Tracking the blue: A MLST approach to characterise the Pseudomonas fluorescens group

• Published in: Food microbiology 2014-05, Vol.39, p.116-126
• Main Authors: Andreani, N.A., Martino, M.E., Fasolato, L., Carraro, L., Montemurro, F., Mioni, R., Bordin, P., Cardazzo, B.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Blue mozzarella; Cheese - analysis; Cheese - microbiology; Food Contamination - analysis; Food industries; Food microbiology; Food spoilage; Fundamental and applied biological sciences. Psychology; Molecular Sequence Data; Multilocus Sequence Typing; Multilocus Sequence Typing - methods; Phylogeny; Pseudomonas fluorescens - classification; Pseudomonas fluorescens - genetics; Pseudomonas fluorescens - isolation & purification; Pseudomonas fluorescens group
• ISSN: 0740-0020; 1095-9998
• DOI: 10.1016/j.fm.2013.11.012

The Pseudomonas fluorescens group comprises several closely related species that are involved in food contamination and spoilage. Specifically, the interest in P. fluorescens as a spoiler of dairy products increased after the cases of “blue mozzarella” that occurred in Italy in 2010. A Multilocus Sequence Typing (MLST) scheme was developed and applied to characterise 136 isolates (reference strains and food borne isolates) at strain level, to reveal the genetic relationships among them and to disclose any possible genetic clustering of phenotypic markers involved in food spoilage (protease, lipase, lecithinase activities and pigmented or fluorescent molecule production). The production of dark blue diffusible pigment was evaluated on several bacterial culture media and directly on mozzarella cheese. The MLST scheme provided precise genotyping at the strain level, and the population analyses of the concatenated sequences allowed major taxa to be defined. This approach was revealed to be suitable for tracking the strains according to their origin, such as dairy plants or food matrices. The genetic analysis revealed the presence of a connection between the blue pigment production and a specific phylogenetic cluster. The development of the online database specific to the P. fluorescens group (http://pubmlst.org/pfluorescens) will facilitate the application of the scheme and the sharing of the data. •A MLST scheme and database were developed for Pseudomonas fluorescens.•5 phenotypic traits involved in spoilage were investigated.•The study highlighted a high heterogeneity between the strains of P. fluorescens.•The blue mozzarella causative strains belong to a single genetic cluster.•The MLST approach is applicable to track the strains involved in food spoilage.