Complex sentence: The bacteria infects endothelial cells and can infect erythrocytes by binding and entering with a large vacuole causing them to proliferate, and demonstrate nuclear atypia (this is known as intraerythrocytic "B.quintana" colonization).
Split into simpler sentences: The bacteria infects endothelial cells and can infect erythrocytes by binding and entering with a large vacuole. Once inside they begin to proliferate and cause nuclear atypia (this is known as intraerythrocytic "B.quintana" colonization).