Modification of the bile salts - Irgasan - brilliant green agar for enumeration of Aeromonas species from food

The present study evaluated the productivity of BIBG medium for the isolati on of Aeromonas spp. from food and describes a modification of the BIBG med ium (mBIBG) (increased pH (8.7), replacement of xylose by soluble starch as a carbon source, decreased concentration of bile salts) to increase its se lectivity and electivity. Using the mBIBG medium, growth of the majority of the Enterobacteriaceae (9/10) was suppressed except for Citrobacter freund ii. The mBIBG medium supported growth of Pseudomonas species but a clear di stinction between Aeromonas and Pseudomonas colonies could be made. Interpr etation of the mBIBG medium should be performed after 24 h of incubation. I t was noted that three of the 27 Aeromonas strains tested did not develop o n the mBIBG medium. The ability or inability to grow on a selective medium is strain-dependent. Enumeration of Aeromonas species (A. hydrophila LMG 37 71, A. caviae LMG 3775, A. veronii biovar veronii LMG 9075, A. veronii biov ar sobria LMG 13071) from artificially contaminated foods (shrimp, minced m eat (beef/pork), precut leek, and shredded carrots) confirmed that the mBIB G medium is suitable for quantitative recovery of aeromonads (ca. 10(2)-10( 7) cfu/g) in the presence of a high background flora (10(5)-10(6) cfu/g). S creening of naturally contaminated foods (vegetables, seafood, meat) for th e presence of Aeromonas resulted in three out of 14 food samples showing pr esumptive Aeromonas colonies on mBIBG. (C) 2000 Elsevier Science B.V. All r ights reserved.