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22 Cards in this Set
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A 2-day-old baby girl suddenly develops abdominal distention, progressive pallid cyanosis, and irregular respirations. The newborn also has "refused" to breast-feed for the past 18 hours. If the mother was treated for a serious infection with antibiotics for 14 days up to and including the day of delivery, which of the following medications did the mother most likely receive?
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Chloramphenicol
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(Microbiology: General Principles, 59%): Gray "baby" syndrome is a disorder that occurs in newborns who have either received chloramphenicol immediately after birth or whose mothers have received the medication close to the delivery date. Symptoms typically appear in the following order: abdominal distention with or without emesis, progressive pallid cyanosis, and vasomotor collapse, frequently accompanied by irregular respiration. Death can occur as early as a few hours after onset of signs and symptoms. Other symptoms may include: loose, greenish stools, a refusal to suck, ashen color (implied by the name gray baby syndrome), and lactic acidosis. Chloramphenicol is an antimicrobial agent used in the treatment of serious infections when less toxic alternatives are inappropriate. *Aztreonam is a beta-lactam antibiotic used primarily in the treatment of gram-negative infections of the urinary tract, lower respiratory tract, and skin, and for intra-abdominal infections. The use of this agent in pregnant or nursing women and infants is considered to be safe and effective. *Clindamycin is an anti-infective agent used in the treatment of serious infections when less toxic alternatives are inappropriate. Although the agent is considered to be safe and effective during pregnancy, it is associated with the development of pseudomembranous colitis and agranulocytosis. *Metronidazole is an antibiotic used primarily in the treatment of anaerobic infections. The use of metronidazole should be restricted in pregnancy, since newborns have a decreased ability to metabolize this medication. When the elimination of metronidazole is decreased, the severity of adverse reactions increases. Adverse reactions include peripheral neuropathy, seizures, irritability, and prfound GI disturbances. *MY INCORRECT ANSWER: SULFAMETHOXAZOLE/TRIMETHOPRIM IS ASSOCIATED WITH THE DEVELOPMENT OF KERNICTERUS, WHICH IS A DISORDER THAT CAN CAUSE ABNORMAL CEREBRAL DEVELOPMENT IN INFANTS. THE MAJORITY OF INFANTS WITH THIS DISORDER GENERALLY DIE WITHIN A FEW WEEKS OF BRITH. THOSE INFANTS WHO SURVIVE ARE OFTEN MENTALLY RETARDED, DEAF, OR PHYSICALLY IMPAIRED.
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A previously healthy 18-month-old girl is brought to the office with 2 days of irritability, poor appetite, and pulling at her left ear. She has no known allergies, and her vaccinations are up-to-date. On examination, the child's temperature is 102.8 F. She is easily consoled by the mother and moves her neck spontaneously without discomfort. There is a clear discharge from the nares. The left tympanic membrane is erythematous, dull, and bulging. Which of the following virulence factors is generally ABSENT in the strains of the causative organisms that produce obits media, compared with those that produce epiglotittis or meningitis?
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polyribitol phosphate
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(Microbiology General Principles, 19%): This is most likely a case of Haemophilus influenzae otitis media. 95% of all cases of invasive disease (epiglotittis, meningitis) due to H. influenzae are caused by type b organisms that possess a polyribitol phosphate capsule. Otitis media is generally not caused by type b organisms. *beta-lactamase is an important pathogenic feature of Moraxella catarrhalis, which is another important cause of otitis media, but would not be an agent of epiglottitis or meningitis. *MY INCORRECT ANSWER: IGA PROTEASE IS PRODUCED BY STREPTOCOCCUS PNEUMONIAE AND NEISSERIA MENINGITIDIS. BOTH OF THESE CAUSE MENINGITIS, BUT NOT AS COMMONLY IN THIS AGE GROUP, AND WOULD NOT BE THE MOST COMMON CAUSES OF OTITIS MEDIA IN THIS CASE. *Lipopolysaccharide is present in all gram-negative bacteria and would not be a distinguishing feature between those that cause otitis media and epiglotitis. *Nonpilus adhesins are mediators of attachment to the epithelium and colonization of the oropharynx, but would not be a primary difference between the agents of otitis media and epiglottitis. *Pili also mediate attachment to the oropharynx, but would not be the major difference between the agents of otitis media and epiglottitis. *Pneumolysin is a cytotoxin produced by S. pneumoniae that destroys ciliated epithelial cells
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A 35-year-old Cajun man living in the bayous of the Mississippi River basin near New Orleans develops a tuberculosis-like illness with formation of masses within the lungs. PPD is negative, but the histoplasmin skin test is positive. CT-guided biopsy of one of the lung masses would be most likely to demonstrate which of the following?
