2,308 research outputs found
Serratia plymuthica dairy industry isolates and their antimicrobial metabolites impact on pathogens
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
The effects of a biocide and a surfactant on the detachment of Pseudomonas fluorescens from glass surfaces
Application of antimicrobial chemicals is a general procedure in the cleaning and disinfection of food-contacting surfaces. Adhesion to glass surfaces and chemically induced detachment of Pseudomonas fluorescens ATCC 13525T were studied in situ, under flow conditions, in a well-controlled parallel plate flow chamber (PPFC). Ortho-phthalaldehyde (OPA) and cetyltrimethyl ammonium bromide (CTAB) were applied separately, at several concentrations, to attached bacteria and their subsequent detachment was monitored. Following treatments the remaining adhered bacteria were characterized in terms of viability and cell size. Simultaneously, the planktonic cell surface was characterized in order to correlate PPFC results with thermodynamic approaches for adhesion evaluation, and surface free energy of chemically treated cells with adhesion strength. About 2.8 Ă 106 cells/cm2 adhered to the glass surface after 30 min of bacterial flow, although thermodynamic analyses evidenced unfavourable adhesion. The independent application of OPA and CTAB promoted bacterial detachment to a small extent (16% of total cells). The remaining adhering bacteria were totally non-viable for OPA â„ 0.75 mM and CTAB â„ 0.25 mM, showing a lack of correlation between bacterial viability and detachment. The cellular size decreased as attachment proceeded and with chemical treatment. Both chemicals altered the cell surface properties, increasing the cell-glass adhesion strength, and promoting the emergence of polar characteristics. The overall results emphasize that OPA and CTAB were markedly ineffective in removing glass-attached P. fluorescens, demonstrating that bacteria can be non-viable but remain strongly attached to the adhesion surface.Fundação para a CiĂȘncia e a Tecnologia (FCT) - Project CHEMBIO â POCI/BIO/61872/2004; SFRH/BD/
31661/2006; SFRH/BPD/20582/2004
Sodium dodecyl sulfate allows the persistence and recovery of biofilms of Pseudomonas fluorescens formed under different hydrodynamic conditions
The effect of the anionic surfactant sodium dodecyl sulfate (SDS) on Pseudomonas fluorescens biofilms was
investigated using flow cell reactors with stainless steel substrata, under turbulent (Re=5200) and laminar
(Re=2000) flow. Steady-state biofilms were exposed to SDS in single doses (0.5, 1, 3 and 7 mM) and biofilm
respiratory activity and mass measured at 0, 3, 7 and 12 h after the SDS application. The effect of SDS on biofilm
mechanical stability was assessed using a rotating bioreactor. Whilst high concentrations (7 mM) of SDS promoted
significant biofilm inactivation, it did not significantly reduce biofouling. Turbulent and laminar flow-generated
biofilms had comparable susceptibility to SDS application. Following SDS exposure, biofilms rapidly recovered over
the following 12 h, achieving higher respiratory activity values than before treatment. This phenomenon of posttreatment
recovery was more pronounced for turbulent flow-generated biofilms, with an increase in SDS
concentration. The mechanical stability of the biofilms increased with surfactant application, except for SDS
concentrations near the critical micellar concentration, as measured by biofilm removal due to an increase in external
shear stress forces. The data suggest that although SDS exerts antimicrobial action against P. fluorescens biofilms,
even if only partial and reversible, it had only limited antifouling efficacy, increasing biofilm mechanical stability at
low concentrations and allowing significant and rapid recovery of turbulent flow-generated biofilms.Fundação para a CiĂȘncia e a Tecnologia (FCT
Influence of biofilm composition on the resistance to detachment
Bacillus cereus and Pseudomonas fluorescens were used to develop monoculture biofilms in a bioreactor rotating system using a stainless steel cylinder for biofilm formation. The biofilms were allowed to
grow for 7 days, exposed continuously to a Reynolds number of agitation (ReA) of 2,400. Afterwards, the biofilms were characterised in terms of respiratory activity, amount of biomass, cellular density, cellular size
and total and extracellular proteins and polysaccharides. The biofilm mechanical stability was assessed by sequential submission of the biofilms to increasing ReA, respectively, 4,000, 8,100, 12,100 and 16,100.
The results showed that P. fluorescens biofilms were five times more active, had a higher amount of biomass, cellular density, a reduced cellular size and a four-fold higher amount of extracellular proteins and
polysaccharides than B. cereus biofilms. The application of shear stress forces higher than the one under which the biofilm was formed (ReA Œ 2,400) caused biomass removal. The high percentage of removal occurred with the implementation of a ReA of 8,100 for both B. cereus and P. fluorescens biofilms.
The total series of ReA did not give rise to total biofilm removal, as only about 76% of P. fluorescens biofilm mass and 53% of B. cereus biofilm mass were detached from the cylinders. This latter result evidences that B. cereus had a higher mechanical stability than P. fluorescens biofilms. The overall results
demonstrate that P. fluorescens and B. cereus formed physiologically distinct biofilms, B. cereus biofilms mainly being constituted by cells and P. fluorescens biofilms largely constituted by extracellular proteins and polysaccharides. B. cereus biofilms had a substantially higher mechanical stability than P. fluorescens biofilms.IBQF
Portuguese Foundation for Science and Technology
Dirac and Majorana heavy neutrinos at LEP II
The possibility of detecting single heavy Dirac and Majorana neutrinos at LEP
II is investigated for heavy neutrino masses in the range . We study the process as a clear signature for heavy neutrinos. Numerical estimates for
cross sections and distributions for the signal and the background are
calculated and a Monte Carlo reconstruction of final state particles after
hadronization is presented.Comment: 4 pages, 8 figure
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