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Chlamydia Defies Antibiotic Therapy: Presented at ICAAC

By Michael Smith

SAN DIEGO, CA -- October 2, 2002 -- Chlamydia pneumoniae - responsible for various respiratory tract infections and implicated in many other conditions - is difficult to eradicate, even with high doses of antibiotics, according to researchers.

Hideaki Ikejima, MD, PhD, of the University of South Florida presented these study findings at the Interscience Conference on Antimicrobial Agents and Chemotherapy.

Dr. Ikejima and colleagues have previously shown that more than 80 percent of healthy blood donors carry C. pneumoniae in their peripheral blood leucocytes. That finding, said Dr. Ikejima, prompted them to wonder whether antibiotic treatment would have any effect on C. pneumoniae in peripheral blood, which is considered a type of bacteria, even though it can only grow in host cells.

The issue is made more pressing, he said, because "recent studies indicate that this pathogen may also be involved in a variety of chronic inflammatory diseases," including atherosclerosis, asthma arthritis, multiple sclerosis, and Alzheimer's disease.

To test the potential for antibiotic treatment, the researchers isolated peripheral blood mononuclear cells (PBMCs) from the donations of healthy blood donors, who had given blood for transfusion.

The isolated PBMCs were cultured in tissue culture medium with 10% fetal bovine serum and concanavalin A (ConA) in the presence or absence of antibiotics for three days. The antibiotics tested were azithromycin, clarithromycin, minocycline, and tosfloxacin.

Before and after cultivation of PBMCs, C. pneumoniae inclusions and specific gene transcripts in cells were assessed by immunostaining and real-time RT-PCR, respectively.

After cultivation, both tests showed increased C. pneumoniae, regardless of whether antibiotics were present or not; in fact, even 10-fold blood concentrations (of about 40 micrograms per millilitre) of antibiotic did little to inhibit the growth, Dr. Ikejima said.

The finding shows that antibiotic treatment is unlikely to eradicate or even inhibit C. pneumoniae resident in leukocytes, Dr. Ikejima said. But, he added, "eradication of this pathogen from blood is an urgent matter for the health care of individuals."

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