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22 Φεβ 2013 (πριν από 4 χρόνια και 6 μήνες)

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Introduction

Biofilm


Assemblages of the microbial cells (Kolkare et al 2009)


Develop on all solid surfaces


Zobell (1943)


Adsorption of organic compounds


Enable diverse microbial communities (Marshall 1972)

Problems


water processes, including corrosion, loss of process efficiency such as heat
transfer, and health issues such as Legionella infection.

Biofilm forming organism


bacteria, fungi, algae, protazoa


Biofilms in the dairy industry


Dairy industry equipment can lead to serious hygiene problems and
economic losses due to food spoilage and equipment impairment (Bremer,
Fillery, & McQuillan, 2006; Gram, Bagge
-
Ravn, Ng, Gymoese, & Vogel,
2007).


Dairy biofilms are predominated by bacterial extracellular polymeric
substances (EPS).

Biofilms in humans


All surfaces of the body exposed to the external environment (skin, teeth,
mouth, respiratory and gastrointestinal epithelia).


It has been estimated that 65% of human infections involve biofilms (Potera,
1999).


Staphylococcus epidermidis


Dental plaque is the biofilm that has received the most attention


Bacterial Biofilm


Bacteria in nature are either in a planktonic

state (“free
-
swimming”), or
adhered

to surfaces and become sessil (Joseph. L et al 2007).


Adopting sessile mode of Life

o
concentrate nutrients

o
metabolic interactions

o
resistance to harmful chemicals and environmental stress


P.

aeruginosa

Algal Biofilms


Biofilms dominated by algae will grow on any surface


In natural ecosystems, algal biofilms are familiar on trees and fences, on
stones in rivers, and on the seashore.


unicellular, colonial or simple filamentous organisms


Diatoms are dominated in aquatic environment


Green unicellular algae is dominated in terrestrial environment.

Fungal Biofilm


Transplantation procedures, immunosuppression, the use of chronic
indwelling devices, and prolonged intensive care unit stays have increased
the prevalence of fungal disease.


Candida is the major fungal pathogen of humans causing a variety of
afflictions ranging from superficial mucosal diseases to deep seated
mycoses.


Candida biofilms are difficult to eradicate especially because of their very
high antifungal resistance

Processes governing biofilm formation (Breyers & Ratner, 2004). Courtesy from the American Society for Microbiology


Biofilm formation comprises a sequence of steps (Breyers & Ratner, 2004).

Biofilm formation

Properties


Specialized attachment structures/surface properties of the cell


Extracellular polymeric substances (EPS)


Cell

cell communication




Approach for biofilm mitigation


biofilm prevention


preventing biofilm formation would be a more logical option than treating it.


no known technique.


The main strategy to prevent biofilm formation is to clean and disinfect
regularly before bacteria attach firmly to surfaces (Midelet & Carpentier,
2004; Simo˜es et al., 2006).

Cleaning and disinfection


Disinfectants do not penetrate the biofilm matrix


Therefore, cleaning is the first step.


Surfactants or alkali products


Disinfectants are more effective in the absence of organic material

The green strategy for biofilms control


enzymes, phages and
bioregulation

Enzyme
-
based detergents


enzyme
-
based detergents as bio
-
cleaners, also known as ‘‘green
chemicals’’


Due to the EPSheterogeneity, a mixture of enzymes may be necessary for
sufficient biofilm degradation


Lactobacillus bulgaricus, Lactobacillus lactis, Streptococcus thermophilus
(Blum 2003)


proteases and polysaccharide hydrolysing enzymes may be useful (Meyer,
2003)

Control using phages


Phages are ubiquitous in nature.


highly specific, non
-
toxic, feasible approach for controlling several
microorganisms involved in biofilm formation (Kudva, Jelacic, Tarr,
Youderian, & Hovde, 1999).


The technology for this has not yet been successfully developed.


A bacteriophage (L. monocytogenes phage ATCC 23074
-
B1) was used
successfully in L. monocytogenes biofilm inactivation (Hibma, Jassim, &
Griffiths, 1997).


This enzymatic phage had the ability to attack the bacterial cells in the
biofilm and the biofilm matrix, substantially reducing the biofilm cell counts
(more than 99.9% of removal).


Control through microbial interactions/metabolite
molecules


Metabolite can interfere with biofilm formation and development (Carpentier
& Chassing, 2004; Kives et al., 2005; Røssland, Langsrud, Granum, &
Sørhaug, 2005; Tait & Sutherland, 1998; Valle et al., 2006).


Many bacteria are capable of synthesizing and excreting biosurfactants with
anti
-
adhesive properties (Desai &Banat, 1997; Nitschke & Costa, 2007;
Rodrigues, van der Mei, Teixeira, & Oliveira, 2004; van Hamme, Singh, &
Ward, 2006).


Surfactin from Bacillus subtilis disperses biofilms without affecting cell
growth and prevents biofilm formation by microorganisms such as
Salmonella enterica, E. coli, and Proteus mirabilis

(Mireles, Toguchi, &
Harshey, 2001).


Biopreservatives, such as nisin, lauricidin, reuterin and pediocin, have been
well documented for their biofilm control potential against microorganisms
commonly found in dairy processing facilities, including L. monocytogenes
(Dufour et al., 2004; Garcia
-
Almendarez, Cann, Martin, Guerrero
-
Legarreta,
& Regalado, 2008; Mahdavi, Jalali, & Kermanshahi, 2007; Zhao et al.,
2004).


Valle et al. (2006) demonstrated that E. coli expressing group II capsules
release a soluble polysaccharide into their environment that induces
physicochemical surface alterations, which prevent biofilm formation by a
wide range of Gram
-
positive and Gram
-
negative bacteria.


More recently, Davies and Marques (2009) found that P. aeruginosa
produces cis
-
2
-

decenoic acid, which is capable of inducing the dispersion of
established biofilms and of inhibiting biofilm development.


Conclusions



Microbial control in food processing has the main aims of
reduction/eradication of microbes and their activity, and the prevention/control
of the formation of biological deposits on the process equipment.


Nowadays, the most efficient practical means for limiting microbial growth
includes good production hygiene, a rational running of the process line, and
effective use of cleaning and disinfectant products.


Due to the increased resistance of biofilms to conventional disinfection
processes, novel means for their control are constantly sought through the
control of environmental factors on the process line and the use of new
control strategies.


Much more needs to be learned about the impact of antimicrobial products on
microbial biofilms and their recovery responses to damage, as
microorganisms can develop resistance and subsequently survive previously
effective control procedures.


The discovery of new biofilm control strategies, following the specifications
needed to be used in food industry, and based on the use of biological
-
based
solutions with high antimicrobial activity and specificity seem to be a step
ahead in overcoming the biofilm resistance issue.


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