Published on November 28, 2013
Biofilms • Communities of organisms attached to a solid surface – Can be nonliving or living tissue surface • Evolve over time consisting of many species • Most important, they are a multiorganism cooperative population • Two main types of biofilms – Sessile • Permanently anchored to a surface • Covalently bonded to the surface • Planktonic – Free floating • Movement to new habitats
Biofilms (Cont’d) • Examples of biofilms – Water pipes – Ventilator system of airplanes or convention centers – Wine casks causing spoilage – Serious lung infections of CF patients • Problems with susceptibility
Natural Biofilm on a Metal Surface
Environmental and Cultural Factors That Affect Biofilm Development
Biofilms: Community of Cells • Most important characteristics – Attachment efficiency – Nutritional resources – Substrata – Environment shear stress or force
Variables Important in Cell Attachment and Biofilm Formation
Stage I – Development I Stage II – Development II • Reversible binding to surface • Increased attachment via fimbriae and pili • Irreversible binding and aggregate formation • Decreased motility • Exopolysaccharide (EPS) trap nutrients and planktonic bacteria Stage III – Maturation I Stage IV – Maturation II • Colony thickness of greater than 10 um thick • Colony thickness of greater than 100 um thick • Some bacteria detach but are trapped in the film Stage V Stage 0 • Breaking off of bacteria leads to start of new biofilms • Planktonic state
Stages in Biofilm Formation (Cont’d) • Active growing cells • Persister cells – Cells in a dormancy-like state • Importance – Cells not actively growing may not be affected by drugs » Cell wall inhibitors » Ribosome inhibitors • Communication between bacteria – Quorum sensing (QS) • Pheromones – Gram positive – low-molecular-weight homoserines – Gram negative – peptides and proteins
Architecture of Biofilms • Outer layer – Most dynamic and metabolically active cells • Intermediate layer – Still active but less so – Genetic reservoir for genes involving nutrient utilization and drug resistance • Inner surface layer – Persister cells • Dynamic system – Defends itself as a group • Freely exchanging traits and retaining resistance
Mechanisms of Pathogenicity
Biofilms as a Defense Mechanism • When culturing organisms – Catheter tips, artificial joints, etc. – Isolation of individual organisms can be hard to culture • Sessile – Isolated colonies may not reflect the colonies permanently attached to the plastic surface • Planktonic – Isolated colonies may not contain antibiotic resistance, but other colonies in the group may contain resistance • Look susceptible in a dish but not in the patient – Treatment failure
Biofilms as a Defense Mechanism (Cont’d) • Protect against pH changes • Interference with immune function – Prevent phagocytosis – Prevent antigen exposure to antibodies • Sticky EPS glues biofilm together; stops clearance • Organization of biofilm – Slow-growing organisms attached to surface show increase resistance to antibiotics
Biofilms as a Defense Mechanism (Cont’d) • Gene transfer – Transformation – Conjugation • Greater genetic potential as a group than alone – Eventually the virulence factors cluster, causing a worsening of disease
Diseases Associated with Biofilms • Primarily indwelling medical devices – Examples include • Artificial heart valves • Prostheses • Catheters • Can be tissue and vessels as well – Some disease as it progresses from acute to chronic diseases
Dental Biofilms • Plaque – Caries (cavities) – Periodontal disease • Dental cleaning removes plaque – Biofilm develops again • Acquired pellicle – Organisms produce glycans to produce slime layer • Sugars – Broken down to acids that damage teeth
Laboratory Consequences Associated with Biofilms • Cultures – Require growth to get colonies • Problem is colonies won’t grow under normal conditions • False negatives – Improper sample collection • Swabs or culturing outer surface of equipment • Aggregates of organisms – Single colonies can represent up to 100,000 bacteria of mixed origin • Thus amounts of each organism are greatly underestimated or not considered significant • Antibiotic susceptibility – Single isolates that are members of a biofilm may not represent the genetic potential or resistance of a community
Detection of Biofilms • PCR with pathogen-specific probes • Confocal laser scanning microscopic imaging – CLSM
Potential Interventions • Establishing biofilms in 96 well plates – Minimal biofilm elimination concentration (MBEC) • Help select successful concentrations of drugs and appropriate concentration • Treatment outcomes – Prevent metastasis – Reduce bioburden – Prevent attachment • Other treatments – Sonication to disrupt biofilm – Toxic compounds (silver)
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