Galleria mellonella larvae as an alternative model to determine the pathogenicity of avian pathogenic Escherichia coli.

The pathogenicity of avian pathogenic Escherichia coli (APEC) can be reliably determined using a biological model with 1-day-old chicks. However, public concerns regarding the use of vertebrates in research have led to the exploration of other biological models. Alternative infection models, including Galleria mellonella larvae, have also been studied. This study aimed to evaluate whether G. mellonella larvae are a viable in vivo model for evaluating the pathogenicity of APEC isolates and to determine the best protocol for this model. First, the pathogenicity index (PI) in vivo was determined for 40 APEC isolates from 1-day-old chicks. The same isolates were then used to establish the best protocol for the determination of PI in larvae of G. mellonella by determining the LD₅₀, melanization, cytotoxicity test, total haemocyte count, mortality rate, construction of survival curves, and larval disease score. Cytotoxicity tests and total haemocyte counts were not suitable for distinguishing the pathogenicity groups. LD₅₀ was a useful tool for differentiating between high and low pathogenicity but not for intermediate pathogenicity. Similarly, melanization could be used as a variable to characterize the pathogenicity of APEC isolates but should be associated with other variables. Mortality rates and survival curves were useful tools for characterizing nonpathogenic and highly pathogenic isolates. In this study, G. mellonella larvae were a viable model, and the larval disease score was the main variable that determined the pathogenicity of APEC isolates in the G. mellonella model. RESEARCH HIGHLIGHTS: Galleria mellonella larvae are a viable model for determining APEC pathogenicity. Larval disease score is the main variable for determining APEC pathogenicity. Response variables should be evaluated up to 24 h post-inoculation. [ABSTRACT FROM AUTHOR]