Department of Biomolecular Sciences and Biotechnology, Università degli Studi di Milano, Milano, Italy.
BMC Microbiol. 2009 Dec 22;9:270. doi: 10.1186/1471-2180-9-270.
Acinetobacter baumannii is emerging as an important nosocomial pathogen. Multidrug resistance, as well as ability to withstand environmental stresses, makes eradication of A. baumannii difficult, particularly from hospital settings.
Over a six-year period, 73 isolates of A. baumannii were collected from infected patients in two hospitals in Italy. While 69 out of the 73 isolates displayed identical multidrug antibiotic resistance pattern, they were susceptible to carbapenems. Genetic profiles of these 69 isolates, determined by Pulsed Field Gel Electrophoresis (PFGE), indicated that they were genetically related and could be clustered in a specific clone, called SMAL. We tested the ability of the SMAL clone to form biofilm, an important determinant for bacterial colonization of the human host and for persistence in the hospital environment. Biofilm formation by A. baumannii SMAL, measured as surface adhesion to polystyrene, is strongly affected by growth conditions, being impaired in rich growth media such as LB, while being favoured in glucose-based medium. Surface adhesion in glucose-based media is inhibited by treatment with cellulase, suggesting that it depends on production of cellulose or of a chemically related extracellular polysaccharide. Exposure of A. baumannii SMAL to subinhibitory concentrations of imipenem resulted in biofilm stimulation and increased production of iron uptake proteins. Growth in iron-supplemented medium also stimulated surface adhesion, thus suggesting that increased intracellular iron concentrations might act as an environmental signal for biofilm formation in A. baumannii SMAL.
Our results indicate that exposure to subinhibitory concentrations of imipenem can stimulate biofilm formation and induce iron uptake in a pathogenic strain of A. baumannii, with potential implications on antibiotic susceptibility and ability to persist in the human host.
鲍曼不动杆菌正在成为一种重要的医院获得性病原体。其多重耐药性以及耐受环境压力的能力使得消除鲍曼不动杆菌变得困难，尤其是在医院环境中。
在六年的时间里，从意大利两家医院的感染患者中收集了 73 株鲍曼不动杆菌。虽然 73 株分离株中的 69 株表现出相同的多药抗生素耐药模式，但它们对碳青霉烯类药物敏感。通过脉冲场凝胶电泳（PFGE）确定的这 69 株分离株的遗传图谱表明，它们具有遗传相关性，可以聚类成一个特定的克隆，称为 SMAL。我们测试了 SMAL 克隆形成生物膜的能力，生物膜是细菌定植宿主和在医院环境中持续存在的重要决定因素。通过测定对聚苯乙烯的表面粘附，发现 SMAL 克隆的生物膜形成受到生长条件的强烈影响，在富含 LB 等生长介质的条件下受到抑制，而在基于葡萄糖的介质中则受到促进。基于葡萄糖的介质中的表面粘附会被纤维素酶处理所抑制，这表明它依赖于纤维素或化学相关的胞外多糖的产生。将鲍曼不动杆菌 SMAL 暴露于亚抑菌浓度的亚胺培南会刺激生物膜形成并增加铁摄取蛋白的产生。在铁补充培养基中生长也会刺激表面粘附，这表明增加细胞内铁浓度可能作为鲍曼不动杆菌 SMAL 生物膜形成的环境信号。
我们的研究结果表明，亚抑菌浓度的亚胺培南暴露可以刺激致病性鲍曼不动杆菌的生物膜形成并诱导铁摄取，这可能对其抗生素敏感性和在宿主中持续存在的能力产生影响。
