Automated Impedance Measurements for Rapid Screening of Milk Microbial Content.

Methods for the direct and indirect assessment of the bacterial content of milk

Effect of diluent type on viability of yeasts enumerated from foods or pure culture.

Evaluation of the Stomacher for Preparation of Food Homogenates.

Aims: To investigate the influence of suspension media on the survival of Escherichia coli M23 exposed to nonthermal, lethal stresses.



Methods and Results:  Populations of E. coli M23 suspended in minimal medium (MM) or in different nutrient-rich broths were exposed to water activity 0·90 and/or pH 3·5 and inactivation was determined by culture-based enumeration. In response to the osmotic or acid challenges, E. coli M23 displayed enhanced survival in MM rather than in complex broth. That trend was reversed when populations were exposed to low water activity in combination with low pH. Comparison of microbial survival in three complex media indicated that even relatively small differences in composition influenced inactivation. In most media the combination of lethal stresses resulted in a synergism, which enhanced bacterial inactivation; however, an exception (tryptone soya broth) was observed.



Conclusions:  The suspension medium strongly influences the inactivation of E. coli M23 by osmotic and/or acid stresses. This should be considered when comparing studies of microbial survival that use different media and when broth-derived data are intended to represent specific environments (e.g. food matrices).



Significance and Impact of the Study:  The specific effects of synthetic media need to be appreciated when studying bacterial inactivation in conditions relevant to food-manufacturing regimes.

https://sfamjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1472-765X.2006.01993.x

Effect of suspension media on nonthermal inactivation of Escherichia coli.

A comparison was made between Butterfield's buffered phosphate solution. 0.1% peptone in distilled water. 0.5% peptone in distilled water, 0.85% NaCl in distilled water, and pure distilled water as diluents for total bacterial counts of 28 different food samples. Plates were incubated at 35 and 22 C for 2 and 5 days, respectively. Butterfield's diluent afforded the highest overall mean count for most samples regardless of the incubation temperature. Highest counts occurred with all diluents at 22 C. Although Butterfield's diluent. 0.1% peptone, and 0.5% peptone appeared to yield higher counts for most samples than did distilled water or 0.85% NaCl, statistically the mean counts obtained for the live diluents used were not significantly different from each other. It appears that no single diluent is suited for every possible sample type.

J. L. Oblinger

Papers

Evaluation of Diluents Used for Total Counts1