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2-5 micrometer yeast with a thin cell wall but no true capsule
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(Microbiology Respiratory: 37%): A variety of fungi can produce tuberculosis-like lung disease. The positive histoplasmin skin test identifies this patient's probably cause as Histoplasma capsulatum, which causes histoplasmosis. Histoplasmosis is observed most frequently in the Ohio-Mississippi River valleys of the U.S. The organism is a small (2-5 micrometer) yeast, which despite the name, has no true capsule. *4-10 micrometer yeast with broad slimy capsule describes Cyrptococcus, which can cause tuberculosis-like pulmonary disease, and is usually seen in immunosuppressed patients, notably those with AIDS or hematopoietic disorders. *5-25 micrometer yeast with thick, refractile wall and broad-based budding desribes Blastomyces, which can cause tuberculosis-like pulmonary disease and can also be seen in the Missippi-Ohio River basins and elsewhere in North America (particularly the mid-Atlantic states). *10-60 MICROMETER YEAST WITH MULTIPLE BUDDING DESCRIBES PARACOCCIDIOIDES, WHICH CAN CAUSE TUBERCULOSIS-LIKE PULMONARY DISEASE AND IS FOUND IN SOUTH AND CENTRAL AMERICA. *20-60 micrometer nonbudding spherule with endospores describes Coccidioides, which can cause tuberculosis-like pulmonary disease and is found in the southwest and far west of the U.S. (San Joaquin Valley fever).
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A Washington, D.C., letter carrier is brought to the emergency department of a local hospital by his wife, who fears that he is having a heart attack. The man is suffering severe substernal pain accompanied by a fever of 40 C (104 F) and cough. ON radiographic examination, there is pronounced mediastinal widening. A sample of blood is cultured on blood agar, and nonhemolytic, rough gray colonies are produced. During which stage of the bacterial growth curve shown above would the maxiumum number of the infectious forms inhaled by this patient produced?
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stationary phase
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(Microbiology General Principles, 27%): The patient is displaying the symptoms of inhalation anthrax, also known as woolsorter's diseasse, when it is naturally acquired. The infectious ofrm in this disease is the spore of Bacillus anthracis, which is produced in culture situations when environmental conditions become insuffiecient for continued growth and multiplication. Maximum spore formation usually occurs during the stationary phase, when cell growth cease because of a developing lack of nutrients or accumulation of toxins. FLAT-TOP PART OF GRAPH = CORRECT ANSWER *The lag phase is the initial period of adaptation, prior to growth, which occurs when organisms are introduced to a new environment. It is not a period in which spore formation would occur. *The acceleration phase is the initial phase of bacterial multiplication, when cell division has not reached a maximum. This is not a period in which spore formation would occur. *THE EXPONENTIAL PHASE IS THE PERIOD OF THE BACTERIAL GRWOTH CURVBE WHEN EACH BACTERIUM IN THE CULTURE IS UNDERGOING BINARY FISSION AT THE MAXIMUM POSSIBLE RATE. THIS IS NOT A PERIOD IN WHICH SPORE FORMATION WOULD OCCUR. *The retardation phase is the phase of the bacterial growth curve when toxic metabolic products beging to accumulate and nutrient levels begin to be insufficient to support continued growth. Although spore formation could begin as early as this stage, it would not reach maximum levels until the maximum stationary phase. *During the phase of decline and death, the lack of nutrients and the accumulation of toxins become so severe that any viable organisms usually die before they can form spores.
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A 54-year-old man presents with complaints of shortness of breath, a sore tongue, and a "pins-and-needles" sensation in his feet. Laboratory examination revelas macrocytosis, anemia, and hypersegmented neutrophils. Antibodies to intrinsic factor are detected in the patient's serum. Which of the following class II antigens would be most likely to play a contributing role in the etiology of this patient's disease?
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DR5
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(Immunology General Principles, 34%): The disease with autoantibodies to intrinsic factor is pernicious anemia (atrophic gastritis and megaloblastic anemia secondary to vitamin B12 deficiency). Pernicious anemia is associated with the DR5 class II antigen (relative risk 5); DR5 is also associated with juvenile rheumatoid arthritis. *DR2 is associated with Goodpasture syndrome, allergy, multiple sclerosis, and nacrolepsy. *DR3 is associated with celiac spure, Type 1 diabetes mellitus, and systemic lupus erythematosus. *DR4 IS ASSOCIATED WITH PEMPHIGUS VULGARIS, RHEUMATOID ARTHRITIS, AND TYPE 1 DIABETES MELLITUS *DR7 is associated with steroid-responsive nephrotic syndrome.
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A sexually active 18-year-old woman presents with a fever of 38.9 C (102 F) for the past 24 hours and lower abdominal pain and anorexia for the past 5 days. ON physical examination, there is generalized tenderness of the abdomen, and the cervix is erythematous with motion tenderness. There is no rash nor any lesions on the external genitalia. A smear of the odorless cervical discharge contains sloughed epithelial cells and scant neutrophils. Which of the following would likely be found in the exudate?
