One of three blood culture bottles drawn from a patient with unexplained fevers reveals gram-positive cocci
growing in clusters. Which of the following tests would be most uful in determining whether this organism is a part of the normal skin flora?
A. Bacitracin resistance
B. Catala
C. Coagula
D. Novobiocin resistance
E. Optochin resistance
Explanation:
The correct answer is C. Gram-positive cocci in clusters are staphylococci. Staphylococcus aureus is a common pathogen that should not be considered normal skin flora. Other staphylococci, especially Staphylococcus
epidermidis, may contaminate blood cultures and can be differentiated from Staphylococcus aureus by the
coagula test. S. aureus is the only coagula-positive staphylococcus.
Bacitracin nsitivity differentiates Streptococcus pyogenes from the other beta-hemolytic streptococci, which are bacitracin resistant (choice A).
The catala test (choice B) is ud to differentiate streptococci from staphylococci. Staphylococci produce
catala and can generate oxygen bubbles in hydrogen peroxide, whereas streptococci cannot.
Novobiocin resistance (choice D) differentiates the coagula-negative staphylococci into S. epidermidis
(novobiocin nsitive) and S. saprophyticus (novobiocin resistant).
Optochin resistance (choice E) differentiates the major pathogenic alpha-hemolytic streptococci. S. pneumoniae is optochin- and bile-nsitive whereas S. viridans is resistant to both optochin and bile.
A 4-month-old infant prents with failure to thrive, progressive muscular weakness, and poor head control. On
questioning, the mother states that she typically feeds the baby soy-bad formula sweetened with honey. Which of the following organisms is most likely to be responsible for the child's prentation?
A. Clostridium botulinum
B. Clostridium difficile
C. Clostridium perfringens
D. Clostridium tetani
E. Corynebacterium diphtheriae
Explanation:
The correct answer is A. The baby has infant botulism (floppy baby syndrome), which is due to germi
nation of Clostridium botulinum spores (found in honey) in the baby's gastrointestinal tract. Patients improve when honey is removed from the diet. This disorder is most common in children under the age of six months; older children and adults do not appear to be vulnerable to this form of botulism, but are susceptible to botulism caud by
ingestion of preformed toxin.
Clostridium perfringens(choice C) caus gas gangrene and gastroenteritis, and it is not associated with
ingestion of honey.
Clostridium tetani (choice D) caus tetanus, and does not cau a food-borne illness in infants.
Corynebacterium diphtheriae(choice E) caus diphtheria in susceptible individuals.
A 35-year-old woman prents to her gynecologist with complaints of burning on urination for the past 2 days.
Dipstick test of her urine demonstrates marked positivity for leukocyte estera, but no reactivity for
nitrite. Urine culture later grows out large numbers of organisms. Which of the following bacteria are most likely to be
responsible for this patient's infection?小菜的做法大全
A. Enterobacter sp.
B. Enterococcus faecalis
C. Escherichia coli
D. Klebsiella pneumoniae
E. Pudomonas aeruginosa
Explanation:
The correct answer is B. The positive leukocyte estera test indicates the prence of neutrophils in the urine,
suggesting a bacterial infection. The nitrite test exploits the fact that most Enterobacteria (gram-nega
tive enteric rods) are able to form nitrite from nitrate; thus, the nitrite test is ud to diagno urinary tract infections. One
limitation of this method is the fact that enterococci (gut streptococci) do not produce nitrite from nitrate, but can nonetheless cau urinary tract infections. Enterococcal urinary tract infections are often nosocomial and
classically acquired in the intensive care unit, although they can occur in other ttings.
Enterobacter sp. (choice A), Escherichia coli(choice C), Klebsiella pneumoniae(choice D), and Pudomonas
aeruginosa(choice E) can cau urinary tract infections and would usually be picked up by the dipstick for
nitrites. Fal-negative results might still be en with the organisms if the infection was light, the bladder had been recently emptied prior to collection, and the urine was "new" and had not yet grown enough bacteria to和珅相当于现在什么官
produce a positive result.
