‘Biofilms is a community of micro-organism irreversibly attached to a surface, bring forthing extracellular polymeric substances ( EPS ) , exhibiting an altered phenotype compared with matching planctonic cells, particularly with reagard to cistron written text, and interacting with each other ‘ ( D.Lindsay, December 2006 )
2.1 Biofilm consist of three constituents:
Surface of fond regard is a nucleus factor for bacterial biofilm formation. It is conditioned by surface assimilation of organic and inorganic foods that influence subsequent bacterial fond regard. ( D.Lindsay, December 2006 )
Extracellular polymeric substances ( EPS ) may account for 50 % to 90 % of the entire organic C of biofilms. It is besides considered as the primary matrix stuff of the biofilm that serves as a storage installation for foods. ( D.Lindsay, December 2006 )
The bacteriums are the best studied micro-organism with regard to colonisation of surfaces and subsequent biofilm formation. ( D.Lindsay, December 2006 )
The biofilm formation occurs in the undermentioned consecutive stages:
Figure 1: The consecutive stages of biofilm formation ( Paul Stoodley, 2003 )
2.2 Attachment- during the attachment unattached bacterial cells settees on surface, arrange in bunchs and attach.
Reversible Attachment – the weakest nexus in the formation of biofilms. Reversible fond regard of bacterial cells to a surface can happen by deposit and Browian Motion ( the random gesture of micro atoms suspended in liquid ) of microbic cells ; motion by motile bacteriums, or electrostatic and physical interactions between the bacterial cell surface and micro-organism itself. ( D.Lindsay, December 2006 )
Irreversible fond regard – after reversible fond regard to the surface bacterial cells produce EPS ‘due to stimulation of membrane edge centripetal proteins of the bacterial cell, which allows for the development of cell-to-cell Bridgess that in bend, cement the cells to the surface ‘ ( Donlan, 2002 )
2.3 Colonization ( growing ) and Quorum Sensing
The surface colonisation is the concluding stage in the formation of biofilms. ‘Attached bacteriums turn and split, organizing microcolonies that are considered to b the basic organisational units of a biofim. ‘ ( Costerton et al. , 1994 )
2.4 Quorum Feeling
The procedure of the biofilm formation becomes interesting during the stage of colonisation. Microorganisms within the biofilm can pass on through the phenomenon called quorum detection.
‘Quorum sensing- is a mechanism in which bacterium coordinate the look of certain cistrons in response to their population denseness by bring forthing, let go ofing and observing little signal molecules. This mechanism was 1st discovered in the marine bacteria Vibrio fisher and was thought to be restricted to merely a limited series of species. Subsequently on, similar system was found to be present in many other bacteriums. Biofilm formation has been recognised to be a quorum-sensing-regulated phenomenon for an ever-increasing figure of bacteriums. ‘ ( Defoirdt et al. , 27 October 2004 ) This phenomenon allows acknowledging that there is heavy population of other bacterial cells ‘it is more inclined to fall in them and lend to the formation of a biofilm ‘ . ( A.Proal, 26 may 2008 )
Harmonizing to Deborah A. Hogan quorum feeling in bacterium is mediated by little diffusible signalling molecules that accumulate in the extracellular environment. ( D.A.Hogan, Apr. 2006 ) Signal export involve: ‘Passive diffusion across the membrane, the action of efflux pump and specific transporters ‘ . ( J.P et al. , 1999 ) .When a signal is sufficiently high the blood relation regulator is activated within the local population of cells, taking to coordinated cistron look. ( D.A.Hogan, Apr. 2006 )
Three Major Quorum feeling systems:
C
Figure 2: Three Quorum feeling systems ( Miller & A ; Bassler, 2001 )
AHL-mediated quorum feeling a the I protein is the AHL synthase enzyme. , The AHL molecules diffuse through the plasma membrane. As bacterial cells denseness additions, the AHL concentration additions as good and one time a critical concentration has been reached, AHL binds to the R protein, a response regulator. The AHL-R protein complex activates or inactivates written text of the mark cistrons. ‘ ( Defoirdt et al. , 27 October 2004 )
Peptide-mediated quorum feeling in Gram-positive bacteriums a ‘a peptide signal ( PS ) precursor protein is cleaved let go ofing the signal molecule. The peptide signal is transported out of the cell by an ATP binding cassette ( ABC ) transporter. Once a critical extracellular peptide signal concentration is reached a detector kinase ( SK ) protein is activated to phosphorylate the response regulator ( RR ) . The phosphorylated response regulator activates written text of the mark cistrons ‘ ( Defoirdt et al. , 27 October 2004 )
Some bacteriums ( e.g. marine bacteria Vibrio harveyi ) possess two quorum feeling systems. ( Miller et al. , 2002 )
Quorum feeling in Vibrio harveyi a there is two types of signal molecules. ‘AI-1 is and AHL and its biogenesis is catalysed by the luxLM enzyme. AI-2 is a furanosyl borate diester ; its biogenesis is catalysed by the LuxS enzyme. AI-1 and AI-2 are detected at the cell surface by the LuxN and LuxP-LuxQ receptor proteins, severally. At low cell denseness, LuxN and LuxQ autophosphorylate and reassign phosphate to LuxO via LuxU. The phosphorulated LuxO is an active represser for the mark cistrons. At high cell denseness, LuxN and LuxQ interact with their autoinducers and alteration from kinases to posphatases that drain phosphate away from LuxO via LuxU. The dephosphorylated LuxO is inactive.Subsequently, written text of the mark cistrons is activated by LuxR ‘ ( Defoirdt et al. , 27 October 2004 )
2.5 Withdrawal
D, Lindsay and A.Von Holy surveies suggested that withdrawal is an active procedure that is regulated by the attached cell population. There are several schemes of how biofilm bacterium disseminate into other countries for farther surface colonisation. ( D.Lindsay, December 2006 ) :
Cells located at the fringe of the biofilm are released into the environing environment and return to the planctonic province. , This scheme is adopted by P.aeruginosa, which produces and alginate enzyme that dissolves the alginate matrix, let go ofing cells into environing environment, ( D.Lindsay, December 2006 )
‘Bacteria may change assorted surface constituents, such as glycolipids, peptidolipids, lipopolysaccharides, which may change cell surface hydrophobicity, easing reliase of a surface edge cell e.g. E.coli and P.aeruginosa cells de-adhere from biofilms by increasing their cell surface hydrophobicity. ‘ ( D.Lindsay, December 2006 )
Biofilm can be made up of individual or multiple species. Harmonizing to K.D. Xu it is estimated that dental biofilms contain more than 500 different bacterial species ; conversely, in latter phases of the disease, the primary bacteria in the lungs of Cyctic Fibrosis patients is P.aeruginosa. ( Xu, 2000 ) While mixed-species biofilms predominate in nature, individual species biofilms can be found in clinical scenes, including medical implants. ( Yi et al. , Oct 2004 )
Antibiotic Resistance and alterations in biofilms manner of growing
The opposition of bacterial biofilms to antibiotics is higher compared with planctonic cells. Biofilms bing cells become 10-100 times more immune to the antimicrobic agents. ( Xu, 2000 )
Harmonizing to Philip S. Stewart and J. William Costerton the mechanism of antimicrobic opposition, such as outflow pumps, modifying enzymes, and mark mutants, do non responsible for the protection of bacterial biofilms. ( Stewart & A ; Costerton, 14 July 2001 )