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Iodine-staining intraepithelial inclusion bodies
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(Microbiology Reproductive, 27%): The presentation is typical for PID. Chlamydia trachomatis (serotypes D-K) is the most common bacterial cause of sexually transmitted disease in this country and is the most likely agent on the list to produce the symptoms described. It is an ATP-defective organism that must therefore live intracellularly in the human host and can be visualized inside epithelial cells with iodine, Giemsa, or fluorescent-antibody stains. The remainder of the answer choices refer to other agents that could be found in the female genital tract, either by sexual transmission or by contamination with fecal flora, but they are not the best choices. *A naked, icosahedral double-stranded circular DNA virus refers to human papilloma virus, which is the most common cause of STDs in the U.S., but presents with anogenital warts. *Intraneutrophilic gram-negative diplococci refers to Neisseria gonorrhoeae, which would be expected to prestn with dysuria and neutrophilic exudate. *Intranuclear inclusion bodies surrounded by halos ("owl's eyes") refers to cytomegalovirus, a common STD in the United States, but not a common agent of PID. Most cases in average adults are manifested by mononucleosis-like symptoms. *Lactose-fermenting gram-negative bacilli would be consistent with Escherichia coli. Although this organism is the most common cause of urinary tract infections in women in the United States, it would not be epected to cause PID. *Pear-shaped flagellated protozoa refers to the protozoan parasite Trichomonas vaginalis, the only protozoan STD in the world. Infection would be characterized by a malodorous, cheesy exudate, and there would be more erythema of the external genitalia than of the cervix. *Pleomorphic, gram-negative rods are consistent with Hemophilus ducreyi, which causes chancroid, and presents in a different manner. *SPIROCHETES ON DARK-FIELD MICROSCOPY REFERS TO TREPONEMA PALLIDKUM, THE CAUSATIVE AGENT OF SYPHILIS, WHICH WOULD PRODUCE RASH AND/OR CHANCRE, DEPENDING ON THE STAGE OF THE INFECTION.
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Approximately 1 week after starting therapy for a complicated urinary tract infection caused by Proteus mirabilis, a 13-year-old girl develops leg cramps, myalgia, and arthralgias. Which of the following medications was this patient most likely prescribed?
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lomefloxacin
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(Microbiology Renal/Urinary, 54%): Lomefloxacin is a fluroquinolone antibiotic indicated for the treatment of a wide variety of infections caused by both gram-negative and gram-positive organisms. This agent is primarily used in the treatment of lower respiratory tract and urinary tract infections. Lomefloxacin and other fluroquinolone antibiotics have been associated wtihi the development of arthropathy, myalgias, and leg cramps when administered to children younger than 18. *Azithromycin is a macrolide antibiotic that is generally well-tolerated. The most common side effects of this agent are mild nausea and abdominal pain. *METRONIDAZOLE IS AN ANTIPROTOZOAL AND ANTIBACTERIAL ASSOCAITED WITH THE DEVELOPMENT OF CONVULSIVE SEIZURES AND PERIPHERAL NEUROPHATHY. FURTHERMORE , THIS AGENT CAN PRODUCE A DISULFIRAM-LIKE REACTION WHEN TAKEN WITH ALCOHOL. *Rifampin is an agent used to treat all forms of tuberculosis. It is also used in asymptomatic carriers of Neisseria meningitidis. Rifampin is associated with the development of hepatotoxicity, hyperbilirubinemia, porphyria, and possibly cancer. *Tetracycline is an antibiotic known to cause photosensitivity, pseudotumor cerebri, and a variety of maculpapular rashes.
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A 35-year old man develops hemiparesis, ataxia, homonymous hemianopa, and cognitive deterioration. An MRI of the brain demonstrates widespread areas of abnormal T2 signal in the white matter. An electroencephalogram is remarkable for diffuse slowing over both cerebral hemispheres. Brain biopsy revelas demyelination with abnormal oligodendrocytes, some of which contain eosinophilic inclusions. This patient's condition is most closely related to which of the following diseases?
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AIDS
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(Microbiology Nervous, 40%): The condition is progressive multifocal leukoencephalopathy, which is a rapidly progressive demyelinating disorder in which the JC virus (a papovavirus) infects oligodendroglial cells in the brain. The eosinophilic inclusions represnt accumulations of JC virus. PML occurs in about 1% of AIDS patients, and is the AIDS-defining illness in half of the patients who develop the condition. There is no effective treatment for this disorder. *Shingles and post-infectious encephalitis can follow chickenpox, but varicella is not associated specifically with demyelination. *MEALES CAN CAUSE AN ENCEPHALITIS, AND IN SOME CAUSES, SUBACUTE SCLEROSING PANENCEPHALITIS (SSPE) MAY FOLLOW PREVIOUS MEASLES INFECTION. THESE DISORDERS WOULD AFFRECT NOT ONLY WHITE MATTER, BUT GRAY MATTER AS WELL. ALSO, SSPE USUALLY OCCURS BEFORE THE AGE OF 18. (WHITE MATTER:OLIGODENDROCYTES) *Syphilis can cause meningitis, encephalitis, and psinal cord damage, but the disease process would not be limited to the white matter. *Tuberculosis can cause a granulomatous meningitis, typically affecting the base of the brain.
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A bacterium cultured from the bloodstream of an HIV-positive patient is determined by electron microscopy to possess an envelope. The basic structure of the envelop is diagrammed above. The culture isolate is subjected to Gram's staining. Provided that the laboratory technologist conducts this test properly which of the following reagents will give this organism its primary color in the staining procedure?