A 37-year-old woman prents with 3 days of progressive joint pain in her ankles, knees, and wrists. She recalls
three similar episodes over the past veral years. On examination, she has a temperature of 38.7 C, her blood
尿频的原因有哪些
pressure is 110/70 mm Hg, and her heart rate is 90/min. She has a diffu petechial rash over her trunk and
extensor surfaces. Her ankles and knees are swollen, red, and tender with decread range of motion, and there
is tenderness over the tendon sheaths of her hands and forearms. Blood cultures are negative. Aspiration of joint fluid reveals a white cell count of 22,000/mm3 with no visible organisms, but culture on chocolate agar is positive. Which of the following is an attribute of the causative organism that allows it to produce recurrent infections?
A. It is an intracellular pathogen
B. It is resistant to ceftriaxone
C. It is resistant to complement-mediated lysis
D. Its capsule is not immunogenic
E. Its pili undergo antigenic and pha variation
Explanation:
The correct answer is E. This is a ca of Neisria gonorrhoeae arthritis. Patients are continuously susceptible to reinfection becau of antigenic variation and pha variation of the pili.
N. gonorrhoeae is not an intracellular pathogen (choice A), although it may be found intracellularly in
neutrophils after it has been phagocytized.
Ceftriaxone (choice B) is the drug of choice for N. gonorrhoeae.
Gonococci are especially susceptible to complement-mediated lysis, not resistant to it (choice C).
N. gonorrhoeae has an insignificant capsule that does not play a major role in the pathogenesis, but its capsule is immunogenic (compare with choice D). Streptococcus pyogenes is the best know
n example of a
nonimmunogenic capsule, made of hyaluronic acid, but virtually all other capsules are immunogenic.
A Pap smear from a woman with chronic cervicitis shows cytoplasmic inclusions within epithelial cells. Fluorescent antibodies identify both the inclusions and "elementary bodies." The intracellular organisms causing the
infection are unusual becau they cannot synthesize which of the following?
A. ATP
B. Cholesterol
C. DNA
D. Proteins
E. RNA
Explanation:
The correct answer is A. The dia is chlamydial cervicitis. This venereally transmitted infection is usually suspected after treatment for gonorrhea fails to relieve symptoms. However, a few cas are picked up when cytoplasmic inclusions compod of aggregates of chlamydia are identified on Pap smears. Confirmation can be made with fluorescent antibodies that pick up both the aggregates and individual bacteria known as
"elementary bodies." The organisms are obligate intracellular parasites becau they have lost the ability to
synthesize ATP. Although some authors consider them to be "bacteria," others do not, since this is such a
fundamental difference between the chlamydia and free living bacteria.
Failure to synthesize cholesterol (choice B) is not usually cited as a problem specific to any type of organism, although virus are not able to do so without using host machinery.
Some virus cannot synthesize DNA (choice C), but the dia in question is not caud by a virus.
Protein synthesis (choice D) by virus requires host ribosomes.
Some virus cannot synthesize RNA (choice E), but the dia in question is not caud by a virus.
A patient with colorectal cancer develops pticemia complicated by endocarditis. You would expect the blood
cultures to grow
A. Streptococcus agalactiae
B. Streptococcus bovis
C. Streptococcus pneumoniae
D. Streptococcus pyogenes
E. Streptococcus viridans
Explanation:
戒烟壁纸The correct answer is B.Streptococcus bovis is a Group D streptococcus. There is a significant association
between S. bovis bacteremia and endocarditis with carcinoma of the colon and other colonic dias. Every
patient with S. bovis bacteremia should undergo gastrointestinal and cardiac evaluation. Up to 50% of patients
with S. bovis bacteremia are reported to have underlying colonic malignancies. In another study, 25-50% of
cas of S. bovis bacteremia were associated with endocarditis, especially in patients with preexisting valvular
lesions.
Streptococcus agalactiae(choice A) is an important cau of maternal and neonatal bacteremia and neonatal
meningitis. It is part of the normal flora of the gastrointestinal tract and the female genital tract.
