Abstract and Introduction
Almost all micro-organisms subsist in elaborate colonies that are embedded in biofilms of self-produced exopolymer matrices. The biofilm allows the micro-organisms to adhere to any surface, living or nonliving. The adaptive and genetic changes of the micro-organisms within the biofilm make them resistant to all known antimicrobial agents. Thus, the diagnostic and therapeutic strategies used to fight acute infections are not effective in eradicating medical device biofilm-related infections or chronic biofilm diseases. Today, vascular catheter-related bloodstream infections are the most serious and costly healthcare-associated infections. The purpose of this article is to describe the biofilm form of life, the mechanisms of resistance to current forms of treatment, and the clinical implications for effective strategies to diagnose and treat catheter-related bloodstream infections.
Bacteria first appeared on earth about 3.6 billion years ago, long before the appearance of Homo sapiens around 100,000 years ago. Micro-organisms have developed extraordinary survival mechanisms that allow them to live in almost any environment on the planet. Man was unaware of the existence of bacteria until the 17th century, when Anton van Leeuwenhoek (1632-1723) invented a rudimentary compound microscope. Van Leeuwenhoek was the first person to visualize, graphically illustrate, and label "animalcules" (bacteria) that he found in plaque scraped from his own teeth.
It wasn't until almost 2 centuries later, in 1884, that Robert Koch described a method to identify a specific micro-organism as a cause of disease. This led to the establishment of pure culture techniques that today remain the cornerstone of diagnostic and prescriptive antibiotic therapy.
Microbiologists usually study micro-organisms in a liquid homogeneous suspension and plate culture format, which provides a very biased view of microbial life in nature and disease. More recent direct microscopic observations and direct quantitative recovery techniques demonstrate unequivocally that more than 99.9% of bacteria grow as aggregated "sessile" communities attached to surfaces, rather than as "planktonic" or free-floating cells in liquid. Micro-organisms commonly attach to living and nonliving surfaces, including medical devices, and form biofilms that lead to colonization and sometimes infection.
A biofilm develops when the attached cells excrete polymers that facilitate adhesion, matrix formation, and alteration of the organism's phenotype with respect to growth rate and gene transcription. The physical and genetic profiles of micro-organisms within the protected biofilm community are profoundly different from their existence as unprotected independent cells.
The hallmark of biofilm-related infections is the dramatic resistance to antimicrobials and to host defenses. Patients with chronic infectious diseases, such as otitis media and osteomyelitis, experience cycles of acute exacerbation and remission. Many chronic infections result in treatment failure, suppression of infection followed by reoccurrence, or the inability to culture micro-organisms despite obvious clinical symptoms. Medical device-related infections also fit this profile and typically require removal of the device, despite appropriate therapy as indicated by standard methods in hospital microbiology labs.
Microbial biofilms, which often are formed by antimicrobial-resistant organisms, are responsible for 65% of infections treated in the developed world. Table 1 lists medical devices known to be associated with biofilm development, and Table 2 lists chronic diseases known to be associated with biofilm infections.
Medical devices are critical in modern-day medical practice. At the same time, they are major contributors to morbidity and mortality. The use of a medical device is the greatest exogenous predictor of healthcare-associated infection. Most nosocomial infections occur at 4 major body sites -- the urinary tract, respiratory tract, bloodstream, and surgical wound sites -- and 3 of those are common sites for medical devices. In fact, 95% of urinary tract infections are associated with a urinary catheter, 86% of pneumonias are associated with mechanical ventilation, and 87% of bloodstream infections are associated with an intravascular device. The last type, catheter-related bloodstream infection (CRBSI), is the most life threatening and is associated with significant medical costs.
The increased incidence and associated risks of catheter-related infections have drawn considerable attention from national organizations such as the Institute of Medicine, the Centers for Disease Control and Prevention (CDC), the Agency for Healthcare Research and Quality, and the Joint Commission for Accreditation of Healthcare Organizations. Catheter-related infections will continue to pose a serious threat unless prevention strategies, diagnostic techniques, and treatment modalities are implemented to address the pathogenic mechanisms of CRBSI and the microbiology of biofilms associated with vascular access devices.
Topics in Advanced Practice Nursing eJournal. 2005;5(3) © 2005 Medscape
Cite this: Catheter-Related Infections: It's All About Biofilm - Medscape - Aug 18, 2005.