Povidone-iodine and silver nitrate are equally effective in eradicating staphylococcal biofilm grown on a titanium surface: an in-vitro analysis

Abstract

Background: There is no consensus on the irrigation solution and concentration that should be used when performing a debridement, antibiotics, and implant retention (DAIR) surgery.

Aim: To determine the minimum biofilm eradication concentration (MBEC) of five antibacterial solutions and to compare their efficacies in eradicating staphylococcal biofilm embedded on a titanium surface.

Methods: Meticillin-sensitive Staphylococcus aureus (MSSA) and meticillin-resistant S. aureus (MRSA) ATCC standard strains were grown over porous Ti-6Al-4V acetabular screw-caps. Antibacterial solutions were povidone-iodine, rifampicin, silver nitrate, copper sulphate, and chlorhexidine. MBEC values were calculated for MSSA and MRSA. After 24 h, screw-caps were exposed for 3 min to each solution. Bacterial separation from each specimen was performed with vortex agitation and footprint on agar plate in triplicate. Colony forming units (cfu) were counted pre- and post-agitation, and the delta of cfu/mL was calculated for each solution. A threefold log reduction in cfu was considered a measure of solution efficacy. Comparison between groups was made with Fisher's test.

Findings: MBEC values for MSSA and MRSA, respectively, were as follows: 8000 μg/mL and 16,000 μg/mL for povidone-iodine; 64 μg/mL and 128 μg/mL for rifampicin; 10,000 μg/mL and 5120 μg/mL for silver nitrate; 900 μg/mL and 900 μg/mL for copper sulphate; 16 μg/mL and 32 μg/mL for chlorhexidine. Rifampicin, copper sulphate and chlorhexidine were ineffective against MSSA and MRSA biofilm compared with povidone-iodine (P<0.01) and silver nitrate (P=0.015) that had a delta cfu reduction >8 log. Povidone-iodine and silver nitrate showed negative footprints without visible MSSA (P=0.005) and MRSA (P=0.014).

Conclusions: Povidone-iodine and silver nitrate were the only irrigating solutions capable of eradicating at least 99.9% of 24-h biofilm.

Keywords: Biofilm; Irrigation solution; Periprosthetic joint infection; Povidone-iodine.