Lab Diagnosis of Microbial Infections Flashcards

Question

Infection of a brain, lung, or abdominal abscess would probably be caused by which bacteria

Answer 1

bacteriodes, Staph aureus, Strep pyogenes (GAS)

Answer 2

Staph aureus

Answer 3

C. perfringens

Answer 4

Pasteurella multocida

Answer 5

Start with a specimen in a transport medium, then do a low speed centrifugation to pellet large things (our cells, bacterial cells, fungal cells) to the bottom. Small viruses will remain in the supernatant. Then add antibiotics to the supernatant and then inoculate a cell monolayer grown under culture. The virus will cause cytopathic effect and the appearance of the monolayer changes

Answer 6

Four-fold rise in specific convalescent vs acute titer

Answer 7

* Non-specific testing * Rapid plasma reagin (RPR) * Venereal Disease Research Lab (VDRL) * Beef heart cardiolipin (diphosphatidylglycerol) is the antigen, conjugated to carbon particles, which clumps in the presence of antibody to T. pallidum if positive, follow up with: * Specific testing * Fluorescent treponemal antibody absorption (FTA-ABS) * Patient serum is absorbed with non-Tp treponemes, then reacted with fixed T pallidum on a slide * Fluorescent anti-human IgG is added to visualize the bound bacteria

Answer 8

T. palladium cannot be grown in culture (just rabbit testicles)

Answer 9

Antigen may be present at higher levels earlier in an infection than antibodies while the immune response is being formed

Answer 10

detecting antigen have source with virus in it and add it to a series of tubes with commercial neutralizing antibodies against suspected causative antigens and then look on a monolayer plate for inhibition of the virus. Need a control to make sure its working properly.

Answer 11

often used for strep throat and for flu infections Called lateral flow immunoassays and can typically read in about 15 minutes and they are accurate Take collected samples (throat swab) and put it in a medium that breaks up the bacteria to release the antigens and then we add a droplet of sample onto a well on a wickable paper so that the sample will flow. It will encounter antibody to antigens present in that organism to make sure the organism is present. Once they bind they are concentrated and trapped to a line via another antibody fixed to the slide. The second fixed line binds the antibody to make sure its present as a control. Doesn't tell you which antigen you are binding, you assume it is the right antigen

Answer 12

• ELISA (antibody testing) • Murex Single Use Diagnostic System (SUDS) -Assays antibodies and presence of p24 • OraQuick (home testing) -Saliva antibodies ``` • Western blot (confirmatory test) -Positive: p24, gp41 and/or gp120/160 -Indeterminate: some bands, but not those above -Negative: no bands ```

Answer 13

denature nucleic acid of target organism and then bring primers to amplify the DNA via PCR

Answer 14

* Particularly useful when organism is difficult to routinely grow and isolate * Often becoming the “gold standard” of diagnosis * Fairly rapid, and because of amplification, very sensitive * Can be used to detect pathogen before significant immune response * Can be used to determine pathogen load ``` • Uses (there are plenty others) • HIV • HBV, HCV • Chlamydia, GC ```

Answer 15

PCR could be too specific and would give false positives if other flora were introduced

Answer 16

useful in identification of gram- rods uses enterotubes with agar 'cubes' that can change color depending on whats in it. Use an inoculating rod with organism for each rod and can see each the change in each cube. Uses a scoring system to identify

Answer 17

common UTi-causing bacteria can reduce nitrate to nitrite. Can be assayed using the dipstick format

Answer 18

Matrix-Assisted Laser Desorption Ionization Time-of-Flight add bacteria in a sample and use a laser to ionize the proteins and then line them up through an electrostatic field. They are then sprayed and they "fly" through an analyzer and the small proteins fly faster than the heavier ones. Read on computer.