September 2, 2010 at 5:21 pm #2925HarrisonKeymaster2 pts
Biofilm infections: Newer understanding of old problem
The problem with biofilm is always present in our daily lives. The clogging of oil pipes, sewage lines and even stains on the exterior glass of high-rise buildings are examples of biofilms. The adverse impact of biofilm is also felt in medical field, especially in orthopedics.
The organisms are capable of aggregating in a protective environment, as well as surviving in the harshest. Organisms in a biofilm develop a sophisticated method of communication that allows them to escape immune surveillance and antibiotic therapy. The high rate of failure seen with irrigation and debridement of an infected prosthesis or the inability to treat an established periprosthetic infection, can all be explained by formation of biofilm.
The inability of standard culture techniques to isolate an organism in cases of suspected infection or so-called aseptic loosening has fueled interest in investigation of biofilms.
Biofilm formation represents a highly evolved prokaryotic defense mechanism against external stresses. The matrix of extracellular polymeric substance (EPS) that surrounds and protects a biofilm community deters most physical insults.
Biofilm communities are far less susceptible to antimicrobial agents than planktonic organisms because most antimicrobial agents work by disrupting active metabolic processes, and biofilms contain large pockets of inactive, sessile bacteria which are unaffected by these agents. Finally, infecting organisms have developed methods for hijacking the bodys defense mechanisms and matrix proteins to adhere to surfaces and form biofilms.
A clearer understanding of the problems associated with prosthetic joint infection (PJI) due to biofilm formation requires an appreciation of the physiology of biofilms. Biofilms undergo a five-stage developmental process: First, they form tenuous attachments to a surface; second, cells develop strong adhesions to that surface; third, they form aggregates; fourth, these aggregates develop into a mature biofilm; and fifth, the biofilm disperses. Interestingly, cells often disperse in still-associated clumps, which are capable of seeding new surfaces and perpetuating an infection. The fact that Staphylococcus organisms tend to follow this pattern, moreover, explains the tendency for the development of satellite infections in patients with such infections.
Methods for attacking biofilms have tended to focus on the first and fifth stages of development; ie, on preventing the initial attachment of the bacteria, and on hijacking bacterial dispersal mechanisms for the purpose of dissolving the infection in a more controlled fashion.
Biofilms can be directly visualized using various microscopic techniques including scanning electron microscopy (SEM), confocal laser microscopy and, more recently, fluorescence in-situ hybridization (FISH) techniques. Numerous researchers have directly observed biofilms in cases in which intraoperative cultures have grown no organism. More recently, ultrasonication of explanted components to loosen any adherent organisms has been shown to vastly increase the recovery of viable organisms from intraoperative specimens. Tunney and colleagues were among the first to demonstrate the value of this method. Of 120 retrieved implants, they were able to culture organisms from 26 implants, of which only five had had associated positive tissue cultures at the time of surgery. Histopathological examination of available tissue samples from these patients revealed inflammatory cells in all cases, and SEM imaging confirmed the presence of biofilm on the components.
Advanced proteomics and genetic methods have also been developed to identify biofilms. Kobayashi and colleagues, and numerous others, have investigated the role that both standard and quantitative polymerase chain-reactions (PCR and qPCR) using universal primers of the 16 S rRNA gene may have in identifying a bacterial presence in the case of medical implants. The high sensitivity of these methods, however, has fueled recent efforts to improve the specificity of these molecular techniques.
The Center for Genomic Studies at Allegheny is developing protocols for identification of orthopedic pathogens using the IBIS T5000 technology, with confirmation by FISH imaging. IBIS operates on the same principle as PCR, but uses a cocktail of species-specific primers for a wide range of pathogenic organisms rather than universal primers in order to detect infecting organisms. Their results to date have supported the increased specificity of the IBIS techniques.
Orthopedic implant-associated infections are difficult to treat, both physically and psychologically, for the patient and the surgeon. Organisms capable of forming biofilms tend to be more virulent, as Hawser and Douglas described in their investigations of infection by Candida species. In a presumed infection, without the confirmation of a positive culture it becomes difficult to determine based on known methods for diagnosing infection whether a patients condition warrants an extensive, aggressive resection of all components with placement of an antibiotic-impregnated spacer, or whether less drastic measures may be taken. With biofilm formation, this question becomes more troubling, since eradication of a subclinical infection supported by a well-entrenched biofilm community cannot be effective without aggressive treatment, but subjecting a patient to such treatment without confirmation of the presence of infection may not be warranted.
Molecular methods for detecting biofilms are promising, particularly since their findings have been confirmed by direct visualization of biofilm structures using microscopy techniques. Eradication of biofilm-associated infections is advancing as various naturally occurring and newly synthesized antimicrobial agents come under investigation for their potential use in deterring biofilm formation. Current research has focused on developing a clearer picture of the patterns of transcriptional regulation of biofilm-specific genes, as well as of signaling methods employed by biofilms in their various stages of development. In both cases, the goal is to find ways to target and interfere with these processes in order to reduce the burden of biofilm infection. Other authors have investigated whether the use of antibiotic-impregnated bone cement in primary arthroplasties reduces the likelihood of PJI.
In terms of the problems posed by biofilms, however, perhaps the most important obligation that orthopedic surgeons now have is to perform a careful re-evaluation of the concept of PJI. Numerous authors have advocated treating culture-negative patients for whom there is a high clinical suspicion as though they are infected.
In terms of our growing knowledge of biofilms, all cases of so-called aseptic loosening should be evaluated for the possibility of infection, standard workup protocols should be adhered to (ie, serological investigations such as erythrocyte sedimentation rate and C-reactive protein, and the surgeon should maintain a high clinical suspicion for infection.
Javad Parvizi, MD, FRCS, editor of Infection Watch, can be reached at the Rothman Institute, 925 Chestnut St., 5th Floor, Philadelphia, PA 19107.
Gristina AG, Costerton JW. Bacterial adherence to biomaterials and tissue: the significance of its role in clinical sepsis.J Bone Joint Surg (Am); 1985;67:264-273.
Hawser SP, Douglas LJ. Biofilm Formation by Candida Species on the Surface of Catheter Materials in Vitro. Infection and Immunity. 1994; 62,3:915-921.
Kobayashi H, Oethinger M, Tuohy MJ, et al. Improved detection of biofilm-formative bacteria by vortexing and sonication: a pilot study. Clin Orthop Relat Res. 2009;467(5):1360-1364.
Tunney MM, Patrick S, Gorman SP, Nixon JR, et al. Improved detection of infection in hip replacements: A currently underestimated problem. J Bone Joint Surg (Br). 1998;80:568572.
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