Like all medical/diagnostic tests, COVID-19 tests are characterized by their sensitivity and their specificity. Sensitivity is:  a.  the ability to detect a true negative. b.  the ability to detect a true positive. c.  the ability to generate a true negative. d.  the ability to generate a true positive. [sensitivity] Specificity is: a.  the ability to detect a true negative. b.  the ability to detect a true positive. c.  the ability to generate a true negative. d.  the ability to generate a true positive. [specificity]  

You have become a practicing clinician (congratulations!). Your patient presents with an infected wound that is oozing fluid.  You test some of the fluid. Use the results shown here, and the dichotomous key (below) to guide your treatment for the patient. Note the pink bacteria.                    Note the yellow color. Note the pink color.  Note that the citrate tube is green. What is the shape and arrangement of the cells shown in the image, above?  Be sure to use the technical terms for shape and arrangement for your answer.  [arrangement] Based on the Gram stain results, metabolic test results, and cell morphology and arrangement, which bacterial species is most likely causing the patient’s infection? [species] Which of the following antibiotics could be used to treat the patient’s infection? a. ampicillinb. erythromycinc. penicillin [antibiotic]

Why can hydrogen peroxide be used as a home remedy for “strep throat”? That is, what weakness of the “strep” bacteria does hydrogen peroxide exploit? a.  Streptococcus species lack catalase. b.  Streptococcus species lack superoxide dismutase. c.  Streptococcus species lack peroxidase. d.  Streptococcus species lack oxidase. [peroxide] What is the name (Genus) of a Gram-positive bacterial species that is catalase-positive? a.  Streptococcus b.  Staphylococcus c.  Salmonella d.  Pseudomonas [Genus]

A pharmaceutical sales rep visits your community clinic where COVID-19 screening is available.  The rep presents two COVID-19 tests.  Test A has a sensitivity of 65% and a specificity of 95%.  Test B has a sensitivity of 90% and a specificity of 75%.  Which test would you choose for your clinic (1 point) and why?  Note:  to receive credit for your answer, you must include correct figures (false negative percent and false positive percent) for each test (4 points).  (5 points, total)

Briefly explain why the streak plate method is better for generating pure cultures than using broth to dilute microbes.  (2 points)

Your patient has impetigo, a skin infection caused by Staphylococcus aureus.  You test bacteria grown from fluid from the lesions for antibiotic sensitivity. Impetigo lesions What is an antibiotic, tested here, that could be used to treat the patient’s infection, effectively? a. ampicillinb. Bactrimc. streptomycin [antibiotic] What is the name of the enzyme that bacteria use to degrade penicillin and other antibiotics of its class? a. β-lactamaseb. hexose kinasec. glucose-6-phosphate dehydrogenased. RuBisCo [enzyme] Among the antibiotics tested listed, above, which one works by inhibiting a metabolic/biochemical pathway? a. aminoglycosideb. beta-lactamc. macrolided. sulfonamide (eg., Bactrim) [metabolic] What is the most common mechanism of resistance to sulfonamide antibiotics such as Bactrim? [Bactrim] a.  beta-lactamase b.  bypass c.  efflux pumps d.  carbapenimase  

Your patient who’s on a ventilator has pneumonia caused by Pseudomonas aeruginosa.  You have tested bacteria cultured from his pleural effusions (lung fluid) for antibiotic sensitivity. What is an antibiotic tested here that could be used to treat the patient’s infection? a. ampicillinb. tetracyclinec. Bactrimd. streptomycin [antibiotic] What is the mechanism of action of ampicillin/penicillin? a. inhibit cell wall formationb. inhibit protein synthesisc. inhibit cell membrane functiond. inhibit metabolism [mechanism] Why are Pseudomonas bacteria resistant to so many antibiotics?  [resistant] a.  They bypass the metabolic pathways affected by the antibiotics. b.  They have a number of efflux pumps. c.  They are uncommonly sensitive to mutation. d.  They produce beta-lactamase, naturally.

You are working with Doctors Without Borders in Polynesia, and meet with a patient who has grossly swollen feet and legs (see below).  (3 points, total) A smear of the patient’s blood is shown, below. What is the name of the disease that is causing your patient’s distress?  [disease] a.  bilharzia b.  dracunculiasis c.  elephantiasis d.  trichinellosis What is the proper name (Genus + specific epithet) of the pathogen that is causing the disease?  [propername] a.  Schistosoma mansoni b.  Dracunculus medininensis c.  Wuchereria bancrofti d.  Trichinella spiralis How is this pathogen transmitted to humans?  [transmission] a.  larvae in water b.  ingestion of copepods c.  mosquito bite d.  undercooked pork

You are working with a patient in the community clinic who complains of a sore throat (see below for a picture of the patient’s throat).  You submit throat swabs to the clinical lab for culturing and identification.  See below for results of lab tests. Growth on blood agar – note clear zone around colonies Gram stain – note chains of purple cocci Catalase test – no bubbles What is the proper name of the bacterium that is the most likely cause of the patient’s distress? a. Staphylococcus aureusb. Staphylococcus epidermidisc. Streptococcus pneumoniaed. Streptococcus pyogenes [propername] What do we mean when we say “beta-hemolysis”? a. lysis of red blood cells with incomplete degradation of hemoglobinb. lysis of red blood cells with no degradation of hemoglobinc. lysis of red blood cells with complete degradation of hemoglobind. no lysis of red blood cells or hemoglobin [beta-hemolysis] What do we mean when we say “alpha-hemolysis”? a. lysis of red blood cells with incomplete degradation of hemoglobinb. lysis of red blood cells with no degradation of hemoglobinc. lysis of red blood cells with complete degradation of hemoglobind. no lysis of red blood cells or hemoglobin [alpha-hemolysis]

For much of the 20th century, people who lived in the Southern United States were stereotyped as being slow-witted and lazy.  However, it is believed that much of this behavior was due to infestation with hookworm which can cause severe anemia due to it feeding on the host’s blood.  What is the proper name (Genus and specific epithet) of this parasite?