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Safranin
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(Microbiology General Principles, 33%): The envelope diagrammed is that of a gram-negative organism. The gram-negative envelope is characterized by the presence of two membranes and a thin peptidoglycan layer (cell wall). As a result, a gram-negative organism will be decolorized during the washing step of the staining, and will finally exhibit the color of the counter stain, safranin, which is a pale red/pink. *Carbolfuchsin is the primary stain in the acid-fast staining technique. Organisms in the genus Mycobacterium will retain this color and Nocardia will be partically acid-fast. All other bacteria are non acid-fast and would retain the secondary stain, methylene blue. *CRYSTAL VIOLET IS THE PRIMARY STAIN IN THE GRAM'S STAIN. IT IS THE COLOR THAT WOULD BE RETAINED IN GRAM-POSITIVE BACTERIA THAT POSSESS A THICK PEPTIDOGLYCAN LAYER. *Gram's iodine is the critical reagent in the Gram's stain, but it does NOT directly impart color to bacteria. The function of Gram's iodine is to create a large complex of the primary stain, crystal violet, to molecules within the cell. The larger complexes cannot be washed out through the impermeable peptidoglycan layer of the gram-positive bacterium, so gram-positives remain purple, which gram-negatives are decolorized to subsequently take up the color of the secondary stain, safranin. *Methylene blue is the secondary stain in the acid-fast staining procedure. Non-acid-fast bacteria would take up this color after being decolorized by the acid-alcohol washing stage. Acid-fast bacteria such as the mycobacteria would retain the primary stain, carbolfuchsin, and would be impermeable to the penetration of the secondary stain.
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A 3-year-old male presents with a skin rash and epistaxis. He has had several, severe sinopulmonary infections. A careful history reveals that his maternal uncle died of bleeding complications following an emergency cholecystectomy. What additional findings are likely in this case?
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low platelet count and low serum IgM levels
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( Immunology Multisystem, 41%): This clinical scenario is typical for Wiskott-Aldrich syndrome. This is a sex-linked recessive disorder presenting with the triad of thrombocytopenia, eczema, and recurrent sinopulmonary infections. Serum IgM levels are low but IgG, IgA, and IgE levels are increased. Patients have a defective response to polysaccharide antigens, which is due to a cytoskeletal defect in T cells that inhibits their binding to B cells. *A CD4/CD8 ratio of < 1.5:1 is the pattern seen in AIDS due to selective tropism of the CD4+ T-helper cell population. *CEREBELLAR ATAXIA IS PART OF THE ATAXIA-TELANGIECTASIA SYNDROME. THE ATAXIA DEVELOPS BETWEEN AGE 2 AND 5. THE DEFECT IS ASSOCIATED WITH A DNA REPAIR ENZYME DEFICIENCY. *Elevated platelet count and increased serum levels of IgG, IgA, and IgE is not associated with a particular syndrome. Polyclonal gammopathies result in an increase in immunoglobulin of more than one class. This benign alteration is frequently seen in viral or bacterial infections. Thrombocythemia may be associated wtih a myeloproliferative syndrome or with a secondary reactive process. *Low platelet count and low serum IgG are not associated with any particular disorder.
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A 24-year-old woman presents with a 3-day history of fever, chills, chest pain, and cough productive of reddish-brown sputum. Past medical history includes a splenectomy 1 year ago. A chest x-ray film indicates consolidation of the right lower lobe. Blood cultures are positive for alpha-hemolytic gram-posotive diplococci. Immunity to the causative organism is based on which of the following?
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IgG antibodies to a surface acidic polysaccharide
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(Microbiology Respiratory, 48%): The patient in this question has pneumococal pneumonia, which must be considered in any patient with chills, fever, chest pain, and cough productive of purulent, rust-colored sputum. Streptococcus pneumoniae is an alpha-hemolytic, gram-positive coccus that grows in chains. It can be easily distinguished from other alpha-hemolytic streptococci because it is exquisitely sensitive to bile and bilelike compounds, such as optochin. It is the most common cause of community-acquired pneumonia and the most common cause of community-acquired meningitis in adults older than age 30.00The only recognized virulence factor of S. pneumoniae is its carbohydrate capsule (which contains acidic polysaccharides). Antibody to a specific capsule type is necessary to overcome infection. Mor ethan 80 capsule types have been recognized. The 23 types that most commonly cause diseasse are contained in a vaccine that is recommended for high-risk groups, including the elderly and those undergoing splenectomy. INcreased susceptibility is also found in patients with Hodgkin diseasse, chronic lymphocytic leukemia, and myeloma. The vaccine should still be given to patients with these conditions, but it is less successful. *The alternative complement pathway is important in clearing Nesisseria infections. Individuals with deficiencies in C5 through C 8 are at increased risk of diseasse from Neisseria. *The fimbria of Streptococcus pyogenes (Group A beta-hemolytic streptococcus) is composed of an alpha-helically coiled M protein. j Antibody against a specific M type will prevent infection. However, raising antibodies to M proteins can lead to rheumatic fever, so Strep throat infections are routinely treated with penicillin to prevent an antibody response. *THE C CARBOHYDRATE IS AN ANTIGEN OF BETA-HEMOLYTIC STREPTOCOCCI USED TO DIVIDE THEM INTO DIFFERENT GROUPS. ANTIBODY AGAINST C CARBOHYDRATE IS NOT PROTECTIVE.
