Instruction: Please choose the best answer for each question. A tiny worm was passed in the stool of a 6-year-old child with perianal pruritus, especially at night. The worm measured 10 mm in length with a pointed tail, and eggs were recovered by Scotch tape method. What species does this represent?

Instruction: Please choose the best answer for each question. A 36-year-old man developed a painful purulent urethral discharge following a 2-week vacation to Thailand. Gram stain reveals gram-negative diplococci. Iron, obtained through surface receptors, is essential for the microorganism’s virulence factors. From which molecule does it obtain iron?

Instruction: Please choose the best answer for each question. A 52-year-old man develops abscesses after surgery to repair an abdominal gunshot wound. Gram stain of the foul-smelling exudate reveals numerous PMNs and several gram-negative rods that did not grow on blood plates in the presence of oxygen. Metabolism of oxygen results in toxic reactive oxygen species. Which antibiotic is the best choice for treating this infection?

Instruction: Please choose the best answer for each question. A teenaged boy suffered a foot laceration while swimming in a polluted river and developed a foul-smelling wound exudate. One isolated bacterium lacked superoxide dismutase, catalase, and peroxidase. Which statement best describes this microorganism?

Instruction: Please choose the best answer for each question. A 20-year-old pregnant woman presents with a 4-day history of fever, chills, myalgia, and painful genital lesions that began as vesicles. Pelvic exam reveals extensive vesicular and ulcerative lesions on the left labia minora and majora with marked edema and inguinal lymphadenopathy. Which microorganism causing genital ulcers can be demonstrated by dark-field microscopy?

Instruction: Please choose the best answer for each question. Twenty-eight hours after eating undercooked chicken, a 50-year-old farmer presents with abdominal pain, cramping, bloody diarrhea, and nausea. A stool isolate is biochemically identified as Salmonella enterica, but it cannot be serotyped. Which component has the organism lost?

Instruction: Please choose the best answer for each question. A 2-year-old infant is diagnosed with meningitis. Lumbar puncture reveals numerous neutrophils and gram-positive cocci in pairs that appear encapsulated. She is started on intravenous β-lactams. Alteration of which target most likely leads to development of resistance in the most likely etiologic agent of this child’s meningitis?

Instruction: Please choose the best answer for each question. An immunocompromised patient is suspected of having aspergillosis due to Aspergillus fumigatus. Which clinical condition is most likely to occur?

Instruction: Please choose the best answer for each question. A 42-year-old alcoholic man presents with fever, chills, cough, and chest x-ray suggestive of pneumonia. Gram-stained smear of sputum shows many PMNs and gram-positive cocci in pairs and chains. Which is the correct order of procedural steps when performing the Gram stain?

Instruction: Please choose the best answer for each question. A 78-year-old woman with suspected Streptococcus pneumoniae meningitis has a CSF Gram stain in which the iodine treatment step is mistakenly omitted. How will the bacteria appear on the slide?

Instruction: Please choose the best answer for each question. A 3-year-old girl from a day care center has a severe, intractable cough with leukocytosis and lymphocyte predominance. Which approach is most appropriate for diagnosis of this illness?

Instruction: Please choose the best answer for each question. A 55-year-old man presents with severe bilateral pulmonary infiltrate, leukocytosis, elevated enzymes, and elevated creatine kinase after visiting a restaurant with a large water fountain that was misty on the day of his visit. Which finding would be expected on a Gram stain that was counterstained with safranin for 3 minutes (prolonged counterstain)?

Instruction: Please choose the best answer for each question. Several strains of Streptococcus pneumoniae isolated from patients vary in virulence. Mixing cultures causes nonvirulent strains to become pathogenic in laboratory animal experiments. Uptake by a recipient cell of soluble DNA released from a donor cell is defined as which process?

A nonspore-forming, gram-positive bacillus was isolated from a throat specimen from a primary school–aged child who had not been vaccinated with the DTaP vaccine. The strain isolated carried a bacteriophage on which the gene for toxin was encoded. How did this strain become toxigenic?

An increase in antibiotic resistance has been observed in Staphylococcus aureus, Pseudomonas aeruginosa, and E. coli strains isolated from patients in medical centers. Direct transfer of a plasmid between two bacteria is defined as which of the following?

A 24-year-old female presented with pain during urination. Gram stain of the uncentrifuged urine revealed the presence of gram-negative rods. What virulence factor is essential for the survival of these uropathogenic bacteria in the urinary tract?

