Establishment of a novel clinical relevant mouse model for accurately assessing in vivo growth of E.coli and their response to host defense

XIANG Fei; ZHU Haiyan; LI Yangmei; LIU Peng; LIU Fei; WANG Zhezhe; XIE Xuemei; REN Qian; GUO Rongxia; XIE Xinyan; WANG Tong; XU Yuanfu; WANG Xiaoxue; LUO Hongbo

doi:10.13431/j.cnki.immunol.j.20170124

Abstract：Chemo-and radiotherapy are extensively used to treat various hematological malignancies and solid tumors.Neutropenia and related infection are the most important dose-limiting toxicities of these anti-cancer treatments,impacting on quality of life and clinical outcomes,with the potential to cause death.Here,we developed a novel clinically relevant mouse model to accurately assess the response of bacteria to host immune defense system in the neutropenic patients.Neutropenia was induced in mice by cyclophosphamide (CPA),a commonly used anticancer drug.To minimize the mouse-to-mouse variability,we mixed isogenic WT and mutant Escherichia coli K-12 cells,and the mixture (1 ∶ 1 ratio)was intra-peritoneally (i.p.) injected into the CPA treated mice.The mice were sacrificed at 0-3 days and the cardiac blood,peritoneal lavage fluid,and homogenized organs were collected.Then the total number of viable bacterial cells in each compartment was assessed by plating samples on LB agar plates;the phenotype and the identity of each colony were determined by PCR and direct observation under fluorescence microscope.The ratio of the two input bacterial stains was calculated thereafter.Data showed that CPA treatment significantly reduced granulocyte count to 10％ of the normal level in peripheral blood and to 5％ of the normal level in the bone marrow.Three days after the injection of a 1 ∶ 1 mixed bacterial population containing WT E.coli K-12 bacteria and mutated E.coli K-12 bacteria with lower proliferation rate,the ratio of the viable WT bacteria to mutated bacteria in the inflamed peritoneal cavity and several other organs significantly increased from 1 to 5 (P＜0.01).As a control,the ratio of the viable WT bacteria to WT bacteria under the same condition remained unaltered.Thus,in this study,we have established a new clinical relevant mouse model,which could be used to accurately measure the in vivo response of bacteria to host immune defense system.This model should be of importance and can facilitate the development of novel therapeutic strategies for treating infectious diseases,particularly those associated with bacterial infection in patients under chemo-and/or radiotherapy.