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.