Rapid identification of pathogens in blood cultures with a modified fluorescence in situ hybridization assay

Abstract

We evaluated a modified fluorescence in situ hybridization (FISH) assay for rapid (<1 h) identification of microorganisms in growth-positive blood cultures. The results were compared to those of the standard FISH technique and conventional culturing. The rapid identification of microorganisms with modified FISH can have important effects on clinical management of patients with bloodstream infections.

FIG. 1.

Fluorescent microscopy (magnification, ×100) of microorganisms from blood culture fluids after FISH. Patient A was an 85-year-old man with a history of relapsing urinary tract infections and chronic prostatitis. He presented with fever, pollakisuria, mental status alterations, and a crural wound after collapse. No painful prostate was found upon rectal examination. Leukocyturia was present, but no microorganisms were cultured from urine samples. Ceftriaxone treatment was initiated based on suspicion of urosepsis. Gram-negative rods seen in the Gram stain of the positive blood culture were identified as Pseudomonas aeruginosa by FISH within 1 h, whereas final identification was obtained only the next morning. The figure shows fluorescence of the eubacterial probe with the Pseudomonas aeruginosa strain, which was identical to the fluorescence observed with the Pseudomonas aeruginosa-specific probe. Patient B was a 71-year-old woman who was admitted for debulking of a lung tumor because of vascular compression. Postoperatively, she developed fever and dyspnea. Empirically, clarithromycin and ceftriaxone therapy was started for possible postobstruction pneumonia. Yeasts seen in a Gram stain of blood culture fluid were identified with the species-specific probe as Candida albicans (shown in the figure) within 1 h by FISH. Culture identification was available late the next day.