A 48-year-old woman has a perforated sigmoid diverticulitis and undergoes laparotomy for repair of the perforation. She remains septic and is treated with high-dose, broad-spectrum antibiotic therapy including clindamycin. Two weeks later, she develops a severe diarrhea. On sigmoidoscopy, there is extensive tan to green exudate overlying the colonic mucosa, with minimal erythema of the mucosa, and no ulcerations or masses noted. These findings are most likely due to which of the following mechanisms of injury?
A Escherichia coli endotoxin
B Staphylococcus aureus superantigen
C Corynebacterium diptheriae exotoxin
D Vibrio parahemolyticus enterotoxin
E Clostridium difficile enterotoxin
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After 10 days of multidrug antitubercular therapy, a 47-year-old homeless man now has a sputum that is clear of acid-fast bacilli, even though a chest radiograph demonstrates bilateral upper lobe cavitary lung disease. However, the most recent sputum specimen does show branching septate hyphae. The presence of these hyphae is most likely due to infection with which of the following organisms?
A Aspergillus fumigatus
B Cryptococcus neoformans
C Candida parapsilosis
D Mucor circinelloides
E Actinomyces israeli israeli
In an experiment, mechanisms for production of infection are studied. It is observed that viral organisms often produce a limited extent of tissue damage. Viral characteristics and host responses are analyzed in these viral infections. Which of the following mechanisms is most likely to determine the extent of viral infection?
A Neutrophilic response
B Cell tropism
C Size of inoculum
D Macrophage response
E Interferon level
A 15-year-old boy has had eye pain for the past 2 days. He does not use contact lenses. On physical examination he has conjunctival inflammation with ulceration involving the right eye. There is penetration into the cornea, starting at the upper limbus. Laboratory studies include a conjunctival scraping which shows elementary bodies next to epithelial cell nuclei. Eventually, this process resolves with pannus formation. The scarring leads to loss of vision. Other young persons in his community have been similarly affected. Which of the following organisms is most likely responsible for these findings?
A Herpes simplex virus
B Hemophilus ducreyi
C Chlamydia trachomatis
D Pseudomonas aeruginosa
E Acanthameba
The probability of your being blamed for poor venipuncture technique when obtaining a blood culture will increase when which of the following organisms is reported on the microbiology laboratory report as present in 1 of 4 bottles collected?
A Pseudomonas aeruginosa
B Listeria monocytogenes
C Streptococcus pyogenes
D Enterobacter aerogenes
E Staphylococcus epidermidis
For the past 3 weeks, a 24-year-old man has felt tired and has had a low grade fever. Physical examination reveals axillary, cervical, and inguinal adenopathy along with a palpable spleen tip. He has mild scleral icterus. His temperature is 37.5 C. Laboratory studies show a positive monospot test. His condition gradually improves over the next month. Which of the following peripheral blood findings is most likely to be found in this man?
A Ring forms in erythrocytes
B Atypical lymphocytes
C Howell-Jolly bodies in erythrocytes
D Gram negative diplococci in neutrophils
E Markedly decreased platelets
A 26-year-old primigravida experiences a mild diarrheal illness lasting 3 days in the 28th week of pregnancy. However, a week later she does not feel any fetal movement, and an ultrasound confirms fetal death with lack of fetal cardiac activity. An induction is performed, and a macerated fetus is delivered stillborn. Autopsy reveals microabscesses in multiple fetal organs and in the placenta. Blood and lung cultures from the fetus are collected, and there is growth of organisms that appear as short gram positive. By which of the following routes did the mother most likely acquire this infection?
A Aerosolized droplet nuclei
B Injection drug use
C Sexual intercourse
D Penetrating trauma
E Contaminated food
A 45-year-old woman has developed a fever with a severe non-productive cough over the past 4 days. On physical examination her temperature is 38.2 C. Crackles are auscultated over both lungs. A chest radiograph reveals bilateral interstitial infiltrates. A sputum culture shows normal flora. She has an increased cold agglutinin titer. She receives a course of erythromycin therapy and improves over the next week. Which of the following infectious agents is most likely to be the cause for her illness?
