Diabetic foot ulcers may become non-healing in spite of adequate systemic antibiotic treatment. The penetration of systemically-administered antibiotics to the site of infection is variable as well as uncertain.

Investigators in the United Kingdom developed an in vitro model to determine the effectiveness of different treatments for infected diabetic foot ulcers in a wound-like environment. The activity of systemic levels of antibiotics was compared with that of topically applied antibiotics.

This happens to be the first study to have harvested bacteria from diabetic foot infections and recreated similar polymicrobial biofilms to those present in vivo for individual subjects. Treatment with levels of gentamicin that are attained in serum after systemic administration led to a 0-2 log reduction in bacterial viability of P. aeruginosa, S. aureus or a polymicrobial biofilm. Addition of gentamicin loaded calcium sulfate beads led to a 5-9 log reduction in P. aeruginosa, S. aureus and polymicrobial biofilms.

Systemically administered antibiotics were thus reported to be inadequate for the treatment of these infections, considering the increased concentrations required to inhibit cells in a biofilm. Topical antibiotics are a more effective and promising alternative.

Source: Price BL, Morley R, Bowling FL, et al. Susceptibility of monomicrobial or polymicrobial biofilms derived from infected diabetic foot ulcers to topical or systemic antibiotics in vitro. PLoS One. 2020 Feb 18;15(2):e0228704.