Is sonication of antibiotic-loaded cement spacers useful in two-stage revision of prosthetic joint infection?

BACKGROUND: In a two-stage exchange protocol for prosthetic joint infection (PJI), bacteria surviving over the antibiotic-loaded cement spacers may cause the persistence of infection with renewed clinical symptoms following the surgery. Culture after sonication of removed prosthesis is more sensitive than conventional periprosthetic tissue culture for the microbiological diagnosis of PJI. The aim of this study was to assess whether sonication of the spacer at the time of the second-stage procedure may improve the diagnosis of persistent PJI. METHODS: We evaluated by microbiological culture the sonication fluid from 222 cement spacers implanted in a two-stage exchange protocol in 157 patients affected by PJI. A mean of 1.3 (range, 1-4) spacer per patient was performed. RESULTS: In 53 out of 222 spacers analyzed infection was confirmed according to the MSIS criteria. In 22 cases the infection was confirmed by both cultures on periprosthetic tissue and on sonication fluid from the spacers. In 23 cases persistent PJI was identified because of only cultures of periprosthetic tissue and 8 because of results obtained after spacer sonication. The sensitivity of periprosthetic tissue cultures was higher than that of cultures performed on sonication fluid (84.9% vs 56.6%, p < .001). CONCLUSIONS: Even though sonication of cement spacers has performances inferior than those reported for prosthesis, it can be considered a complementary method to unravel persistent infection during a two-stage exchange protocol for PJI.

Detection of biofilm formation in Staphylococcus epidermidis from implant infections. Comparison of a PCR-method that recognizes the presence of ica genes with two classic phenotypic methods.

Biofilm-forming ability is increasingly being recognized as an important virulence factor in Staphylococcus epidermidis. This study compares three different techniques for the detection of biofilm-positive strains. The presence of icaA and icaD genes responsible for biofilm synthesis was investigated by a PCR method in a collection of 80 S. epidermidis strains isolated from orthopedic implant infections. The results from molecular analysis were compared with those obtained by two classic phenotypic methods, the Congo red agar (CRA) plate test and the microtiter plate test (MtP). Fifty-seven percent of all the examined strains were found icaA/icaD-positive, of which only three were not positive for CRA test. Differently, by the MtP method, 66% of the strains were found to be biofilm-producers but only a limited agreement with the PCR-method was noticeable because of the observation of (icaA/icaD+)/MtP- strains (8%) and of a surprising ambiguous result of (icaA/icaD-)/MtP+ strains (16%). The category of the weak biofilm-producers provided the highest contribution to these mismatching results (10%). The better agreement between the CRA plate test with the molecular detection of ica genes indicates the former as a reliable test for the phenotypic characterization of virulence of clinical isolates. However, MtP method remains a precious tool for the in vitro screening of different biomaterials for the adhesive properties using a reference strain.

Antibiotic resistance in exopolysaccharide-forming Staphylococcus epidermidis clinical isolates from orthopaedic implant infections.

The opportunistic pathogen Staphylococcus epidermidis is able to produce biofilm and to frequently cause implant infections. In recent years, it has also exhibited an increasing antimicrobial drug resistance. Here, the resistance to a panel of 16 different antibiotics in 342 clinical strains of S. epidermidis from orthopaedic implant infections has been investigated. The isolates were pheno- and genotyped for extracellular polysaccharide production, relevant to staphylococcal biofilm formation, in order to ascertain possible associations with antibiotic resistance. Approximately 10% of the isolates were found to be sensitive to all screened antibiotics. In all, 37-38% were resistant to beta-lactams such as oxacillin and imipenem, while the resistance to penicillin, ampicillin, cefazolin, cefamandole, was consistently observed in over 80% of the strains. Erythromycin- and clindamycin- resistant strains were approximately 41% and 16%, respectively. Of the isolates, 10% was resistant to chloramphenicol, 23% to sulfamethoxazole and 26% to ciprofloxacin. Resistance to vancomycin was never observed. Interestingly, exopolysaccharide-producing strains exhibited a significantly higher prevalence in the resistance to the four aminoglycosides (gentamicin, amikacin, netilmicin, tobramycin), to sulfamethoxazole and to ciprofloxacin with respect to non-producing isolates. Moreover, multiple resistance to antibiotics was more frequent among exopolysaccharide-forming strains.

Search for the insertion element IS256 within the ica locus of Staphylococcus epidermidis clinical isolates collected from biomaterial-associated infections.

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.

Evaluation of bacterial adhesion of Streptococcus mutans on dental restorative materials.

Bacterial adhesion to the surface of composite resins and other dental restorative materials is an important parameter in the aetiology of secondary caries formation. The aim of the present study was to investigate the adhesion of a Streptococcus mutans strain (ATCC 25175) on the surface of different restorative materials. The test materials examined included three flowable composites (Filtek Flow, Tetric Flow, and Arabesk Flow), three microhybrid composites (Clearfil APX, Solitaire 2, and Z250), two glass-ionomers (Fuji IX, Fuji IX fast), a compomer (F2000), an ormocer (Admira), and a control reference material (tissue culture grade, surface treated polystyrene). The adhesion tests were carried out in 24-well plates. Quantitative turbidimetric measurements were finally performed in order to indirectly evaluate the amount of bacteria retained on the material surface after in vitro exposure to the bacteria suspension. Under these conditions, with the exception of the Admira ormocer and the Fuji IX fast glass ionomer, which were found to be more adhesive, all the other material surfaces showed a similar susceptibility to bacterial adhesion, exhibiting values not significantly different than the reference polystyrene control. Furthermore, the release of fluoride from some of the test surfaces did not appear capable to reduce early bacterial adhesion.