Journal of M et hods M icrobiological Journal of Microbiological Methods 28 (1997) 89–97 Effect of the growth medium on the cellular fatty acid composition of aeromonads: consequences for the chemotaxonomic differentiation of DNA hybridization groups in the genus Aeromonas a, b a a a * ¨ Geert Huys , Peter Kampfer , Marc Vancanneyt , Renata Coopman , Paul Janssen , a Karel Kersters a Laboratorium voor Microbiologie, Universiteit Gent, K.L. Ledeganckstr. 35, 9000 Ghent, Belgium b ¨ ¨ Institut f ur Angewandte Mikrobiologie, Justus-Liebig-Universitat Giessen, Senckenbergstr. 3, 35390 Giessen, Germany Received 14 October 1996; revised 25 November 1996; accepted 2 December 1996 Abstract A total of 30 genotypically-characterized Aeromonas strains, encompassing DNA hybridization groups (HGs) 1, 2, 3 (A. hydrophila), 4, 5A (A. caviae), and 8 (A. veronii biogroup sobria), were cultivated on two different media, nutrient-rich trypticase soy agar (TSA) and nutrient-poor R2A medium, and their fatty acid methyl esters (FAMEs) were analyzed using an automated gas–liquid chromatographic system. A comparison of the respective HG-specific FAME compositions revealed that the difference in nutritional value of both media induced a pronounced quantitative effect on the overall branched-chain fatty acid (BFA) content. Strains grown on TSA medium generally produced significant amounts of the BFAs 13:0 iso, 15:0 iso, 15:0 iso 3OH, iso 17:1 v9c, and 17:0 iso, whereas these BFAs were detected in much lower concentrations or even were absent in R2A cultures. To compensate for this depletion, strains cultivated on R2A agar produced higher amounts of the major fatty acids 16:1 v7c and 16:0. The consequences of the observed medium-dependent shift in fatty acid production for the chemotaxonomic differentiation of HGs in Aeromonas were determined by constructing a similarity matrix from the mean FAME library entries and by multivariate grouping via principal components analysis. Results obtained from both mathematical approaches clearly demonstrated a higher resolving power of the TSA medium for the distinction of the six Aeromonas HGs examined in this study. In conclusion, when a standardized FAME protocol needs to be designed for taxonomic purposes, we recommend a thorough evaluation of the influence of the growth medium on bacterial fatty acid composition.  1997 Elsevier Science B.V. Keywords: Aeromonas; Chemotaxonomy; Fatty acid composition; Growth medium 1. Introduction microbial flora in various types of fresh water environments [1–3] but can also be found frequently Aeromonads constitute a substantial part of the in foods [4,5] or clinical specimens [6–8]. These organisms are widely recognized as the causative * agents for a large spectrum of septicemic diseases in Corresponding author. Tel.: 132 9 2645121; fax: 132 9 2645346; e-mail: geert.huys@rug.ac.be cold-blooded animals [9–11], and extensive clinical 0167-7012 / 97 / $17.00  1997 Elsevier Science B.V. All rights reserved PII S0167-7012(96)00969-4