Drug resistance in relation to use of silver sulphadiazine cream in a burns unit.

Topical chemoprophylaxis of extensive burns with silver sulphadiazine cream led to a large increase in the proportion of sulphadiazine-resistant Gram-negative bacilli in a burns unit. When all sulphonamide treatment in the ward was stopped; the incidence of sulphonamide-resistant strains fell back to levels similar to those recorded when silver sulphadiazine treatment was introduced. This was associated with a large reduction in the incidence of resistance of certain Gram-negative bacilli (especially Klebstella sp) to several antibiotics. Transferable resistance to sulphadiazine, shown by conjugation experiments with Escherichia coli K12, was found in a majority of the strains of Klebsiella sp tested, and in other species. A pattern of transferable resistance to tetracycline, cephaloridine, chloramphenicol, ampicillin, carbenicillin, and sulphadiazine (T Ce Cl A Ca S) was found in four of the 22 strains of Klebsiella tested, and closely related patterns were transferred by five other strains. These patterns of resistance were commonly found in Klebsiella sp isolated from burns in the period before the withdrawal of sulphonamides from the ward but were found in none of the Klebsiella strains isolated in the first six months after that period. Strains of Acinetobacter and Proteus, in which transferable resistance was not found, showed no appreciable fall or rise in sulphadiazine resistance; there was no fall in resistance of these organisms to tetracycline, cephaloridine, chloramphenicol, ampicillin or carbenicillin on withdrawal of sulphonamides from the ward, but there were substantial falls in resistance of Acinetobacter to kanamycin, gentamicin, trimethoprim, and tetracycline which were probably not caused by the withdrawal of sulphonamides.