Antimicrobial susceptibility of the pathogens of bacteraemia in the UK and ireland 2001-2002: The BSAC Bacteraemia Resistance Surveillance Programme

Objectives: To describe the current patterns of antimicrobial resistance in the major pathogens of bacteraemia in the UK and Ireland, to highlight any unexpected resistance patterns and to act as a reference baseline for future studies. Methods: In 2001 and 2002, 5092 blood culture isolates were collected by 29 laboratories distributed across the UK and Ireland. A single central laboratory re-identified the isolates and measured MICs by the BSAC agar dilution method. Results: Oxacillin resistance was found in 42% of Staphylococcus aureus and 76% of coagulase-negative staphylococci. Streptococci were generally susceptible to beta-lactams, but tetracycline resistance was common (except in Streptococcus pneumoniae) and particularly common among group B isolates (82% resistant). Nine percent of S. pneumoniae had reduced susceptibility to penicillin (MICs 0.12-1 mg/L), but none required greater than or equal to2 mg/L for inhibition. High-level gentamicin resistance was seen in 43% of Enterococcus faecalis, often in combination with raised ciprofloxacin MICs (greater than or equal to32 mg/L), but these isolates remained susceptible to ampicillin and imipenem. Only linezolid and tigecycline showed in vitro potency against a large proportion of Enterococcus faecium. Vancomycin resistance was restricted to enterococci (20% of E. faecium, 3% of E. faecalis) and a single isolate of coagulase-negative staphylococci (0.2%, MIC of 8 mg/L). Escherichia coli isolates were commonly resistant to amoxicillin (56%) and tetracycline (88%) but remained susceptible to ceftazidime, piperacillin/tazobactam and imipenem. Extended-spectrum beta-lactamases were detected in 2% of E. coli (none in 2001, 3.2% in 2002), 5% of Klebsiella spp. and 8% of Enterobacter spp. Resistance rates of Pseudomonas aeruginosa to ciprofloxacin, ceftazidime, gentamicin, imipenem and piperacillin/tazobactam were between 4% and 7%. Among the newly licensed and developmental agents, there was no resistance to linezolid in Gram-positive organisms. Ertapenem had a wide spectrum, covering Enterobacteriaceae, streptococci and oxacillin-susceptible staphylococci. MICs of tigecycline were low for Gram-positive species and Enterobacteriaceae except Proteeae and Enterobacter spp. Conclusion: Antimicrobial resistance among major bloodstream pathogens to those antimicrobials often selected for empirical therapy was relatively uncommon in 2001-2002, usually <10%. An important exception was oxacillin resistance in S. aureus.