A 55-year-old British teacher presents with weight loss, weakness, muscle atrophy, and declining cognitive function. Her history reveals that her favorite meal is soup made with cow brain, which she has eaten almost every week since she was 10 years old. Which of the following best describes the most likely etiologic agent of her symptoms?

Over 200 isoniazid-resistant strains of Mycobacterium tuberculosis isolated from different patients in the northwestern region of Russia are screened by a PCR-restriction fragment length polymorphism assay. This analysis reveals a 93.6% prevalence of a specific G to C mutation in the katG in strains from patients with both newly and previously diagnosed cases of tuberculosis. Which of the following best describes the type of mutation that resulted in isoniazid resistance in these strains?

A 25-year-old man presents to the emergency room with several red, swollen, tender bite wounds on both arms that he stated occurred yesterday when he rescued his dog from a dogfight involving three other dogs, whose owner(s) is unknown. His right wrist and left elbow are also swollen and there is axillary lymphadenopathy on the left side. Gram stain of purulent material from the worst wound shows small gram-negative pleomorphic coccobacilli. The patient reports his last tetanus vaccination was 2 years ago. In addition to antibiotics, which of the following should be included in this patient’s treatment?

A patient presents to the emergency room with vomiting, diarrhea, high fever, and delirium. Upon physical examination, you notice large buboes, which are painful on palpation, and purpura and ecchymoses suggestive of disseminated intravascular coagulation. Gram stain on aspirate of a bubo reveals gram-negative rods with bipolar staining. Which of the following antibiotics is the drug of choice for empiric therapy?

Which of the following pathogens would most likely be seen in bacterial meningitis of the newborn?

A 3-year-old girl who has missed several scheduled immunizations presents to the emergency room with a high fever. She is irritable and has a stiff neck. Fluid from a spinal tap reveals 20,000 white blood cells per milliliter with 85% polymorphonuclear cells. Which of the following is the drug of choice for empiric therapy against organisms of childhood meningitis?

During the course of his hospital stay, a severely burned 60-year-old male develops a rapidly disseminating bacterial infection. Small gramnegative rods that are oxidase positive are cultured from green pus taken from the burn tissue. Which combination of antibiotics is the best choice for empiric therapy against this etiologic agent?

Laboratory results of a clinical specimen from a patient with hospital-acquired pneumonia reveal the presence of methicillin-resistant Staphylococcus aureus (MRSA). Which of the following drugs is the best empiric treatment?

A young, essentially healthy woman was concerned about her loss of job time due to recurrent UTIs. Her physician prescribed an antibiotic, which would control microbial nucleotide synthesis by inhibiting dihydrofolic acid reductase in bacteria up to 50,000 times more than in mammalian cells. Which of the following agents work by this mechanism?

Neisseria meningitidis, group B, is identified as a case of local meningitis outbreak in a military training camp. Which of the following protects this organism from complement-mediated phagocytosis by neutrophils?

A 64-year old female with a history of COPD visited her physician because of recent poor health symptoms, including, cough, fever, and night sweats, weakness, and 20-pound weight loss. Chest X-ray demonstrated a nodular infiltrate in the upper lobe. Laboratory staining of sputum revealed acid-fast organisms. Which characteristic of the most likely organism is responsible for this staining result?

In 2001, a number of governmental offices received mailed envelopes that contained an unknown white powder. Several employees were contaminated and developed cutaneous and/or inhalational anthrax. Which of the following is responsible for the antiphagocytic properties of this organism?

During the course of his hospital stay, a severely burned 60-year-old male develops a rapidly disseminating bacterial infection. Small gram-negative rods that are oxidase positive are cultured from green pus taken from the burn tissue. Which combination of antibiotics is the best choice for empiric therapy against this etiologic agent?

Laboratory results of a clinical specimen from a patient with hospital-acquired pneumonia reveal the presence of methicillin-resistant Staphylococcal aureus (MRSA). Which of the following drugs is the best empiric treatment?

A small brownish irregular macule on the palm of a 13-year-old girl is examined by a dermatologist in her Louisiana home town. A skin scraping from the lesion is obtained for microscopic observation and culture. Microscopic examination of the specimen shows brownish filaments or hyphae and yeast cells. The most likely diagnosis is

A 52-year-old woman presents with fever of 103°F, headache, right flank pain, nausea and vomiting, and urinary frequency with hematuria and dysuria. Renal ultrasound demonstrates a right urinary stone with right hydronephrosis. Which of the following antibiotics is the most appropriate treatment option?

