Galleria mellonella as a model to evaluate the effect of tetracycline against Campylobacter coli strains

Campylobacter spp. is one of the leading causes of foodborne bacterial gastrointestinal illnesses in humans, primarily through chicken meat. The prevalence of antibiotic-resistant Campylobacter strains in chicken is increasing worldwide. This fact makes it necessary to evaluate antimicrobial effectiveness, particularly through in vivo models such as Galleria mellonella larvae (GML). In this work, GML were infected with strains of C. coli and treated with tetracycline (8, 12, 15, 20, and 40 mg/mL); after that, all groups were cultivated at 37°C for 4 days without feeding. In this period, mortality, bacterial load in hemolymph, and hemocyte count were assessed. The results showed that the group treated with 8 and 12 mg/mL of tetracycline had its mortality reduced to less than 10% in the first 3 days. In contrast, higher doses (15, 20, and 40 mg/ml) showed no significant difference compared to the infected group without antibiotic treatment. Bacterial load decreased by more than 3 log₁₀ in the first 0.5 hours in the treated groups. No difference was observed in the number of hemocytes between treated and untreated larvae. Treatment with tetracycline at 12 mg/ml was the most effective in reducing larval mortality and controlling C. coli infection. These results suggest the usefulness of the Galleria mellonella larvae model in evaluating antibiotic dosages against C.coli.