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Development of resistance and lack of efficacy in patients with S. aureus infections: 6 case reports Six patients experienced persistent or recurrent Staphylococcus aureus bacteraemia despite vancomycin and subsequent daptomycin treatment [dosages not stated]. Isolates were later determined to be resistant to daptomycin. A 78-year-old diabetic woman with aortic stenosis and intra-arterial stents was diagnosed with meticillin-resistant S. aureus (MRSA) bacteraemia. She received a 19-day course of vancomycin at the appropriate dose, followed by daptomycin for 15 days [routes not stated]. Her cultures were persistently positive for MRSA so she was switched to oral linezolid. She died soon afterwards, with bacteraemia that persisted for 36 days. A 61-year-old male diabetic presented with an infected, necrotic foot ulcer and positive cultures for MRSA. His treatment consisted of leg amputation and IV vancomycin, which was replaced by IV daptomycin after 7 days because of persistent bacteraemia. Echocardiography revealed mitral valve regurgitation with a 1cm vegetation. He received daptomycin for 11 days, but died with persistent bacteraemia. A 28-year-old female diabetic presented with prosthetic mitral valve endocarditis secondary to borderline oxacillinresistant S. aureus. Her bacteraemia initially resolved with a 29-day course of IV vancomycin. However, treatment had to be switched to IV daptomycin because of recurrence on treatment day 28. Her bacteraemia finally resolved with meropenem and moxifloxacin. She was discharged receiving long-term oral antibacterial suppression. A 75-year-old female cancer patient developed MRSA bacteraemia, osteomyelitis and discitis. Seven days of IV vancomycin and 18 days of IV daptomycin failed to clear her bacteraemia; but it resolved after starting IV linezolid. She was later discharged receiving oral linezolid. A 75-year-old female diabetic developed catheter-related MRSA bacteraemia when she was hospitalised for hypoglycaemia. A small mitral valve vegetation was found on echocardiography. She received vancomycin and daptomycin for 11 and 20 days, respectively [routes not stated], but her bacteraemia persisted. She died despite treatment change to linezolid. A 63-year-old man was hospitalised for generalised, allergic exfoliative dermatitis. He developed persistent MRSA bacteraemia, spinal discitis and mitral regurgitation with endocarditis. Despite 17 and 29 days of IV vancomycin and daptomycin, respectively, his bacteraemia persisted. His condition resolved after 9 days of IV linezolid. He was discharged improved, receiving longterm oral linezolid. Author comment: "The exact mechanism for development of daptomycin resistance remains unclear . . . [but] appear to commonly result in a single phenotype where the organism developed an excessively thickened cell wall, conferring concomitant reduced susceptibility to vancomycin." Hsu LY, et al. Six cases of daptomycin-non-susceptible Staphylococcus aureus bacteraemia in Singapore. Journal of Medical Microbiology 59: 1509-13, No.