Catalase

Biochemical characteristics of the strains were investigated using API ZYM, 20A and 50CH strips (BioMérieux) according to the manufacturer's instructions. A 20‐min‐thermic shock of fresh colonies at 80°C was done in order to test sporulation. Catalase (BioMerieux) activity was determined in 3% hydrogen peroxide solution and oxidase activity was assessed using an oxidase reagent (Becton‐Dickinson).
Cellular fatty acid methyl ester (FAME) analysis was performed by gas chromatography/mass spectrometry (GC/MS). Two samples were prepared with approximately 17 mg of bacterial biomass per tube for strain Marseille‐P2849^T and 5 mg per tube for strain Marseille‐P3277^T. Briefly, fatty acid methyl esters were separated using an Elite 5‐MS column and monitored by mass spectrometry (Clarus 500—SQ 8 S, Perkin Elmer, Courtaboeuf, France) as previously described (Dione et al., 2016). Spectral database search was performed using MS Search 2.0 operated with the Standard Reference Database 1A (NIST, Gaithersburg, USA) and the FAMEs mass spectral database (Wiley, Chichester, UK).
Antibiotic susceptibility was tested using the E test gradient strip method (BioMerieux) to determine the minimal inhibitory concentration (MIC) of each tested antibiotic on blood Colombia agar media (BioMerieux, France).

The L. plantarum strain previously isolated in the Applied and Environmental Microbiology Research Group was preserved in cryovials Cryioinstant (Ref: 409113/6, Deltalab S.L., Spain) in the − 80 °C freezer. The microorganism was recovered by incubating two porous beads in 30 mL of MRS broth (Ref: BK070HA, Biokar Diagnostics, France) for 24 h at 37 °C in aerobic environment.
After the incubation period, a serial dilution was prepared up to the concentration of 10^–8. From the dilution bank, MRS agar (Ref: BK089HA, Biokar Diagnostics, Francia) was seeded to establish the concentration of the microorganism and a blood agar (Ref: 254005, Becton Dickinson, Germany) was also seeded to evaluate its possible hemolytic capacity. Plates were incubated at 37 °C for 24 h, in aerobic environment.
So, to corroborate the absence of contamination throughout the preservation period, the strain was identified by phenotypic and molecular tests.
The tests carried out for phenotypical identification were Gram stain, spore stain and enzymatic tests of Catalase and Oxidase (Ref: 55 635, bioMérieux SA, France). The methodologies used have been the traditional in Microbiology¹⁶ .
Then, an API 50 CH gallery (Ref: 50 300, bioMérieux SA, France) was inoculated with API 50 CHL Medium (Ref: 50 410, bioMérieux SA, France) to corroborate the identification of the strain.