Biofilms in chronic infections — MCQs

An investigator is studying the growth of an organism in different media. The organism is inoculated on a petri dish that contains heated sheep blood, vancomycin, nystatin, trimethoprim, and colistin. The resulting growth medium is incubated at 37°C. Numerous small, white colonies are seen after incubation for 48 hours. This organism is most likely to cause which of the following conditions?

A team of intensivists working in a private intensive care unit (ICU) observe that the clinical efficacy of vancomycin is low, and proven nosocomial infections have increased progressively over the past year. A clinical microbiologist is invited to conduct a bacteriological audit of the ICU. He analyzes the microbiological reports of all patients treated with vancomycin over the last 2 years and takes relevant samples from the ICU for culture and antibiotic sensitivity analysis. The audit concludes that there is an increased incidence of vancomycin-resistant Enterococcus fecalis infections. Which of the following mechanisms best explains the changes that took place in the bacteria?

A 67-year-old woman comes to the physician because of fever, chills, myalgias, and joint pain 1 month after undergoing aortic prosthetic valve replacement due to high-grade aortic stenosis. She does not drink alcohol or use illicit drugs. Her temperature is 39.3°C (102.8°F). She appears weak and lethargic. Physical examination shows crackles at both lung bases and a grade 2/6, blowing diastolic murmur over the right sternal border. Laboratory studies show leukocytosis and an elevated erythrocyte sedimentation rate. The causal organism is most likely to have which of the following characteristics?

A 25-day-old male infant presents to the emergency department because his mother states that he has been acting irritable for the past 2 days and has now developed a fever. On exam, the infant appears uncomfortable and has a temperature of 39.1 C. IV access is immediately obtained and a complete blood count and blood cultures are drawn. Lumbar puncture demonstrates an elevated opening pressure, elevated polymorphonuclear neutrophil, elevated protein, and decreased glucose. Ampicillin and cefotaxime are immediately initiated and CSF culture eventually demonstrates infection with a Gram-negative rod. Which of the following properties of this organism was necessary for the infection of this infant?

A 47-year-old woman comes to the physician because of a 6-week history of fatigue and low-grade fever. She has no history of serious illness except for a bicuspid aortic valve, diagnosed 10 years ago. She does not use illicit drugs. Her temperature is 37.7°C (99.9°F). Physical examination shows petechiae under the fingernails and multiple tender, red nodules on the fingers. A new grade 2/6 diastolic murmur is heard at the right second intercostal space. Which of the following is the most likely causal organism?

While testing various strains of Streptococcus pneumoniae, a researcher discovers that a certain strain of this bacteria is unable to cause disease in mice when deposited in their lungs. What physiological test would most likely deviate from normal in this strain of bacteria as opposed to a typical strain?

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 54-year-old man comes to the physician because of persistent right knee pain and swelling for 2 weeks. Six months ago, he had a total knee replacement because of osteoarthritis. His temperature is 38.5°C (101.3°F), pulse is 100/min, and blood pressure is 139/84 mm Hg. Examination shows warmth and erythema of the right knee; range of motion is limited by pain. His leukocyte count is 14,500/mm3, and erythrocyte sedimentation rate is 50 mm/hr. Blood cultures grow gram-positive, catalase-positive cocci. These bacteria grow on mannitol salt agar without color change. Production of which of the following is most important for the organism's virulence?

A 65-year-old man is brought to the emergency department after coughing up copious amounts of blood-tinged sputum at his nursing home. He recently had an upper respiratory tract infection that was treated with antibiotics. He has a long-standing history of productive cough that has worsened since he had a stroke 3 years ago. He smoked a pack of cigarettes daily for 40 years until the stroke, after which he quit. The patient appears distressed and short of breath. His temperature is 38°C (100.4°F), pulse is 92/min, and blood pressure is 145/85 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 92%. Physical examination shows digital clubbing and cyanosis of the lips. Coarse crackles are heard in the thorax. An x-ray of the chest shows increased translucency and tram-track opacities in the right lower lung field. Which of the following is the most likely diagnosis?

A 46-year-old Caucasian female presents with cold intolerance, weight gain, and constipation. She has also noticed that her nails have become thinner recently but denies any fever or neck pain. Which of the following is NOT an expected histological finding in the thyroid?