In a keynote address to the annual meeting of the Infectious Diseases Society of America meeting in San Francisco, Calif., Dr. John Bartlett, professor of medicine and chairman of infectious diseases at Johns Hopkins University, Baltimore, Md., said the anthrax strain appears to "induce beta-lactamase" -- an enzyme that makes penicillin ineffective. But experts said that the resistance phenomenon didn't necessarily mean the strain used in the attacks was humanly altered to become a more dangerous form of the bacteria. Even under natural situations, anthrax can create the enzyme.
"I don't think anyone knows yet what this means," said Dr. Lee Harrison, associate professor and head of the Infectious Diseases Epidemiology Research Unit at the University of Pittsburgh School of Medicine.
"Everything I've see so far about this strain leads me to think it is a garden variety strain of anthrax," he told United Press International.
"The ability of anthrax to develop beta-lactamase had been of concern to us," said Dr. Craig Smith, director of infectious disease at the Phoebe Center for Infectious Diseases, Albany, Ga., and a member of the IDSA bioterrorism working group. "It is something we have discussed, and it is one of the factors that went into our recommendations for treatment."
Smith said that anthrax resistance to penicillin "is easily induced either naturally or through fairly simple bioengineering."
Harrison noted that even if the strain stops being sensitive to penicillin "we have other drugs that can do the job." Penicillin is particularly important in fighting anthrax because it can penetrate into the central nervous system and attack the bacteria there, Harrison said, but he added that there still are other drugs that can accomplish the same thing.
Bartlett said that the possible emergence of resistance to penicillin "doesn't mean that the anthrax in these attacks is engineered." But he said that phenomenon was the reason medical authorities suggested the use of Cipro, from the class of antibiotics known as fluoroquinolones, as the main drug to fight anthrax. "We need something more than penicillin," he said.
However, Bartlett suggested that optimal treatment of both the skin form of anthrax and the inhalation form of the disease --which has already felled three people -- would likely require additional antibiotics to Cipro, such as tetracycline, doxycycline, clindamycin, rifampin and vancomycin.
"We may need Cipro plus another drug or maybe Cipro plus another two drugs," Bartlett said. Bartlett noted that cephalosporin antibiotics would not be considered for use against anthrax due to natural resistance factors.
Bartlett said that no matter what drugs are required to combat the anthrax outbreaks "the country has a supply of drugs that is going to be adequate. We right now have enough antibiotics to treat 2 million people for 60 days and that will increase so we can treat 12 million people for 60 days. There will be enough of it -- if it is necessary."
Presently, Bartlett said, about 10,000 people are receiving antibiotics to prevent anthrax based on the possibility that they were exposed in South Florida and in the New York and Washington, DC, metropolitan areas.