Pathogenic oral biofilms are universal, chronic, and costly. Despite advances in understanding the mechanisms of biofilm formation and persistence, novel and effective treatment options remain scarce. Nanoparticle-mediated eradication of the biofilm matrix and resident bacteria holds great potential. Particularly, nanoparticles that target specific microbial and biofilm features utilizing non-toxic materials are well-suited for clinical translation. However, much work remains to characterize the local and systemic effects of therapeutic agents topically applied to chronic biofilms, such as those that cause dental caries. This perspective summarizes the pathogenesis of oral biofilms, describes current and future nanoparticle-mediated treatment approaches, and highlights outstanding questions that are paramount to answer to effectively target and treat oral biofilms.

Biofilms are surface-bound, structured microbial communities underpinning persistent bacterial infections. Biofilms often create acidic pH microenvironments, providing opportunities to leverage responsive drug delivery systems to improve antibacterial efficacy. Here, the antibacterial efficacy of novel formulations containing pH-responsive polymer nanoparticle carriers (NPCs) and farnesol, a hydrophobic antibacterial drug, were investigated. Multiple farnesol-loaded NPCs, which varied in overall molecular weight and corona-to-core molecular weight ratios (CCRs), were tested using standard and saturated drug loading conditions. NPCs loaded at saturated conditions exhibited ~300% greater drug loading capacity over standard conditions. Furthermore, saturated loading conditions sustained zero-ordered drug release over 48 hours, which was 3-fold longer than using standard farnesol loading. Anti-biofilm activity of saturated NPC loading was markedly amplified using Streptococcus mutans as a biofilm-forming model organism. Specifically, reductions of ~2–4 log colony forming unit (CFU) were obtained using microplate and saliva-coated hydroxyapatite biofilm assays. Mechanistically, the new formulation reduced total biomass by disrupting insoluble glucan formation and increased NPC-cell membrane localization. Finally, thonzonium bromide, a highly potent, FDA-approved antibacterial drug with similar alkyl chain structure to farnesol, was also loaded into NPCs and used to treat S. mutans biofilms. Similar to farnesol-loaded NPCs, thonzonium bromide-loaded NPCs increased drug loading capacity ≥ 2.5-fold, demonstrated nearly zero-order release kinetics over 96 hours, and reduced biofilm cell viability by ~6 log CFU. This work provides foundational insights that may lead to clinical translation of novel topical biofilm-targeting therapies, such as those for oral diseases.

Flavonoids are natural polyphenolic compounds with myriad biological activities and potential as prophylactic and therapeutic agents. However, poor aqueous solubility and low bioavailability have limited the clinical utility of flavonoids, suggesting that drug delivery systems (DDSs) may improve their clinical relevance. Therefore, loading of a representative flavonoid (i.e., myricetin) into a diblock, polymeric nanoparticle carrier (NPC) DDS with a cationic corona and hydrophobic core was investigated. Absorbance and fluorescence spectroscopy results revealed association constants and standard Gibbs free energy values that align with previously reported values (K a = ∼1–3 × 104 M–1; ΔG° = −5.4 to −6.0 kcal mol–1), suggesting that NPCs load myricetin via electrostatic interactions. The zeta potential and gel electrophoresis analysis confirmed this loading mechanism and indicated that NPCs improve myricetin solubility >25-fold compared to myricetin alone. Finally, the dual-drug loading of NPCs was tested using a combination of myricetin and a hydrophobic drug (i.e., farnesol). Electrostatic loading of NPCs with myricetin at concentrations ≤1.2 mM did not affect NPC core loading and release of farnesol, thus demonstrating a novel formulation strategy for the dual-drug-loaded NPC. These findings offer key insights into the NPC DDS design that may enhance the clinical relevance of flavonoid-based therapeutic approaches.

'Candidatus Liberibacter asiaticus' is the bacterium implicated as a causal agent of the economically damaging disease of citrus called huanglongbing (HLB). Vertical transmission of the organism through seed to the seedling has not been demonstrated. Previous studies using real-time polymerase chain reaction assays indicated abundant bacterial 16S rRNA sequences in seed coats of citrus seed but the presence of intact bacterial cells was not demonstrated. We used microscopy to verify that intact bacterial cells were present in citrus seed coats. Bacterial cells with the morphology and physical dimensions appropriate for 'Ca. L. asiaticus' were seen in phloem sieve elements in the vascular bundle of grapefruit seed coats using transmission electron microscopy (TEM). Fluorescence in situ hybridization (FISH) analyses utilizing probes complementary to the 'Ca. L. asiaticus' 16S rRNA gene revealed bacterial cells in the vascular tissue of intact seed coats of grapefruit and pummelo and in fragmented vascular bundles excised from grapefruit seed coats. The physical measurements and the morphology of individual bacterial cells were consistent with those ascribed in the literature to 'Ca. L. asiaticus'. No bacterial cells were observed in preparations of seed from fruit from noninfected trees. A small library of clones amplified from seed coats from a noninfected tree using degenerate primers targeting prokaryote 16S rRNA gene sequences contained no 'Ca. L. asiaticus' sequences, whereas 95% of the sequences in a similar library from DNA from seed coats from an infected tree were identified as 'Ca. L. asiaticus', providing molecular genetic corroboration that the bacterial cells observed by TEM and FISH in seed coats from infected trees were 'Ca. L. asiaticus'.

Dental caries (i.e., tooth decay), which is caused by biofilm formation on tooth surfaces, is the most prevalent oral disease worldwide. Unfortunately, many anti-biofilm drugs lack efficacy within the oral cavity due to poor solubility, retention, and penetration into biofilms. While drug delivery systems (DDS) have been developed to overcome these hurdles and improve traditional antimicrobial treatments, including farnesol, efficacy is still modest due to myriad resistance mechanisms employed by biofilms, suggesting that synergistic drug treatments may be more *