Question 1

A 76-year-old man with intermittent fevers has blood cultures drawn three times.The second set is positive and grew out of a Corynebacterium spp.This organism is considered:

Accepted Answer

Growth of Bacillus spp. ,Corynebacterium spp. ,Propionibacterium acnes,or coagulase-negative staphylococci in one of several cultures should be considered a probable contaminant.

Question 2

In the case of infants and small children,how much blood is usually drawn for bacterial culture?

Accepted Answer

For infants and small children,only 1 to 5 mL of blood should be drawn for bacterial culture.

Question 3

Brucella infections usually result in which type of bacteremia?

Accepted Answer

In septic shock,bacterial endocarditis,and other endovascular infections,organisms are released into the bloodstream at a fairly constant rate (continuous bacteremia).In addition,during the early stages of specific infections,including typhoid fever,brucellosis,and leptospirosis,bacteria are continuously present in the bloodstream.

Question 4

The possibility of an abscess should be considered if this bacterial group is isolated in the blood:

Accepted Answer

Organisms associated with neoplastic disease include C.septicum and other uncommonly isolated clostridial species,Streptococcus bovis,A.hydrophila,Plesiomonas shigelloides,and Campylobacter spp.If the S.anginosus bacterial group is isolated in the blood,then the possibility of an abscess should be considered.

Question 5

A patient who has an existing heart condition has dental surgery but neglects to inform her dentist of this disorder.She later develops endocarditis as a consequence of the procedure.Which of the following organisms most likely caused endocarditis?

Accepted Answer

The primary causes of infective endocarditis are the viridans streptococci,made up of several species (Box 67-2).These organisms are normal inhabitants of the oral cavity,often gaining entrance to the bloodstream as a result of gingivitis,periodontitis,or dental manipulation.Heart valves,especially those previously damaged,present convenient surfaces for attachment of these bacteria.Streptococcus sanguinis and S.mutans are frequently isolated in streptococcal endocarditis.

Question 6

If tachyzoites are found circulating in blood,then the infection would be classified as a:

Accepted Answer

If tachyzoites of the parasite Toxoplasma gondii are found in circulating blood,then the infection would be classified as a parasitemia.

Question 7

A 26-year-old woman who has a Gardnerella vaginalis infection becomes immunocompromised,which causes the organism to enter the bloodstream.She has several fever spikes;therefore blood cultures are drawn and placed in blood culture media containing sodium polyanethol sulfonate (SPS).After 5 days of incubation,the blood cultures are negative.Which of the following statements explains this discrepancy?

Accepted Answer

In addition to its anticoagulant properties,SPS is also anticomplementary and antiphagocytic and interferes with the activity of some antimicrobial agents,notably aminoglycosides.SPS,however,may inhibit the growth of a few microorganisms,such as some strains of Neisseria spp. ,G.vaginalis,Streptobacillus moniliformis,and all strains of Peptostreptococcus anaerobius.

Question 8

Which virus found in the blood involves infecting certain T lymphocytes and possibly macrophages?

Accepted Answer

HIV,the virus that causes acquired immunodeficiency syndrome (AIDS),attacks helper T cells and possibly macrophages.

Question 9

A 36-year-old emergency medical technician (EMT)is exposed to a patient with brucellosis.Blood cultures are drawn from the EMT and reported as negative after 1 week.Which of the following statements explains this discrepancy?

Accepted Answer

Brucella spp.may grow slowly;therefore cultures must be incubated for a minimum of 3 weeks.Cultures should be handled in a biologic safety cabinet.

Question 10

Granulicatella spp.and Abiotrophia spp.are dependent on which nutritional additive for optimal growth?

Accepted Answer

Granulicatella spp.and Abiotrophia spp.are unable to multiply without the addition of 0.001% pyridoxal hydrochloride,also called thiol or vitamin B₆.These streptococci are known as nutritionally variant or satelliting streptococci and have been associated with bacteremia and endocarditis.

Question 11

The BACTEC automated blood culture system detects organisms by monitoring a rise in carbon dioxide (CO₂)levels using which type of sensor?

Accepted Answer

The BACTEC 9240, BACTEC 9120, and BACTEC 9050 are fully automated blood culture systems that use fluorescence to measure CO₂ released by organisms. A gas-permeable fluorescent sensor is on the bottom of each vial (Figure 67-6).

Question 12

A consequence of sepsis is disseminated intravascular coagulation (DIC),which is characterized by numerous small blood vessels becoming clogged with clotted blood and bleeding as a result of the depletion of coagulation factors.Although any circulating pathogen can cause DIC,it is most often a consequence of ________ sepsis.

Accepted Answer

Although most often a consequence of gram-negative bacterial sepsis,DIC can occur with septicemia involving any circulating pathogen,including parasites,viruses,and fungi.

Question 13

Saponin,polypropylene glycol,SPS,and ethylenediaminetetraacetic acid (EDTA)are all components in which blood culture system?

Accepted Answer

The Isolator (Wampole Laboratories,Cranbury,NJ)is a commercially available lysis centrifugation system.The Isolator consists of a stoppered tube containing saponin to lyse blood cells,polypropylene glycol to decrease foaming,SPS as an anticoagulant,EDTA to chelate calcium ions and inhibit the complement cascade and coagulation,and a small amount of an inert fluorochemical (Fluorinert,3M Company,St.Paul,MN)to cushion and concentrate the microorganisms during 30-minute centrifugation at 3000 11ea5c86_236c_629c_8438_f591fd7189ae_TB6072_11 .(Figure 67-6).

Question 14

Patients receiving lipid-supplemented parenteral nutrition are at risk for developing fungemia caused by which organism?

Accepted Answer

Fungemia,the presence of fungi in blood,is usually a serious condition,primarily occurring in patients who are immunosuppressed and in those with a serious or terminal illness.C.albicans is by far the most common species,but M.furfur can often be isolated in patients,particularly neonates,receiving lipid-supplemented parenteral nutrition.

Question 15

The most common portal of entry for bacteremia is:

Accepted Answer

The most common portals of entry for bacteremia are the genitourinary tract (25%),respiratory tract (20%),abscesses (10%),surgical wound infections (5%),biliary tract (5%),miscellaneous sites (10%),and uncertain sites (25%).

Quiz 66: Bloodstream Infections