2. Bacterial Adhesion to Biomaterial Surfaces. Yuehuei H. An, Richard J. Friedman, Robert A. Draughn,. Edwin A. Smith, and Joseph F. John. 1. Introduction and ...
2 Bacterial Adhesion to Biomaterial Surfaces Yuehuei H. An, Richard J. Friedman, Robert A. Draughn, Edwin A. Smith, and Joseph F. John
1. Introduction and Terminology Research into bacterial adhesion and its significance is a large field involving different aspects of nature and human life, including marine science, soil and plant ecology, the food industry, and, most important, the field ofbiomedicine. Adhesion of bacteria to human tissue surfaces and implanted biomaterial surfaces is an important step in the pathogenesis of infection (1-3). The exact mechanism by which these foreign body infections occur still remains unclear. It is thought that certain strains of bacteria, particularly Staphylococcus epidermidis, one species of the coagulase-negative staphylococci, secrete a layer of glycocalyx once adhesion occurs on the surface, making themselves less accessible to human host defense mechanisms (4) and significantly decreasing antibiotic susceptibility (5-10). The bacteria can remain dormant on the material surface for a long period of time until the environment changes and allows them to overgrow, as occurs with decreased host immune function or poor tissue ingrowth around the prosthesis. Morethan200,000primaryhipand 150,000 primary knee arthroplasties are performed
each year in the United States, and between 0.5 and 2.5% will become infected within 10 yr(Table 1). Infection following total joint arthroplasty can have catastrophic results for the patient, both physically and psychologically, leading to failure of the arthroplasty, prolonged hospitalization, possible amputation, and even death (11). The challenge still remains for better preventive and therapeutic measures. In this chapter, common pathogens causing prosthetic joint infection, the mechanisms of bacterial adhesion and prosthetic infection, the experimental methods for bacterial adhesion and prosthetic infection, and the preventive strategies for prosthetic infection will be discussed. To lessen confusion and improve our understanding, the following terms are defined according to the literature (12-14) and our own experience.
1.1. Adhesion, Adherence, and Attachment Bacterial adhesion is a process whereby bacteria adhere firmly to a surface by a complete interaction between the two, including an initial phase of reversible, physical contact and a time-dependent phase of irreversible chemical and cellular adherence. Energy is
From: Human Biomaterials Applications Edited by D. L. Wise, et al. Humana Press Inc., Totowa, NJ
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An et al. Table 1 The Involvement of S. epidermidis and S. aureus in Total Jomt Replacement
First author (yr), ref
Total cases
Infected cases
Percent infecteda
Percent, S. epi orCNSb
Josefsson ( 1993) (2 7)
1688
15 32 110 67 131 63 33 38
1.3
20 37 26 13 35 40 18 18 26
Merritt (1992) (28) Sanzen (1988) (29) Maderazo (1988) (30) Fitzgerald (1985) (31) Inman (1984) (20) Cherney (1983) (32) Kamme (1981) (24) Total after 1980 Fitzgerald (1977) (33) Benson (1975) (19) Todd (1972) (34) Charnley (1972) (22) Patterson (1972) (35) Wilson (1972) (36) Total before 1980 a Numbers b Numbers
3215 321 320 368 100
42 17 17 85 30 12
1.3 5.3 5.3
8.2 12.0
19 0 12 5 0 42 13
Percent, S. aureui 46 15 23 43 29 19 27 23
Percent, othersb
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34 58 51 44 36 41 55 59 46
24 12 0 40 10 8 16
57 88 88 56 90 50 71
of infection cases/total cases =percent of infection. of certain bacteria cultured/total positive cultures = percent.
consumed in the formation of an adhesive junction between the bacteria and surface. Adherence is a general description of bacterial adhesion, or the initial process of attachment ofbacteria directly onto a surface, and is not a proper alternative to adhesion. Attachment can be defined as the initial stage ofbacterial adhesion, and refers more to the physical contact than the complicated chemical and cellular interactions, and usually is reversible. 1.2. Adhesin and Receptor
Adhesin is a substance (a surface macromolecule, commonly lectins or lectin-like proteins or carbohydrate) produced by bacteria thought to be specific for that adhesion (1 5, 16). Generally, any structures responsible for adhesive activities can be called adhesins. Bacteria may have multiple adhesins for different surfaces (different receptors) (17). A receptor is a component (both known and putative) on the surface ofbiomaterials or host tissue that is bound by the active site of an adhesin during the process of specific adhesion (12).
1.3. Adsorption and Deposition
Adsorption is the accumulation of molecules onto a solid surface at a concentration exceeding that in the bulk fluid and is brought about as a result of random Brownian motion. Deposition normally is used to describe the accumulation of particles at a fluid interface brought about by the application of an external force. In most circumstances, gravitational forces cause particles to settle on the bottom of an aqueous container.
