Biofilm formation by ESBL-producing strains of Escherichia coli and Klebsiella pneumoniae

Objectives: Biofilm production in extended spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae provides a favourable environment for the exchange of antibiotic-resistance genes and could facilitate widespread dissemination. We aimed to assess biofilm development in ESBL-producing E. coli and K. pneumoniae isolates and determine how development relates to microbiological characteristics and clinical outcomes. Methods: 147 ESBL-producing E. coli and 82 K. pneumoniae were genetically characterized. Biofilm formation was measured at 1.5, 4, 6, and 24 h during culture in blood heart infusion using a microbead immobilization assay (BioFilm Ring test.). Results were given as biofilm formation index (BFI) with lower values indicating increased presence of biofilm (range = 0-21). Results: In total, 57.1% of strains were strong producers of biofilm (BFI < 2), whereas 13.4% lacked biofilm production (BFI > 18). Standard biofilm production (BFI < 7) was common in E. coli isolates (61.9%). For E. coli, biofilm production was less frequently observed in ST131 clones (p = 0.03) but more frequently in strains harbouring toxin (p = 0.008) or adhesin (p = 0.008) virulence factor genes. Despite almost all K. pneumoniae having standard biofilm production (90.2%), there was a 2.4-times higher odds of observing biofilm in ST29/147/323 versus other ST-types (p = 0.13). Patients with standard biofilm producing isolates were not at increased risk of transfer to intensive-care (odds-ratio = 2.80, 95%CI = 0.59-13.21) or death within 12-months (odds-ratio = 1.61, 95%CI = 0.75-3.43). Conclusion: In these ESBL-producing strains, biofilm production is linked to certain virulence factors in E. coli and is common in K. pneumoniae. Further exploration of whether biofilm production increases dissemination and risk of severe clinical outcomes is needed in larger collections of isolates.