Non-susceptibility trends among Pseudomonas aeruginosa and other non-fermentative Gram-negative bacteria from bacteraemias in the UK and Ireland, 2001-06

Background: Pseudomonas and Acinetobacter spp. are important opportunists, notorious for resistance. Pseudomonas spp. are collected in the British Society for Antimicrobial Chemotherapy (BSAC) bacteraemia surveillance, with Acinetobacter spp. and Stenotrophomonas maltophilia well represented in the 'other Gram-negatives' group. Methods: Data for collected isolates were reviewed together with LabBase bacteraemia reports to the Health Protection Agency (HPA). Isolates with unusual resistances were subjected to molecular investigation. Results: From 2001 to 2006, the BSAC surveillance collected 1226 Pseudomonas aeruginosa, 240 Acinetobacter spp. - 125 of them Acinetobacter calcoaceticus/baumannii (Acb) complex - and 165 S. maltophilia. Among P. aeruginosa, non-susceptibility rates to β-lactams and gentamicin fluctuated, without trend, below 10%; those to ciprofloxacin ranged from 16% to 22%. One P. aeruginosa isolate from 2001 had VIM-2 metallo-β-lactamase. For Acb, the BSAC data indicated frequent non-susceptibility, except to imipenem, where only five non-susceptible isolates were collected, all after 2003, four of them belonging to the OXA-23 clone 1 lineage which is prevalent in Southeast England. Reports to the HPA indicated rising imipenem non-susceptibility in Acb (P < 0.0001). Co-trimoxazole retained near-universal activity against S. maltophilia. Among new antibiotics, doripenem MICs were ≤4 mg/L for most imipenem-resistant P. aeruginosa but ≥16 mg/L for Acb OXA-23 clone 1. Ceftobiprole had higher MICs than ceftazidime for P. aeruginosa, but 81% of the isolates were inhibited at ≤4 mg/L. Tigecycline had activity against most Acb, including OXA-23 clone 1, and also against S. maltophilia. Conclusions: Most P. aeruginosa from bacteraemias in the UK and Ireland remain relatively susceptible by international standards; in contrast, multiresistance is widespread in Acb, with imipenem non-susceptibility emerging.