Question 1

The most common etiologic agent of septic arthritis accounting for approximately 70% of infections is:&#10;A)Streptococcus pyogenes.&#10;B)H.influenzae.&#10;C)S.aureus.&#10;D)Streptococcus mitis.

Accepted Answer

Overall,S.aureus is the most common etiologic agent of septic arthritis,accounting for approximately 70% of infections.In adults younger than 30 years of age,however,N.gonorrhoeae is isolated most frequently.H.influenzae has been the most common agent of bacteremia in children younger than 2 years of age,and,consequently,it has been the most frequent cause of infectious arthritis in these patients,followed by S.aureus.

Question 2

Which fungal condition is most often detected in the bone marrow?&#10;A)Brucellosis&#10;B)Histoplasmosis&#10;C)Tuberculosis&#10;D)Leishmaniasis

Accepted Answer

The diagnosis of diseases,including brucellosis,histoplasmosis,blastomycosis,tuberculosis,and leishmaniasis,can sometimes be made by the detection of organisms in the bone marrow;however,only histoplasmosis is a fungus.

Question 3

Most cases of peritonitis in patients on continuous ambulatory peritoneal dialysis (CAPD)are caused by:&#10;A)Staphylococcus epidermidis and S.aureus.&#10;B)Escherichia coli.&#10;C)Klebsiella pneumoniae.&#10;D)Streptococcus spp.&#10;E)viral agents.

Accepted Answer

More than 13,000 patients with end-stage renal disease are maintained on CAPD.In this treatment,fluid is injected into the peritoneal cavity and subsequently removed,which allows the exchange of salts and water and the removal of various wastes in the absence of kidney function.Because the dialysate fluid is injected into the peritoneal cavity via a catheter,this break in the skin barrier places the patient on dialysis at significant risk for infection.Most infections originate from the patient's own skin flora.S.epidermidis and S.aureus are the most common etiologic agents,followed by streptococci,aerobic or facultative gram-negative bacilli,Candida spp. ,Corynebacterium spp. ,and others.The oxygen content of peritoneal dialysate is usually too high for the development of anaerobic infection.Among the gram-negative bacilli isolated,Pseudomonas spp. ,Acinetobacter spp. ,and the Enterobacteriaceae are frequently observed.

Question 4

Fluids should be processed for direct microscopic examination.If one organism is observed per oil immersion field,then at least _____ organisms per milliliter of specimen are present.&#10;A)102&#10;B)103&#10;C)104&#10;D)105

Accepted Answer

All fluids should be processed for direct microscopic examination.In general,if one organism is observed per oil immersion field,then at least 10⁵ organisms per milliliter of specimen are present.

Question 5

Any tissues received in the clinical microbiology laboratory should be minced and homogenized in a biosafety cabinet.If lung tissue is sent and processed,then which organism should be examined using direct fluorescent antibody (DFA)testing?

A)Listeria
B)Legionella
C)Leishmania
D)Leptospira

Accepted Answer

Tissue may be inoculated to tissue culture cells for isolation of viruses and should be manipulated in a laminar flow biologic safety cabinet.Brain,lung,spinal fluid,and blood are generally good specimens for viral isolation.Tissue may be examined by immunofluorescence for the presence of herpes simplex virus,varicella-zoster virus,cytomegalovirus,or rabies viral particles.Lung tissue should be examined by DFA test for Legionella spp.

Question 6

Human bites and animal bites caused by ________ and _________,respectively,can ultimately lead to an underlying bone infection.&#10;A)Eikenella corrodens;Actinomyces spp.&#10;B)Pasteurella multocida;Peptostreptococcus spp.&#10;C)Prevotella spp. ;S.aureus&#10;D)E.corrodens;P.multocida

Accepted Answer

Breaks in skin from other causes,such as a bite wound or trauma,also may be the initial event leading to underlying bone infection.For example,a human bite may lead to infection with E.corrodens,whereas an animal bite may result in P.multocida osteomyelitis.

Question 7

Pericardial fluid may be inoculated in blood culture broth and processed as a blood culture,provided the broth contains which anticoagulant?&#10;A)Heparin&#10;B)Ethylenediaminetetraacetic acid (EDTA)&#10;C)Citrate&#10;D)Coumadin

Accepted Answer

With respect to pericardial,pleural,synovial,and peritoneal fluids,the inoculation of blood culture broth bottles at the bedside or in the laboratory may be beneficial.An additional specimen should be submitted to the laboratory for a Gram stain.The specimen in the blood culture bottle is processed as a blood culture,facilitating the recovery of small numbers of organisms and diluting out the effects of antibiotics.Citrate or sodium polyanethol sulfonate (SPS)may be used as an anticoagulant.

Question 8

The proper technique for processing clotted body fluids sent to the laboratory for fungal culture is:&#10;A)grinding them in a mortar and pestle or glass tissue grinder.&#10;B)placing small amounts of whole material from the clot directly onto media.&#10;C)centrifugation with glass beads.&#10;D)filtration under pressure.

Accepted Answer

Any body fluid received in the laboratory that is already clotted must be homogenized to release trapped bacteria and minced or cut to release fungal cells.Either processing such specimens in a motorized tissue homogenizer or grinding them manually in a mortar and pestle or glass tissue grinder allows recovery of bacteria.Hand grinding is often preferred,because motorized grinding can generate considerable heat and thereby kill microorganisms in the specimen.Grinding may lyse fungal elements;therefore it is not recommended with specimens processed for fungi.Small amounts of whole material from a clot should be aseptically cut with a scalpel and placed directly onto media for the isolation of fungi.

Question 9

A 68-year-old man has an osteomyelitis infection as a result of bacteremia.The most common etiologic agent found in this infection is:&#10;A)Haemophilus spp.&#10;B)S.aureus.&#10;C)Pseudomonas aeruginosa.&#10;D)Fusobacterium necrophorum.

Accepted Answer

S.aureus,seeded during bacteremia,is the most common etiologic agent of osteomyelitis among patients of all age groups.The toxins and enzymes produced by this bacterium,as well as its ability to adhere to smooth surfaces and produce a protective glycocalyx coating,seem to contribute to the organism's pathogenicity.

Question 10

The most common etiologic agent of septic arthritis in adults younger than 30 years of age is:&#10;A)Neisseria gonorrhoeae.&#10;B)Staphylococcus aureus.&#10;C)Haemophilus influenzae.&#10;D)Streptococcus agalactiae.

Accepted Answer

Overall,S.aureus is the most common etiologic agent of septic arthritis,accounting for approximately 70% of all such infections.In adults younger than 30 years of age,however,N.gonorrhoeae is isolated most frequently.

Deck 75: Normally Sterile Body Fluids, Bone and Bone Marrow, and Solid Tissues