Rapid presumptive identification of gram-negative rods directly from blood cultures by simple enzymatic tests.
Gram-negative rods were presumptively identified directly from blood cultures within 15 min as Escherichia coli, a member of the Klebsiella-Enterobacter group, or oxidase positive. Samples of artificially seeded blood cultures (193 cultures) and patient blood cultures (78 cultures) were filtered into a Dynadepth test card with the Bac-T-Screen instrument (Vitek, Inc., Hazelwood, Mo.). Triton X-100 was then filtered into the test card to lyse the blood cells but not the entrapped bacteria, and either methylumbelliferone-labeled substrates or oxidase reagent was applied to the filter surface. The oxidase test was read within 30 s, and the methylumbelliferone and indole tests were read after a 10-min incubation at room temperature. Positive beta-galactosidase, beta-glucuronidase, and indole test results predicted the identification of E. coli with a 96 to 100% sensitivity and a 99 to 100% specificity. Positive beta-xylosidase and beta-galactosidase test results and negative oxidase and beta-glucuronidase test results were 85 to 93% sensitive and 100% specific for a Klebsiella-Enterobacter organism. A positive oxidase test result and negative beta-glucuronidase, beta-xylosidase, and indole test results were highly predictive of Pseudomonas aeruginosa (sensitivity, 100%; specificity, 99%). The procedures described are rapid and simple and provide a direct presumptive identification of the gram-negative rods most commonly found in blood cultures.
Sepúlveda
J L
JL
Department of Pathology, Methodist Hospital, Houston, Texas.
Stager
C E
CE
Davis
J R
JR
D001431:Bacteriological Techniques; D004754:Enterobacter / Q000302:isolation & purification; D004926:Escherichia coli / Q000302:isolation & purification; D005374:Filtration; D006090:Gram-Negative Bacteria / Q000302:isolation & purification*; D006801:Humans; D007709:Klebsiella / Q000302:isolation & purification; D010088:Oxidoreductases; D011550:Pseudomonas aeruginosa / Q000302:isolation & purification; D018805:Sepsis / Q000175:diagnosis* / Q000382:microbiology
D010088:Oxidoreductases