Bacteremia caused by Enterobacter asburiae misidentified biochemically as Cronobacter sakazakii and accurately identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: a case report

BACKGROUND: Biochemical analyses of causative bacteria do not always result in clear identification, and new technologies aimed at improving diagnostic accuracy continue to be developed. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry is a rapid and accurate technique for bacterial identification. Misidentification of Cronobacter sakazakii is related to clinical and industrial problems. Here, we encountered a case of rare bacteremia in which the causative organism Enterobacter asburiae was biochemically misidentified as C. sakazakii before being correctly identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. CASE PRESENTATION: An 87-year-old Asian man with no diabetes or active disease developed bacteremia and was admitted to our hospital. While the route of infection could not be determined despite various examinations, the clinical course was good following antibiotic therapy. Biochemical analyses identified the causative organism as C. sakazakii, but colonies on the blood agar medium showed a grayish coloration, differing from the yellowish coloration of typical Cronobacter colonies. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was therefore performed, identifying the bacterium as E. asburiae on three independent analyses. This result was confirmed by multilocus sequence analysis using five housekeeping genes. CONCLUSIONS: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry may reduce misidentification of bacteria as C. sakazakii and improve the reporting rate of E. asburiae. This technique should be considered when biochemical bacterial misidentification is suspected.