Microbial genetics and drug resistance Practice Questions

Question 1

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?

Accepted Answer

Alteration of peptidoglycan synthesis

Answer

Increased efflux across bacterial cell membranes

Answer

Production of beta-lactamase

Answer

Alteration of penicillin-binding proteins

Answer

Alteration of ribosomal targets

Question 2

An 18-year old college freshman presents to his university clinic because he has not been feeling well for the past two weeks. He has had a persistent headache, occasional cough, and chills without rigors. The patient’s vital signs are normal and physical exam is unremarkable. His radiograph shows patchy interstitial lung infiltrates and he is diagnosed with atypical pneumonia. The patient is prescribed azithromycin and takes his medication as instructed. Despite adherence to his drug regimen, he returns to the clinic one week later because his symptoms have not improved. The organism responsible for this infection is likely resistant to azithromycin through which mechanism?

Accepted Answer

Insertion of drug efflux pumps

Answer

Mutation in topoisomerase II

Answer

Methylation of ribosomal binding site

Answer

Presence of a beta-lactamase

Answer

Decreased binding to RNA polymerase

Question 3

A 64-year-old female with type 2 diabetes mellitus comes to the physician because of a 1-week history of painful red swelling on her left thigh. Examination shows a 3- x 4-cm, tender, fluctuant mass. Incision and drainage of the abscess are performed. Culture of the abscess fluid grows gram-positive, coagulase-positive cocci that are resistant to oxacillin. Which of the following best describes the mechanism of resistance of the causal organism to oxacillin?

Accepted Answer

Altered target of the antibiotic

Answer

Degradation of the antibiotic

Answer

Decreased uptake of the antibiotic

Answer

Decreased activation of the antibiotic

Answer

Acetylation of the antibiotic

Question 4

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?

Accepted Answer

Plasmid loss

Answer

Point mutation

Answer

Gain of function mutation

Answer

Viral infection

Answer

Loss of function mutation

Question 5

A 24-year-old male presents to the emergency room with a cough and shortness of breath for the past 3 weeks. You diagnose Pneumocystis jiroveci pneumonia (PCP). An assay of the patient's serum reveals the presence of viral protein p24. Which of the following viral genes codes for this protein?

Accepted Answer

gag

Answer

pol

Answer

rev

Answer

env

Answer

tat

Question 6

A 63-year-old female recovering from a total shoulder arthroplasty completed 6 days ago presents complaining of joint pain in her repaired shoulder. Temperature is 39 degrees Celsius. Physical examination demonstrates erythema and significant tenderness around the incision site. Wound cultures reveal Gram-positive cocci that are resistant to nafcillin. Which of the following organisms is the most likely cause of this patient's condition?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Escherichia coli

Answer

Streptococcus viridans

Answer

Staphylococcus epidermidis

Question 7

A 35-year-old female presents to the emergency room complaining of diarrhea and dehydration. She has been experiencing severe watery diarrhea for the past 3 days. She reports that she has been unable to leave the bathroom for more than a few minutes at a time. The diarrhea is profuse and watery without visible blood or mucus. She recently returned from a volunteer trip to Yemen where she worked at an orphanage. Her past medical history is notable for psoriasis for which she takes sulfasalazine. The patient drinks socially and does not smoke. Her temperature is 99°F (37.2°C), blood pressure is 100/55 mmHg, pulse is 130/min, and respirations are 20/min. Mucous membranes are dry. Her eyes appear sunken. Capillary refill is 4 seconds. The patient is started on intravenous fluid resuscitation. Which of the following processes is capable of transmitting the genetic material for the toxin responsible for this patient's condition?

Accepted Answer

Transduction

Answer

Transposition

Answer

Conjugation

Answer

Endospore formation

Answer

Transformation

Question 8

A 27-year-old man presents to the emergency department with weakness and a fever for the past week. The patient is homeless and has a past medical history of alcohol and IV drug abuse. His temperature is 102°F (38.9°C), blood pressure is 107/68 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for a tremulous patient with antecubital scars and a murmur over the left lower sternal border. Blood cultures are drawn and the patient is started on vancomycin and ceftriaxone and is admitted to the ICU. The patient's fever and symptoms do not improve despite antibiotic therapy for which the initial identified organism is susceptible. Cultures currently reveal MRSA as one of the infective organisms. Which of the following is the best next step in management?

Accepted Answer

Transesophageal echocardiography

Answer

Obtain new blood cultures

Answer

CT scan of the chest

Answer

Nafcillin and piperacillin-tazobactam

Answer

Vancomycin and gentamicin

Question 9

A 46-year-old woman presents to her primary care physician with complaints of increasing left upper quadrant discomfort. She has a known history of type 1 Gaucher disease. On physical examination, her spleen is palpable 8 cm below the costal margin. Routine laboratory work reveals severe pancytopenia. After consultation with the patient on the risks of her condition, the patient decides to undergo a splenectomy. Which of the following is more likely to occur as a consequence of splenectomy in this patient?

Accepted Answer

Pneumococcal septicemia

Answer

Thrombocytopenia

Answer

Leukopenia

Answer

Staphylococcal septicemia

Answer

Anemia

Question 10

A 35-year-old man comes to the emergency department with fever, chills, dyspnea, and a productive cough. His symptoms began suddenly 2 days ago. He was diagnosed with HIV 4 years ago and has been on triple antiretroviral therapy since then. He smokes one pack of cigarettes daily. He is 181 cm (5 ft 11 in) tall and weighs 70 kg (154 lb); BMI is 21.4 kg/m2. He lives in Illinois and works as a carpenter. His temperature is 38.8°C (101.8°F), pulse is 110/min, respirations are 24/min, and blood pressure is 105/74 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 92%. Examinations reveals crackles over the right lower lung base. The remainder of the examination shows no abnormalities. Laboratory studies show:
Hemoglobin 11.5 g/dL
Leukocyte count 12,800/mm3
Segmented neutrophils 80%
Eosinophils 1%
Lymphocytes 17%
Monocytes 2%
CD4+ T-lymphocytes 520/mm3(N ≥ 500)
Platelet count 258,000/mm3
Serum
Na+ 137 mEq/L
Cl- 102 mEq/L
K+ 5.0 mEq/L
HCO3- 22 mEq/L
Glucose 92 mg/dL
An x-ray of the chest shows a right lower-lobe infiltrate of the lung. Which of the following is the most likely causal organism?

Accepted Answer

Streptococcus pneumoniae

Answer

Legionella pneumophila

Answer

Pneumocystis jirovecii

Answer

Staphylococcus aureus

Answer

Cryptococcus neoformans

Microbial genetics and drug resistance

Study Resources

Lessons

Questions

Flashcards

Lessons

Bacterial genome structure

Horizontal gene transfer mechanisms

Plasmids and mobile genetic elements

Transposons and integrons

Beta-lactamase types and mechanisms

MRSA resistance mechanisms

VRE resistance mechanisms

Fluoroquinolone resistance

Aminoglycoside resistance

Multi-drug resistant gram-negatives

Biofilm-associated resistance

Evolution of antimicrobial resistance

Antimicrobial stewardship principles

Practice Questions

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About Microbial genetics and drug resistance for USMLE

Lessons in Microbial genetics and drug resistance

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