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 (<i>Porphyromonas gingivalis</i>, <i>Tannerella forsythia</i>, <i>Prevotella intermedia/nigrescens</i>, <i>Parvimonas micra</i>, <i>Campylobacter rectus</i>, <i>Fusobacterium nucleatum</i>, and <i>Streptococcus constellatus</i>) 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. <i>Streptococcus</i> species, particularly <i>Streptococcus oralis</i>, 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 <i>Streptococcus</i> 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.