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The image for July in our 2018 calendar depicts an RNA binding protein used by Salmonella bacteria as a tool to cause disease, including typhoid, in humans.

Tricks of the (Infection) Trade

During infection, the Salmonella bacterium can live within our immune cells. These cells produce damaging agents in an attempt to kill the bacteria, but often Salmonella continues to survive and multiply inside the very cells that are meant to fight against the infection. To do this, the bacteria use a host of protein tools (called virulence factors) to get into the cells and ward off the host's immune system. Shown in the image to the left, outlined in black, is one of these protein tools, a Salmonella protein termed Hfq (PDB 2ylc), which mediates small RNA-based gene regulation in the bacteria. In the background the artist has depicted two bacteria of the species Salmonella enterica, including their long tail-like appendages called flagella.

 The oligomeric structure formed by six protein chains of Hfq.

The Sinister Story of Typhoid Mary

Mary Mallon (born in 1869) was the first asymptomatic typhoid carrier identified. She was infected with the bacterium Salmonella enterica, the causative agent Typhoid, however she had no symptoms of the disease. Suspicions were only raised once a sanitation engineer, George Soper, realised that the families where she worked as a cook tended to have outbreaks of typhoid fever. Thoughout her life she worked for at least 7 families in New York, and over the course of this time is known to have infected 51 people, three of which died. Despite the large body of evidence that accumulated over the years, she vehemently denied her role. Being asymptomatic and perfectly healthy, she would not accept that she could be a disease carrier. She refused to stop working as a cook and even used different names to evade the authorities. This meant that the exact number of typhoid deaths that she caused is not known, and it could even be upwards of 50 people.
The Artwork

This artwork is an intaglio print by Emily Field at in Cambridge. The overlay, of Hfq, was created in PyMol.