Fluoroquinolone resistance — MCQs

A 22-year-old female with no past medical history presents to her primary care physician with a 3-day history of knee pain. She denies any recent injury or trauma. On physical examination her knee is warm, erythematous, and has diminished range of movement. The patient reports having multiple sexual partners over the last year and does not use protection regularly. Her blood pressure is 124/85 mmHg, heart rate is 76/min, and temperature is 38.3℃ (101.0℉). A joint aspiration is performed and a growth of gram-negative diplococci is noted on bacterial culture. What is the treatment of choice for this patient's condition?

A 67-year-old man presents to the physician with profuse watery diarrhea along with fever and crampy abdominal pain. He has been taking an antibiotic course of cefixime for about a week to treat a respiratory tract infection. At the doctor’s office, his pulse is 112/min, the blood pressure is 100/66 mm Hg, the respirations are 22/min, and the temperature is 38.9°C (102.0°F). His oral mucosa appears dry and his abdomen is soft with vague diffuse tenderness. A digital rectal examination is normal. Laboratory studies show: Hemoglobin 11.1 g/dL Hematocrit 33% Total leucocyte count 16,000/mm3 Serum lactate 0.9 mmol/L Serum creatinine 1.1 mg/dL What is most likely to confirm the diagnosis?

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?

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 15-year-old boy presents with his father to the urgent care department with a 5-day history of frequent diarrhea, occasionally mixed with streaks of blood. Stool cultures are pending, but preliminary stool samples demonstrate fecal leukocytes and erythrocytes. The patient's vital signs are within normal limits, and he is started on outpatient therapy for presumed Shigella infection. Which of the following was the young man most likely started on?

A 67-year-old male with a past medical history of diabetes type II, obesity, and hyperlipidemia presents to the general medical clinic with bilateral hearing loss. He also reports new onset vertigo and ataxia. The symptoms started a day after undergoing an uncomplicated cholecystectomy. If a drug given prophylactically just prior to surgery has caused this patient’s symptoms, what is the mechanism of action of the drug?

A 24-year-old woman presents to her physician's office complaining of a worsening cough with large volumes of mucoid sputum every morning and thick, foul-smelling sputum almost every time she coughs. She says that this cough started about one month ago and has been increasing in intensity. Over-the-counter medications are ineffective. Past medical history is significant for cystic fibrosis diagnosed at the age of 6 years, and pneumonia twice in the past 2 years. Other than a cough, she has no fever or any other concerns. A sputum sample grows aerobic, non-lactose fermenting, oxidase-positive, gram-negative bacillus. Which of the following treatment regimens is the most beneficial for her at this time?

A 61-year-old woman who recently emigrated from India comes to the physician because of a 2-month history of fever, fatigue, night sweats, and a productive cough. She has had a 5-kg (11-lb) weight loss during this period. She has a history of type 2 diabetes mellitus and poorly controlled asthma. She has had multiple asthma exacerbations in the past year that were treated with glucocorticoids. An x-ray of the chest shows a cavitary lesion of the posterior apical segment of the left upper lobe with consolidation of the surrounding parenchyma. The pathogen identified on sputum culture is found to be resistant to multiple drugs, including streptomycin. Which of the following mechanisms is most likely involved in bacterial resistance to this drug?

A 23-year-old woman presents to your office for a gynecological exam. She says that she has been in good health and has no complaints. She has been in a steady monogamous relationship for the past year. Physical examination was unremarkable. Screening tests are performed and return positive for gonorrhea. You treat her with an intramuscular injection of ceftriaxone and 7 day course of doxycycline. What else is recommended for this case?

An investigator studying fungal growth isolates organisms from an infant with diaper rash. The isolate is cultured and exposed to increasing concentrations of nystatin. Selected colonies continue to grow and replicate even at high concentrations of the drug. Which of the following is the most likely explanation for this finding?