If the full name of any germ could be a household word, it would be Escherichia coli O157:H7, a bacterium that has in the past caused severe food poisoning linked to Jack in the Box hamburgers, Taco Bell lettuce and prepackaged spinach. Now E. coli O157:H7 is being overshadowed by more virulent strains of what is normally a benign gut microbe. This spring a recently identified strain of E. coli, O104:H4, killed dozens of people in Europe and landed hundreds more in the hospital. The U.S. Centers for Disease Control and Prevention is now following at least six types of so-called Shiga toxin E. coli, which, like O104:H4 and O157:H7, cause bloody diarrhea and, in extreme cases, fatal kidney failure. Below are some surprising facts you may have missed in this spring’s headlines.

Antibiotics can worsen an E. coli infection. Giving antibiotics, including fluoroquinolones such as Cipro, can kill a patient who has been sickened by any strain of Shiga toxin E. coli. The reason: when the bacteria die, they release the toxin in massive amounts. Fortunately, one particular group of drugs, called carbapenems, seems to not trigger a major toxin release, but these drugs are generally prescribed only in special circumstances. This explains why travelers who bring antibiotics with them as a precautionary measure should not take them if they develop bloody diarrhea. E. coli O104:H4 is resistant to at least 14 antibiotics. Why this is so remains a mystery, particularly because many of these drugs are not usually used to treat E. coli infections. Somewhere along the line, either these bacteria or other bacteria with which they exchanged genetic material must have developed in an environment that was awash in antibiotics—possibly a hospital or a farm. E. coli O104:H4 may eventually show up in the U.S. The CDC has already confirmed a few cases in U.S. residents who had recently traveled to Germany. Whereas health officials do not believe the current outbreak will spread in the U.S., a similar strain of E. coli could evolve here independently at some point. E. coli O157:H7 is becoming less of a threat. That is because the government has made it mandatory for food producers to report its presence to health authorities. But the number of ailments caused by the other Shiga toxin E. coli strains is growing rapidly. Many food-safety specialists believe that requiring food producers to report more E. coli strains to the government would help reduce the incidence of illness.