Tese de doutoramento em "Chemical and Biological Engineering"; Candida species are opportunistic yeasts that colonize the human body. Among the more well known and more virulent is Candida albicans. Although for several years, until 1995, another species, Candida dubliniensis, was mismatched with that one. Both Candida species possess similar phenotypic and genotypic characteristics. As this species has not been fully studied, it became important to understand its behaviour and its properties. Candida dubliniensis is mainly found in the mouth of some HIV patients. So, its behaviour in the oral cavity was chosen as the objective of the present work.
The main goal of this work was the comparison of those two species in terms of the ability to adhere to inert surfaces and epithelial cells, to form biofilms and susceptibility to antifungal agents.
The characteristics and behaviours under concern were assayed in two strains of each species. Artificial saliva solution was used in order to simulate the oral conditions. Yeast cells and inert surfaces were characterized in terms of physico-chemical surface properties (surface tension parameters, degree of hydrophobicity and zeta potential) as well as elemental surface composition determined by X-ray Photoelectron Spectroscopy.
Adhesion to inert surfaces was assayed on acrylic...
A relatively novel biocide, ortho-phthalaldehyde (OPA), was tested to control biofilms formed by Pseudomonas fluorescens on stainless steel surfaces. The toxic action of OPA was assessed in terms of inactivation and removal of the biofilm by means of, respectively, the determination of the respiratory activity and the variation in the dry weight of the biofilms. For comparison, the activity of OPA against suspended bacteria was also evaluated. The results showed that higher concentrations of OPA and longer exposure
times are needed to inactivate P. fluorescens biofilms than planktonic populations, thus denoting that sessile bacteria have a reduced susceptibility to OPA. This appears to be associated with the reaction with the proteins of the matrix, as demonstrated by the reduction of the antimicrobial action of OPA in the presence of a protein (bovine serum albumin).
The application of OPA appeared to cause little effect in the removal of biofilms from the metal slides since the mass of biofilm that remained on the surfaces, after biocide treatment, was within the same range as those observed in the control tests. These results suggest that, with OPA application, biofilms can be inactivated but stay attached to the surfaces, decreasing thereby the success of the chemical treatment.; Instituto de Biotecnologia e Química Fina (IBQF).
Fundação para a Ciência e a Tecnologia (FCT) - POCTT/1999/BIO/35683.
A biofilm of Arthrobacter viscosus supported on granular activated carbon (GAC) removed between 100% and 50% of Pb (II) and between 100% and 30% of Fe (II) from solution with initial concentration between 8-85 mgPb 1ˉ¹ and 2.5-42 mgFe 1ˉ¹ and a flow residence time of 1.2 min. The maximum uptake capacities of the system biofilm/GAC ranged from 4.8 mgPb/gGAC to 24.2 mgPb/gGAC and 1.8 mgFe/gGAC to 18.4 mgFe/gGAC. The behaviour of granular activated carbon with two different surface treatments (treated with HNO3 or H2O2) was studied and best results were achieved with the support treated with HNO3. The polysaccharide and polymeric net was also studied, and it was concluded that the production of polysaccharides and polymers was much higher in the GAC-HNO3.; Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS/P/EQU/12017/1998.
The action of the cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), respectively, a cationic and an anionic surfactant were investigated to control mature biofilms formed under turbulent and laminar flow, by P.fluorescens. The sanitizer action of the surfactants on biofilms was assessed by means of respiratory activity and variation of biofilm mass, immediately, 3, 7 and 12 h after the treatment of the chemicals. The latter experimental times were
tested in order to assess the biofilm regrowth. The structure of the biofilms was assessed before and after surfactant treatment by SEM. The results showed that, laminar biofilms were more susceptible to the action of CTAB than those formed under turbulent flow. Concerning SDS, both
biofilms showed analogous susceptibility to the surfactants. However, total inactivation of the cells within the biofilms was not achieved for both types of biofilms. CTAB application by itself did not promoted the detachment of biofilms from the surface. Regarding SDS, higher concentrations
applied promoted significant biofilm inactivation. Turbulent and laminar flow had analogous
susceptibility to SDS application. However, SDS did not promoted the detachment of biofilms from
the metal surfaces. The structure of the biofilms was changed after the application of both
surfactants. It was found that after CTAB and SDS application...
