# Amoxicillin and metronidazole resistance of bacteria isolated from dental implants with peri-implant diseases: a pilot cross-sectional study

## TL;DR

This study finds that bacteria from dental implants with gum disease are resistant to amoxicillin and metronidazole but remain sensitive to clindamycin.

## Contribution

The study reports 100% resistance to amoxicillin and metronidazole in peri-implant bacteria, highlighting a potential clinical concern.

## Key findings

- All 10 bacterial isolates showed resistance to amoxicillin and metronidazole.
- All isolates remained sensitive to clindamycin.
- Two isolates were identified as Streptococcus salivarius via 16S rRNA sequencing.

## Abstract

Peri-implant mucositis is a reversible inflammatory lesion of the mucosa surrounding a dental implant, caused by the accumulation of bacterial plaque and biofilm formation, without bone loss. If peri-implant mucositis is not addressed, it can progress to peri-implantitis, characterized by significant inflammation and infection of the peri-implant mucosa accompanied by the loss of supporting bone. Clinical evidence suggests that the management of peri-implant infections consists of mechanical debridement of the implant, surgical intervention and the administration of antibiotics. However, limited information is available regarding antibiotic resistance in bacteria causing peri-implant diseases. This study is focused on assessing the antibiotic resistance of bacteria isolated from explanted dental implants with peri-implant infections to amoxicillin, clindamycin and metronidazole. To this end, biofilms were recovered using titanium curettes from dental implants of 10 patients with peri-implant infections: patients with peri-implant mucositis (n=4) exhibited redness, swelling or bleeding and absence of bone loss; patients with peri-implantitis (n=6) were diagnosed based on probing depth ≥6 mm and presence of bone loss. Antibiotic sensitivity was assessed using the Kirby–Bauer disc diffusion method in accordance with the Clinical and Laboratory Standards Institute at 10 µg per disc of amoxicillin, 30 µg per disc of clindamycin and metronidazole at a concentration of 50 µg per disc. The results were expressed as the diameters of inhibition zones for each antibiotic. Two peri-implant bacteria were identified by sequencing of their 16S rRNA. Peri-implant bacteria showed resistance to amoxicillin and metronidazole at 100% (10 out of 10). All isolates from dental implants with peri-implant infections (10 out of 10) were sensitive to clindamycin. Two isolates, M29 and P30 strains, were identified as Streptococcus salivarius by 16S rRNA sequencing. Our findings reveal emerging resistance to amoxicillin and metronidazole in clinical isolates from implants with peri-implant infections, yet bacterial susceptibility to clindamycin remains.