Deck 58: Normally Sterile Body Fluids, Bone and Bone Marrow, and Solid Tissues

Question 1

The most common etiologic agent of septic arthritis in adults younger than 30 years of age is

A)Neisseria gonorrhoeae.
B)Staphylococcus aureus.
C)Haemophilus influenzae.
D)Streptococcus agalactiae.

Answer 1

A
Overall, Staphylococcus 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, Neisseria gonorrhoeae is isolated most frequently.

Question 2

Most cases of peritonitis in patients on continuous ambulatory peritoneal dialysis are caused by

A)Staphylococcus epidermidis and S.aureus.
B)Escherichia coli.
C)Klebsiella pneumoniae.
D)Streptococcus spp.
E)viral agents.

Answer 2

A
More than 13,000 patients with end-stage renal disease are maintained on continuous ambulatory peritoneal dialysis (CAPD). In this treatment, fluid is injected into the peritoneal cavity and subsequently removed, which allows exchange of salts and water and 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 dialysis patient at significant risk for infection. Most infections originate from the patient's own skin flora; Staphylococcus 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 development of anaerobic infection. Among the gram-negative bacilli isolated, Pseudomonas spp., Acinetobacter spp., and the Enterobacteriaceae are frequently seen.

Question 3

Proper technique for processing clotted body fluids sent to the laboratory for fungal culture is

A)grinding them in a mortar and pestle or glass tissue grinder.
B)placing small amounts of whole material from the clot directly onto media.
C)centrifugation with glass beads.
D)filtration under pressure.

Answer 3

A
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 better 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 isolation of fungi.