A 70 year old male went to the emergency room complaining of fever, diarrhea, intestinal cramps and a sore throat. Blood cultures were negative for bacteria, but stool cultures isolated a gram positive rod-shaped bacterium. When asked about any new or unusual food he had consumed, the patient stated the he had consumed a ripened farm cheese his daughter had given him that she had brought back from a recent trip to Mexico. A sample of the cheese was sent to the laboratory. Further culturing revealed the same type of bacterium and that this microbe grew best at 4o C, rather than 37o C.
- What is the route of infection?
I am assuming that you meant 40 degrees C instead of 4 degrees C. I cannot imagine that a bacteria found on food in Mexico would thrive at near frigid temperatures.
It seems to me that the likely culprit here is Clostridium difficile. This is an elongated-shaped bacteria that is Gram positive to staining and can cause serious intestinal pain and diarrhea along with flu style symptoms. Other possible bacterial culprits like salmonella and E. coli are Gram negative to staining and are not the perpetrators here.
C. difficile thrives in oxygen deficient environments at the human body temperature. In humans this means the gastrointestinal tract, hence it is not found in blood but in feces. This is how it is transferred from person to person. It is present in spores with hard outer coatings that are difficult to penetrate and kill the bacteria, hence its ease in spreading. In most healthy people, the bacteria would simply be crowded out amongst the other, beneficial gut flora. But in older people or people with weakened systems, the C. difficile can spread in the intestines and cause serious health problems. So the cheese in Mexico was infected with the bacteria from being handled by a person with poor hygiene and the spores stayed alive as the cheese travelled to the US and was eventually eaten by the elderly host victim.