Figure 1From: The molecular mechanism of acute lung injury caused by Pseudomonas aeruginosa: from bacterial pathogenesis to host responseGram-negative bacterial protein secretion system. In the type I and II secretion systems, bacteria secrete toxins into the extracellular space (upper image). In the type III and IV secretion systems, bacteria directly secrete toxins into the cytosol of target eukaryotic cells through the secretion apparatus (lower image).Back to article page