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Category: Clinical Microbiology
Blood Cultures, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817435/9781555815271_Chap3_4-1.gif /docserver/preview/fulltext/10.1128/9781555817435/9781555815271_Chap3_4-2.gifAbstract:
When bacteria or fungi overcome the host's normal defense mechanisms and enter the bloodstream through the lymphatics or from extravascular sites, they can quickly disseminate throughout the body, causing severe illness. In addition, the by-products of their metabolism can lead to septic shock, among the most serious complications of infectious diseases. Rapid recognition and immediate institution of appropriate treatment are essential. Laboratory diagnosis of bacteremia and fungemia depends on blood cultures, which are probably the most important cultures performed by the microbiology laboratory. Because the culture methods are so sensitive, the procedure must be carefully controlled beginning at the preanalytical stage (collection), to avoid the misinterpretation of a procurement-associated skin commensal microorganism as an agent of infection.
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Identification flowchart for Brucella spp. from cultures
Identification flowchart for Brucella spp. from cultures
Visible signs of growth caused by organisms commonly encountered in blood cultures
Visible signs of growth caused by organisms commonly encountered in blood cultures
Initial processing and reporting results from positive blood culture bottles a
aIncubate aerobic plates in 5% CO2 and anaerobic plates under anaerobic conditions. For any subsequent positive companion bottles or other positive bottles “collected” within the same 48 h as the first positive bottle, subculture only to BAP unless the Gram stain is different or the original culture did not grow on BAP. In addition, for subsequent positive cultures, inoculate MAC or EMB and either CNA (Columbia colistin-nalidixic acid agar) or PEA (phenylethyl alcohol agar) if gram-negative rods are present and a direct coagulase if gram-positive cocci in clusters are present.
bDisk testing is a screen for identification of LactoBacillus, Erysipelothrix, Bacillus, Leuconostoc, Pediococcus, and vancomycin-resistant and -dependent Enterococcus or Staphylococcus organisms that are penicillin susceptible (see procedure 3.17.4 for details on potency and QC). Disks will also detect mixed cultures but are not a substitute for a standard susceptibility test. A streak of S. aureus ATCC 25923 perpendicular to but not touching the line of the initial inoculum will aid in identification of group B streptococci and Listeria.
cRead test up to 4 h and update report and notify physician if test result is positive. Remove coagulase from incubator at ≤4 h and incubate at room temperature for remainder of 24 h.
dFor methods for preparation of inoculum for direct testing of automated or manual commercial multitest kit identification systems and for AST, see text.
Initial processing and reporting results from positive blood culture bottles a
aIncubate aerobic plates in 5% CO2 and anaerobic plates under anaerobic conditions. For any subsequent positive companion bottles or other positive bottles “collected” within the same 48 h as the first positive bottle, subculture only to BAP unless the Gram stain is different or the original culture did not grow on BAP. In addition, for subsequent positive cultures, inoculate MAC or EMB and either CNA (Columbia colistin-nalidixic acid agar) or PEA (phenylethyl alcohol agar) if gram-negative rods are present and a direct coagulase if gram-positive cocci in clusters are present.
bDisk testing is a screen for identification of LactoBacillus, Erysipelothrix, Bacillus, Leuconostoc, Pediococcus, and vancomycin-resistant and -dependent Enterococcus or Staphylococcus organisms that are penicillin susceptible (see procedure 3.17.4 for details on potency and QC). Disks will also detect mixed cultures but are not a substitute for a standard susceptibility test. A streak of S. aureus ATCC 25923 perpendicular to but not touching the line of the initial inoculum will aid in identification of group B streptococci and Listeria.
cRead test up to 4 h and update report and notify physician if test result is positive. Remove coagulase from incubator at ≤4 h and incubate at room temperature for remainder of 24 h.
dFor methods for preparation of inoculum for direct testing of automated or manual commercial multitest kit identification systems and for AST, see text.
Urea-positive fastidious gram-negative coccobacilli similar to Brucella a
aReactions extracted from references 9 and 12. NA, not applicable; V, variable; CCB, coccobacilli.
b O. ureolytica is primarily a uropathogen.
cA. actinomycetemcomitans is urea negative and rarely oxidase positive. Urea-positive Actinobacillus organisms are from animal sources.
dGrows only on CHOC, or on blood agar associated with staphylococcus colony.
eUse rapid urea test to increase sensitivity.
fTSI, triple sugar iron agar.
Urea-positive fastidious gram-negative coccobacilli similar to Brucella a
aReactions extracted from references 9 and 12. NA, not applicable; V, variable; CCB, coccobacilli.
b O. ureolytica is primarily a uropathogen.
cA. actinomycetemcomitans is urea negative and rarely oxidase positive. Urea-positive Actinobacillus organisms are from animal sources.
dGrows only on CHOC, or on blood agar associated with staphylococcus colony.
eUse rapid urea test to increase sensitivity.
fTSI, triple sugar iron agar.