1.4. Hydrophobicity and Hydrophilicity The structure of water in the region near any surface (such as a solid material surface or bacterial surface) is perturbed over distances of up to several tens of molecular layers. Hydrophobicity or hydrophilicity are relative descriptions. Near a hydrophobic surface the water is less structured in terms of intermolecular hydrogen bonding between the water molecules, whereas water is more structured near a hydrophilic surface. Water contact angle (WCA) is a good example of the
Bacterial Adhesion to Biomaterial Surfaces
hydrophobic or hydrophilic nature ofa surface. A high WCA represents hydrophobicity and a low value represents hydrophilicity (12). 1.5. Glycocalyx and Biojilm Glycocalyx, or slime, is defined as an extracellular substance (the exopolymers composed mainly of polysaccharides) produced by the bacteria that may be partially free from the bacteria after dispersion in a liquid medium (water soluble), and can be removed from bacterial cells by washing. An accumulated biomass of bacteria and extracellular material (basically slime) on a solid surface is called a biofilm. 1. 6. Substrate and Substratum The former is a material utilized by microorganisms as a source ofenergy, but it is often used as an alternative to substratum. Substratum is a solid surface to which a microorganism may adhere.
2. Common Pathogens of Prosthetic Infection When an infection occurs, many questions are raised, such as whether it is acute or chronic, where the bacteria came from, and what species or strains the bacteria belongs to, since the therapeutic strategy should be planned according to the answers. Orthopedic prosthetic infections can be classified into early and late infections. Different authors have been using different time periods to define the two stages of infection, such as 3 wk, 3 mo (18,19), 1 yr (20), or even 2 yr with three stages (21). Prosthetic infection should be defined as a deep infection around the implant, whereas a superficial wound infection that heals without subsequent involvement of the implant should not be included. Early infections feature an acute process and are relatively superficial, whereas late infections happen months or even years after a clinically successful joint arthroplasty, and are mostly deep infections. According to several reports, staphylococci are the most important pathogens of prosthetic infection. S. epidermidis, which
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was once recognized as nonpathogenic, is a major cause of late or chronic infections, whereas S. aureus still remains one ofthe most common pathogens for prosthetic infections, especially relatively early ones (22-24). Table 1 shows a roughly equal incidence of S. epidermidis and S. aureus causing prosthetic hip joint infections, and agrees with the calculation by Sanderson (25,26). Staphylococci are members of the family Micrococcaceae, characterized as gram-positive, nonmotile, catalase-positive, coagulasenegative, aerobic, or faculatively anaerobic cocci. Strains are distinguished by coagulase production and mannitol fermentation. S. aureus is coagulase-positive and S. epidermidis is coagulase-negative. Coagulasenegative staphylococci are a normal component of the skin flora, and S. epidermidis is the most common and predominant species (37,38). To date, more than 20 species have been identified. Coagulase-negative staphylococci are recognized widely as significant pathogens in patients with infections associated with orthopedic prostheses or implants, prosthetic heart valves, vascular prostheses, cerebrospinal fluid shunts, urinary tract catheters, peritoneal dialysis catheters, and other implants. S. aureus causes a more severe and rapid infection than S. epidermidis and its effects, therefore, may be more clinically obvious at an early stage following surgery. Additional organisms isolated from orthopedic prosthetic infections include Escherichia coli, Klebsiella group, Micrococcaceae, Pseudomonas group, Proteus spp., peptococci, streptococci, and anaerobes (19,26,29,33,39-41).
3. Mechanisms of Bacterial Adhesion and Prosthetic Infection 3.1. Mechanisms of Bacterial Adhesion Physiochemical and cellular aspects of bacterial adhesion are rather complicated topics, as noted by Dankert et al. (1 3), Dougherty (42, 43), and Gristina (44-46). A tremendous amount of
22 work has been done to understand the natural process ofbacterial adhesion to biomaterial surfaces, yet many questions remain unanswered (13,47). Basically, bacterial adhesion can be described as a two-phase process that includes an initial, instantaneous, reversible, physical phase (Phase One) and a time-dependent, irreversible, molecular and cellular phase (Phase Two) ( 47, 48). This concept has been accepted by the majority of researchers (13,44).
3.1.1. Physicochemical Interactions Between Bacteria and Material Surfaces (Phase One) Like tissue cells growing in an in vitro culture, bacteria prefer to grow on available surfaces rather than in the surrounding aqueous phase (49), a traitfrrstnoted by Zobell in 1943 (50). Planktonic bacteria move to or are moved to a material surface through and by the effects of physical forces, such as Brownian motion, van der Waals attraction forces, gravitational forces, the effect ofsurface electrostatic charge, and hydrophobic interactions. These physical interactions act as long- and short-range interactions (13,51). The long-range interactions (nonspecific, distances > 150 nm) between cells and material surface are described by mutual force, which is a function of the distance and free energy. Short-range interactions become effective when the cell and the surface come into close contact (