A relatively novel antimicrobial agent, ortho-phtalaldehyde (OPA), was tested in the control of biofilms formed by
Pseudomonas fluorescens on stainless steel surfaces. The toxic action of OPA was assessed by means of activity tests and dry
weight of the biofilms. For comparative purposes, the activity of OPA against bacterial suspended cultures was also evaluated.
The results showed that concentrations of OPA higher than 15 mg L-1 inactivate the planktonic populations while having a
lower effect against the P. fluorecens biofilms. The inactivation of the biofilm was only attained with the higher OPA
concentrations (50 and 100 mg L-1) and for longer exposure times (3 h). The application of OPA appears to cause little effect in
the removal of biofilms from the metal slides since the amount of biofilm mass that remained on the surfaces, after biocide
treatment, stills to be very high and representative. These results suggest the fact that, with OPA application, biofilms can be
inactivated but stay attached to the surfaces, decreasing, by this way, the success of the chemical treatment.; Fundação para a Ciência e a Tecnologia (FCT), project POCTT/1999/BIO/35683.
This paper presents results obtained with biofilms formed under turbulent flow by a mixed suspension ofPseudomonas fluorescens and kaolin particles and compares them with biofilms formed in the absence of clay particles. The results show that the presence of kaolin particles leads to: higher accumulation of biomass in biofilm systems; higher stability of the biofilms when substrate is suppressed; higher values of the respiratory coefficient of the suspended cell cultures; increase in the mass transfer rates throughout the biofilm thickness. The results suggest that the kaolin particles enhance microbial activity in the biofilm and may cause changes in the physical structure of the biofilm, making it a more strong and open matrix.; Junta Nacional de Investigação Científica e Tecnológica (JNICT).
In this study a methodology was applied in order to ascertain the mechanical stability of biofilms, by using a stainlesssteel
(SS) rotating device immersed in a biological reactor where biofilms formed by Pseudomonas fluorescens were
allowed to grow for 7 days at a Reynolds number of agitation of 2400. The biofilms developed with this system were
characterised in terms of amount of total, extracellular and intracellular proteins and polysaccharides, amount of mass,
metabolic activity and mechanical stability, showing that the biofilms were active, had a high content of extracellular
constituents and an inherent mechanical stability. In order to assess the role of chemical agents on the mechanical
stability, the biofilms were exposed to chemical agents followed by mechanical treatments by submission to increase
Reynolds number of agitation. Seven different chemical agents were tested (two non-oxidising biocides, three
surfactants and two oxidising biocides) and their effects on the biofilm mechanical stability were evaluated. The increase
in the Reynolds number increased the biofilm removal, but total biofilm removal was not found for all the conditions
tested. For the experiment without chemical addition (only mechanical treatment)...
Simões, M.; Pereira, Maria Olívia; Correia, Alexandra; Sampaio, Paula; Pais, Célia; Vieira, M. J.
Fonte: American Society of MicrobilogyPublicador: American Society of Microbilogy
Tipo: Conferência ou Objeto de Conferência
Publicado em //2003ENG
Relevância na Pesquisa
From the assessment of the recovery capability of pseudomonas
fluorescens atcc 13525t after exposure to several glutaraldehyde (gta)
concentrations (100, 200 and 400 mg/l) and exposure times (1 and 2
hours), it was found that, for gta concentrations above 100 mg/l,
whatever the exposure time, bacterial cells presented different
growth patterns in solid media. after this statement, the recovered
cells were initially characterized using api ne20 strips and species
identification was obtained using the api database. the type culture
and the cells obtained after treatment with concentrations below
200 mg/l were identified as p. fluorescens. conversely, the identification
of cells exposed to higher concentrations of gta failed. the
electrophoretic profiles of both the type culture and the cells
exposed to gta were obtained by pcr, using the primer t3b. the
results showed identical profiles for the type culture and the cells
exposed to low gta concentrations, and a totally different pattern for
cells exposed to gta concentrations above 200 mg/l. sequencing of
the 16s rdna gene is under way in order to further clarify the
differences observed. the p. fluorescens atcc 13525 (used as control)
and the cells treated with 200 mg/l of gta during 2 hours were
selected for further studies. a comparative study was carried out
between the above referred cells in terms of morphological
In this study, a methodology is proposed to evaluate the mechanical stability of biofilms, by using a stainless steel rotating device where biofilms formed by Pseudomonas fluorescens were allowed to grow for 7 days at 300 rmp. Those biofilms were afterwards submitted to the joined action of chemical agents and mechanical cleaning. Two cationic surfactants (cetyltrimethyl ammonium bromide - CTAB and benzalkonium chloride - BC) were the agents tested. Mechanical cleaning was performed by the variation of the rotation speeds of the rotating device. The following conclusions can be drawn: the biofilm has an inherent mechanical stability; the increase in the rotation speed increased the biofilm removal, but total biofilm removal was not found for the surfactants. BC promoted the increase in the biofilm mechanical stability while CTAB promoted the weakening in the biofilm mechanical stability. From this study, it can be stated that the chemical treatment is far from being a tool that induces massive biofilm detachment and even the synergistic chemical and mechanical treatment did not promoted total biofilm removal.
