CAN SUSCEPTIBILITY TO AN ANTIMICROBIAL BE RESTORED BY HALTING ITS USE- THE CASE OF STREPTOMYCIN VERSUS ENTEROBACTERIACEAE

To test the widespread view that resistance disappears in the absence of antimicrobial use, we tested streptomycin against 477 Enterobacteri aceae from the Royal London Hospital. Twenty per cent proved resistant although streptomycin is little used at the hospital and streptomycin resistance in Gram-negative bacteria is caused by mechanisms that do not compromise the drugs that are used. Up to 70% of the observed resi stance was associated with cross-resistance to spectinomycin and the p resence of ant(3 '')-la, an integron-associated gene carried in Tn21-t ype transposons. This genetic organization may have conserved streptom ycin resistance in the absence of direct selection pressure.