A microbe that causes middle ear infections has developed resistance to a wide range of antibiotics, a new study finds.

The offender is a strain of Streptococcus pneumoniae, a bacterium best known for causing pneumonia. However, the microbe can also trigger middle ear infections, meningitis, sinus infections, and various respiratory ailments.

Immunization with a vaccine called pneumococcal 7-valent conjugate prevents infection by the seven most common strains of S. pneumoniae. But in recent years, physicians have encountered strains of S. pneumoniae not covered by the vaccine that have become impervious to some antibiotics.

Janet R. Casey and Michael E. Pichichero of the University of Rochester (N.Y.) now report that one strain that has cropped up in at least nine children since 2003 is resistant to all 18 drugs currently approved for use against middle ear infections in children. They report the finding in the Oct. 17 Journal of the American Medical Association.

The researchers used an adult antibiotic called levofloxacin (Levaquin) to kill the resistant microbe. But this drug isn't approved for use in children.

Between 2001 and 2006, health officials in Massachusetts recorded 94 invasive pneumococcal infections caused by this same S. pneumoniae strain. By 2004, signs of drug resistance showed up in many of these infections, which typically manifest as pneumonia, bacteremia, or meningitis.

Stephen I. Pelton, a pediatrician at the Boston University Medical Center, says that the troublesome strain accounted for only 5 percent of S. pneumoniae infections in 2000 in Massachusetts but more than 40 percent by 2004. Pelton and his colleagues report the data in the Oct. 19 Morbidity and Mortality Weekly Report.

The S. pneumoniae strain, dubbed 19A, has also shown up in Canada, France, Spain, and Israel. "It's a disturbing trend," Pelton says.

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