Review Question - QID 211189

Planktonic bacteria are the free-floating bacteria that spread, often leading to sepsis and active infection. They attach to an inert substrate and undergo apoptosis to create a matrix for a biofilm in its planktonic stage.

A biofilm occurs when adherent cells become embedded within an extracellular matrix that is composed of extracellular polymeric substances. The development of a bacterial biofilm is a multi-stage process. In the first step, free-floating individual bacteria bind to a substrate (planktonic stage). After attachment, quorum sensing (cell-to-cell communication) allows for the maturation of the biofilm and expression of its genes that activate virulence factors (sessile stage). These microbial cells growing within the biofilm are physiologically distinct from planktonic cells. The formed glycocalyx allows the biofilm to adhere to a prosthesis while making it resilient to antibiotics. Typically, prosthetic explant is indicated with infection >4 weeks due to biofilm infection, which has invaded the prosthetic-bone interface.

Masri et al. prospectively reviewed 49 patients undergoing a modified 2-stage exchange arthroplasty for infected total hip and knee arthroplasties using the prosthesis of antibiotic-loaded acrylic cement with tobramycin and vancomycin. They reported on the intra-articular concentrations of tobramycin and vancomycin at the time of removal. They concluded that the dose of vancomycin in the cement did not influence the elution of either tobramycin or vancomycin, and they recommend the use of at least 3.6 g of tobramycin and 1 g of vancomycin per package of bone-cement.

Nana et al. reviewed the high affinity of microorganisms to adhere to foreign materials commonly used in orthopedics, including cobalt-chromium, titanium, polyethylene, and polymethylmethacrylate (PMMA) cement by forming biofilms. They report that S. aureus and S. epidermidis, are the most common biofilm-forming bacteria found in orthopedics, and, when combined with P. aeruginosa, they represent nearly 75% of biofilm infections. They concluded that while no current guidelines exist for treating these infections, recent studies have shown that biofilm growth can be fully inhibited when PMMA is mixed with both daptomycin and gentamicin.

McNamara et al. reviewed the mechanism of Vancomycin. They report on its increased use due to the growing resistance of many gram-positive bacteria to β-lactam antibiotics. They conclude that unlike penicillins and cephalosporins, cross-resistance with vancomycin does not develop and it possesses activity against nearly all gram-positive bacteria, with no usefulness against gram-negative bacilli.

Illustration A is the microscopic visualization of a Staphylococcus aureus biofilm. Illustration B demonstrates the stages of biofilm formation.

Incorrect Answers:
Answer 1: Sessile stage involves the formation of biofilm and its expression.
Answer 3: Maturation is the development of the sessile, no-growth, biofilm.
Answer 4: Metabolic is not a distinct stage in biofilm formation.
Answer 5: Dispersion is the release of free-floating planktonic bacteria for a mature biofilm.