Laboratory of Infection Biology, Department of Biomedicine, University Hospital Basel, Basel, Switzerland.
Antimicrob Agents Chemother. 2011 Jul;55(7):3510-6. doi: 10.1128/AAC.00172-11. Epub 2011 May 16.
Daptomycin (DAP) is bactericidal against methicillin-resistant Staphylococcus aureus (MRSA) in vitro, but it failed to eradicate MRSA in an experimental model of implant-associated infection. We therefore investigated various factors which could explain treatment failure by evaluating DAP activity, including the role of different cell wall components, adherence, biofilm, and calcium ions (Ca(2+)) in vitro and in vivo. In the tissue cage infection model, DAP was active only prophylactically and against low inocula. To identify the mechanisms of treatment failure, the in vitro activity of DAP against planktonic and adherent growing S. aureus and S. epidermidis mutants, differing in their capacity of biofilm formation and adherence, was determined. For planktonic staphylococci, the MIC was 0.625 μg/ml. For adherent staphylococci, DAP reduced biofilms at 30 μg/ml. However, it did not kill adherent bacteria up to 500 μg/ml, independent of biofilm biosynthesis (the ica mutant strain), nuclease (the nuc1/nuc2 mutant strain), LPXTG-anchored adhesin (the srtA mutant strain), autolysin (the atl mutant strain), or alanyl-LTA (the dltA mutant strain). Resistance of adherent staphylococci was not due to mutations of adherent bacteria, since staphylococci became DAP susceptible after detachment. Phenotypic tolerance was not explained by inactivation of DAP or inability of initial Ca(2+)-DAP complex formation. However, the addition of up to 100 mg/liter (2.5 mmol/liter) Ca(2+) gradually improved bactericidal activity toward adherent staphylococci in vitro and increased the prevention rate in the cage model from 40% to 60%. In summary, adherent staphylococci are resistant to DAP killing unless Ca(2+) is supplemented to physiologic concentrations.
达托霉素（DAP）在体外对耐甲氧西林金黄色葡萄球菌（MRSA）具有杀菌作用，但在植入物相关感染的实验模型中未能消除 MRSA。因此，我们研究了各种因素，包括细胞壁成分、黏附、生物膜和钙离子（Ca（2+））的作用，以解释治疗失败的原因，这些因素在体外和体内均进行了评估。在组织笼感染模型中，DAP 仅具有预防作用，且仅对低接种量有效。为了确定治疗失败的机制，我们测定了 DAP 对浮游和黏附生长的金黄色葡萄球菌和表皮葡萄球菌突变株的体外活性，这些突变株在生物膜形成和黏附能力上存在差异。对于浮游状态的金黄色葡萄球菌，MIC 为 0.625 μg/ml。对于黏附状态的金黄色葡萄球菌，DAP 在 30 μg/ml 时可减少生物膜。然而，即使在 500 μg/ml 时，DAP 也不能杀死黏附状态的细菌，而与生物膜生物合成（ica 突变株）、核酸酶（nuc1/nuc2 突变株）、LPXTG 锚定黏附素（srtA 突变株）、自溶素（atl 突变株）或丙氨酰-LTA（dltA 突变株）无关。黏附状态的金黄色葡萄球菌的耐药性不是由于黏附细菌的突变引起的，因为金黄色葡萄球菌在脱离后对 DAP 变得敏感。表型耐受性不能用 DAP 的失活或初始 Ca（2+）-DAP 复合物形成的能力来解释。然而，体外添加高达 100 mg/L（2.5 mmol/L）的 Ca（2+）逐渐提高了对黏附状态金黄色葡萄球菌的杀菌活性，并使笼模型中的预防率从 40%提高到 60%。综上所述，除非补充生理浓度的 Ca（2+），否则黏附状态的金黄色葡萄球菌对 DAP 的杀伤具有耐药性。
