Bacteria — MCQs

A 6-year-old boy presents with fever, sore throat, hoarseness, and neck enlargement. The symptoms started 3 days ago and progressed gradually with an elevated temperature and swollen lymph nodes. His family immigrated recently from Honduras. He was born via spontaneous vaginal delivery at 39 weeks after an uneventful gestational period and he is now on a catch-up vaccination schedule. He lives with several family members, including his parents, in a small apartment. No one in the apartment smokes tobacco. On presentation, the patient’s blood pressure is 110/75 mm Hg, heart rate is 103/min, respiratory rate is 20/min, and temperature is 39.4°C (102.9°F). On physical examination, the child is acrocyanotic and somnolent. There is widespread cervical edema and enlargement of the cervical lymph nodes. The tonsils are covered with a gray, thick membrane which spreads beyond the tonsillar bed and reveals bleeding, erythematous mucosa with gentle scraping. The lungs are clear to auscultation. Which of the following is the target of the virulence factor produced by the pathologic organism infecting this child?

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 2-year-old boy is brought to the emergency department because of fever, cough, and ear pain over the past 2 days. He has had recurrent respiratory tract infections and several episodes of giardiasis and viral gastroenteritis since he was 6 months of age. Examination shows decreased breath sounds over both lung fields and bilateral purulent otorrhea. His palatine tonsils and adenoids are hypoplastic. Quantitative flow cytometry of his blood shows decreased levels of cells that express CD19, CD20, and CD21. Which of the following is the most likely cause of this patient's condition?

A 46-year-old woman presents to the emergency department complaining of bloody diarrhea, fatigue, and confusion. A few days earlier she went to a fast-food restaurant for a college reunion party. Her friends are experiencing similar symptoms. Laboratory tests show anemia, thrombocytopenia, and uremia. Lactate dehydrogenase (LDH) is raised while haptoglobin is decreased. Peripheral blood smears show fragmented red blood cells (RBCs). Coombs tests are negative. Which of the following is the responsible organism?

A 28-year-old man presents to the clinic complaining of chronic joint pain and fatigue for the past 2 months. The patient states that he usually has pain in one of his joints that resolve but then seems to move to another joint. The patient notes no history of trauma but states that he has experienced some subjective fevers over that time. He works as a logger and notes that he's heard that people have also had these symptoms in the past, but that he does not know anyone who is currently experiencing them. What is the most likely etiologic agent of this patient's disease?

An 11-month-old boy presents to his pediatrician with severe wheezing, cough, and fever of 38.0°C (101.0°F). Past medical history is notable for chronic diarrhea since birth, as well as multiple pyogenic infections. The mother received prenatal care, and delivery was uneventful. Both parents, as well as the child, are HIV-negative. Upon further investigation, the child is discovered to have Pneumocystis jirovecii pneumonia, and the appropriate treatment is begun. Additionally, a full immunologic check-up is ordered. Which of the following profiles is most likely to be observed in this patient?

An 8-year-old female presents to her pediatrician with nasal congestion. Her mother reports that the patient has had nasal congestion and nighttime cough for almost two weeks. The patient’s 3-year-old brother had similar symptoms that began around the same time and have since resolved. The patient initially seemed to be improving, but four days ago she began developing worsening nasal discharge and fever to 102.6°F (39.2°C) at home. Her mother denies any change in appetite. The patient denies sore throat, ear pain, and headache. She is otherwise healthy. In the office, her temperature is 102.2°F (39.0°C), blood pressure is 96/71 mmHg, pulse is 128/min, and respirations are 18/min. On physical exam, the nasal turbinates are edematous and erythematous. She has a dry cough. Purulent mucous can be visualized dripping from the posterior nasopharynx. Her maxillary sinuses are tender to palpation. Which of the following organisms is most likely to be causing this patient’s current condition?

A 6-day-old boy is brought to the emergency room with a fever. He was born to a G1P1 mother at 39 weeks gestation via vaginal delivery. The mother underwent all appropriate prenatal care and was discharged from the hospital 1 day after birth. The boy has notable skin erythema around the anus with some serosanguinous fluid. The umbilical stump is present. The patient is discharged from the emergency room with antibiotics. He returns to the emergency room at 32 days of age and his mother reports that he has been clutching his left ear. The left tympanic membrane appears inflamed and swollen. The umbilical stump is still attached and is indurated, erythematous, and swollen. The boy's temperature is 99°F (37.2°C), blood pressure is 100/60 mmHg, pulse is 130/min, and respirations are 20/min. A complete blood count is shown below: Hemoglobin: 14.0 g/dL Hematocrit: 42% Leukocyte count: 16,000/mm^3 with normal differential Platelet count: 190,000/mm^3 A deficiency in which of the following compounds is most likely the cause of this patient's condition?

A medical technician is trying to isolate a pathogen from the sputum sample of a patient. The sample is heat fixed to a slide then covered with carbol fuchsin stain and heated again. After washing off the stain with clean water, the slide is covered with 1% sulfuric acid for decolorization. The sample is rinsed again and stained with methylene blue. Microscopic examination shows numerous red, branching filamentous organisms. Which of the following is the most likely isolated pathogen?

A 42-year-old woman comes to the emergency department because of worsening severe pain, swelling, and stiffness in her right knee for the past 2 days. She recently started running 2 miles, 3 times a week in an attempt to lose weight. She has type 2 diabetes mellitus and osteoporosis. Her mother has rheumatoid arthritis. She drinks one to two glasses of wine daily. She is sexually active with multiple partners and uses condoms inconsistently. Current medications include metformin and alendronate. She is 161 cm (5 ft 3 in) tall and weighs 74 kg (163 lb); BMI is 29 kg/m2. Her temperature is 38.3°C (100.9°F), pulse is 74/min, and blood pressure is 115/76 mm Hg. She appears to be in discomfort and has trouble putting weight on the affected knee. Physical examination shows a 2-cm, painless ulcer on the plantar surface of the right toe. The right knee is swollen and tender to palpation. Arthrocentesis of the right knee with synovial fluid analysis shows a cell count of 55,000 WBC/μL with 77% polymorphonuclear (PMN) cells. Which of the following is the most likely underlying cause of this patient's presenting condition?