A NOVEL, SELECTIVE SYNTHETIC ACETAMIDE CONTAINING CULTURE-MEDIUM FOR ISOLATING PSEUDOMONAS-AERUGINOSA FROM MILK

A selective synthetic medium has been developed both in liquid (Z-brot h) and solid (Z-agar) forms for selective isolation of Pseudomonas aer uginosa from foods. The simple, easy to prepare peptone-free synthetic medium contained acetamide that is metabolized to ammonia and acetic acid providing nitrogen and carbon supply. The medium contained no inh ibitors. Selectivity of the liquid medium was tested by inoculation of pure cultures of different bacteria belonging to the groups Bacillus, Pseudomonas, Enterobacteriaceae and Staphylococcus. It was found that the selectivity of the medium was complete for the examined range of bacteria. However, a similar result was obtained when nitrofurantoin b roth was used. Applicability of the synthetic agar medium was also tes ted by a nation-wide inter-laboratory test using two milk samples cont aining 10(3)/ml (sample I) and 10(5)/ml (sample II) Pseudomonas aerugi nosa. According to this test, no microbiologically relevant difference s were found between the results obtained by Z-agar and cetrimide-agar a frequently used selective agar in case of sample II. However, a rel evant and statistically significant difference was found in the result s of sample I in favour of the Z-agar, that could indicate the presenc e of a low number of bacteria. Concerning repeatability and reproducib ility, Z-agar proved to be superior to cetrimide agar. (C) 1998 Elsevi er Science B.V. All rights reserved.