Observations on the possible origin of Mycoplasma fermentans incognitus strain based on antibiotic sensitivity tests.

Mycoplasma fermentans (incognitus strain), isolated during transfection studies in NIH/3T3 cells with DNA extracted from Kaposi's sarcoma tissue from a patient suffering from AIDS, showed high levels of resistance to numerous aminoglycoside antibiotics (MICs > 250 to > 500 mg/L) and in this respect matched the aminoglycoside resistance patterns of M. fermentans strains isolated recently from tissue culture cells. Two M. fermentans strains isolated from urine deposits from AIDS patients, without the use of cell cultures, and six M. fermentans isolates from patients with acute respiratory infections differed markedly from the incognitus strain, in that they were sensitive to aminoglycosides (MIC range 0.25-25 mg/L). A much older strain (K7) isolated from leukaemic bone marrow tissue in the 1960s, with the aid of cell cultures, was resistant to streptomycin (MIC > 250 mg/L) but sensitive to other aminoglycosides (MIC range 0.625-6.25 mg/L). These results suggest that, although the aminoglycoside-resistance in M. fermentans incognitus could have developed during the isolation process or through treatment of the AIDS patient with aminoglycosides, in view of the unusual manner in which the strain was isolated, its multiple aminoglycoside resistance and the fact that other M. fermentans strains isolated from AIDS patients, without the use of tissue culture cells, were aminoglycoside-sensitive, it is more likely that it was a tissue culture contaminant.