Psychrotrophic Growth of Microorganisms in a Cultured Milk Product.

Characterization of psychrotrophic bacteria from cultured milk has shown that most (72%) of the psychrotrophs which were isolated originated from the starter culture. Streptococcus lactis subsp. diacetilactis was the most abundant organism and dominated both Streptococcus cremoris and Leuconostoc cremoris , which was the least abundant. The doubling time of S. lactis subsp. diacetilactis at 7 C was 20 h and 54 h in Trypticase Soy Broth at pH 7.0 and 5.0, respectively. This indicates a growth potential which could be significant to the quality of the product over a long storage period. Psychrotrophic coliforms which had optimal growth temperatures within the range of 15 to 30 C could also be found in small numbers. Their survival in the product was limited and it was concluded that they have little effect on shelf-life.

High levels of microbial contamination of vegetables irrigated with wastewater by the drip method.

The public health aspects of the use of wastewater in agriculture and the effects of the drip irrigation method on the contamination of vegetables were studied. The method used was to simulate enteric microorganisms' dissemination by contaminated irrigation water in the field. The vegetables were irrigated with an effluent inoculated with a high titer of traceable microorganisms: poliovirus vaccine and a drug-resistant Escherichia coli. The dissemination of the marker organisms in the field was followed, and the effects of certain manipulations of the drip irrigation method on the contamination of the crops by the effluent were examined. It was shown that drip irrigation under plastic sheet cover with the drip lines placed either on the soil surface or buried at a depth of 10 cm significantly reduced crop contamination from inoculated irrigation water even when massive doses of bacteria and viruses were used. The microbial contamination was found to persist in the irrigation pipes and in the soil for at least 8 and 18 days, respectively. The data indicate that the recovery of the marker organisms was affected by soil texture and environmental conditions.

Microbial Contamination of Vegetables Irrigated with Sewage Effluent by the Drip Method.

The effect of the drip irrigation method on microbial contamination of vegetables irrigated with wastewater was evaluated. The density of microbial contamination on surfaces of cucumbers and eggplants irrigated with sewage effluent was determined, using a controlled washing procedure. The fecal coliform count on vegetables irrigated with wastewater was 38-fold higher than on vegetables irrigated with fresh water. However, agrotechnical manipulations of the drip method, such as sub-irrigation or covering the soil and the drip lines with plastic sheets, reduced bacterial contamination considerably. Similarly, the bacterial contamination on vegetables which were irrigated with sewage effluent during the first stage of growth (up to flowering) and subsequently with fresh water was not different from the contamination on vegetables which were irrigated with fresh water. The viral contamination on 27 vegetable samples which were collected from sewage irrigated experimental plots was below the level of detection. It is proposed that the drip method may be considered for wastewater irrigation of crops in accordance with generally accepted public health criteria.

Extracellular nuclease activity of fish spoilage bacteria, fish pathogens, and related species.

The production of extracellular deoxyribonuclease and ribonuclease by 23 marine and 3 dairy strains of Pseudomonas putrefaciens, 15 strains of fish-pathogenic fluorescent pseudomonads, 38 strains of fluorescent pseudomonads isolated from haddock, and 34 related organisms was determined by an agar plate method. All strains of P. putrefaciens produced both deoxyribonuclease and ribonuclease. Of the other 87 organisms examined, 26.5% produced ribonuclease and 14.5% produced deoxyribonuclease. All organisms which produced deoxyribonuclease also produced ribonuclease. Deoxyribonuclease production by P. putrefaciens is suggested as a useful criterion of identity for members of this intense fish spoilage species.