Invasive species drive polymicrobial resistance to amoxicillin in oral biofilms through beta-lactamase release

Since bacterial biofilms often cause refractory infections, antimicrobial susceptibility testing (AST) is highly desirable even for oral peri-implant biofilms. However, characterization of polymicrobial drug resistance is challenging due to high diversity and complexity of these biofilms. In this work, we developed laser-assisted AST and detected polymicrobial amoxicillin resistance in peri-implantitis. TEM-1 beta-lactamase production enabled Enterobacter sp. strain to protect its otherwise susceptible biofilm cohabitants. To understand the beta-lactamase driven cross-protection in human microbiome we aggregated genomic and patient microbial data, developed a cross-protection assay, studied representative strain collection and established a complex biofilm in vitro model (with an average of 133 species from 164 found in dental plaque). Multiple oral invader species and only a single typical oral microorganism were able to cross-protect. Diverse bla genes conferred activity. Invaders not only cross-protected the biofilm from antibiotic, but also supported expansion of opportunistic pathogens like Fusobacterium species. Cross-protection in complex biofilms depended on the diffusion rate and population size of invader that could be bio-controlled with a phage. Deciphering polymicrobial resistance might support the development of diagnostic and therapeutic approaches to combat implant-associated biofilm infections in the human mouth.