Biofilms Practice Questions

Question 1

A 37-year-old woman with a history of anorectal abscesses complains of pain in the perianal region. Physical examination reveals mild swelling, tenderness, and erythema of the perianal skin. She is prescribed oral ampicillin and asked to return for follow-up. Two days later, the patient presents with a high-grade fever, syncope, and increased swelling. Which of the following would be the most common mechanism of resistance leading to the failure of antibiotic therapy in this patient?

Accepted Answer

Production of beta-lactamase enzyme

Answer

Intrinsic absence of a target site for the drug

Answer

Use of an altered metabolic pathway

Answer

Altered structural target for the drug

Answer

Drug efflux pump

Question 2

Blood cultures are sent to the laboratory and empiric treatment with intravenous vancomycin is started. Blood cultures grow gram-negative bacilli identified as Cardiobacterium hominis. Which of the following is the most appropriate next step in management?

Accepted Answer

Switch to intravenous ceftriaxone

Answer

Switch to intravenous gentamicin

Answer

Switch to intravenous ampicillin

Answer

Switch to intravenous cefazolin

Answer

Add intravenous rifampin

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 65-year-old man presents with low-grade fever and malaise for the last 4 months. He also says he has lost 9 kg (20 lb) during this period and suffers from extreme fatigue. Past medical history is significant for a mitral valve replacement 5 years ago. His temperature is 38.1°C (100.6°F), respirations are 22/min, pulse is 102/min, and blood pressure is 138/78 mm Hg. On physical examination, there is a new onset 2/6 holosystolic murmur loudest in the apical area of the precordium. Which of the following organisms is the most likely cause of this patient’s condition?

Accepted Answer

Enterococcus

Answer

Candida albicans

Answer

Coagulase-negative Staphylococcus spp.

Answer

Escherichia coli

Answer

Pseudomonas aeruginosa

Question 5

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?

Accepted Answer

Streptococcus sanguinis

Answer

Staphylococcus epidermidis

Answer

Streptococcus pyogenes

Answer

Streptococcus pneumoniae

Answer

Enterococcus faecalis

Question 6

A 59-year-old man presents to the emergency room for a fever that has persisted for over 4 days. In addition, he has been experiencing weakness and malaise. His past medical history is significant for a bicuspid aortic valve that was replaced 2 years ago. Physical exam reveals nailbed splinter hemorrhages, tender nodules on his fingers, and retinal hemorrhages. An echocardiogram shows aortic valve vegetations and culture reveals a gram-positive alpha-hemolytic organism that grows as cocci in chains. The organism is then exposed to optochin and found to be resistant. Finally, they are seen to ferment sorbitol. The most likely cause of this patient's symptoms is associated with which of the following?

Accepted Answer

Dental procedures

Answer

Pneumonia

Answer

Colon cancer

Answer

IV drug use

Answer

Sexual activity

Question 7

A 3-year-old female is found to have unusual susceptibility to infections by catalase-producing organisms. This patient likely has a problem with the function of which of the following cell types?

Accepted Answer

Neutrophils

Answer

Natural killer cells

Answer

Eosinophils

Answer

B cells

Answer

T cells

Question 8

A 20-year-old woman presents for a follow-up visit with her physician. She has a history of cystic fibrosis and is currently under treatment. She has recently been struggling with recurrent bouts of cough and foul-smelling, mucopurulent sputum over the past year. Each episode lasts for about a week or so and then subsides. She does not have a fever or chills during these episodes. She has been hospitalized several times for pneumonia as a child and continues to struggle with diarrhea. Physically she appears to be underweight and in distress. Auscultation reveals reduced breath sounds on the lower lung fields with prominent rhonchi. Which of the following infectious agents is most likely associated with the recurrent symptoms this patient is experiencing?

Accepted Answer

Pseudomonas

Answer

Mycobacterium avium

Answer

Histoplasma

Answer

Pneumococcus

Answer

Listeria

Question 9

A 45-year-old male presents to his primary care physician complaining of drainage from his left great toe. He has had an ulcer on his left great toe for over eight months. He noticed increasing drainage from the ulcer over the past week. His past medical history is notable for diabetes mellitus on insulin complicated by peripheral neuropathy and retinopathy. His most recent hemoglobin A1c was 9.4%. He has a 25 pack-year smoking history. He has multiple sexual partners and does not use condoms. His temperature is 100.8°F (38.2°C), blood pressure is 150/70 mmHg, pulse is 100/min, and respirations are 18/min. Physical examination reveals a 1 cm ulcer on the plantar aspect of the left great toe surrounded by an edematous and erythematous ring. Exposed bone can be palpated with a probe. There are multiple small cuts and bruises on both feet. A bone biopsy reveals abundant gram-negative rods that do not ferment lactose. The pathogen most likely responsible for this patient’s current condition is also strongly associated with which of the following conditions?

Accepted Answer

Otitis externa

Answer

Waterhouse-Friedrichsen syndrome

Answer

Gastroenteritis

Answer

Toxic shock syndrome

Answer

Rheumatic fever

Question 10

A group of microbiological investigators is studying bacterial DNA replication in E. coli colonies. While the cells are actively proliferating, the investigators stop the bacterial cell cycle during S phase and isolate an enzyme involved in DNA replication. An assay of the enzyme's exonuclease activity determines that it is active on both intact and demethylated thymine nucleotides. Which of the following enzymes have the investigators most likely isolated?

Accepted Answer

DNA polymerase I

Answer

DNA ligase

Answer

Telomerase

Answer

Primase

Answer

DNA topoisomerase

Biofilms

Study Resources

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Questions

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Lessons

Biofilm formation stages

Extracellular polymeric substances

Quorum sensing in biofilms

Biofilm-associated antimicrobial resistance

Biofilms in device-related infections

Biofilms in chronic infections

Biofilms in endocarditis

Biofilms in cystic fibrosis

Biofilms in otitis media and sinusitis

Detection methods for biofilms

Biofilm disruption strategies

Novel anti-biofilm therapies

Prevention of biofilm formation

Practice Questions

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About Biofilms for USMLE

Lessons in Biofilms

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