Presence of aminoglycoside acetyltransferase and plasmids in Mycobacterium fortuitum. Lack of correlation with intrinsic aminoglycoside resistance.

Isolates of the 3 biovariants of Mycobacterium fortuitum exhibited 3 patterns of resistance when tested against 9 aminoglycosides. Examination of cell lysates from the 3 groups revealed 15/15 isolates to contain an aminoglycoside acetyltransferase (AAC) resembling AAC (3)-III or (3)-IV found in bacterial species. The enzyme did not appear to confer resistance, as its activity did not correlate with any pattern of resistance. The DNA extraction revealed plasmids in only 2 of 8 isolates tested, suggesting no relationship of plasmids to intrinsic aminoglycoside resistance or the presence of the AAC. These studies, combined with current knowledge of ribosomal resistance, suggest altered cellular transport or permeability as the mechanism of intrinsic aminoglycoside resistance in this species, although the patterns of resistance are different from those observed in other bacteria with nonenzymatic aminoglycoside resistance. This is the first demonstration of specific aminoglycoside-modifying enzymes among mycobacterial species and the first report of plasmids in M. fortuitum.