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A British dairy farmer develops fever with chills, myalgia,s headache, skin rash, and vomiting. He is quite ill and is hospitalized. Blood cultures demonstrate tightly coiled, thin, flexible spirochetes shaped like a Shepherd's crook. The spirochetes are easily cultrued in serum-enriched nutrient agar. Which of the following organisms should be suspected?
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Leptospira interrogans
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(Microbiology General Principles, 64%): The only spirochete among the choices is Leptospira interrogans, so even if you didn't know the diseasses these organisms produce, you may have been able to answer the question. Leptospirosis, which this patient has, is caused by a spirochete; if you were presented with a list of spirochetes in the choices, the phrase "Shepherd's crook" should tip you off to Leptospira. Clinically, leptospirosis may range from nearly asymptomatic, or at least indistinguishable from other minor flu-like illnesses, to a potentially fatal form (Wal's diseasse) with jaundice, bleeding, renal failure, and skeletal muscle necrosis. Spread is via contact with blood or urine from infected animals, notably rats. Leptospirosis is found worldwide, but its more severe forms are most likely to occur in the tropics. *BRUCELLA ABORTUS IS A GRAM-NEGATIVE COCCUS AND IS ONE OF THE CAUSES OF BRUCELLOSIS. *Brucella melitensis is a gram-negative coccus and is one of the causes of brucellosis. *Pseudomonas mallei and Pseudomonas pseudomallei are small gram-negative bacilli that cause melioidosis.
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A high school student badly burned in an automobile accident develops a skin lesions on the burn area during his hospitalization. Which of the following best describes the causative agent?
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An oxidase-postive, aerobic, gram-negative bacillus
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(Microbiology General Principles, 64%): NOTE TO SELF: PICTURE LOOKED LIKE ANTHRAX; THEREFORE, DON'T BE FOOLED BY THE PICTURES! FOCUS ON THE QUESTION STEM! This is a case of ecthyma gangrenosum, the hallmark lesion of Pseudomonas aeruginosa infection. It is a common nosocomial infection in patients with cystic fibrosis, neutropenia, or severe burns. Pseudomonas aeruginosa is a gram-negative rod that is oxidase positive, aerobic ( a non-fermenter) and catalse positive. It is a prodigious producer of a capsule (slime layer) and is also distinguished by its production of a blue-green pigment and a grape-like odor. *CLOSTRIDIUM IS AN ANEROBIC, SPORE-FORMING GRAM-POSITIVE ROD. CLOSTRIDIUM WOULD NOT BE A COMMON PATHOGEN IN BURN PATIENTS AND WOULD NOT CAUSE SUCH A LESION. *Bacillus is a gram-positive, aerobic, spore-forming rod. Superficially, the skin lesion of anthrax (the anthrax eschar) might resemble the lesion caused by Pseudomonas, but would not be a common finding in burn patients, and indeed is quite rare in the U.S. *A gram-posotive, coagulase-negative coccus could be Staphylococcus epidermidis, Staphylococcus saprophyticus, or any of the members of the genus Streptococcus. None of these agents would be likely to produce a lesion such as that shown. Staphylococcus epidermidis is a member of the normal skin flora and is best know for its ability to colonize intravenous catheters and the endocardium via its production of a biofilm. Staphylococcus saprophyticus is best known as an agent of urinary tract infection in young, sexually active women, and the streptococci cause a wide variety of diseases, such as pharyngitis, meningitis, cullulitis, and endocarditis. *Staphylococcus aureus is a gram-posotive, coagulase-positive occus. It is a member of the normal skin flora and causes abscesses, furuncles, and boils, but not the lesion in the image here.
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A newborn infant has multiple, hemorrhagic, cutaneous lesions and does not respond to sound. Head CT scan shows periventricular calcifications. Which of the following infectious agents is the most likely cause of this child's presentation?
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cytomegalovirus
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(Microbiology Multisystem: 44%): The infectious agents listed are all important causes of congenital disease. The triad of cutaneous hemorrhages ("blueberry muffin baby"), deafness , and periventricular CNS calcifications suggest congenital CMV infection, the most common cause of intrauterine fetal viral infection. Other manifestations include microceaphaly and hepatosplenomegaly. *Neonatal herpes may be congenital, but more commonly is acquired during vaginal delivery. The infection is characterized by vesicles on the skin and mucous membranes, encephalitis, or disseminated disease. *Congenital rubella can cause mental retardation, heart abnormalities, blindness, encephalitis, and motor abnormalities. *Congenital syphilis can cause death in utero, or a variety of problems including abnormal teeth, bones, and central nervous system. *TOXOPLASMOSIS CAN BE EITHER ACQUIRED DURING DELIVERY (MILD) OR CONGENITAL (SEVERE). SEVERE INFECTIONS CAN STILLBIRTH, CHORIORETINITIS, INTRACEREBRAL CALCIFICATIONS, AND HYDRO- OR MICROCEPHALY.
