‘Jumping Genes’ Blamed for Resistant Bacteria

Infectious bacteria equipped with “jumping genes” are becoming increasingly resistant to antibiotics, forcing development of new treatment strategies for several diseases, scientists say.

“There are certain parts of the United States--mostly on the two coasts--where resistance to penicillin and other common drugs are more likely to be found,” said Clyde Thornsberry of the Centers for Disease Control in Atlanta.

Resistant strains of bacteria that cannot be killed by the usual battery of antibiotic drugs are responsible for such diseases as meningitis, ear infections and strains of gonorrhea that have reached epidemic proportions in some parts of the country.

“On a global scale it is even worse,” said Thornsberry, who heads the center’s microbe-disease branch. “Resistant bacteria are more common in Asia and Africa than in Europe or the United States.”

In underdeveloped countries, he told a recent meeting of the American Society for Microbiology in Los Angeles, people can buy penicillin and other powerful antibiotics over the counter.

This practice has led to tougher bacterial strains that have evolved to successfully fight off the drugs by chemically neutralizing them.

“So far, the bacteria are smarter than we are and they always find a way to get around those drugs,” he said. “They are able to do this with transposons--jumping genes.

“In many of these cases, the genes for production of the resistance mechanism is for production of an enzyme that inactivates the drug.

“Many of these are on plasmids--small pieces of DNA in the bacterial cell that carry genes just like a chromosome and can be transferred from one bacterial cell to another. This is a very efficient way to spread resistance.”

In the United States, resistant bacteria are very common in hospitals, where they have developed the necessary mechanisms to resist a variety of antibiotics.

“Enormous amounts of antibiotics are used in hospitals, and if you compare organisms in hospitals to those in a community, you’ll find the hospital strain to be much more resistant,” Thornsberry said.

“They’re nothing like an infection acquired outside of a hospital.”

Aside from drug-resistant strains of gonorrhea, Thornsberry said, scientists also are concerned with various bacteria that cause respiratory infections and the Haemophilius influenzae microbe that largely infects children.

“This organism is the most common cause of meningitis in children and is one of the most common causes of otitis media,” he said of the ear infection that afflicts both children and adults.

Ampicillin, the drug most commonly used against H. influenzae , has to be used in combination with other antibiotics because resistance to it now exceeds 20% in people for whom it is prescribed.