Biofilms And Infection: What You Should Know
- Volume 19 - Issue 11 - November 2006
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While the concept of infections has been studied for many years, our current understanding of infections is based upon studies and observations of planktonic bacteria. This is free floating bacteria that cause diseases such as pneumonia, sepsis, urinary tract infections, gas gangrene and many other examples. These types of infections often respond well to antibiotics and resolve without recurrence.
However, there are several infections that occur out of the typical sequence of planktonic bacterial infections. These infections occur postoperatively after a patient has received an implant. However, instead of presenting in the typical three- to five-day period, these infections present weeks to months later. One may see a temporary symptomatic response to antibiotics but the infection returns again at a later time despite a full course of antibiotics.
In 1978, bacteria were described as matrix-enclosed aggregates. These aggregates were immobilized on the surfaces or at interfaces in the ecosystems in which they were known to predominate.1,2 Now a new category of infection has emerged that differs radically from acute bacterial disease. Infections from biofilm present as less aggressive infections. They often persist for months or years, and they progress though periods of quiescence that alternate with periods of acute exacerbation.3
Why Biofilms Have Been A Research Dilemma
Research has demonstrated that bacteria live in matrix-enclosed communities that closely resemble the biofilms that are the predominant form of bacteria growth in industrial and environmental ecosystems. Researchers often identified and cultured bacteria. In the lab, the isolated bacterium was sensitive to the appropriate antibiotics used by researchers. However, when these antibiotics were given to humans, they were unable to resolve the infection completely. This incomplete or partial resolution of the condition led many investigators to refer to these chronic disease states as “sterile inflammatory conditions.” Furthermore, in many instances, there was no bacterium that researchers could culture from the source.3
Traditional methods for detecting bacteria usually involve mechanical removal of the organism (often by swabbing) and their propagation in liquid or on solid media. Using standard swabbing and culture (plating) techniques, researchers in a 2003 study of 3,000 patients with bacterial colonization concluded (as most similar studies have) that 10.8 percent of these individuals carried Staphylococcus aureus.4
The study authors subsequently examined subsets of these individuals, using polymerase chain reaction (PCR) to identify S. aureus by its DNA and using fluorescent in situ hybridization (FISH) probes to identify cells of this species by their 16S RNA content. They found that 100 percent of these individuals carried this organism. Then they examined whether individuals who yielded positive data in swab and plate tests carried more S. aureus as detected by PCR and FISH, and found there was no correlation.4
If certain bacteria are present on a tissue or an inert surface, the swab may or may not pick them up. They may be present in huge aggregates of hundreds of cells that will yield only one colony on plating. Alternatively, they may be expressing the set of genes that constitute the biofilm phenotype and are unable to grow in the culture conditions provided.
How Biofilm Forms And What Makes It Unique
There is a growing interest in the research of biofilms. Biofilms are estimated at 1 million nosocomial infections each year in the U.S.