Preliminary evaluation of a rapid lateral flow calprotectin test for the diagnosis of prosthetic joint infection

Aims

This pilot study tested the performance of a rapid assay for diagnosing prosthetic joint infection (PJI), which measures synovial fluid calprotectin from total hip and knee revision patients.

Methods

A convenience series of 69 synovial fluid samples from revision patients at the Norfolk and Norwich University Hospital were collected intraoperatively (52 hips, 17 knees) and frozen. Synovial fluid calprotectin was measured retrospectively using a new commercially available lateral flow assay for PJI diagnosis (Lyfstone AS) and compared to International Consensus Meeting (ICM) 2018 criteria and clinical case review (ICM-CR) gold standards.

Results

According to ICM, 24 patients were defined as PJI positive and the remaining 45 were negative. The overall accuracy of the lateral flow test compared to ICM was 75.36% (52/69, 95% CI 63.51% to 84.95%), sensitivity and specificity were 75.00% (18/24, 95% CI 53.29% to 90.23%) and 75.56% (34/45, 95% CI 60.46% to 87.12%), respectively, positive predictive value (PPV) was 62.07% (18/29, 95% CI 48.23% to 74.19%) and negative predictive value (NPV) was 85.00% (34/40, 95% CI 73.54% to 92.04%), and area under the receiver operating characteristic (ROC) curve (AUC) was 0.78 (95% CI 0.66 to 0.87). Patient data from discordant cases were reviewed by the clinical team to develop the ICM-CR gold standard. The lateral flow test performance improved significantly when compared to ICM-CR, with accuracy increasing to 82.61% (57/69, 95% CI 71.59% to 90.68%), sensitivity increasing to 94.74% (18/19, 95% CI 73.97% to 99.87%), NPV increasing to 97.50% (39/40, 95% CI 85.20% to 99.62%), and AUC increasing to 0.91 (95% CI 0.81 to 0.96). Test performance was better in knees (100.00% accurate (17/17, 95% CI 80.49% to 100.00%)) compared to hips (76.92% accurate (40/52, 95% CI 63.16% to 87.47%)).

Conclusion

This study demonstrates that the calprotectin lateral flow assay could be an effective diagnostic test for PJI, however additional prospective studies testing fresh samples are required.

Cite this article:Bone Joint Res. 2020;9(5):202–210.

Further diversity of the Staphylococcus intermedius group and heterogeneity in the MboI restriction site used for Staphylococcus pseudintermedius species identification

Species identification of 200 beta-hemolysin-producing canine staphylococcal isolates was performed using a recently described polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method (based on MboI restriction of a pta gene fragment), supplemented with biochemical testing and sequencing of housekeeping genes. The PCR-RFLP method misclassified a small fraction (approximately 1%) of the Staphylococcus pseudintermedius population as a result of heterogeneity in the MboI restriction site. A potentially novel species within the Staphylococcus intermedius group (SIG) was found, having closest similarity to S. intermedius based on sequence comparison to the genes sodA, pta, hsp60, tuf, and full-length 16S ribosomal DNA, thus demonstrating further species diversity within the SIG.

Francisella asiatica sp. nov. isolated from farmed tilapia (Oreochromis sp.) and elevation of Francisella philomiragia subsp. noatunensis to species rank as Francisella noatunensis comb. nov., sp. nov

