Silkworm model of biofilm formation: In vivo evaluation of antimicrobial tolerance of a cross-kingdom dual-species (Escherichia coli and Candida albicans) biofilm on catheter material

Abstract

Biofilms are formed by microorganisms and their products on the surface of materials such as medical devices. Biofilm formation protects microorganisms from antimicrobial agents. Bacteria and fungi often form dual-species biofilms on the surfaces of medical devices in clinical settings. An experimental system to evaluate in vivo biofilm formation by the pathogenic fungus Candida albicans was established using silkworms inserted with polyurethane fiber (PF), a catheter material. In the present study, we established an in vivo experimental system using silkworms to evaluate the antimicrobial tolerance of Escherichia coli in single- and dual-species biofilms formed on the surface of the PF. The injection of E. coli into the PF-inserted silkworms led to the formation of a biofilm by E. coli on the surface of the PF. E. coli in the biofilm exhibited tolerance to meropenem (MEPM). Furthermore, when E. coli and C. albicans were co-inoculated into the PF-inserted silkworms, a dual-species biofilm formed on the surface of the PF. E. coli in the dual-species biofilm with C. albicans was more tolerant to MEPM than E. coli in the single-species biofilm. These findings suggest the usefulness of an in vivo experimental system using PF-inserted silkworms to investigate the mechanisms of MEPM tolerance in E. coli in single- and dual-species biofilms.

A Silkworm Infection Model for Evaluating <i>In Vivo</i> Biofilm Formation by Pathogenic Fungi

“…By utilizing the catheter-material-inserted silkworm infection model, an experimental system has been established to evaluate the impact on the antibiotic tolerance of Escherichia coli caused by cross-kingdom dual-species biofilm formation with C. albicans 50) . E. coli is a frequently isolated Gramnegative bacterium in bloodstream infections 51,52) .…”

“…The interactions between E. coli and C. albicans in cross-kingdom dual-species biofilms have been studied in vitro [53][54][55][56] . An in vivo experimental system using silkworms for the cross-kingdom dual-species biofilm by E.coli and C. albicans was established using the clinical E. coli isolate RB-3, known for its high biofilm-forming capacity in vitro 50) . E. coli in the crosskingdom dual-species biofilm on the surface of PF inside silkworm showed tolerance to the carbapenem antibiotic meropenem (MEPM) (Fig.…”

“…E. coli in the crosskingdom dual-species biofilm on the surface of PF inside silkworm showed tolerance to the carbapenem antibiotic meropenem (MEPM) (Fig. 2) 50) . Even when co-administering MEPM and the echinocandin antifungal drug micafungin (MCFG) against the silkworm with the cross-kingdom dualspecies biofilm by E. coli and C. albicans, the viable cell numbers for both microbes on the surface of PF did not decrease 50) .…”

“…Even when co-administering MEPM and the echinocandin antifungal drug micafungin (MCFG) against the silkworm with the cross-kingdom dualspecies biofilm by E. coli and C. albicans, the viable cell numbers for both microbes on the surface of PF did not decrease 50) . These results suggest that E. coli and C. albicans in the cross-kingdom dual-species biofilm on the surface of PF inside silkworms become tolerant to antibiotics and antifungal drugs, respectively 50) . The catheter-material-inserted silkworm infection model demonstrated that treatment of infection with the cross-kingdom dual-species biofilm is difficult in vivo.…”

“…Viable E. coli cells in the cross-kingdom dual-species biofilm by E. coli and C. albicans on the surface of PF were determined. The data were taken from Eshima et al50) and were partly modified.…”