اكبر مكتبة اسئلة واجوبة في التحاليل الطبية " حصري جدا "

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سابدأ منذ غدا ان شاء الله اضافة مكتبة اسئلة واجوبة في التحاليل الطبية

اذا كنت طالبا في التحاليل الطبية او حتى موظفا لن تحتاج لغيرها فهي ستضم الاف الاسئلة في التحاليل الطبية


انتظروني غدا

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 useful in determining whether this organism is a
part of the normal skin flora?


A. Bacitracin resistance

B. Catalase

C. Coagulase

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
coagulase test. S. aureus is the only coagulase-positive staphylococcus.

Bacitracin sensitivity differentiates Streptococcus pyogenes from the other beta-hemolytic streptococci, which
are bacitracin resistant (choice A).

The catalase test (choice B) is used to differentiate streptococci from staphylococci. Staphylococci produce
catalase and can generate oxygen bubbles in hydrogen peroxide, whereas streptococci cannot.

Novobiocin resistance (choice D) differentiates the coagulase-negative staphylococci into S. epidermidis
(novobiocin sensitive) and S. saprophyticus (novobiocin resistant).

Optochin resistance (choice E) differentiates the major pathogenic alpha-hemolytic streptococci. S. pneumoniae
is optochin- and bile-sensitive whereas S. viridans is resistant to both optochin and bile.

A patient with colorectal cancer develops septicemia 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:

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 diseases. 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
cases of S. bovis bacteremia were associated with endocarditis, especially in patients with preexisting valvular
lesions.

Streptococcus agalactiae(choice A) is an important cause 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 cause 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 predisposes patients to severe infections
with S. pneumoniae and other encapsulated organisms. S. pneumoniae infections are also more frequent and
unusually severe in patients with sickle cell anemia, multiple myeloma, alcoholism, and hypogammaglobulinemia.
S. pneumoniae is now the leading cause of invasive bacterial respiratory disease in patients with AIDS.

Streptococcus pyogenes(choice D) is the most common cause of bacterial pharyngitis. Complications include
paratonsillar abscesses, otitis media, and sinusitis. Long-term sequelae 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 diseases.

Streptococcus viridans(choice E), or the viridans Streptococci, are the most common cause of subacute
bacterial endocarditis, which should be suspected in cases of viridans streptococcal bacteremia. One species of
viridans Streptococci, Streptococcus milleri, is frequently associated with pyogenic abscesses, especially of the
liver.