Evaluation of two different semi-automated homogenization techniques in microbiological diagnosis of periprosthetic joint infection: disperser vs. bead milling method

Background

In microbiological diagnosis of periprosthetic joint infection (PJI) there is no consensus regarding the most suitable and optimal number of specimens to be cultured or the most effective technique of tissue processing. This comparative study analysed the accuracy of two semi-automated homogenization methods with special focus on the volume and exact origin of each sample.

Methods

We investigated a total of 722 periprosthetic tissue samples. PJI was defined according to the new scoring system for preoperative and intraoperative criteria. We compared the performance of our routinely used single tissue processing by disposable high-frequency disperser with the bead milling method.

Results

Eighty patients were included. Among forty classified PJIs, 34 patients yielded positive culture results. In 23 cases (68%) exact concordant results were generated with both techniques. However, in seven cases (20%) processing by the disperser and in four cases (12%) by bead milling provided additional positive samples, but without significant difference since the major definition criteria were met in all cases. The percentage of positive results was influenced by the volume and origin of the tissue samples. Results for small tissue samples tended to be better using the bead milling method. This might lead to improved preoperative arthroscopic diagnosis, as the volume of biopsies is generally limited. Six patients had negative results due to previous antimicrobial therapy. Forty other patients were classified as aseptic failures. Neither procedure resulted in any contamination.

Conclusion

Both methods enable reliable processing of tissue samples for diagnosis of PJI and are suitable for routine use.

Microbiological diagnosis of polymicrobial periprosthetic joint infection revealed superiority of investigated tissue samples compared to sonicate fluid generated from the implant surface

OBJECTIVES

In the microbiological diagnosis of periprosthetic joint infection (PJI), there is much discussion about the methodology of obtaining proper specimens, the processing technique, and suitable culture media. This retrospective study was conducted to analyse the accuracy of our culture techniques.

METHODS

Tissue samples and components from 258 patients after revision arthroplasty of the hip, knee, and shoulder were investigated, and the results of tissue cultures (TC) were compared to those of sonicate fluid cultures (SFC). Furthermore, an evaluation was performed of the influence of different culture media on the detection rate.

RESULTS

PJI was confirmed in 186 patients. The overall sensitivity of TC was no different to that of SFC (91.3% vs 90.8%, P = 1). In 153 cases (82.3%), TC and SFC showed concordant positive results. Results were discordant in 33 cases (17.7%). When differentiated according to the type of infection, TC showed significantly better results than SFC in detecting polymicrobial infections (97.0% vs 67.0%, P = 0.004). There were also significant differences between the culture media regarding the yield of microorganisms.

CONCLUSIONS

TC was more effective in detecting co-infections. The best results were obtained using both TC and SFC. The choice of culture media has a significant influence on the quality of results.

Whole genome analyses of CMY-2-producing Escherichia coli isolates from humans, animals and food in Germany

Background

Resistance to 3rd-generation cephalosporins in Escherichia coli is mostly mediated by extended-spectrum beta-lactamases (ESBLs) or AmpC beta-lactamases. Besides overexpression of the species-specific chromosomal ampC gene, acquisition of plasmid-encoded ampC genes, e.g. bla_CMY-2, has been described worldwide in E. coli from humans and animals. To investigate a possible transmission of bla_CMY-2 along the food production chain, we conducted a next-generation sequencing (NGS)-based analysis of 164 CMY-2-producing E. coli isolates from humans, livestock animals and foodstuff from Germany.

Results

The data of the 164 sequenced isolates revealed 59 different sequence types (STs); the most prevalent ones were ST38 (n = 19), ST131 (n = 16) and ST117 (n = 13). Two STs were present in all reservoirs: ST131 (human n = 8; food n = 2; animal n = 6) and ST38 (human n = 3; animal n = 9; food n = 7). All but one CMY-2-producing ST131 isolates belonged to the clade B (fimH22) that differed substantially from the worldwide dominant CTX-M-15-producing clonal lineage ST131-O25b clade C (fimH30). Plasmid replicon types IncI1 (n = 61) and IncK (n = 72) were identified for the majority of bla_CMY-2-carrying plasmids. Plasmid sequence comparisons showed a remarkable sequence identity, especially for IncK plasmids. Associations of replicon types and distinct STs were shown for IncK and ST57, ST429 and ST38 as well as for IncI1 and ST58. Additional β-lactamase genes (bla_TEM, bla_CTX-M, bla_OXA, bla_SHV) were detected in 50% of the isolates, and twelve E. coli from chicken and retail chicken meat carried the colistin resistance gene mcr-1.