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A 9-month-old infant is brought to the Health Department to receive the second dose of OPV (ORAL POLIO VACCINE), 2 weeks after the first vaccination. The child has mild diarrhea, so the decision is made to defer further immunizations. Bacteriologic examination of a stool culture is unremarkable; however, a small, single-stranded positive RNA virus is isolated from the specimen. This same agent was isolated from sewage effluent the preceding week. The viral isolate was not inactiviated by ether. Which of the following viruses was most likely isolated?
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poliovirus
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(Microbiology Multisystem, 44%): Poliovirus, which is a single-stranded +RNA virus, is naked (i.e., non-enveloped) and hence will not be inactivated by lipid solvents such as ether. The live virus vaccine had colonized the intestinal tract of the infant and was still being shed 2 weeks after the earlier oral dose. This same virus, the vaccine strain, is likely to be found in sewage, as all vaccinated infants will shed virus for a period of time after immunization with OPV. *Adenoviruses and parvovirus B19 may also cause diarrheal disease and both are non-enveloped; however, they both have a DNA genome. *Hepatitis C is an enveloped, single-stranded +RNA virus; its major target organ is the liver; not the intestinal tract. It is a fragile agent that does not survive well outside the body and would not be isolated from raw sewage effluent. *ROTA VIRUS IS THE MAJOR CAUSE OF DIARRHEAL DISEASE IN INFANTS UNDER THE AGE OF 2 YEARS. IT IS A MEMBER OF THE REOVIRUS FAMILY AND, AS SUCH, IS DOUBLE-STRANDED. THIS VIRUS CAUSES HOSPITALIZATION OF 30% TO 40% OF THE INFECTED INFANTS AND KILLS HUNDRES OF THOUSANDS OF INFANTS IN DEVELOPING NATIONS WHERE ACCESS TO HOSPITALS IS NOT READILY AVAILABLE. THERAPY FOR THE WATERY DIARRHEA PRODUCED BY THIS AGENT IS FLUID AND ELECTROLYTE REPLACEMENT.
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A 55-year-old woman with type 2 diabetes seeks treatment from her primary care physician for painful, burning urination. She is given a course of ampicillin, but returns to her physician a week later with complaints of fever and flank pain. At the time of her second visit, her temperature is 40 C (104 F), and she is tachycardic, with a blood pressure of 90/50 mm Hg. She has a petechial rash on her trunk and mucous membranes, and her fingertips show signs of peripheral vascular coagulopathy. A blood culture is positive for growth of gram-negative lactose-fermenting bacilli. Which of the following substances is the most likely cause of these symptoms?
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lipid A
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( Microbiology General Principles, 54%): Septic shock is a feared, potentially fatal complication of systemic infections by a wide variety of gram-negaitve organisms. The primary toxic agent is the lipopolysaccharide in the gram-negative bacterial celll wall. Further, it has been established that the most toxic part of the lipopolysaccharide is lipid A. Biochemically, lipid A consists of a backbone of alternating heptose and phosphate groups linked through 2-keto-3 deoxyoctonic acid (KDO) to lipid. The pathophysiologic effects of lipopolysaccharide are related to triggering release of potent cytokines (IL-1, TNF) and activation of complement and coagulation cascades. *Common core polysaccharide is a portion of the lipopolysaccharide that is the same in all gram-negative bacteria. *Lecithinase is an enzyme produced by Clostridium perfringens that damages cell membranes. *O-SPECIFIC POLYSACCHARIDE IS A PORTION OF THE LIPOPOLYSACCHARIDE THAT INDUCES SPECIFIC IMMUNITY. *Peptidoglycan is found in both gram-positive and gram-negative bacteria, and can be indirectly linked to lipopolysaccharide.
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A neonate is born at term with multiple problems. He is small for gestational age and has cataracts, hepatosplenomegaly, and thrombocytopenia with purpura. Further studies demonstrate patent ductus arteriosus, bone lucency, pneumonia, and meningoencephalitis. The mother is a 15-year-old girl who had no prenatal care and had a mild maculopapular rash in mid-pregnancy. Which of the following is the most likely diagnosis?
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congenital rubella
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(Microbiology Multisystem, 75%): The rubella virus is one of the causes of devastating prenatal infection. In adults and older children, the virus can cause aymptomatic infection or a relatively mild febrile illness (German measles) with upper respiratory symptoms, lymphadenopathy, maculopapular rash, and sometimes joint symptoms. The effects on the fetus range from apparently asymptomatic infection to multiple anomalies to death in utero. Among the more common abnormalities are intrauterine growth retardation, involvement of the senses and nervous system (e.g., meningoencephalitis, cataracts, retinopathy, hearing loss), cardiac involvement (e.g., patent ductus arteriosus, pulmonary arterial hypoplasia), hepatosplenomegaly, purpura (due to thrombocytopenia), blush red skin lesions (secondary to dermal erythropoiesis), and pneumonia. Apparently, asymptomatic babies should be monitored for subsequent development of hearing loss, mental retardation, endocrinopathies, and (rarely) progressive encephalitis. Treatment is supportive, as no specific antibiral therapy is available for this infection. The rubella vaccine should be given to women of childbearing age who are not pregnant at the time. *CYTOMEGALOVIRUS INFECTIONS CAN CAUSE AYMPTOMATIC TO DEVASTATING DISEASE IN NEWBORNS; LOOK FOR PERIVENTRICULAR CALCIFICATIONS AND MOTHERS WITH A FLU-LIKE ILLNESS. *Congenital syphilis can cause devastating disease in newborns and can occur in early forms (look for the rash of secondary syphilis) or late forms (look for bone and teeth abnormalities). *Congenital toxoplasmosis can produce devastating infection in newborns; look for a maternal history of cleaning cat litter boxes. *Neonatal listeriosis can produce devastating infection in newborns; look for murky brown amniotic fluid secondary to amnionitis.
