Staph Bacteria Are Active Gene Swappers

W A S H I N G T O N, July 9, 2001 -- The bacteria that cause serious and sometimesfatal staph infections are able to swap genes with relatives inorder to adapt to new environments and cause even greater medicalmischief, a study shows.

Researchers using a new technology to analyze the gene structureof bacteria found that Staphylococcus aureus can easily exchangegenes with other bacteria strains and can acquire resistance toantibiotics within a very short time.

Staphylococcus aureus, or staph, is an extremely troublesomebacterium that causes a variety of illnesses. It is a major causeof hospital-acquired infection. Staph causes such things as thescalded skin disease that strikes infants, toxic shock syndrome andsystemic blood poisoning called sepsis.

Drug-Resistant Staph

Antibiotics once controlled the bacteria, but strains of staphare now resistant to the drugs.

"This is the first time we've been able to do such an extensivegenetic comparison of these strains of Staphylococcus aureus,"said Dr. James M. Musser, senior author a study appearing Tuesdayin the Proceedings of the National Academy of Sciences.

Musser is head of a bacterial research lab at the NationalInstitute of Allergy and Infectious Disease's Rocky MountainLaboratories in Hamilton, Mont. NIAID is one of the NationalInstitutes of Health.

In the study, Musser and his colleagues analyzed the genes of 36of the most troublesome strains of staph and concluded thatvirtually any of the bacteria's 2,817 strains could acquire thegenes to become resistant to antibiotics.

"This is occurring at a far more greater frequency than weanticipated," said Musser. "The drug-resistant strains can becreated many times. It is not a single strain that is created onceand then spreads."

Instead, he said the genetic combination that providesresistance can arise independently in many different places, manydifferent times.

Such an easy evolution of drug resistance "has sent a wave ofterror through people responsible for public health," said Dr.Abigail A. Salyers, a microbe researcher at the University ofIllinois, Urbana. "They know this organism will become a majorpathogen if antibiotics no longer work."

Salyers, who is president of the American Society forMicrobiology, said the work by Musser and his group is importantbecause it confirms what has long been suspected — that whole genestructures can jump from bacteria to bacteria, creating new strainsof antibiotic bugs within a matter of hours. "One of the important findings in this paper is that theantibacterial resistance gene is being acquired by lateraltransfer," or from bacteria-to-bacteria, she said. This has longbeen suspected, but Salyers said the Musser paper presents newevidence.

Staph is among the most common human bacteria. It is carried byabout a third of the population. It can be picked up fromcountertops or door knobs, but is more frequently transferredthrough skin-to-skin contact, such as shaking hands.

The bacteria can invade the body through breaks in the skin andset up a virulent systemic infection, particularly among peoplewith weakened immune systems — infants, the elderly, the injured orthe ill.

Salyers said that thousands of people die annually of staphinfection, but once the death toll was even higher.

Infected Wounds

Before World War II, more than half of all fatalities in warscame from wounds that were infected by staph or other bacteria,said Salyers. A simple, untreated scratch on the hand or foot oftenwas enough to set off a raging and lethal infection.

Antibiotics beat staph into the medical background, but startingin the 1980s, antibiotic resistant strains evolved. Drugs that onceworked, suddenly did not.

Salyers said staph is back and presenting a significant newthreat while researchers scramble to learn more about ways to fightit. "Virtually anything new we find out about staph aureus is animportant finding because of its potential as a major public healththreat," said Salyers.