Streptococcus pneumoniae(choice C) is a leading cau of community-acquired pneumonia, meningitis in
adults, otitis media (especially in children), and sinusitis. Spontaneous peritonitis due to S. pneumoniae is
reported in children with ascites from nephrotic syndrome. Asplenia predispos patients to vere infections
with S. pneumoniae and other encapsulated organisms. S. pneumoniae infections are also more frequent and
unusually vere in patients with sickle cell anemia, multiple myeloma, alcoholism, and hypogammaglobulinemia. S. pneumoniae is now the leading cau of invasive bacterial respiratory dia in patients with AIDS.
长春房地产报
Streptococcus pyogenes(choice D) is the most common cau of bacterial pharyngitis. Complications include
qq修改密码
paratonsillar abscess, otitis media, and sinusitis. Long-term quelae include rheumatic fever and
poststreptococcal glomerulonephritis. S. pyogenes is also responsible for many skin and soft tissue infections.
The organism also produces many toxins that produce a variety of dias.奔跑吧兄弟歌曲
Streptococcus viridans(choice E), or the viridans Streptococci, are the most common cau of subacute
bacterial endocarditis, which should be suspected in cas of viridans streptococcal bacteremia. One species of
viridans Streptococci, Streptococcus milleri, is frequently associated with pyogenic abscess, especially of the
liver.
A 54-year-old woman suffering from influenza deteriorates and develops shaking chills and a high fever. Physical
examination is remarkable for dullness to percussion at the left ba and decread breath sounds on the left.
Chest x-ray confirms the diagnosis of lobar pneumonia, presumed to be caud by Streptococcus pneumoniae.
The patient has no known drug allergies. Which of the following antibiotics would be most appropriate to treat the patient's condition?
A. Cefotaxime
B. Chloramphenicol
C. Erythromycin
D. Penicillin
E. Vancomycin
Explanation:
The correct answer is D. Penicillin remains the first-line drug of choice for pneumococcal pneumonia, except in
patients with penicillin allergy and in the relatively few areas in which pneumococcal strains with high-level
penicillin resistance exist. Alternative therapies include erythromycin and vancomycin.
The third-generation cephalosporin cefotaxime (choice A) is not usually ud for pneumococcal pneumonia.
兰媛媛
Chloramphenicol (choice B) is not usually ud for pneumococcal pneumonia.
Erythromycin (choice C) is a good alternative therapy for pneumococcal pneumonia, but is usually ud only
when a penicillin allergy is prent.
Vancomycin (choice E) is not the first-line therapy, but it is a good alternative in patients allergic to penicillin or
when high-level penicillin resistance (relatively uncommon) is prent.
An otherwi healthy 3-year-old child is brought to the pediatrician with umbilicated, flesh-colored papules on his
trunk. This condition is related to infection with which of the following virus?
A. Cytomegalovirus
B. Herpesvirus 6
C. Parvovirus
D. Poxvirus
E. Variola
Explanation:
The correct answer is D. The lesions are characteristic of molluscum contagiosum, which is a typically benign
and lf-limited condition caud by a poxvirus. The dia can be transmitted either venereally or t
hrough
non-venereal contact. The other virus listed do not cau similar skin lesions. Patients with advanced HIV
infection may develop a vere, generalized, and persistent eruption, often involving the face and upper body.
Cytomegalovirus (choice A) caus congenital infections and disminated infections in immunosuppresd
patients.
Herpesvirus 6 (choice B)caus roola (exanthem subitum).
Parvovirus (choice C) caus aplastic cris in patients with hemolytic anemia.
Variola (choice E) is the smallpox virus.
A 39-year-old black man prents with complaints of anorexia, malai, fatigue, dark urine, and upper abdominal
discomfort. He admits to homoxuality, but denies blood transfusions, alcohol intake, or intravenous drug
abu. On physical examination, the patient has a temperature of 100.2 degrees F, scleral icterus, and jaundice.
His liver is palpable below the right costal margin, and there is moderate right upper quadrant tenderness. Liver
function test results are as follows: total bilirubin 12.4%, SGOT 980 units, SGPT 1200 units. Serologic findings
are as follows: anti-hepatitis A IgM negative, HBsAg positive, anti-HBc IgM positive, HBeAg positive, anti-HBsAb negative, hepatitis C negative. When this patient enters the window period, what would likely be the first change
in his rologic findings?
