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Rapid identification of Aeromonas species in stool samples with chromogenic media and matrix-assisted laser desorption ionization time of flight mass spectrometry: an institutional experience

Aim: To evaluate the routine use of chromogenic media together with matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI TOF) in gastrointestinal infections caused by Aeromonas spp. as rapid, practical, cost-effective and reliable methods. Materials and methods: Between August 2007 and March 2012, a total of 13,194 stool specimens of patients were included in the study. The stool samples and the reference strains were inoculated onto Cefsulodin Irgasan Novobiocin agar, sheep blood agar, eosinmethylene blue agar, and Hektoen enteric agar media together with CHROMagar Salmonella Plus. All the Salmonella and Aeromonas suspected colonies were identified with an automated system (Phoenix) and MALDI TOF. Results: Some of the pink colonies resembling Salmonella were identified as Aeromonas spp. without any discordance (100%) between the systems. A total of 86 Aeromonas strains were identified: 30 A. caviae, 27 A. hydrophila, 16 A. veronii, 11 A. sobria, and 2 A. salmonicida. When analyzed macroscopically, those Aeromonas species had prominent colony appearance differences from classically detected Salmonella on CHROMagar Salmonella Plus media. Conclusion: A combination of CHROMagar Salmonella Plus and MALDI TOF will help to detect Aeromonas species in 24 h in a costeffective, practical, and reliable manner.

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