The plea made many years ago (27) to replace the ill-defined coli-aerogenes (‘coliform’) bacteria as indicator organisms in foods processed for safety with the Enterobacteriaceae which are taxonomically accurately defined and as a rule more abundant has of late been more generally accepted. This called for development of a rigorously standardized formula for violet red bile glucose agar and for assessment of the optimal incubation temperature. Four reference strains of Enterobacteriaceae. 120 samples of minced meat and 100 samples of frozen broiler chickens were used in these studies. Considerable differences in the performance of commercially available dried formulae, when used as poured plates were observed. These applied both to productivity and to the type of colony produced by a given pure culture. As expected, replacement of lactose plus glucose by an equimolar amount of glucose did not influence the performance of the medium. Intrinsic toxicity of some batches of medium to non-stressed Enterobacteriaceae appeared to be mainly responsible for substandard performance. It could be overcome by careful selection of the preparations of crystal violet and particularly the bile salts (39) used in the formulae. Incubation at 30 C led to higher confirmed colony counts in minced meat than at 37 C. However, incubation temperature did not greatly influence similar counts in broiler drip. This observation could be substantiated by identification of the types of Enterobacteriaceae isolated from the two commodities. Psychrotrophic species predominated in minced meats, which are often made from raw materials stored for some time under refrigeration, whereas mesophilic species were in the majority on frozen broilers, which are generally frozen shortly after slaughter.

Nine pure cultures of species of Enterobacteriaceae were stressed by rapid freezing in tryptone soya broth (TSB) to — 22°C and subsequent storage at that temperature for 7 d. About one to two log cycles kill and at least one additional log cycle sublethal impairment was achieved. Numbers of colonies of these cultures in poured plates of violet red bile glucose (VRBG) agar, with 67 u/ml of catalase added at 47°C, were only slightly higher than those in plain VRBG, both incubated overnight at 30°C. Two hours incubation of TSB suspensions at 17–25° C resulted in almost complete restoration of the ability of cells to develop colonies in VRBG, without, however, leading to any significant multiplication. Similar experiments with 32 samples of frozen minced meat, 27 samples of frozen surface water, 18 of frozen chicken liver and 14 of fresh sausage substantiated the results obtained in the studies on pure cultures. In the experiments with the nine pure cultures the influence of the nutrient composition of the solid enumeration media: ‘minimal’ agar, TSB agar (TSBA) and Mueller‐Hinton agar with Polyvitex nutrient supplement (MHA), on the recovery of Enterobacteriaceae stressed by freezing was also studied. Colony numbers in TSBA and MHA were virtually identical. The glucose mineral salts medium led to lower recovery, indicating that so‐called ‘minimal medium recovery’ of stressed bacterial populations is not a common phenomenon.

Some selective culture media, prepared from commercially available dried preparations function poorly, and the same applies to an occasional non‐selective culture medium. This calls for systematic monitoring of media before they are used in actual diagnostic work. Classic plating or dilution‐to‐extinction techniques are often found too cumbersome. Hence a simple streaking technique (‘ecometric’ evaluation) was developed earlier for this purpose. It was subsequently simplified further and its accuracy and precision were assessed in this study. After it had been found that the simplified ecometric procedure allowed a reasonably accurate analysis of the selective and productive properties of media, it was used to evaluate 16 selective media, currently used in food microbiology. Results obtained agreed well with observations on the functioning made during routine examination of various foods. Finally an attempt was made to assess whether ecographic inoculation would allow the study of micro‐organisms under repressive conditions, particularly refrigeration temperature. It appeared that this was indeed possible.

A simple method for the detection of Pseudomonas aeruginosa in bottled water and aqueous pharmaceutical and cosmetic preparations is described. Subsequent to enrichment in Thom et al.'s (1971) nitrofurantoin broth at 42 °C, streaking positive cultures on to King et al.'s (1954) agar with nitrofurantoin added and incubating at 42 °C. Stabbing colonies into single, three 2 cm layer tubes (violet red bile dextrose agar/plain agar/SIM medium) and identifying strains by their non‐fermentative attack on glucose, motility, oxidase reaction and failure to produce H2S or indole.