Antimicrobial susceptibility of Nocardia spp. – experience in England and Wales

Abstract number: 1733_615

Hill R.L.R., Pike R., Warner M.

Objectives:Nocardia are responsible for a variety of cutaneous, lung and central nervous system infections. Although antibiotic therapy with co-trimoxazole is put forward as the treatment of choice, the reliability of such an agent is uncertain. We have therefore investigated the susceptibility of patient-isolates from a variety of lesions.

Methods: During 2004–06, all Nocardia spp. referred to the Antibiotic Resistance Evaluation Unit, a national reference service for England and Wales, were characterised by MIC profiling. Demographic and clinical data were also collated.

Results: Of 48 referred patient-isolates, 22 were unspeciated whilst there were 7 each of N. farcinica and N. cyriacigeorgica. There were three N. asteroides; other species amounted to 1 or 2 isolates each. MICs of co-trimoxazole were 0.25–0.03 for N. farcinica (sensitive), 0.03–32 for N. cyriacigeorgica (2/7 isolates resistant), 4–>256 for N. asteroides (3/3 resistant), 0.25–>32 for other speciated isolates (3/12 resistant) and 0.06–>32 for unspeciated Nocardia (18/29 resistant), Overall, 26/58 (44.8%) Nocardia spp. were resistant to co-trimoxazole. Of other antibiotics, 5/48 (10.4%) isolates were resistant to linezolid (MICs 0.25–64), 24/48 (50%) resistant to Amikacin, 8/48 (16.7%) resistant to imipenem.

The majority of patients were male (36, 75%); ages ranged from 28 to 87y. 27.1% presented with cerebral abscesses, followed by 18.9% with lung lesions. Other abscesses accounted for 12.6% whilst Nocardia were isolated from blood in 10.4%. Skin/wound infections accounted for 8.3% isolates, whilst eye lesions, multiple abscesses, synovial fluid and osteolysis accounted for 6.3, 4.1, 4.1%, respectively. Of 6 isolates from cerebral abscesses tested for susceptibility to moxifloxacin, MICs were 0.25–4 (66.6% sensitive). Only one isolate from cerebral pus was sensitive to doxycycline but only one was resistant to linezolid (MIC = 64); 2 were resistant to co-trimoxazole (MIC 4–>32).

Conclusion: Whilst about half of all isolates were resistant to co-trimoxazole, susceptibility amongst isolates from cerebral abscesses was more common. Overall, linezolid was the most reliably active agent although moxifloxacin may be useful for cerebral abscesses. The variability in antibiotic susceptibility highlights the need for continued surveillance of the susceptibility of these organisms to determine effective therapeutic strategies.