Animals
Pregnant CD-1 mice (8–10 days in lactation; 50 ± 5 g; purchased from SPF Biotechnology Co., Ltd, Beijing, China) were housed at room temperature with a 12 h light/12 h dark cycle and had free access to food and water in China Agricultural University Laboratory Center (Beijing, China). All animal care and experimental protocols in the study were conducted in accordance with the animal ethics committee of the National Institutes of Health Guide for the Care and Use of Laboratory Animals (GB14925-2010, China). Twenty mice were randomly treated under one of four conditions as follows: (i) Control group (PBS alone); (ii) 1 × 103 CFU E. coli treatment for 12 h (E. coli group); (iii) 1 × 105 CFU LCZ pre-injection for 24 h, followed by 1 × 103 CFUE. coli treatment for 12 h (LCZ + E. coli group); and (iv) 1× 105 CFU LCZ treatment for 24 h (LCZ group). Both LCZ and E. coli were diluted by PBS. Mice were anesthetized with Zoletil 50 (Virbac, Barneveld, France), and all treatments were conducted through intramammary injection via the teat canal of the fourth teat. E. coli was injected 24 h after LCZ pretreatment. After treatments, the mice were sacrificed by cervical dislocation, and the mammary tissues were collected.