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 d exposed continuously to a
Reynolds number of agitation (ReA) of 2400. Afterwards, the biofilms were characterized 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, 4000, 8100, 12100 and 16100. The results showed that P. fluorescens biofilms were 5 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 = 2400) caused biomass removal. The high percentage of removal occurred with the implementation of a ReA of 8100 for both B. cereus and P. fluorescens biofilms. The total series of ReA did not give rise to total biofilm removal, since 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 physiological distinct biofilms...
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...
The ability of a biofilm of Bacillus coagulans supported on granular activated carbon (GAC) to biosorb Cr(VI) was investigated in batch and
column studies so it may be applied to low metal concentration wastewater treatment. The quantification of polysaccharides and polymeric net
revealed a value of 9.19 mg/gbiosorbent for the polysaccharides and 75 mg/gbiosorbent, for the polymeric net. The results obtained with open systems
showed uptake values of 1.50, 1.98 and 5.34 mg/gbiosorbent, respectively, for initial concentrations of 10, 50 and 100 mg/L of Cr(VI). Column studies
performed with an industrial effluent showed values of Cr uptake of 0.090 mg/gbiosorbent, for an initial concentration of 4.2 mg/L. The presence of
functional groups on the cell wall surface of the biomass that may interact with the metal ion, was confirmed by FTIR. The equilibrium studies
in batch systems were described by Freundlich, Langmuir, Reddlich–Peterson, Dubinin–Radushkevich, Sips and Toth model isotherms. Best fit
was obtained with Toth model isotherm. Data from column studies were described by Adams–Bohart and Wolborska models. These models were
found suitable for describing the dynamic behaviour of the columns with respect to the inlet chromium concentration. The whole study showed
that the biofilm tested is very promising for the removal of Cr(VI) in industrial wastewater.; Fundação para a Ciência e a Tecnologia (FCT) - POCTI/QUI/44840/2002.; FEDER.
The aim of this work was to assess the feasibility of a Sequential Batch Biofilm Reactor
(SBBR) to perform carbon and nitrogen removal: from support design to reactor operation.
The experimental part was conducted in two phases. In the first phase, different supports
were tested to select the most suitable one for SBBR operation. In the second phase, the
most appropriate support was used in a SBBR to perform carbon and nitrogen removal. The
results demonstrate that the support with the highest internal surface area presented a
higher biomass accumulation. Time profiles of nitrogen ions and acetate concentration
showed the typical behaviour of a SBBR performing carbon and nitrogen removal. Poly-bhydroxybutyrate
(PHB) was formed immediately after acetate depletion and was
subsequently consumed for biomass growth, owing to the high oxygen concentration in the
The pollution caused by heavy metals is one the major environmental problems that is
imperative to be solved. New technologies, easy to implement and to adapt to any
system, deserve special attention and are the focus of this presentation. This paper
aims to investigate the biosorption behaviour of a biofilm of E. coli supported on kaolin
clay for the treatment of cadmium, iron, nickel and chromium aqueous solutions. The
effect of metals initial concentrations were studied and the relationship between pH and
removal efficiency were analysed. Adsorption characteristics of a biosorbent can be
depicted by an adsorption isotherm. Langmuir, Redlich-Peterson and Sips are
commonly used for the description of adsorption data and were applied to the
experimental results described by this report. The presence of functional groups in the
suspended biomass that may have a role in biosorption process was confirmed by
FTIR. It was demonstrated that a biofilm of E. coli supported on kaolin is able to
remove Cr (VI), Cd (II), Ni (II) and Fe (III) from aqueous solutions. The isotherms were
fitted and the best fit for chromium and nickel was obtained with the Redlich-Peterson
model isotherm and for cadmium the best fit was the obtained with the Sips model. In
terms of removal percentage...