A Cytomegalovirus
B Pneumocystis carinii (jirovecii)
C Nocardia asteroides
D Mycoplasma pneumoniae
E Respiratory syncytial virus
(54) A 5-year-old boy has had an outbreak of skin lesions on his face and hands over the past week. Initially, the lesions are noted to be 0.5 to 1 cm erythematous macules, but within 2 to 4 days they develop into pustular lesions. As the pustules break, they form shallow ulcers covered with dried serum forming a honey-colored crust. Several other family members acquire this infection. Which of the following organisms is most likely to cause these findings?
(55) A 29-year-old woman has had chronic pelvic pain for the past 6 years years. She has the sudden onset of severe acute abdominal pain. On physical examination she is afebrile. There is marked tenderness to palpation in the lower abdomen. Her pregnancy test is positive. An ultrasound scan shows no intrauterine gestational sac. At laparotomy, a ruptured right fallopian tube is present that contains a small embryo. There are muliple peritoneal adhesions. Which of the following organisms is most likely to cause these findings?
A Neisseria gonorrheae
B Streptococcus pneumoniae
C Staphylococcus aureus
D Legionella pneumophila
E Diptheroids
F Herpes simplex virus
G Human papillomavirus
H Epstein-Barr virus
(56) A 41-year-old man has developed a chronic deforming genital skin infection with extensive ulceration over the past month. On physical examination he is afebrile. Which of the following organisms is most likely to cause his infection?
(57) A 29-year-old woman has noted a worsening sore in her genital region for the past 3 weeks. On physical examination there is a necrotic, draining 2.5 cm ulcer present on the left labia minora. Which of the following organisms is most likely to cause her infection?
A Treponema pallidum
C Calymmobacterium donovoni
D Neisseria gonorrheae
E Chlamydia trachomatis
H Trichomonas vaginalis
(58) A tuberculin skin test is performed on a 35-year-old woman as part of a health screening examination. Two days later there is an area of erythema with palpable induration that is 15 mm in circumference at the site of PPD injection. Which of the following microscopic findings is most likely to be present at this site?
(59) A 55-year-old woman is undergoing chemotherapy for metastatic breast carcinoma. Over the past week she has developed a non-productive cough with fever. On physical examination her temperature is 37.6 C. Laboratory studies include a shell vial on her sputum which is positive for cytomegalovirus. Which of the following microscopic features of infection is most likely to be present in her lungs?
A Intranuclear inclusions
B Mast cell infiltrates
C Gummatous necrosis
D Microabscess formation
E Lymphoid nodules
F Ulceration
G Macrophage proliferation
H Fibrosis
(60) A previously healthy 25-year-old man has developed a severe watery diarrhea over the past day. On physical examination he has a temperature of 37.4 C, pulse 110/minute, respiratory rate 17/minute, and blood pressure 100/60 mm Hg. Palpation of his abdomen shows no tenderness or masses. There is no hepatosplenomegaly. A stool sample is negative for occult blood. A radiograph of the abdomen shows no free air. Which of the following organisms is most likely to be cultured from his stool?
(61) A 27-year-old previously healthy woman develops fever and chills along with a low volume diarrhea. A week later she has marked diffuse abdominal pain. Her spleen tip is palpable. She has a diffuse erythematous skin rash. A week later her condition has not improved. She has generalized lymphadenopathy. A CBC shows Hgb 12.7 g/dL, Hct 37.9%, MCV 87 fL, platelets 169,000/microliter, and WBC count 4500/microliter with WBC differential of 34 segs, 2 bands, 45 lymphs, 16 monos, 2 eos, and 1 basophil. A stool sample is positive for for occult blood. Which of the following organisms is most likely to be cultured from his blood?
