**Question:** E. coli causes: September 2011

**Core Concept:** Escherichia coli (E. coli) is a common bacterium found in the intestines of humans and warm-blooded animals, and can be both beneficial and pathogenic depending on the strain and host conditions. The question refers to the year "September 2011," which might imply a specific outbreak or event associated with E. coli.

**Why the Correct Answer is Right:**

The correct answer, **E. coli O157:H7**, is a strain of E. coli that is particularly pathogenic and can cause severe illnesses. The acronym "O157:H7" refers to the serogroup, which is a classification based on the bacterium's antigenic properties. Serogroup O157 indicates the presence of O-antigen, while H7 indicates the presence of H7 flagellin. This strain is particularly harmful due to its ability to produce Shiga toxins (Stx1 and Stx2), which cause gastrointestinal symptoms and hemolytic uremic syndrome (HUS), a serious complication leading to kidney failure.

**Why Each Wrong Option is Incorrect:**

A. E. coli as a whole is a common bacterium, but only specific strains like O157:H7 are pathogenic and cause illnesses like those mentioned above.
B. E. coli can cause urinary tract infections (UTIs) and gastrointestinal symptoms, but it is not specific to the September 2011 outbreak.
C. E. coli is a common bacterium, but without specifying a strain, it does not accurately represent the September 2011 event.
D. E. coli can cause UTIs and gastrointestinal symptoms, but September 2011 specifically refers to a particular outbreak caused by the O157:H7 strain.

**Clinical Pearl / High-Yield Fact:**

The E. coli O157:H7 outbreak in September 2011 was a significant event involving contaminated meat products, particularly hamburgers, from a major fast-food chain. This outbreak caused severe gastrointestinal illnesses and hemolytic uremic syndrome (HUS) in affected individuals, resulting in high morbidity and mortality rates. It highlights the importance of food safety measures and the potential consequences of consuming contaminated food products.

**Correct Answer:** E. coli O157:H7

**Why This is Correct:**

E. coli O157:H7 is a specific strain associated with gastrointestinal illnesses and HUS, which is consistent with the September 2011 outbreak mentioned in the question. The strain produces Shiga toxins (Stx1 and Stx2) that lead to the mentioned symptoms and complications.