An HIV-positive patient, after treatment with tenofovir/emtricitabine plus ritonavir-boosted atazanavir, has a CD4 T-cell count of 325/μL and a viral load of less than 50 copies of HIV RNA/mL. Previously her CD4+ T-cell count was 280/μL and viral load was 100,000 copies/mL. Which of the following best describes this patient?

An HIV-positive patient with a viral load of 100,000 copies/mL of HIV RNA and a drop in his CD4 T-cell count from 240 to 50/μL has been diagnosed with Pneumocystis jiroveci pneumonia. Which of the following is the best description of the stage of this patient's HIV disease?

During a medical checkup for a new insurance policy, a 60-year-old grandmother is found to be positive by a conventional EIA screening test for antibodies against HIV-1. She has no known risk factors for exposure to the virus. Which of the following is the most appropriate next step?

In 2003, the zoonotic severe acute respiratory syndrome (SARS) coronavirus caused a pandemic in which over 8000 people were infected and the mortality rate was 10%. In 2012, a novel coronavirus was isolated from 12 persons in Saudi Arabia, Qatar, and Britain with severe respiratory illness; so far, 50% have died. Which of the following syndromes is more commonly caused by other known types of human coronaviruses?

Several children in a day care center for preschoolers developed fever, irritability, lack of appetite, and a vesicular rash found on their hands, feet, and mouths. With which virus were these children most likely infected?

A 15-year-old boy is taken to his pediatrician after experiencing fever, malaise, and anorexia followed by tender swelling of his parotid glands. Which of the following is the most likely complication to occur in this patient?

An otherwise healthy 65-year-old male was in a car accident and broke several ribs on the left side. Approximately 12 days later, he developed a painful, well-circumscribed vesicular rash over the left rib cage that persists for several weeks. The rash is most likely due to which of the following?

A 3-year-old child who had not been immunized presents at the physician’s office with symptoms of coryza, cough, conjunctivitis, and photophobia. He has a low-grade fever, and small, bluish-white ulcerations are seen on the buccal mucosa opposite the lower molars. What is the causative agent of this child's symptoms?

A sexually active woman was seen for a routine gynecologic exam that included a Pap smear. The report indicated cervical intraepithelial neoplasia. In situ hybridization showed the presence of human papillomavirus (HPV) type 16 genomes within the neoplastic cells. Which of the following processes is required for HPV to lead to the development of cancer?

Two siblings, ages 2 and 4, experience fever, rhinitis, and pharyngitis that result in laryngotracheobronchitis. Both have a harsh, bark-like cough and hoarseness. Which of the following viruses is the leading cause of their syndrome?

An outbreak of hepatitis occurred in an area of India with poor sanitation. Most of the patients reported fever, nausea with vomiting, and weight loss occurring over several days followed by jaundice and pruritus. Testing quickly ruled out HAV. A number of women in the area are pregnant. For which of the following are these women at risk?

An 18-year-old man was taken to an emergency medicine department because of fever and headache for 36 hours and now complaint of a stiff neck. No bacterial agents appeared to be involved and an initial diagnosis of aseptic meningitis was made. Which of the following laboratory findings in the examination of his cerebrospinal fluid led to this diagnosis?

A nurse develops clinical symptoms consistent with hepatitis. She recalls sticking herself with a needle approximately 5 months before, after drawing blood from a patient. Serologic tests for HBsAg, and antibodies to HBsAg and HAV are all negative; however, she is positive for HBcAg IgM antibody. Which of the following characterizes the current health state of the nurse?

A local school district finds a large number of student absences, with the children presenting with rhinorrhea, nasal obstruction, headache, and malaise, but no fever. A strain of rhinovirus is the most likely etiologic agent of these infections. By which method is this virus most frequently spread?

Which of the following describes an axial filaments?

A 65-year-old female, with history of poorly controlled diabetes for 15 years, was admitted due to Cerebrovascular Disease (Stroke). Patient has been on indwelling catheter for 1 week. She was noted to have cloudy IFC output otherwise asymptomatic. Urine culture grew Candida albicans. CBC revealed normal results. What is the appropriate management in this patient?

Which of the following should be screened for asymptomatic bacteriuria?