title: Rapid presumptive identification of gram-negative rods directly from blood cultures by simple enzymatic tests.
abstract: 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.
authors.affiliation: Department of Pathology, Methodist Hospital, Houston, Texas.
authors.forename: J L
authors.initials: JL
authors.lastname: Sepúlveda
authors.forename: C E
authors.initials: CE
authors.lastname: Stager
authors.forename: J R
authors.initials: JR
authors.lastname: Davis
mesh_terms: 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
chemical_list: D010088:Oxidoreductases