urea
Serology for specific antibody
Term
How is Vibrio cholera cultured?
Definition
Oxidase positive and can grow both in aerobic and anaerobic conditions
Grown on Thiosulfate Citrate Bile Salt Sucrose (TCBS) medium which inhibits gram pos
Term
How is Virbrio cholera detected by serology?
Definition
H and O antigens (especially enterobacteriae)
Term
How is cholera diagnosed?
Definition
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
Term
How is Campylobacter jejuni cultured?
Definition
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)
Term
How is campylobacter diagnosed?
Definition
Stool isolation and culture via Campy-blood agar or Skirrow agar
Plates are to be incubated in microaerophilic condition
Term
How is salmonella cultured?
Definition
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
Term
How is Salmonella poisoning diagnosed?
Definition
Hektoen enteric agar medium
Bile salts and the indicator dyes inhibit the Gram-pos
Fails to ferment lactose
H2S forms black colonies
Term
How do common GI pathogens present on Hektoen enteric agar cultures?
Definition
Fermenters produce yellow-pink colonies (e. g. E. coli)
H2S producers (salmonella) form colonies with black precipitate
Shigella colonies are green or transparent
Term
How is shigella cultured?
Definition
Selective Hektoen enteric agar
Does not produce urease or H2S, most do not ferment, colonies are green or transparent
Term
How is shigella diagnosed?
Definition
Culture on selective Hektoen enteric agar
Slide agglutination tests using O group specific antisera (A, B, C, D)
Term
How is rotavirus diagnosed?
Definition
Shed in large amounts in the stool (only during an active infection), and a variety of molecular and enzymatic tests can confirm infection
Term
How is Trichuris trichiura (Whipworm) diagnosed?
Definition
Eggs in stool
Term
How is Enterobius vermicularis (Pinworm) diagnosed?
Definition
Tape test from perianal region reveals eggs
Term
How is Ascaris lumbricoides (Roundworm) diagnosed?
Definition
Eggs in stool (negative in early infection)
Term
How is Necator americanus and Ancylostoma duodenale (Hookworm) diagnosed?
Definition
Eggs in fresh stool, larvae in old stool
Term
How are Cestode (tapeworms) or Taenias diagnosed?
Definition
Detection of eggs or proglottids in stool
Cystercerci: plain films reveal calcified “puffed rice” lesions
Term
How is a biliary trematode (fluke) infection diagnosed?
Definition
Ova can be identified in stools, dilation of ducts by imaging
Term
How is a liver trematode (fluke) infection diagnosed?
Definition
Fever, hepatomegaly or liver pain, proper clinical setting
Serology, as ova may not be detected in stool
Term
What types of media are capable of culturing Staph aureus
Definition
Β-hemolytic sheep’s blood agar

Selective media:
Mannitol salt agar
Phenylethylalcohol agar (PEA
Term
What types of media are capable of culturing Clostridium perfringens?
Definition
EYA (egg yolk agar) with anti-toxin A in ½ of the plate: precipitate forms around colonies, indicates lecithinase activity

Double-zone of hemolysis on blood agar
Term
How is botulin toxin food poisoning diagnosed?
Definition
Presence of organism and/or toxin in vomitus, gastric fluid, or stool
Term
How is Bacillus cereus food poisoning diagnosed?
Definition
Samples of contaminated food must be cultured
Identification in stool specimens of symptomatic patients is strong evidence
Grows rapidly on sheep blood agar
Term
How is Cryptosporidium infections diagnosed?
Definition
Modified Ziehl-Nielsen acid-fast stain
Microscopic observations of small, acid-fast oocysts in smears of fecal specimens
Term
How is Giardia lamblia diagnosed?
Definition
Microscopic identification of cysts or trophozoites in feces
Term
How is Entamoeba histolytica diagnosed?
Definition
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
Term
How is a Cylcospora cayetanensis infection diagnosed?
Definition
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
Term
Haemophilus influenza is grown on what type of media?
Definition
Chocolate blood agar
Requires the 2 erythrocyte growth factors X (hemin)
and V (nicotinamide adenine dinucleotide) for growth
Term
Strep pneumonia is cultured on what media?
Definition
Blood agar medium results in alpha-hemolysis (partial hemolysis)
Can grow very quickly under optimal conditions
Term
How do you differentiate Staph epidermidis from Staph aureus?
Definition
Staph epidermidis is coagulase-negative whereas Staph aureus is positive
Term
How is Chlamydia trachomatis diagnosed?
Definition
Immunofluorescence
Term
How is Francisella tularensis cultured?
Definition
Grown on chocolate agar
Term
How is Toxoplasma gondii diagnosed?
Definition
Indirect immunofluorescent assay (IFA)
Ring enhancing lesions on imaging is indicative
Term
Hemophagocytic Syndrome can interfere with the diagnosis of what treatable infectious disease?
Definition
Visceral leishmaniasis
Term
What initial diagnostic tests should be performed if Hemophagocytic syndrome is suspected?
Definition
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
Term
How is Rickettsia diagnosed?
Definition
Giemsa stain is preferred
Term
How is malaria diagnosed?
Definition
Giemsa or Wright stains are gold standard
Term
What are other forms of malarial diagnosis?
Definition
Malarial RDTs (rapid diagnostic test)
Term
How is Babesiosis diagnosed?
Definition
Direct blood smears show tetrad formation in RBCs
Indirect fluorescent antibody test
Term
How is Bartonellosis diagnosed?
Definition
Serologic testing
Microscopic examination of Giemsa-stained blood smears
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