Lopes, Susana Patrícia; Machado, Idalina; Vieira, M. J.; Pereira, Maria Olívia
Fonte: Universidade do MinhoPublicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 02/09/2009ENG
Relevância na Pesquisa
The majority of lab‐scale studies involves a single species to form biofilms and to later
evaluate the effect of the antimicrobials against these biofilms. However, in real systems,
biofilms can be found as a complex consortium of species where the biofilm behaviour is the
sum of the synergistic and antagonistic interactions between the different species. It is not
surprising that disinfection protocols developed with a single species biofilm can fail when
applied to a real system. The central query of this study was to understand the behaviour of
binary biofilms when exposed to high doses of benzalkonium chloride (BZK), a general
disinfectant in health care facilities.
P. aeruginosa (ATCC 10145), P. aeruginosa adapted to 4.0 mM of BZK (PA4) and Escherichia
coli k12 were the strains used to form single and binary biofilms. The mixed‐species biofilms
were obtained by a combination of 50% of suspended inocula of each specie: E. coli with P.
aeruginosa and E. coli with PA4. The role of surface preconditioning with BZK on biofilm
properties was also investigated. Biofilms where formed for 24 h in 96 plates (non‐ and
conditioned with 0.7 mM of BZK for 30 min), being then treated with 1.0 mM of BZK. Crystal
violet (CV) together with XTT...
This study investigated the physiology and behaviour following treatment with ortho-phthalaldehyde (OPA), of Pseudomonas fluorescens in both the planktonic and sessile states. Steady-state biofilms and planktonic cells were collected from a bioreactor and their extracellular polymeric substances (EPS) were extracted using a method that did not destroy the cells. Cell structure and physiology after EPS extraction were compared in terms of respiratory activity, morphology, cell protein and polysaccharide content, and expression of the outer membrane proteins (OMP). Significant differences were found between the physiological parameters analysed. Planktonic cells were more metabolically active, and contained greater amounts of proteins and polysaccharides than biofilm cells. Moreover, biofilm formation promoted the expression of distinct OMP. Additional experiments were performed with cells after EPS extraction in order to compare the susceptibility of planktonic and biofilm cells to OPA. Cells were completely inactivated after exposure to the biocide (minimum bactericidal concentration, MBC ¼ 0.55 + 0.20 mM for planktonic cells; MBC ¼ 1.7 + 0.30 mM for biofilm cells). After treatment, the potential of inactivated cells to recover from antimicrobial exposure was evaluated over time. Planktonic cells remained inactive over 48 h while cells from biofilms recovered 24 h after exposure to OPA...
The hydrodynamic behaviour of a biofilter fed toluene and packed with an inert carrier was evaluated on start-up and after long-term operation, using both methane and styrene as tracers in Residence Time Distribution experiments. Results indicated some deviation from ideal plug flow behaviour after 2-year operation. It was also observed that the retention time of VOCs gradually increased with time and was significantly longer than the average residence time of the bulk gas phase. Non-ideal hydrodynamic behaviour in packed beds may be due to excess biomass accumulation and affects both reactor modeling and performance. Therefore, several methods were studied for the removal of biomass after long-term biofilter operation: filling with water and draining, backwashing, and air sparging. Several flow rates and temperatures (20–60°C) were applied using either water or different chemicals (NaOH, NaOCl, HTAB) in aqueous solution. Usually, higher flow rates and higher temperatures allowed the removal of more biomass, but the efficiency of biomass removal was highly dependant on the pressure drop reached before the treatment. The filling/draining method was the least efficient for biomass removal, although the treatment did basically not generate any biological inhibition. The efficiency of backwashing and air sparging was relatively similar and was more effective when adding chemicals. However...
