Arciola Carla Renata, Campoccia Davide, Gamberini Simonetta, Rizzi Simona, Donati Maria Elena, Baldassarri Lucilla, Montanaro Lucio
Research Laboratory on Biocompatibility of Implant Materials, Rizzoli Orthopaedic Institute, and Experimental Pathology Department, University of Bologna, Italy.
Biomaterials. 2004 Aug;25(18):4117-25. doi: 10.1016/j.biomaterials.2003.11.027.
Staphylococcus epidermidis biofilm-forming strains produce a polysaccharide intercellular adhesin (PIA), which mediates bacterial cell aggregation and favours the colonisation on prosthetic implants. PIA synthesis is regulated by the icaADBC locus. In vitro, by repeated subcultures of a biofilm-producing strain, the loss of the ability to produce biofilm appears associated with the insertion of the IS256 element into the ica locus. This study was aimed (i) to investigate if the five genes of ica locus are always all present in different strains of S. epidermidis, and (ii) to search if IS256 insertion naturally occurs in ica locus without making recourse to the experimental procedure of repeated subcultures of strains. 120 S. epidermidis clinical isolates from peri-prosthesis infections were investigated both by an original multiplex PCR analysis of the ica genes and by PCR amplification of the IS256 element. Also two reference strains (the biofilm-negative S. epidermidis ATCC 12228 and the biofilm-forming ATCC 35984 [RP62A]) and two biofilm-negative RP62A-derived acriflavin mutants (D9 and HAM892) were analysed. D9 e HAM892 were for the first time shown to contain in ica locus, at the base 3319, a 1300-bp insertion with a DNA sequence corresponding to IS256. Among the 120 clinical isolates, 51 (43%) turned out completely ica-positive, 69 completely ica-negative (57%). The genes of the ica locus appear, in all cases of the present collection, strictly linked each other, so they are either all present or all absent. In this collection, IS256 was present in eight out of the 69 ica-negative strains and in 34 out of the 51 ica-positive strains. IS256, also when present in bacterial genomic DNA, was never found inside the ica locus, thus suggesting that insertion/excision of this element is not a natural occurring mechanism for off/on switching of biofilm production.
表皮葡萄球菌生物膜形成菌株产生一种胞间多糖黏附素（PIA），它介导细菌细胞聚集并有利于在人工植入物上定殖。PIA的合成受icaADBC基因座调控。在体外，通过对生物膜产生菌株进行反复传代培养，生物膜产生能力的丧失似乎与IS256元件插入ica基因座有关。本研究旨在：（i）调查ica基因座的五个基因在不同的表皮葡萄球菌菌株中是否总是全部存在；（ii）寻找IS256插入是否在ica基因座自然发生，而不借助菌株反复传代培养的实验程序。通过对ica基因进行原始多重PCR分析以及对IS256元件进行PCR扩增，研究了120株来自假体周围感染的表皮葡萄球菌临床分离株。还分析了两株参考菌株（生物膜阴性的表皮葡萄球菌ATCC 12228和生物膜形成的ATCC 35984 [RP62A]）以及两株生物膜阴性的源自RP62A的吖啶黄素突变体（D9和HAM892）。首次发现D9和HAM892在ica基因座的3319位碱基处含有一个1300 bp的插入片段，其DNA序列与IS256对应。在120株临床分离株中，51株（43%）结果显示ica完全阳性，69株完全ica阴性（57%）。在本研究收集的所有病例中，ica基因座的基因似乎彼此紧密相连，因此它们要么全部存在，要么全部缺失。在该研究集中，69株ica阴性菌株中有8株存在IS256，51株ica阳性菌株中有34株存在IS256。IS256即使存在于细菌基因组DNA中，也从未在ica基因座内发现，因此表明该元件的插入/切除不是生物膜产生开启/关闭的自然发生机制。
