Polymyxins — MCQs

A forty-five-year-old farmer with past medical history of diabetes, hypertension, and possible narrow angles comes into your emergency room confused, diaphoretic, salivating, vomiting and shedding tears. He has pinpoint pupils. You conclude that he is showing effects of acute organophosphate poisoning. While administering the antidote, you should carefully monitor for which of the following side effects?

A 42-year-old woman with a history of multiple sclerosis and recurrent urinary tract infections comes to the emergency department because of flank pain and fever. Her temperature is 38.8°C (101.8°F). Examination shows left-sided costovertebral angle tenderness. She is admitted to the hospital and started on intravenous vancomycin. Three days later, her symptoms have not improved. Urine culture shows growth of Enterococcus faecalis. Which of the following best describes the most likely mechanism of antibiotic resistance in this patient?

A 77-year-old woman is brought to the emergency department from her nursing home because she was found down overnight. On presentation she was found to be delirious and was unable to answer questions. Chart review shows that she is allergic to cephalosporins. Her temperature is 102.2°F (39°C), blood pressure is 105/52 mmHg, pulse is 94/min, and respirations are 23/min. Physical exam reveals a productive cough. A metabolic panel is obtained with the following results: Serum: Na+: 135 mEq/L Cl-: 95 mEq/L K+: 4 mEq/L HCO3-: 19 mEq/L BUN: 40 mg/dL Creatinine: 2.5 mg/dL Glucose: 150 mg/dL Based on these findings two different drugs are started empirically. Gram stain on a blood sample is performed showing the presence of gram-positive organisms on all samples. One of the drugs is subsequently stopped. The drug that was most likely stopped has which of the following characteristics?

A scientist is studying the mechanisms by which bacteria become resistant to antibiotics. She begins by obtaining a culture of vancomycin-resistant Enterococcus faecalis and conducts replicate plating experiments. In these experiments, colonies are inoculated onto a membrane and smeared on 2 separate plates, 1 containing vancomycin and the other with no antibiotics. She finds that all of the bacterial colonies are vancomycin resistant because they grow on both plates. She then maintains the bacteria in liquid culture without vancomycin while she performs her other studies. Fifteen generations of bacteria later, she conducts replicate plating experiments again and finds that 20% of the colonies are now sensitive to vancomycin. Which of the following mechanisms is the most likely explanation for why these colonies have become vancomycin sensitive?

A 53-year-old woman presents with a severe headache, nausea, and vomiting for the past 48 hours. Vitals show a blood pressure of 220/134 mm Hg and a pulse of 88/min. Urinalysis shows a 2+ proteinuria and RBC casts. Which of the following renal lesions is most likely to be seen in this patient?

A microbiology student was given a swab containing an unknown bacteria taken from the wound of a soldier and asked to identify the causative agent. She determined that the bacteria was a gram-positive, spore-forming bacilli, but had difficulty narrowing it down to the specific bacteria. The next test she performed was the Nagler's test, in which she grew the bacteria on a plate made from egg yolk, which would demonstrate the ability of the bacteria to hydrolyze phospholipids and produce an area of opacity. Half the plate contained a specific antitoxin which prevented hydrolysis of phospholipids while the other half did not contain any antitoxin. The bacteria produced an area of opacity only on half of the plate containing no antitoxin. Which of the following toxins was the antitoxin targeting?

You are treating a neonate with meningitis using ampicillin and a second antibiotic, X, that is known to cause ototoxicity. What is the mechanism of antibiotic X?

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

A 41-year-old homeless man is brought to the emergency department complaining of severe fever, dizziness, and a persistent cough. The patient has a history of long-standing alcohol abuse and has frequently presented to the emergency department with acute alcohol intoxication. The patient states that his cough produces ‘dark brown stuff’ and he provided a sample for evaluation upon request. The patient denies having any other underlying medical conditions and states that he has no other symptoms. He denies taking any medications, although he states that he knows he has a sulfa allergy. On observation, the patient looks frail and severely fatigued. The vital signs include: blood pressure 102/72 mm Hg, pulse 98/min, respiratory rate 15/min, and temperature 37.1°C (98.8°F). Auscultation reveals crackles in the left upper lobe and chest X-ray reveals an infiltrate in the same area. Which of the following is the most appropriate treatment for this patient?

A group of scientists discovered a neurotoxin that prevents neurons from releasing neurotransmitters. They performed a series of experiments to determine the protein that the neurotoxin affected. They used a fluorescent molecule that localizes to synaptic vesicles. In the control experiment, they observed the movement of vesicles from the cell body down the axon and finally to the synapse, and they saw movement from the synapse back to the cell body. When the neurotoxin was applied, the vesicles stopped moving down the axon, but movement back to the cell body still occurred. They also applied tetanospasmin and botulinum toxin to see if these toxins exhibited similar behavior but they did not. Which of the following proteins is most likely affected by this neurotoxin?