Inducible Gene Expression by Nonculturable Bacteria in Milk after Pasteurization
AUTOR(ES)
Gunasekera, Thusitha S.
FONTE
American Society for Microbiology
RESUMO
The viability of bacteria in milk after heat treatments was assessed by using three different viability indicators: (i) CFU on plate count agar, (ii) de novo expression of a gfp reporter gene, and (iii) membrane integrity based on propidium iodide exclusion. In commercially available pasteurized milk, direct viable counts, based on dye exclusion, were significantly (P < 0.05) higher than viable cell counts determined from CFU, suggesting that a significant subpopulation of cells in pasteurized milk are viable but nonculturable. Heating milk at 63.5°C for 30 min resulted in a >4-log-unit reduction in the number of CFU of Escherichia coli and Pseudomonas putida that were marked with lac-inducible gfp. However, the reduction in the number of gfp-expressing cells of both organisms under the same conditions was <2.5 log units. These results demonstrate that a substantial portion of cells rendered incapable of forming colonies by heat treatment are metabolically active and are able to transcribe and translate genes de novo.