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A young military recruit scheduled for overseas assignment begins a course of immunization. The corpsman administering the inoculations warns the private that one of these immunizations is likely to cause swelling and inflammation 24-48 hours after injection and therefore should be administered in his nondominant arm. To which vaccine is the corpsman referring?
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tetanus
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(Immunology General Principles, 47%): Swelling and inflammation at an inoculation site within 1-2 days reflects that the individual has "seen" this immunogen before and is mounting a secondary immune response to it. Of the vaccines on this list, the one that a young military recruit (or any young U.S. resident) will have been previously exposed to (probably multiple times) is the tetanus toxoid. This vaccine is routinely administered at 10 year intervals, or shorter intevals in cases in which there is fear of serious exposure. *Adenovirus is a live, non-attenuated vaccine administered in enteric-coated capsules. *Hepatitis A is not the best choice because at the beginning of a course of immunizations, there would be no underlying preexisting immune response, and thus no inflammation and swelling caused by previously sensitized lymphocytes. The final booster of the series might be expected to cause such inflammation, but not the beginning ones. *HEPATITIS B IS NOT THE BEST CHOICE BECAUSE AT THE BEGINNING OF A COURSE OF IMMUNIZATIONS, THERE WOULD BE NO UNDERLYING PREEXISTING IMMUNE RESPONSE, AND THUS NO INFLAMMATION AND SWELLING CAUSED BY PREVIOUSLY SENSITIZED LYMPHOCYTES. THE FINAL BOOSTER OF THE SERIES MIGHT BE EXPECTED TO CAUSE SUCH INFLAMMATION, BUT NOT THE BEGINNING ONES. *The typhoid vaccine is a single dose vaccine adminstered to individuals likely to travel to endemic areas. It is unlikely to have been administered to this individual before his recruitement into the military, thus he is unlikely to have previously sensitized immune cells. *Yellow fever vaccine is a single dose, attenuated live virus vaccine which is unlikely to have been administered to this individual before his recruitement into the military. Therefore, he is unlikely to have previously sensitized immune cells.
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A 3-year-old child with cystic fibrosis presents with weight loss, irritability, and a chronic productive cough. On physical exam, he is febrile and lung exam reveals intercostal retractions, wheezing, rhonchi, and rales. Chest x-ray demonstrates pathy infiltrates and atelectasis and Gram's stain of the sputum reveals slighly curved, motile gram-negative rods that grow aerobically. The microorganism responsible for this child's pneumonia is also the most common cause of which of the following diseases?
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otitis externa
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( Microbiology Respiratory, 48%): Anytime you see pneumonia in a cystic fibrosis patient, you should suspect Pseudomona aeruginosa. The Gram's stain revealing aerobic, gram-negative rods confirms you suspicion in this case. Now the question is: which of the diseasses listed is also caused by Pseudomonas? The answer is otitis externa. P. aeruginosa is often found in the external ear, especially if the conditions are moist ("swimmer's ear") and there is any sort of inflammation. External otitis is usually a benign process with the only symptoms being an itchy, painful ear. If, however, the organism penetrates the epithelium and invades the soft tissue, cartilage, and cortical bone, the process becomes malignant otitis externai, which can progress to osteomyelitis leading to cranial nerve palsies. This condition is most common in diabetics. *Croup, also called laryngotrachobronchitis, is a respiratory diseasse of childrne that presents with a characteristic "barking" cough. Courp is caused by parainfluenza virus. *Epiglottitis is a potentially fatal infection in children, caused by H. influenzae, which presents with drooling, difficulty breathing, and stridor. The incidence of this disease has dropped dramatically with the introduction of the H. influenzae type b (Hib) vaccine. *Meningitis is caused by numerous different bacteria, depending on the age of the patient. The most common causes include S. pneumoniae (elderly), H. influenzae (unvaccinated children), Group B Strep, and E. coli (neonates), and N. meningitidis (1 month-adult). While P. aeruginosa can cause meningitis, it is not a common cause. *THE MOST COMMON CAUSES OF OTITIS MEDIA INCLUDE S. PNEUMONIAE AND H. INFLUENZAE. EVEN IN CASES OF EXTERNAL EAR INFECTIONS WITH P. AERUGINOSA, THE MIDDLE EAR IS TYPICALLY SPARED.
