Persistence of sulphonamide resistance in Escherichia coli in the UK despite national prescribing restriction

Background There is a clear association between heavy antimicrobial consump tion within a population and the frequent recovery of resistant bacteria, b ut whether a reduction in antimicrobial use can reverse this process is les s clear. We investigated the effect of a national restriction of sulphonami de prescribing in the UK on the prevalence of sulphonamide resistance in Es cherichia coli. Methods Consecutive clinical isolates of E coli were collected at the Royal London Hospital in 1991 and 1999. These collections, each of more than 350 isolates, were compared. Minimum inhibitory concentrations of sulphamethox azole and eight other antimicrobials were determined. The presence and loca tions of sulphonamide-resistance genes were examined by PCR, plasmid extrac tion, Southern hybridisation, and transconjugation. Findings Despite a huge decrease in sulphonamide prescriptions (from 320 00 0 prescriptions per year in 1991 to 7 000 in 1999), the frequency of resist ance remained high in 1999 (165/359 [46.0%] vs 143/360 [39.7%] in 1991; dif ference 6.2% [95% CI -0.9 to 13.3]). Integron- borne sulI was present in 16 .4% of isolates in 1991 and 17.5% in 1999, The prevalence of sulII increase d from 26.7% in 1991 to 36.5% in 1999 (difference 9.8% [3.1 to 16.5] p=0.00 46). SulII was located on large plasmids, at least some of which were conju gative multiresistance determinants. Interpretation These results show that a huge decrease in antibiotic prescr ibing does not necessarily reduce resistance within a useful time. The main reason seems to be the genetic linkage of the index resistance to other re sistance determinants.