Conclusion

We found isolates of distinct E. coli clonal lineages (ST131 and ST38) in all three reservoirs. However, a direct clonal relationship of isolates from food animals and humans was only noticeable for a few cases. The CMY-2-producing E. coli-ST131 represents a clonal lineage different from the CTX-M-15-producing ST131-O25b cluster. Apart from the ST-driven spread, plasmid-mediated spread, especially via IncI1 and IncK plasmids, likely plays an important role for emergence and transmission of bla_CMY-2 between animals and humans.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4976-3) contains supplementary material, which is available to authorized users.

Periprosthetic joint infection caused by anaerobes. Retrospective analysis reveals no need for prolonged cultivation time if sensitive supplemented growth media are used

BACKGROUND

In microbiological diagnosis of periprosthetic joint infection (PJI) culture media and incubation time are controversially discussed, especially if anaerobic bacteria are the causative agent. This study was conducted to demonstrate the influence of sensitive supplemented growth media on the duration of culturing anaerobes.

METHODS

Twenty-five consecutive cases were included in this retrospective study. For definition of PJI, the criteria of the Musculoskeletal Infection Society (MSIS) were considered. Histopathological analysis was interpreted according to the classification by Krenn et al. The quantity and time to positivity of detected anaerobes were monitored. Furthermore, antimicrobial activity within the tissue and sonicate fluid was phenotypically tested.

RESULTS

In all cases, even if the patients had received antibiotics before recovery, culture of anaerobes (Propionibacterium species, Finegoldia magna, Parvimonas micra and Robinsoniella peoriensis), both from tissue samples and prosthetic components, first became detectable in supplemented liver thioglycollate broth within six days (median: four days).

CONCLUSION

Recommendations for prolonged cultivation for up to 14 days mostly aim at detection of anaerobes. Here we present a laboratory procedure that can shorten cultivation time considerably.

Robinsoniella peoriensis, originally isolated from swine manure, and early periprosthetic hip infection: Case report and review of the literature

We report on the first case of a periprosthetic joint infection with the anaerobic spore-forming Gram-positive rod Robinsoniella peoriensis as the causative agent. The bacterium was first isolated from a swine manure storage pit and has so far rarely been associated with human infections.

Molecular Investigation of Carbapenem-Resistant Acinetobacter spp. from Hospitals in North Rhine-Westphalia, Germany

Emergence of carbapenem-resistant Acinetobacter spp., especially Acinetobacter baumannii, in hospitals has been increasingly detected worldwide. In the present study, we analyzed carbapenem-resistant isolates (70 A. baumannii and one Acinetobacter pittii) collected in a period of 4 years (February 2008 to January 2012) in one diagnostic laboratory in Germany. All isolates were carbapenemase positive with OXA-23 as by far the most common enzyme (n = 66, 93%). Carbapenemases OXA-24-like and OXA-58 were not present in the isolates, but genes bla_GIM-1 and ISAba1+bla_OXA-80/82 were found to be the cause of carbapenem resistance in one and four isolates, respectively. Polymerase chain reaction typing revealed that the majority of A. baumannii isolates could be assigned to the very successful international clone 2. ApaI-macrorestriction and pulsed-field gel electrophoresis (PFGE) indicated clonal transmission of resistant strains (eight different PFGE types) within several hospitals. By multilocus sequence typing, the isolates were to be assigned to ST195 (n = 44), ST236 (n = 12), ST208 (n = 4), ST437 (n = 3), ST231 (n = 3), ST448 (n = 2), ST556 (n = 1), and ST945 (n = 1). The wide spread of carbapenem-resistant clones of A. baumannii is facilitated by international travelling and needs continuous surveillance in hospitals and diagnostic laboratories.