Antimicrobial susceptibility among invasive Gram-negative bacteria in the UK and Ireland: the BSAC Bacteraemia Resistance Surveillance Programme 2003

Abstract number: 1134_04_127

Reynolds R., Hope R., on behalf of the BSAC Working Party on Bacteraemia Resistance Surveillance 

Objective:  

To monitor prevalence of established forms of resistance, detect emerging forms, and assess the activity of newer antimicrobial agents.

Methods:  

Bacteraemia isolates were collected from 25 laboratories in the UK and Ireland in 2003, excluding duplicates isolated within one week. MICs were determined centrally using the BSAC agar dilution method and interpreted by BSAC criteria. Isolates with MICs on or above the susceptibility breakpoint for ceftazidime (CAZ) or cefotaxime (CTX) were tested for ESBLs by clavulanate synergy tests (potentiation of 8-fold or more) with CAZ, CTX and cefepime. Results were compared with those from similar surveillance in 2001 and 2002.

Results:  

Table 1 shows resistance rates to important antimicrobials (excluding tetracyclines and glycylcyclines, for which breakpoints are not currently defined). There were no statistically significant trends over the three-year period. The one imipenem-resistant Enterobacter (MIC > 16 mg/L) produced a novel KPC enzyme, KPC-4. Among Enterobacter spp., 32% were CTX-resistant without producing ESBLs and were presumed to be AmpC producers. Multi-resistant isolates with CTX-M ESBLs were noted first in this surveillance in 2002 and persisted in 2003; all remained susceptible to imipenem and ertapenem, and were inhibited by tigecycline at or below 2 mg/L.

Conclusion:  

Although there was no clear increase in prevalence of resistance in these major Gram-negative agents of bacteraemia, beta-lactamases have continued to evolve and spread, and are often associated with multi-resistance. Imipenem, ertapenem and tigecycline retained good activity against ESBL-producers.

Table 1:  Percentage of isolates resistant at MIC level shown (mg/L)