A Clostridium difficile
B Clostridium perfringens
C Salmonella enteritidis
D Salmonella typhi
E Shigella sonnei
F Shigella flexneri
G Vibrio cholerae
H Vibrio vulnificus
(62) A 65-year-old man has noted gradual increase in size during the past 2 years of a nodule on the palm of his right hand. On physical examination there is a firm but relatively painless 1 x 3 cm subcutaneous mass overlying the metacarpal heads. The mass is excised and on microscopic examination shows granulomatous inflammation. Which of the following mycobacterial organisms is most likely to cause this man's mass lesion?
(63) A 6-year-old girl has had a slowly enlarging sore on her upper neck for the past month. On physical examination she has left cervical lymphadenopathy, and the overlying skin shows a 0.5 x 4 cm area of irregular ulceration with induration with pale tan necrotic debris in the ulcer base. A lymph node biopsy is performed and on microscopic examination shows granulomatous inflammation. Which of the following mycoacterial organisms is most likely to cause this girl's illness?
A M. avium-complex
B M. bovis
C M. gordonae
D M. fortuitum
E M. kansasii
F M. marinum
G M. scrofulaceum
H M. tuberculosis
(64) A 21-year-old G2 P1 woman has a screening ultrasound examination at 19 weeks gestation which shows hydrops fetalis. She gives birth at 34 weeks to a male infant with Apgar scores of 5 and 7 at 1 and 5 minutes following an uncomplicated vaginal delivery. The infant is noted to be hydropic, with mild icterus. He has hepatosplenomegaly. An ultrasound of the head suggests periventricular leukomalacia. Which of the following organisms is most likely to be infecting this infant?
(65) A 30-year-old man with HIV infection has had 20 to 30 watery stools per day for the past week. He has lost 5 kg during that time. On physical examination his temperature is 37.2 C, pulse 91/minute, respirations 16/minute, and blood pressure 100/65 mm Hg. His stool is negative for occult blood.
A Escherichia coli
B Cryptosporidium parvum
C Pneumocystis carinii (jirovecii)
D Myobacterium avium-complex
E Pseudomonas cepacia
F Treponema pallidum
G Cryptococcus neoformans
H Cytomegalovirus
(66) A 60-year-old woman has the sudden onset of cough with fever with shaking chills. On physical examination her temperature is 39.3 C. She has crackles at the right lung base on auscultation of her chest. Laboratory studies show Hgb 13.9 g/dL, Hct 40.9%, MCV 88 fL, platelets 386,000/microliter, and WBC count 14,860/microliter with differential count of 75 segs, 9 bands, 12 lymphs, and 3 monos. A sputum gram stain shows gram negative rods. She is most likely to have an infection with which of the following organisms?
(67) A 45-year-old man has had a cough with blood-streaked sputum for 2 weeks. On physical examination his temperature is 37.3 C. Breath sounds are decreased over his upper lung fields. A chest radiograph reveals bilateral cavitary upper lung lobe lesions. A sputum gram stain shows 1+ gram positive cocci, 1+ gram negative bacilli, 1+ gram negative cocci, and budding cells with pseudohyphae. A sputum acid fast stain shows acid-fast bacilli. He is most likely to have an infection with which of the following organisms?
A Mycobacterium kansasii
B Cytomegalovirus
C Ascaris lumbricoides
D Aspergillus fumigatus
E Klebsiella pneumoniae
F Parainfluenza virus
G Bacillus anthracis
H Candida albicans
(68) A previously healthy 40-year-old man has developed a watery diarrhea over the past 3 days following a recent trip. He has about 4 to 5 stools per day. On physical examination he is afebrile. His stool is negative for occult blood. The diarrhea abates in a week without therapy. He is most likely to have been infected with which of the following organisms?
