BURLINGTON, Vt. - Dozens of people who flew in from Detroit this week were told to undergo antibiotic treatment as a precaution against anthrax Thursday after a powdery substance on the Northwest Airlines plane showed evidence of similar bacteria.

While stressing that further testing was likely to show the bacteria wasn't anthrax, State Health Commissioner Dr. Jan Carney issued the advisory for 60 people.

In addition to the 44 passengers and three crew members on the flight, the recommendation covered baggage handlers and emergency personnel who went to the Burlington airport after the plane landed around midnight Monday.

Initial tests did not locate anthrax spores in the powder, officials said. A second-level test showed the presence of bacillus, or rod-shaped bacteria. About 50 types of bacteria, including anthrax, belong to this group. Most are not harmful.

Additional tests to look for anthrax probably won't be completed for up to 72 hours, officials said.

"This bacteria growth means that the substance could be anthrax," Carney said. "We believe that it is possible, but unlikely."

The Northwest jetliner remained on the tarmac in Burlington, though the state has not ordered it quarantined, Carney said.

The substance was found on top of checked baggage that was being removed from the plane, authorities said. They recommended treatment for passengers and crew because air was circulated through the cargo hold and into the passenger cabin.

A Northwest spokesman, Kurt Ebenhoch, said the powdery substance was found on luggage that was stowed beneath a diaper bag.

The fact that bacteria had grown from the substance "is not a surprise to us," Ebenhoch said. "An aircraft cargo compartment is not a sterile environment. It's a bacteria that's a common bacteria."

Most of the 60 people involved had been contacted by Thursday morning and had visited the Health Department, Carney said. Authorities conferred with the Centers for Disease Control and Prevention before issuing the recommendation.

The next level of more sensitive tests on the rod-shaped bacteria in the powder samples will look for specific proteins and other biological features unique to anthrax.