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Increasing evidence shows that bacteria and yeast can adhere to implanted
medical devices or damaged tissue and become the focus of persistent
infections (Costerton et al, 1999). Microbial biofilms that form in
the human body share certain characteristics with biofilms that are
familiar in other environments (see Table 7-1, below; for basic
information about biofilm formation, please refer to
“Module
1: Introduction to Biofilms” ). Some well-established examples of biofilm
infections include cystic fibrosis pneumonia, periodontitis, and
infection of catheters and prosthetic joints.
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| TABLE 7-1. Characteristics of some biofilm infections. |
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CHARACTERISTIC |
CYSTIC FIBROSIS |
PERIODONTITIS |
CENTRAL VENOUS
CATHETER INFECTION |
CHRONIC WOUNDS |
|
Form preferentially on foreign
bodies, dead or damaged tissue |
The
genetic defect in the chloride ion channel predisposes the
lung to infection |
The
tooth surface is not as well-defended as are vascularized
tissues |
Indwelling plastic and metal surfaces are very vulnerable to
microbial colonization |
Necrotic tissue could provide nidus for biofilm formation |
|
Slow to develop |
Persistent infection takes years to establish |
Typically manifests gradually, later in life |
Symptoms may take weeks to manifest |
Symptoms such as pain, exudate and size wax and wane over
weeks to months |
|
Respond poorly or only
temporarily to antibiotics |
Lung
is never cleared of bacteria despite aggressive chemotherapy |
Tetracycline, antiseptic mouthwashes have little efficacy |
Preferred therapy is removal of the infected catheter |
Marginal response to antibiotics; may deteriorate when
antibiotics are stopped |
|
Collateral damage to
neighboring healthy tissue |
Massive neutrophil invasion contributes to gradual loss of
lung function |
Host
responses and bacterial virulence factors lead to progressive
bone loss; teeth fall out |
Infection may disseminate to blood and other locations in body |
Normal healing process of cell differentiation and migration
is arrested |
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Biofilm
infections form preferentially on foreign surfaces as well as dead or damaged tissue. These
infections develop gradually and may be slow to produce overt
symptoms. Once established, however, biofilm infections
persist. They are rarely resolved by host defense mechanisms, even
in individuals with healthy innate and adaptive immune
reactions. Active host responses, such as invading neutrophils,
can even be detrimental since those cells can cause collateral
damage to neighboring healthy host tissue. Biofilm
infections respond only transiently to antibiotic therapy.
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FIGURE
7-1. Diagram of a medical biofilm.
(a) Planktonic bacteria can be cleared
by antibodies and phagocytes, and are susceptible to antibiotics.
(b) Adherent bacterial cells form biofilms preferentially on inert
surfaces, and these sessile communities are resistant to antibodies,
phagocytes, and antibiotics. (c) Phagocytes are attracted to the
biofilms. Phagocytosis is frustrated, but phagocytic enzymes are
released. (d) Phagocytic enzymes damage tissue around the biofilm,
and planktonic bacteria are released from the biofilm. Release may
cause dissemination and acute infection in neighboring tissue. (Courtesy, Science, 21 May, 1999, VOL 284)
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page: Biofilms
display increased tolerance to antimicrobials |
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