(69) A 32-year-old woman has the sudden onset of a seizure which last 2 minutes. On physical examination she is afebrile. She does not have papilledema. A lumbar puncture is performed and yields clear fluid with opening pressure of 120 cm H20. A cell count shows 3 mononuclear cells/microliter. The CSF glucose is 68 mg/dL (serum is 108 mg/dL) and protein 40 mg/dL. Brain MR imaging shows a 2 cm discrete cystic mass in the left frontal region. She is most likely to be infected with which of the following organisms?
A Entameba histolytica
B Giardia lamblia
C Clonorchis sinensis
D Schistosoma hematobium
E Trichinella spiralis
F Taenia solium
G Leishmania donovani
H Plasmodium ovale
(70) The definitive host of Toxoplasma gondii infection.
(71) The probable source for salmonellosis.
A Moo
B Oink
C Meow
D Cluck
E Baa
F Woof
(72) A 50-year-old man has a mixed urinary tract infection complicated by pyelonephritis. He receives multiagent broad spectrum antibiotic therapy for the next 15 days. He now has developed a severe diarrhea. Colonoscopy is performed and reveals areas of mucosal erythema extending from the sigmoid to the cecum with overlying tan to green exudate. Which of the following clostridial species is most likely to produce his illness?
(73) A 76-year-old man is repairing a fence in the pasture. He incurs a deep barbed wire cut to his left hand. He washes the wound and put on a band-aid. There is still some redness and swelling around this cut a week later. He now begins to experience dysphagia and back pain. On physical examination he has increased tone in the masseter muscles, a rigid abdomen, and stiff proximal limb muscles. Which of the following clostridial species is most likely to produce his illness?
A Clostridium botulinum
B Clostridium tetani
C Clostridium perfringens
D Clostridium difficile
E Clostridium novyi
F Clostridium septicum
G Clostridium bifermentans
H Clostridium histolyticum
A 47-year-old man with a history of chronic alcoholism has been complaining of cough, chills and fever. He has had a "cold" for 4 days and has been coughing up yellow-thick tenacious sputum. He denies shortness of breath and chest pain. On physical examination his temperature is 39.7 C, and expiratory rales are heard over both lung fields on auscultation of his chest. A chest radiograph shows patchy bilateral pulmonary infiltrates. Which of the following infectious agents has he most likely acquired?
A Klebsiella pneumoniae
B Adenovirus
C Mycoplasma pneumoniae
D Pneumocystis carinii (jirovecii)
E Mycobacterium tuberculosis
A 35-year-old man presents to the emergency department with a high fever for 3 days. He is now is very lethargic. On physical examination he has a tender palpable spleen tip and heart murmur. His temperature is 38.6 C. While in hospital, his course is complicated by development of multiple discrete 1 to 3 cm lesions in mid and lower lung fields on both the right and left seen on a chest radiograph. These lesions demonstrate an air-fluid level. Which of the following is the most likely diagnosis?
A Staphylococcus aureus abscesses
B Aspergillomas
C Secondary M. tuberculosis
D Pneumococcal pneumonia
E Bronchiectasis with Pseudomonas aeruginosa
A 20-year-old G2 P1 woman gives birth to a term female infant following an uncomplicated pregnancy. The infant develops meconium ileus soon after birth. She is found to have an elevated sweat chloride by iontophoresis, as did her sibling. At age 13 these children are most likely to have which of the following organisms cultured from their sputum?
A Respiratory syncytial virus
B Pseudomonas aeruginosa
D Cytomegalovirus
E Legionella pneumophila
A 74-year-old woman has had Alzheimer's disease for the past 8 years. She has become unable to care for herself and is placed in a nursing home. She is finally bedridden, except for short periods in which she is placed in a wheelchair. She becomes febrile and then dies. Which of the following organisms is most likely to be responsible for her immediate cause of death?
