Determining the pathogenicity of uropathogenic Escherichia coli strains in the Galleria mellonella larvae model

Uropathogenic Escherichia coli (UPEC) is responsible for the majority of urinary tract infections, including those in catheterised patients. Galleria mellonella, an insect species, has been proposed as an alternative in vivo model to study the pathogenicity of E. coli. The aim of this study was to determine the pathogenicity of 48 UPEC strains using the larval disease score obtained from G. mellonella larvae model. The bacteria were also classified according to their phylogenetic group and the ability to form biofilms. The larvae were inoculated with the bacteria and observed for 72 hours. The LD₅₀, mortality rate, and survival curve for each UPEC strain were assessed. A larval disease score (0–10) was determined, which considered mortality, larval activity, cocoon formation and melanisation. Phylogenetic groups were determined by using PCR, and biofilm formation was assessed by using the crystal violet assay. The larval disease score permitted the classification of the bacteria into three pathogenicity groups (low, intermediate and high). Bacteria were classified into six of the seven phylogenetic groups tested (i.e. A, B1, B2, C, D and F), but none were classified into group E. Biofilm-producing strains were detected at both incubation times used. There was no significant association between the larval disease score and the phylogenetic group. The larvae were susceptible to infection by all UPEC strains and the larval disease score deserves attention as a potential means of assessing the pathogenicity of UPEC isolates.