Background and aims: Phenotypical differences from interstrain variability is a known phenomenon,
assessed in this study for V4 and Y S. plymuthica isolates, particularly at antimicrobial metabolites
production and effect on pathogens biofilms.
Methods: Isolates were biochemically characterized, specific growth rates in Tryptic Soy/Skim Milk
Broth determined, and the antimicrobial activity of cell-free spent media tested on Staphylococcus aureus,
Staphylococcus epidermidis, Pseudomonas aeruginosa, Bacillus cereus and Escherichia coli lawns. Their
biofilm removal capacity was assessed on 24h pathogens biofilms, through 30min treatments, and biofilm
formation impairment ability by 10min substratum pre-conditioning.
Results: These siderophores and quorum-sensing inhibitors releasers isolates showed different protease
expression and growth rates in both media. Droplets of isolates cell-free spent TSB presented positive
inhibitory capacity. V4-SMB biofilms had equal mass and specific respiratory activity values, while low
mass Y biofilms were extremely active. Its biofilms in TSB showed the opposite, being V4 biofilms
particularly metabolically active and thicker.
All cell-free SMB/TSB supernatants pre-conditioning led to a steep reduction of the respiratory activity of
S. aureus, E. coli and S. epidermidis biofilms later formed, though increasing their mass. Biofilms
treatment with any supernatant similarly decreased their mass. L. monocytogenes, was particularly affect
by all, S.aureus by TSB/SMB V4-spent, and S. epidermidis by SMB V4-spent.
Conclusions: S. plymuthica isolates registered different biofilm formation ability and cell-free spent
TSB/SMB antimicrobial activity. An understanding of mechanisms underlying antimicrobials actionmode
in single/mixed Gram positive/negative species biofilms is sought