A Staphylococcus aureus
B Respiratory syncytial virus
C Mycobacterium tuberculosis
D Streptococcus pneumoniae
E Mycoplasma pneumoniae
(78) A 25-year-old woman has a 0.8 cm diameter shallow erythematous ulceration with a firm base noted on examination of her labia. The lesion is relatively painless. She is treated with penicillin G. Which of the following organisms is most likely to cause her infection?
(79) A 49-year-old man has had epigstric pain for the past month. Over the past 3 days the pain has occurred at night. The pain is relieved somewhat by eating. On physical examination he has no abnormal findings. An upper GI endoscopy is performed and there is a 1 cm diameter shallow, sharply demarcated ulceration in the first portion of the duodenum. Laboratory studies show a positive urease breath test. He is most likely to be infected with which of the following organisms?
A Epstein-Barr virus
B Escherichia coli
C Candida albicans
D Treponema pallidum
F Proteus mirabilis
G Helicobacter pylori
H Chlamydia trachomatis
A previously healthy 35-year-old woman develops the sudden onset of high fever and chills. She returned from a trip to West Africa about a month ago. On physical examination she has a temperature of 37.2 C. There are no abnormal findings. Over the next 4 days she continues to have febrile episodes, along with malaise and headache. Which of the following infectious agents is most likely to produce these findings?
A Wuchereria bancrofti
B Strongyloides stercoralis
C Echinococcus granulosus
D Toxoplasma gondii
E Plasmodium falciparum
The mother of a 5-year-old child says that he has been irritable for the past week, awakening a couple of times per night. Physical examination reveals perianal erythema, but his stool guaiac is negative. The child is continuing to eat, with no nausea, vomiting, constipation, or diarrhea. Which of the following parasites is this child most likely to have?
A Ascaris lumbricoides
B Enterobius vermicularis
C Trichuris trichiuria
D Strongyloides stercoralis
E Necator americanus
A 10-year-old child has become increasingly lethargic for the past month. On physical examination she appears malnourished and is less than the 30th percentile in weight for age. Laboratory studies show Hgb 8.4 g/dL, hct 24.9%, MCV 70 fL, platelet count 205,600/microliter, and WBC count 6005/microliter. Examination of her stool for ova and parasites is most likely to reveal eggs of which of the following parasites?
A Trichuris trichiuria
C Necator americanus
D Schistosoma mansoni
E Ascaris lumbricoides
A 47-year-old man with a history of systemic lupus erythematosus and lupus nephritis has been receiving immunosuppressive therapy, including corticosteroids. He has developed cough, fever, nausea, and diarrhea over the past 2 days. On physical examination he has a temperature of 37.8 C. There is mild distension and tenderness on palpation of the abdomen. Bowel sounds are reduced. He has perianal erythema. An abdominal radiograph shows dilated loops of bowel. Laboratory studies show Hgb 10.4 g/dL, Hct 30.8%, MCV 72 fL, platelet count 220,800/microliter, and WBC count 9130/microliter with differential count of 59 segs, 5 bands, 18 lymphocytes, 9 monocytes, and 9 eosinophils. Which of the following parasitic infestations is he most likely to have?
A Toxocara canis
C Ancylostoma duodenale
E Leishmania donovani
Several weeks following a vacation to Wisconsin, a family of four has developed fever, headache, weakness, malaise, and myalgia. They recall dining out in Milwaukee, boating and swimming in the Eau Claire river, visiting Uncle Dick's and eating some of his home-made sausage, and fishing in Green Bay. On physical examination they have muscle tenderness. A CBC performed on the father reveals a Hgb of 14.4 g/dL, Hct 43.3%, MCV 94 fL, platelets 266,000/microliter, and WBC count 10,980/microliter with WBC differential of 72 segs, 4 bands, 8 lymphs, 6 monos, and 10 eos. Their symptomatology is best explained by which of the following parasitic diseases?
A Trichinosis
B Giardiasis
C Cryptosporidiosis
D Amebiasis
E Echinococcosis
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