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, eosin-methylene 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 cost-effective, practical, and reliable manner.