peptones and dicloran

A collaborative study was made to evaluate the effectivity of a general purpose medium, tryptone glucose yeast extract (TGY) agar on the detection and enumeration of yeasts from food. Nine laboratories participated in the study and compared five media (four kinds of TGY with different concentrations of glucose, one of them without tryptone, and, for comparison, dichloran rose bengal chloramphenicol (DRBC) agar). Six food samples were investigated by each laboratory and 23 additional food samples were investigated individually by different laboratories. No difference was found in the performance of media with either the samples common to all laboratories or the various samples tested in different ones. A medium consisting of tryptone, glucose and yeast extract, at any concentration of glucose tested, appeared reliable for the detection and enumeration of yeasts from foods, and its performance did not differ from that of DRBC. Omission of tryptone as recommended by ISO provided an even simpler medium of equally good performance. TGY without chloramphenicol may result in higher total counts due to the development of bacteria. DRBC incubated in light results in lower counts compared to that incubated in the dark.

Topics: Aniline Compounds; Chloramphenicol; Colony Count, Microbial; Culture Media; Fluorescent Dyes; Food Microbiology; Fungicides, Industrial; Glucose; Peptones; Reproducibility of Results; Rose Bengal; Yeasts

At the Second International Workshop on Standardisation of Methods for the Mycological Examination of Foods in Baarn, 1990, three selective media for food-borne Fusarium species were recommended: Czapek-Dox Iprodione Dichloran Agar (CZID), Dichloran Chloramphenicol Peptone agar (DCPA) and Pentachloronitrobenzene Peptone agar (PPA). Lack of sufficient data made it impossible to recommend one Fusarium selective medium. In the present study nine laboratories from seven countries compared CZID, DCPA, and PPA by analysing 10 samples of flour spiked with conidia of Fusarium avenaceum and F. verticillioides (= F. moniliforme). The colony forming units were counted. The total counts on each of the three media were within a similar range for each participant, and no significant differences between the three media were evident. However, the development of Fusarium colonies was quite different on the three media, and most collaborators found it possible to differentiate these Fusarium species by pigmentation on CZID. Pigmentation was much less conspicuous on PPA, and inconspicuous in DCPA cultures. CZID is recommended as the best currently available selective medium for Fusarium isolates from foods.

Topics: Aminoimidazole Carboxamide; Aniline Compounds; Chloramphenicol; Colony Count, Microbial; Culture Media; Food Microbiology; Fungicides, Industrial; Fusarium; Hydantoins; Nitrobenzenes; Peptones; Reproducibility of Results

A selective medium containing 2 micrograms of dichloran per ml, 200 micrograms of chloramphenicol per ml, and 1.5% bacteriological peptone was developed for the isolation of Fusarium species and dematiaceous hyphomycetes from cereals. The medium, designated DCPA, was shown to select against species of Aspergillus, Penicillium, Cladosporium, and mucoraceous fungi. DCPA was evaluated for use as an enumeration medium and compared satisfactorily with dichloran-rose bengal-chloramphenicol agar when both media were tested with a range of cereal samples. Fusarium species and dematiaceous hyphomycetes produced well-formed colonies with good conidial production on DCPA, permitting rapid identification of such isolates on this medium.

Topics: Aniline Compounds; Animal Feed; Aspergillus; Chloramphenicol; Cladosporium; Culture Media; Edible Grain; Food Microbiology; Fusarium; Magnesium Sulfate; Mitosporic Fungi; Penicillium; Peptones