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

Abstract

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: 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.

Pseudomonas spp. and Serratia liquefaciens as Predominant Spoilers in Cold Raw Milk

“…Serratia spp. were also detected in raw milk samples stored at 4 °C for 24 h (Lafarge and others ), in bulk tank milk (Decimo and others ) and in a milk‐processing plant (Cleto and others ), but these authors did not evaluate the capacity of heat‐resistant proteolytic enzymes production of Serratia isolates. Teh and others (), in addition to isolating S. liquefaciens from internal surfaces of raw milk road tankers, also showed that this species may produce heat‐resistant proteolytic enzymes.…”

Transcriptomic analysis of the response of Pseudomonas fluorescens to epigallocatechin gallate by RNA-seq

“…Due to its extreme adaptability, versatility and ability to replicate at refrigeration temperatures, long periods of shelf life can easily lead to increased P . fluorescens concentration in food products [4, 32]. Genome-wide transcriptomic analysis is an effective method in studying adaptive responses to the environment by identifying and linking associated transcriptional perturbations.…”

A genomic and transcriptomic approach to investigate the blue pigment phenotype in Pseudomonas fluorescens

“…fluorescens is commonly part of the microflora of a wide range of food matrices, including ready-to-eat vegetables (Caldera and Franzetti, 2014), raw fish (especially sushi or sashimi), meat and dairy products (Arnaut-Rollier et al, 1999;Franzetti and Scarpellini, 2007). This is due to its extreme adaptability and versatility (Silby et al, 2011) and its ability to replicate at refrigeration temperatures (Decimo et al, 2014). Specifically, P. fluorescens can cause undesirable modifications in food products as a result of enzymatic reactions or pigmented molecule production (Andreani et al, 2014).…”