This literature review is a Ph.D. level project on the importance of the type 6 secretion system in mammary pathogenic E coli (bacteria that causes mastitis in cattle). The writer NEEDS to have a background in microbiology or related field; otherwise, it will be very difficult to write a review on this topic. This is a very specific topic, so please feel free to deny it in case you are not from the biomedical science fields (microbiology, immunology, etc.) I can give further information latter.