Term
| How is Hep A detected in serology studies? |
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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 |
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Term
| What is the best diagnostic measure for HBV detection? |
|
Definition
| IgM antibody to HBcAg along with or without HBsAg in the serum |
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Term
|
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 |
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Term
|
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 |
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Term
| The majority of GI pathogenic bacteria grow on what medias? |
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Definition
| Majority are gram-neg and grow on MacConkey agar which inhibits gram-pos growth |
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Term
| How is Hektoen agar used to diagnostically distinguish GI pathogenic bacteria? |
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Definition
Inhibits common colon flora
Selective to recover Salmonella and Shigella spp.
Detects H2S production (black centers to colony) |
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Term
| What does Campylobacter spp. grow on? |
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Definition
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Term
| What makes distinguishing E. coli so difficult? |
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Definition
| 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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Term
| How is Enterotoxigenic E. coli (ETEC) diagnosed? |
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Definition
Characteristic symptoms with ONLY lactose fermenting organisms on differential media
ELISA for toxins |
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Term
| How is Enterohemorrhagic E. coli (EHEC) diagnosed? |
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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 |
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Term
| How is Enteroinvasive E. coli (EIEC) diagnosed? |
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Definition
HE (Hektoen enteric) agar, MacConkey
DNA probes are commercially available |
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Term
| What does Yersinia culture on? |
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Definition
Most enteric media except Salmonella-Shigella agar
Produces urease |
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Term
| How is Yersinia diagnosed? |
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Definition
| Stool culture on enteric media |
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Term
| What media is used to culture Francisella tularensis? |
|
Definition
| Requires special media for growth that is enriched in cysteine |
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Term
| How is Francisella tularensis diagnosed? |
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Definition
Serology is negative the first week but still the best means for confirmation
Diagnosis is usually based on clinical suspicion |
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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 |
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Term
| What media is used to culture Bacteroides fragilis? |
|
Definition
| Forms colonies overnight on blood agar |
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Term
| How is H. pylori cultured? |
|
Definition
Grows on Skirrow media
Requires a microaerophilic atmosphere and is slow (3-5 days) to grow |
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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 |
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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 |
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Term
| How is Virbrio cholera detected by serology? |
|
Definition
| H and O antigens (especially enterobacteriae) |
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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 |
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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) |
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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 |
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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 |
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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 |
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Term
| How do common GI pathogens present on Hektoen enteric agar cultures? |
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Definition
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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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 |
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Term
| How is shigella diagnosed? |
|
Definition
Culture on selective Hektoen enteric agar
Slide agglutination tests using O group specific antisera (A, B, C, D) |
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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 |
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Term
| How is Trichuris trichiura (Whipworm) diagnosed? |
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Definition
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|
Term
| How is Enterobius vermicularis (Pinworm) diagnosed? |
|
Definition
| Tape test from perianal region reveals eggs |
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|
Term
| How is Ascaris lumbricoides (Roundworm) diagnosed? |
|
Definition
| Eggs in stool (negative in early infection) |
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Term
| How is Necator americanus and Ancylostoma duodenale (Hookworm) diagnosed? |
|
Definition
| Eggs in fresh stool, larvae in old stool |
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Term
| How are Cestode (tapeworms) or Taenias diagnosed? |
|
Definition
Detection of eggs or proglottids in stool
Cystercerci: plain films reveal calcified “puffed rice” lesions |
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Term
| How is a biliary trematode (fluke) infection diagnosed? |
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Definition
| Ova can be identified in stools, dilation of ducts by imaging |
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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 |
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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 |
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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 |
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Term
| How is botulin toxin food poisoning diagnosed? |
|
Definition
| Presence of organism and/or toxin in vomitus, gastric fluid, or stool |
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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 |
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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 |
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|
Term
| How is Giardia lamblia diagnosed? |
|
Definition
| Microscopic identification of cysts or trophozoites in feces |
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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 |
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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 |
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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 |
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|
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 |
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|
Term
| How do you differentiate Staph epidermidis from Staph aureus? |
|
Definition
| Staph epidermidis is coagulase-negative whereas Staph aureus is positive |
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|
Term
| How is Chlamydia trachomatis diagnosed? |
|
Definition
|
|
Term
| How is Francisella tularensis cultured? |
|
Definition
|
|
Term
| How is Toxoplasma gondii diagnosed? |
|
Definition
Indirect immunofluorescent assay (IFA)
Ring enhancing lesions on imaging is indicative |
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|
Term
| Hemophagocytic Syndrome can interfere with the diagnosis of what treatable infectious disease? |
|
Definition
|
|
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 |
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Term
| How is Rickettsia diagnosed? |
|
Definition
| Giemsa stain is preferred |
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|
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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