A synthetic culture medium evaluated for detection of coliform bacteria in tomato paprika

Abstract

A simple selective and differentiating synthetic medium (X broth) that is easy to prepare was developed in liquid form for the selective cultivation of coliform bacteria from foodstuffs. This synthetic medium contains an ammonium salt as nitrogen source, lactose as carbon source, and buffers but is free of inhibitors. Its selectivity is based on the fact that coliform bacteria are able to grow if the minimal medium consists of simple inorganic substances as nitrogen sources and lactose as carbon supply. The selectivity of this medium was tested by the inoculation of pure cultures of different microbes belonging to the genera of Staphylococcus, Bacillus, and Pseudomonas and the family Enterobacteriaceae and was found to be complete in this range. The applicability of the synthetic medium was also tested by a nationwide round of tests, using quick-frozen tomato paprika. The selectivity of X broth proved essentially better than that of the standard brilliant green–bile–lactose broth. The results of nationwide tests of coliform bacteria determination demonstrated that there was no difference in reproducibility, but the comparability was significantly better when X broth was used. The advantages of the new synthetic medium are the standard composition, the absence of inhibitors, the reliability, the long keeping quality and the low costs.