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What Are Biofilms?

Hickok, Noreen J., PhD

doi: 10.1097/BRS.0000000000002548
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Department of Orthopaedic Surgery, Sidney Kimmel Medical College of Thomas Jefferson University, Philadelphia, PA.

Address correspondence and reprint requests to Noreen J. Hickok, PhD, Sidney Kimmel Medical College of Thomas Jefferson University, 1015 Walnut St., Suite 501, Philadelphia, PA 19107; E-mail: Noreen.Hickok@jefferson.edu

Received 2 January, 2018

Accepted 5 January, 2018

The manuscript submitted does not contain information about medical device(s)/drug(s).

The National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health's funds under Award Numbers RO1 AR069119 and RO1 AR072513 were received to support this work.

Relevant financial activities outside the submitted work: grants.

Despite aggressive perioperative antibiotic treatments, between 1 in 20 and 1 in 100 patients undergoing spinal surgery develop an infection.1 For patients with traumatic injuries, these rates easily exceed 10%.1 Prevention of spinal infection depends on immune surveillance, stringent sterile measures to minimize bacterial bioburden, and antibiotic prophylaxis. As the topography of the hardware and the bone is complex, the intervertebral disc and fusion mass reside in a relatively hypoxic environment, retention of hardware is required for spinal stability, and antibiotics show attenuated efficacy against implant-associated bacteria,2 infections can cause life-threatening problems in spinal sites.

In the presence of an implant, bacteria adhere and form biofilms (Figure 1), which are three-dimensional networks of bacteria that are encased in an extracellular polymeric substance, an encapsulating slime that contains polysaccharides and nucleic acids. The structures are semipermeable and have channels for nutrient streaming where position within this three-dimensional structure may impact survival. Importantly, once bacteria are formed into biofilms, whether floating or associated with the implant or bone matrix, the bacteria undergo changes in metabolism and gene expression that reduce antibiotic susceptibility.3 This antibiotic recalcitrance occurs due to: (A) reduced metabolic rate—antibiotics generally target functions of rapidly growing cells; (B) secretion of factors that sequester antibiotics; and (C) decreased antibiotic diffusion rates in the biofilm, resulting in lower antibiotic concentrations and increased survival of biofilm bacteria.4 Importantly, the implant surface serves as the perfect host for these organisms. Specifically, it is rapidly coated with fibronectin, collagen, fibrin(ogen), and other serum proteins that facilitate bacterial adherence to the metal and biofilm formation (Figure 2).

Figure 1

Figure 1

Figure 2

Figure 2

Finally, the biofilm matures and reintroduces nonadherent planktonic bacteria into the surrounding space, seeding new colonies from this original nidus of infection. These planktonic bacteria, whether from the biofilm or the original infection, can adhere to the bone extracellular matrix and most likely infiltrate the bone matrix (Figure 3). This localization provides a protected niche until cell death and/or osteolysis releases bacteria from their niches and clinical infection is reestablished. Therefore, with all of the problems associated with the eradication of established infection, it is critical to define new methods and technologies that can serve as successful preventatives.

Figure 3

Figure 3

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Acknowledgments

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

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References

1. Bible JE, Biswas D, Devin CJ. Postoperative infections of the spine. Am J Orthop 2011; 40:E264–E271.
2. Darouiche RO. Antimicrobial approaches for preventing infections associated with surgical implants. Clin Inf Dis 2003; 36:1284–1289.
3. Costerton JW, Stewart PS, Greenberg EP. Bacterial biofilms: a common cause of persistent infections. Science 1999; 284:1318–1322.
4. Costerton JW. Overview of microbial biofilms. J Ind Microbiol 1995; 15:137–140.
Keywords:

bacteria; biofilms; spinal infection

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