Increasing resistance to antimicrobial agents of Gram-negative organisms isolated at a London teaching hospital, 1995-2000

Objectives: To investigate the changes in resistance frequencies of common Gram-negative bacteria in a London teaching hospital. Methods: Antimicrobial susceptibilities were analysed for the 6 years 1995-2000. Gentamicin-resistant isolates from 1995 and 2000 were typed by a repetitive element sequence-based PCR (Rep-PCR) method. Results: Resistance rates for all agents and all organisms were higher in isolates from inpatients than in those from outpatients or general practice. For most agents and most species there was a trend for a highly significant linear increase in resistance over the study period, and there was significant cross-resistance between different agents. Increases in resistance were especially marked in Klebsiella, Enterobacter and Acinetobacter spp., organisms that tend to cause outbreaks of hospital cross-infection. For example, the increases in gentamicin resistance in isolates from inpatients was from 2.9% to 23.5% for Klebsiella spp., from 0.3% to 20.8% for Enterobacter spp. and from 10.1% to 42.2% for Acinetobacter spp. There was much less increase in acquired resistance in Escherichia coli and Pseudomonas aeruginosa, organisms that tend to cause endogenous infections, with gentamicin resistance in isolates from inpatients increasing from 0.4% to 3.2% for E. coli and decreasing from 4.6% to 3.6% for P. aeruginosa. Rep-PCR typing showed considerable diversity amongst gentamicin-resistant isolates of E. coli and P. aeruginosa, but dominance by a limited number of presumably epidemic types of gentamicin-resistant isolates of the other species. Conclusions: Multiple antibiotic resistance has increased dramatically in some hospital isolates, and appears to be associated with hospital cross-infection.