Volume 79, Issue 10 p. M2081-M2090
M: Food Microbiology & Safety

Characterization of Gram-Negative Psychrotrophic Bacteria isolated from Italian Bulk Tank Milk

Marilù Decimo

Corresponding Author

Marilù Decimo

Inst. of Sciences of Food Production, Italian Natl. Research Council, Via Celoria 2, 20133 Milan, Italy

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Stefano Morandi

Stefano Morandi

Inst. of Sciences of Food Production, Italian Natl. Research Council, Via Celoria 2, 20133 Milan, Italy

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Tiziana Silvetti

Tiziana Silvetti

Inst. of Sciences of Food Production, Italian Natl. Research Council, Via Celoria 2, 20133 Milan, Italy

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Milena Brasca

Milena Brasca

Inst. of Sciences of Food Production, Italian Natl. Research Council, Via Celoria 2, 20133 Milan, Italy

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First published: 15 September 2014
Citations: 67

Abstract

en

Eighty psychrotrophic bacterial strains, isolated from different northwest Italian bulk tank milks destined for Grana Padano cheese production, were identified by 16S rRNA gene amplification and partial sequence analysis of the rpoB gene. Pseudomonas spp. were the most commonly occurring contaminants, P. fluorescens being the predominant isolated species, along with Enterobacteriaceae, primarily Serratia marcescens. RAPD-PCR was used to study genetic variability and distinguish closely related strains; a high degree of genetic heterogeneity among the strains was highlighted. All the strains were characterized for their ability to produce proteases, lipases and lecithinases at different temperatures (7, 22, and 30 °C). Forty-one of the psychrotrophic strains were positive for all the enzymatic activities. The highest number of positive strains for all the incubation temperatures was found for lipolytic activity (59), followed by proteolytic (31) and lecithinase (28) activities, and the enzymatic traits varied among the Pseudomonas and Enterobacteriaceae strains. The proteolytic psychrotrophic strains were screened for the presence of the aprX gene, coding for a heat-resistant metalloprotease in Pseudomonas spp. The aprX gene was detected in 19 of 63 Pseudomonas strains, and was widespread in the P. fluorescens strains (14/19).

Pratical Application

pt

The study provides new data on the enzymatic activity of Gram-negative psychrotrophic bacteria, useful in developing strategies to control the proteo-lipolytic spoilage of raw and processed milk that causes gelation, off-flavors, and loss of sensory quality and shelf life.