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A 14-year-old patient is brough in by his parents because of a sore throat. ON physical examination, he is febirle, and has pharyngeal erythemia with a tonsillar absscess. A throat culture on sheep blood agar yields colonies of gram-positive cocci that are surrounded by a zone of complete hemolysis. The organism was also plated on mannitol salt agar; it grew well and cuased the medium to turn yellow. Which of the following microorganisms is the most likely cause of the patient's illness?
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Staphylococcus aureus
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( Microbiology General Principles, 48%): The description of the agent is consistent with a staphylococcal organism (catalase-positive, gram-positive cocci that grows on mannitol salt agar. The organism is most likely S. aureus, as it was able to ferment mannitol (as evidence by the color change in the mannitol salt agar after incubation) and was beta-hemolytic. Other characteristics of this organism are coagulase production and excretion of DNAase from colonies. Staphylococcal organisms are also notorious for formation of abscesses; the patient had an abscess in the tonsillar region. *The diptheria bacilli (Corynebacterium diphteriae) are gram-positive, pleomorphic rods that are arranged in palisades. They are non-hemolytic and would not grow on mannitol salt agar. these organims produce a whitish-gray pseudomembrane on the pharynx or the larynx; constitutional symptoms from toxemia are the major features of diptheria. *Epiglottitis is the most dommon disease of the upper respiratory tract produced by Haemophilus influenzae, a gram-negative, encapsulated rod. It is also a common cause of otitis media in children and may cause bronc hitis, bronchiolitit,s and pneumonia in adults. *Streptococcus salivarius is a gram-positive coccus that is usually alpha-hemolytic. It is normal flora of the oral cavity and is sometimes implicated in subacute bacterial endocarditis, but is not associated with tonsillar abscesses. *STREPTOCOCCUS PYOGENES IS A BETA-HEMOLYTIC, GRAM-POSITIVE COCCUS THAT GROWS IN CHAINS, AS OPPOSED TO THE RANDOM, GRAPE-LIKE CLUSTERS OF THE STAPHYLOCOCCI. THESE ORGANISMS ARE THE MOST COMMON CAUSE OF PHARYNGITIS, WHICH IS USUALLY MANIFESTED BY SEVERE SORE THROAT, REVER, A BEEFY RED PHARYNX, AND A TONSILLAR EXUDATE.
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An 18-year-old man is evaulated for possible immunodeficiency disease because of a life-long history of chronic lung infections, recurrent otitis media, and multiple episodes of bacterial meningitis. While total IgG is normal, the patient is found to have a selective deficiency of IgG2. IgG2 deficiency is most likely to be associated with a deficiency of which of the following other substances?
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IgA
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( Immunology General Principles, 36%): IgG subclass deficiency is one of the more minor forms of immunodeficiency disease, and most patients with this condition who are optimally managed can expect a normal life span. The typical presentation is as illustrated in the question stem. The deficiency may involve eithe ror both IgG2 and IgG3 with or without IgG4 deficiency. (IgG1 is the major form, and its deficiency leads to a deficiency of total IgG, and so, by dfinition, it is not consiered a "subclass" deficiency). A potentially clinically important point is that some patients with IgG2 deficiency also have IgA deficiency an may develop anaphylaxis if given IgA-containing blood products. *C3 DEFICIENCY TENDS TO PRODUCE PYOGENIC INFECTIONS. *C4 deficiency tends to produce an SLE-like syndrome. *IgE deficiency can be seen in some incomplete antibody deficiency syndromes, but is usually not clinically significant. *IgM deficiency occurs as part of severe combined immunodeficiency.
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An 8-year-old child is brought in by her mother with complaints of crampy abdominal pain, nausea, and mild diarrhea for approximately 2 weeks. The day before this visit, she vomited up a cylindrical white worm 30 cm in length, which the mother preserved in a jar. Which of the following is the most likely means by which this organism was acquired?
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ingestion of eggs from human feces
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(Microbiology Gastrointestinal , 49%): This is a case of Ascaris lumbricoides infection, the only helminth infection caused by a cylindrical white worm of this remarkably large size. It is acquired directly, with no intermediate host, from fecal contamination from other human beings, and the stage of the life cycle that is transmitted is the egg. *AUTOINFECTION IS A RARE OCCURRENCE IN HELMINTHIC INFECTIONS, POSSIBLE ONLY WITH STRONGYLOIDES STERCORALIS, THE THREADWORM, AND TAENIA SOLIUM, THE PORK TAPEWORM. *Ingestion of cysts in contaminated water is the normal mechanism of infection used by intestinal protozoa. There are no helmonthic infections in the U.S. transmitted via cysts in water. *Ingestion of eggs from an infected pet occurs in visceral larva migrans, when the ascarids of dogs and cats infect the human, an aberrant host. It would never result in the introduction of an adult worn into the vomitus, as described here. *Mosquito transmission of larvae is a means of transmission of the filarial nematodes, none of which are found in the United States, and none of which would be found in vomitus. *Skin penetration of larvae is the mechanism of infection used by hookworms, threadworms, and Schistosomes. None of these helminths would fit the description of the worm that was recovered in this case, since none of these is larger than one cm length.
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