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

Dao's question on the asymptotic behaviour of fullness

For a local ring (R, \M) of infinite residue field and positive depth, we address the question raised by H. Dao on how to control the asymptotic behaviour of the \M-full, full, and weakly \M-full properties of certain ideals (such notions were first investigated by D. Rees and J. Watanabe), by means of bounding appropriate numbers which express such behaviour. We establish upper bounds, and in certain cases even formulas for such invariants. The main tools used in our results are reduction numbers along with Ratliff-Rush closure of ideals, and also the Castelnuovo-Mumford regularity of the Rees algebra of \M.Comment: 11 pages. Submitted for publicatio

Tensor products and solutions to two homological conjectures for Ulrich modules

We address the problem of when the tensor product of two finitely generated modules over a Cohen-Macaulay local ring is Ulrich in the generalized sense of Goto et al., and in particular in the original sense from the 80's. As applications, besides freeness criteria for modules, characterizations of complete intersections, and an Ulrich-based approach to the long-standing Berger's conjecture, we show that two celebrated homological conjectures, namely the Auslander-Reiten and the Huneke-Wiegand problems, are true for the class of Ulrich modules.Comment: 12 page

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 ¼ 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

Enterobactin : like siderophore gene cluster induction in Cronobacter sakazakii strain

Species belonging to the recently described Cronobacter genus, include several opportunistic foodborne pathogens. These pathogens are capable of causing severe infections in neonates, such as meningitis, septicaemia and necrotizing enterocolitis. Bacterial virulence has been previously correlated with ferric iron acquisition systems. It is known that all plasmid-harbouring Cronobacter species produce an active aerobactin-like siderophore (cronobactin) and the chromosome also contains genes encoding an enterobactin-like siderophore whose production has not been detected so far. Nevertheless it has been determined that, in vivo, enterobactin is upregulated in iron limiting conditions. This work aims to demonstrate that the cluster encoding for the enterobactin-like siderophore synthesis is functional and responsible for the molecule synthesis. To stimulate enterobactin production, the strain used grown in an optimized medium under particular conditions. Overall, siderophore production was detected by using Chrome Azurol S (CAS) indicator solution. A bioinformatic analysis was carried out to identify and annotate the genes in the enterobactin clusters. Genes predicted to be involved in the biosynthesis were mutated by performing Campbell insertions. Enterobactin presence/absence in the wild type and mutant strains, was determined by High Performance Liquid Chromatography. Simultaneously genome analysis showed that some Cronobacter/Enterobacter strains shared iron-siderophore complex receptors, an indicator of the ability to uptake siderophores from unrelated species. This capacity was tested by cross-feeding assays in CAS agar. Results showed that the cluster encoding for the enterobactin-like siderophore is indeed functional and that this molecule might be utilized by other Cronobacter/Enterobacter species

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 × 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 ≥ 0.75 mM and CTAB ≥ 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 Ciência e a Tecnologia (FCT) - Project CHEMBIO – POCI/BIO/61872/2004; SFRH/BD/ 31661/2006; SFRH/BPD/20582/2004