Purpose: To assess the effectiveness of tooth wipes in removing dental biofilm from babies' anterior teeth, as well as to evaluate the babies' behaviour and the guardians' preference concerning hygiene methods. Materials and Methods: In this random blind cross-over study, 50 high caries risk babies, from 8 to 15 months old, were divided into two groups: babies with oral hygiene performed by caregivers (n = 25) or by their mothers (n = 25). The caregivers and mothers removed biofilm using three methods of oral hygiene (tooth wipes, toothbrushes and gauze), one in each experimental phase. Professional cleaning was done before each phase, which had 2 days of biofilm accumulation and 1 experimental day, when caregivers and mothers used one method to remove biofilnn. Examiners blinded to the study design assessed the biofilm index at baseline, prior to and following biofilm removal using each method. The babies' behaviour and the mothers'/caregivers' preference were assessed. Results: The tooth wipes, toothbrushes and gauze significantly reduced the amount of biofilm (P < 0.001). The mothers' group removed more biofilm than the caregivers' group, using toothbrushes or tooth wipes (P < 0.05). Babies in the mothers' group had better behaviour using tooth wipes than toothbrushes (P < 0.05). Mothers and caregivers preferred to use tooth wipes. Conclusions: Tooth wipes are effective in removing biofilrn from babies' anterior teeth and are the method best accepted by mothers...
The main aim of this in vitro study was to evaluate the influence of Streptococcus mutans on the corrosion of titanium.
S. mutans biofilms were formed on commercially pure titanium (CP-Ti) square samples (10 mm × 10 mm × 1 mm) using a culture medium enriched with sucrose. Open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements were used to evaluate the corrosion behaviour of CP-Ti in the presence of S. mutans in Fusayama's artificial saliva. The corrosion of biofilm-free CP-Ti samples was also evaluated in artificial saliva. Biofilms biomass was measured by spectrophotometry, using crystal violet staining, after 1, 2 and 7 days.
The OCP values recorded on CP-Ti in the presence of S. mutans (−0.3 ± 0.02 V vs. SCE) was lower than those on biofilm-free CP-Ti (−0.1 ± 0.01 V vs. SCE) after 2 h of immersion in artificial saliva (p < 0.05). That reveals a high reactivity of titanium in presence of S. mutans. Impedance spectra revealed the formation of a compact passive film on titanium in artificial saliva or in the presence of a 2 days old S. mutans biofilm even though the corrosion resistance of CP-Ti has decreased in presence of a S. mutans biofilm.
The presence of bacterial colonies...
We apply the immersed boundary (or IB) method to simulate deformation and
detachment of a periodic array of wall-bounded biofilm colonies in response to
a linear shear flow. The biofilm material is represented as a network of
Hookean springs that are placed along the edges of a triangulation of the
biofilm region. The interfacial shear stress, lift and drag forces acting on
the biofilm colony are computed by using fluid stress jump method developed by
Williams, Fauci and Gaver [Disc. Contin. Dyn. Sys. B 11(2):519-540, 2009], with
a modified version of their exclusion filter. Our detachment criterion is based
on the novel concept of an averaged equivalent continuum stress tensor defined
at each IB point in the biofilm which is then used to determine a corresponding
von Mises yield stress; wherever this yield stress exceeds a given critical
threshold the connections to that node are severed, thereby signalling the
onset of a detachment event. In order to capture the deformation and detachment
behaviour of a biofilm colony at different stages of growth, we consider a
family of four biofilm shapes with varying aspect ratio. Our numerical
simulations focus on the behaviour of weak biofilms (with relatively low yield
stress threshold) and investigate features of the fluid-structure interaction
such as locations of maximum shear and increased drag. The most important
conclusion of this work is that the commonly employed detachment strategy in
biofilm models based only on interfacial shear stress can lead to incorrect or
inaccurate results when applied to the study of shear induced detachment of
weak biofilms. Our detachment strategy based on equivalent continuum stresses
provides a unified and consistent IB framework that handles both sloughing and
erosion modes of biofilm detachment...