Povidone-Iodine Antimicrobial Activity In Vitro Against Periodontal Bacterial Pathogens

Background Povidone-iodine (PV-I) is known to be active in vitro against periodontal bacterial pathogens, but previous studies most often used ≥5-minute contact times for PV-I testing and/or evaluated laboratory reference strains of bacterial species. This study further examined the antimicrobial effects of PV-I by using a 60-second in vitro treatment time for 10% and 5% PV-I on freshly recovered clinical isolates of subgingival biofilm bacteria from severe human periodontitis lesions. Methods Subgingival biofilm samples from 22 adults with severe periodontitis were mixed in vitro with 10% PV-I, 5% PV-I, or no PV-I (n = 22 samples per group), with residual PV-I neutralized after 60 seconds with sodium thiosulfate. The samples were then inoculated onto enriched Brucella blood agar (EBBA), with samples not treated with PV-I additionally plated onto EBBA supplemented with breakpoint concentrations of either amoxicillin, clindamycin, doxycycline, or metronidazole to detect antibiotic-resistant test species. After 7 days of anaerobic incubation, total viable microbial counts and selected red/orange complex periodontal pathogens (Porphyromonas gingivalis, Tannerella forsythia, Prevotella intermedia/nigrescens, Parvimonas micra, Campylobacter rectus, Fusobacterium nucleatum, and Streptococcus constellatus) were phenotypically identified and quantitated on the EBBA plates, with additional cultivable isolates from PV-I-treated samples identified using matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry. Results Subgingival biofilm samples treated in vitro for 60 seconds with 10% or 5% PV-I yielded significantly lower mean total viable microbial counts (60-68% less) and significantly lower mean total cultivable proportions of red/orange complex periodontal pathogens (0.5%-0.7%) than samples not exposed to PV-I (14.8%) (P < 0.001), with no statistically significant differences between 10% and 5% PV-I in vitro treatments. All evaluated red/orange complex periodontal pathogens were culture-negative in 21 (95.5%) and 19 (86.4%) of the 22 subgingival biofilm samples after 10% and 5% PV-I in vitro treatment, respectively. Antibiotic-resistant and antibiotic-susceptible red/orange complex periodontal pathogens were similarly sensitive in vitro to 10% and 5% PV-I. Streptococcus species, particularly Streptococcus oralis, were the most prevalent cultivable isolates in subgingival samples treated in vitro with 10% or 5% PV-I for 60 seconds. Conclusions Both 10% and 5% PV-I significantly suppressed total viable microbial counts and red/orange complex periodontal pathogens, but not periodontal health-associated Streptococcus species, during 60 seconds of in vitro treatment on subgingival biofilm samples from patients with severe periodontitis, with no statistically significant differences in the antimicrobial activity of the two PV-I concentrations. These in vitro PV-I susceptibility findings with freshly isolated subgingival biofilm bacteria further support the clinical use of PV-I in periodontal therapy as an adjunct to mechanical root debridement in altering a pathogenic subgingival microbiome toward one compatible with periodontal health.