Recovery from mild Escherichia coli O157:H7 infection in young and aged C57BL/6 mice with intact flora estimated by fecal shedding, locomotor activity and grip strength

Escherichia coli 0157:H7 is a food-borne pathogen that can cause severe complications in vulnerable populations. Mouse infection models of E. coli 0157:H7 are usually developed under severe animal suffering classification by depleting the normal flora, in which age plays a role. Objective: To develop a refined method for longitudinal monitoring of E. coli 0157:H7 in young and old mice with intact flora. Methods: We applied discriminant analysis and computed composite standardized scores from 19 variables obtained from physiological parameters, analysis of locomotor activity, grip strength measurement and fecal shedding in 16 aged and 16 young C57BL/6 mice after two mild oral challenges of E. coli 0157:H7. The resulting scores were validated in another experiment performed in 24 aged and 24 young mice including a group (8 aged and 8 young mice) treated with oxytetracycline. Results: We show that our scores are significantly affected in the post-infection period and that can be used to measure and compare the recovery time after a treatment. The scores are most sensitive when separately developed in young and aged mice. Conclusions: We developed a method that minimizes the level of animal suffering and that can be applied in preclinical testing of new therapies.