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NWHSU Microbiology - Lab Final
questions fully solved & updated 2025
Define titer - answer The highest dilution of a sample that tests positive for an antibody. Which immunoglobulin appears first when someone has an infection? - answer IgM Define Prozone. - answer During antibody precipitation tests, its the period of time when antibody concentrations are high and no precipitates are formed, leading to false negatives. How is a positive Western blot for HIV determined? - answer There will be two or more dark bands. what are the reagents in gram staining? - answer Crystal violet, Grams iodine, acetone-alcohol, safranin. In gram staining, what does crystal violet do? - answer stains all gram + and - bacteria. In gram staining, what does grams iodine do? - answer its a mordant that forms violet-iodine complex that binds more. In gram staining, what does acetone-alcohol do? - answer It decolorizes gram
- bacteria. But only if not done for too long.
In gram staining, what does safranin do? - answer counterstains gram - bacteria. What color are gram positive bacteria? - answer Purple What color are gram negative bacteria? - answer pink How do gram stains and wet mounts vary? - answer Gram can determine gram +/-. Wet mounts can tell motility. How are gram stains and wet mounts similar? - answer They both can see arrangement, size, and shape. What is the KOH test to differentiate gram positive from gram negative bacteria? - answer Mix KOH with a colony for 20 seconds. Stringy=negative. Not stringy=positive. Define ubiquity - answer Microorganisms everywhere. What are 3 spore forming bacteria that cause disease? - answer Bacillus Anthracis, Clostridium tetani, Clostridium botulinum. What bacteria causes anthrax? - answer Bacillus Anthracis WHat bacteria causes Lock jaw - answer Clostridium tetani What bacteria causes botulism - answer Clostridium botulinum
Is blood agar selective or differential? - answer Differential What is the catalase test for and what reagent does it use? - answer H2O2. Catalase breaks H2O2 into H2O and O2. Differentiates streptococci (cat-) from staphlococci (cat+) What is the coagulase test for? - answer Coagulase enzyme that breaks fibrinogen to fibrin. Staph aureus (coag+). Other staphs (coag-) How is carbohydrate differentiation determined? - answer Phenol red is used to determine a pH change. Red=no change, Yellow= pH drops and fermentation of carbohydrate has happened. CO2 gas may also be produced HOw does a positive hydrogen sulfide test appear? - answer Dark precipitate forms with Iron when hydrogen sulfide is present. How does a positive urease test appear? - answer Pos=bright pink. Neg=salmon->yellow How does positive citrate test appear? - answer Pos=blue. Neg=green Given a bacterial plate count from a urine culture be able to decide if there is a UTI. - answer (#colonies)x (_mL urine)= colonies/mL. 1K-10K = probable contaminated sample. 10K-100K=possible UTI.
100K= UTI.
Which 3 bacteria does the FDA recommend for disinfectant testing? - answer S. Aureus (gram +, infection of wounds) P. aeriginosa (gram -, often fatal) Salmonella typhi (gram -, hard to disinfect). Given results from antibiotic testing be able to determine resistance of susceptibility to antibiotics - answer Measure zone of inhibition and compare to reference chart to determine resistant, intermediate, or senstive(suceptable) Where does the yeast cryptococcus cause serious infection? - answer Spinal fluid. Define dimorphic fungi. - answer They exist as yeasts and molds Define budding in yeast. - answer Yeast makes a small copy of itself that will grow into a new yeast cell. How would a gram stain be used with fungi - answer Fungi appear gram + but larger than bacteria HOw would a KOH stain be used with fungi? - answer KOH when mixed with tissue will digest tissue, but not fungus. A wet mount can be used to see hyphae. How would an india ink stain be used with fungi? - answer Cryptococcus which causes meningitis can have a clear capsule. What is the scotch tape test for? - answer Pinworm infections
What two roundworms or nematodes have a larval stage migrating through the host lungs? - answer Ascaris lumbricoides, Necator americanus. What two parasites use direct skin penetration as the way to enter the host? - answer Hookworms (necator americanus) and Blood fluke (Schistosoma). What stage of plasmodia in the mosquito is the infective stage for humans? - answer Sporozoite What stage of the plasmodia in the human host is the infective stage for mosquitoes? - answer Gamatocytes What stage in the plasmodia life cycle is occuring when the human host experiences fevers and chills? - answer Erythrocytic cycle when merozoites are released In which host does the asexual reproductive life cycle of plasmodia take place? - answer Human In which host does the sexual reproductive life cycle of plasmodia take place?
- answer Mosquito Where in the human host does Toxoplamsa gondii infect? - answer CNS, heart and skel muscle. In what host does the sexual reproductive cycle of toxoplasma gondii occur? - answer Cats
What parasite causes african sleeping sickness? - answer Trypanosoma brucei What parasite causes changas disease? - answer Trypanosoma cruzi How would an individual get a Trichinella infection? - answer Ingestion of larva in skeletal muscle. What have molecular techniques to identify pathogens replaced some of the traditional methods? - answer They've become cheaper. They can identify bacteria that doesn't grow well on media. What is 16S rDNA and how is it used to identify bacteria? - answer A small subunit of ribosomal DNA. Species have unique 16S rDNA sequences. What is PCR? - answer It marks a region of DNA and replicates it. What are the 3 steps in PCR? - answer -Separate the DNA strands -Annealing the primer to the template -Synthesis of new DNA strands. What are primers? - answer Small pieces of DNA that bind to specific sequences. Signals DNA polymerase to copy the region. What is meant by conserved and variable regions of DNA? - answer Conserved=regions that are similar across species. Variable=regions are more species specific.
