A follow-up survey of transferable, plasmid-encoded trimethoprim resistance in a general hospital (1975-1983).

Urinary isolates of bacteria resistant to trimethoprim were collected at the Whittington Hospital, London, during five three-monthly periods during 1975, 1977, 1979, 1981, and 1983. Seventy-six transferable trimethorpim-resistant isolates so obtained were examined for their antibiotic resistance patterns, trimethoprim resistance (TpR) levels and plasmid molecular weights. Overall between 1975 and 1983 the frequency of transferable TpR rose from 10% to 40% of trimethoprim-resistant isolates, caused mainly by an increasing number of Escherichia coli isolates which cotransferred antibiotic resistance to trimethoprim, streptomycin and spectinomycin. From 1975-1979 the rise in the frequency of transferable TpR was due to a gradual increase amongst in-patient isolates but since 1979 transferable TpR rose rapidly due to a ten-fold increase in out-patient isolates.