Biofilms And Infection: What You Should Know

By Dave Nielson, DPM, FAPWCA and Guy Pupp, DPM, FACFAS

     Formation of a biofilm begins with the attachment of free floating microorganisms to a surface. These first colonized microorganisms adhere to the surface initially through weak, reversible van der Waals forces. If these microorganisms are not immediately separated from the surface, they can anchor themselves more permanently using cell adhesion molecules such as pili. Once colonization has begun, the biofilm grows through a combination of cell division and recruitment mediated by extracellular polysaccharides.

Understanding The Nature Of Biofilms And How It Affects The Impact Of Antibiotics

Biofilms are responsible for many device-related and chronic infections.

     Bacteria that live in a biofilm usually have significantly different properties from free-floating bacteria of the same species as the dense and protected environment of the film allows them to cooperate and interact in various ways. One benefit of this environment is increased resistance to detergents and antibiotics as the dense extra cellular matrix and the outer layer of the cells protect the interior of the community. In some cases, one may see a thousand-fold increase in antibiotic resistance.

     In cases of chronic bacterial diseases, diagnostic microbiology labs have reported that cultures of Pseudomonas aeruginosa from cystic fibrosis (CF) patients were sensitive to antibiotics (e.g. cloxacillin) but pulmonary clinicians saw little improvement when they utilized these antibiotics. The sera of CF patients contained very large amounts of specific antibodies against Pseudomonas but the disease persisted.

     Studies at the Center for Biofilm Engineering in Montana looked at device-related infections that were recalcitrant to antibiotic therapy and insensitive to host defense mechanisms. Researchers studied and collected specimens over a 12-year period. They noted that cells of P. aeruginosa in the sputum and in the lungs (postmortem) of CF patients grew in biofilms, and the cells were surrounded by very large expanses of matrix material.5 Some researchers noted that the cells of the pathogens that caused osteomyelitis in patients and in lab animals grew in enormous biofilms, which consisted of millions of bacterial cells embedded in thick matrix material.6 Researchers studied many other chronic infections, all of which had the existence of biofilms.

     Biofilms are ubiquitous. Nearly every species of bacteria have mechanisms in which they can adhere to surfaces and to each other. Biofilms grow in hot, acidic pools in Yellowstone and glaciers in Antarctica. Biolfilms can form on any solid surface implanted in the human body, such as in the case of dental plaque. Aquatic plants use biofilm to control microbial fouling of their photosynthetic surfaces. One may also
     see biofilms on the interior of pipes and they can lead to clogs and corrosion.
Conventional antibiotics eradicate free-floating bacteria but do not eradicate the biofilm. There is a recurrence of symptoms followed by additional cycles of antibiotics. Researchers have studied gene expression and found that biofilm phenotypes differed from their planktonic counterparts.7

     Common bacteria found in biofilms include gram-positive Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus viridans. Gram-negatives include Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Pseudomonas aeruginosa.

     The biofilm concept offers possible explanations to the following unusual circumstances.
     • Antibiotic coverage is not enough to eradicate the organism.
     • Swabs of an infected area will only propagate a few cells.
     • Blood cultures from patients with overt infectious signs are negative.

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