Bacterial isolates from diseased farmed tilapia (Oreochromis sp.) from Costa Rica (PQ 1104), Atlantic salmon (Salmo salar) from Chile (PQ 1106) and three-line grunt (Parapristipoma trilineatum) from Japan (Ehime-1) were characterized by phenotypic and molecular taxonomic methods. These isolates were Gram-negative, oxidase negative, non-motile, strictly aerobic cocco-bacilli, produced H2S from cysteine supplemented media, which is phenotypically consistent with the genus Francisella. Comparison of 16S rRNA gene sequences and five partial housekeeping gene sequences (groEL, shdA, rpoB, rpoA and pgm) confirmed these isolates to be members of the genus Francisella, with high 16S rRNA similarity (> 99 %) to Francisella philomiragia subsp noatunensis, F. piscicida and Francisella philomiragia subsp philomiragia isolates. Despite the close 16s rRNA relationship with the aforementioned Francisella taxa, isolates PQ 1104 and Ehime-1 form a separate clade on phylogenetic analysis of the 16s rRNA gene and all housekeeping genes investigated, whereas isolate PQ 1106 is highly similar to F. philomiragia subsp noatunensis (NCIMB 14265T) and F. piscicida (DSM 18777T). DNA-DNA hybridization studies revealed mean reassociation values of 60.3 and 72.6 % between isolate PQ 1104 and F. philomiragia subsp noatunensis (NCIMB 14265T) and F. philomiragia subsp philomiragia (ATCC 25015), respectively. Thus, on the basis of molecular genetic evidence, we propose that isolates PQ 1104 and Ehime-1 should be recognised as Francisella asiatica sp. nov. with type strain PQ 1104T (NCIMB and CCUG number not received yet). No separation between F. piscicida and F. philomiragia subsp noatunensis were identified by the same methods and these species constitute heterotypic synonyms for which the epithet noatunensis has priority. However, given the increased evidence of ecological differentiation within the F. philomiragia group and the existence of a specific fish pathogenic clade, we propose that the F. philomiragia subsp noatunensis be elevated to species level as F. noatunensis comb. nov., sp.

Real time PCR detection of Piscirickettsia salmonis from formalin-fixed paraffin-embedded tissues

Piscirickettsia salmonis is the causative agent of piscirickettsiosis, a transmissible disease of salmonid fish. Diagnosis of piscirickettsiosis has traditionally been based upon identification of typical pathological changes by histological investigation, with confirmation by immunohistochemistry on formalin-fixed, paraffin-embedded tissues. However, implementation of more rapid confirmatory techniques, preferably with higher levels of sensitivity and possibilities for quantification, is desirable. A real-time polymerase chain reaction (PCR) assay was designed for specific detection of P. salmonis and tested on samples extracted from formalin-fixed paraffin-embedded material. Construction of a PCR-target mimic allowed determination of detection limits, linearity of the real-time PCR and quantitative detection of P. salmonis. The present study demonstrates the capability of the described real time PCR assay for detection of P. salmonis from paraffin-embedded material with a high degree of sensitivity and specificity. Implementation of this assay constitutes an important development for a rapid and secure diagnosis of piscirickettsiosis.

Francisella philomiragia subsp. noatunensis subsp. nov., isolated from farmed Atlantic cod (Gadus morhua L.)

Seven bacterial isolates from farmed Atlantic cod displaying chronic granulomatous disease were characterized by phenotypic and molecular taxonomic methods. The isolates were Gram-negative, facultatively intracellular, non-motile, strictly aerobic coccobacilli which produced H2S from cysteine-supplemented media and are therefore phenotypically consistent with members of the genus Francisella. Comparison of 16S rRNA gene sequences and six partial housekeeping gene sequences (groEL, shdA, rpoB, rpoA, pgm and atpA) confirmed the organism as a member of the genus Francisella, with Francisella philomiragia as its closest relative (99.3 % 16S rRNA gene sequence similarity, 92.2–99.0 % housekeeping gene sequence similarity). Despite the close relationship with F. philomiragia, isolates from Atlantic cod could be readily distinguished phenotypically and genetically from F. philomiragia ATCC 25015T. DNA–DNA hybridization studies revealed a mean reassociation value of 68 %. Thus, on the basis of phenotypic and molecular genetic evidence, we propose that the strains isolated from Atlantic cod should be recognized as Francisella philomiragia subsp. noatunensis subsp. nov. with the type strain 2005/50/F292-6CT (=NCIMB 14265T=LMG 23800T). Francisella philomiragia ATCC 25015T (=DSM 735T) is reclassified as Francisella philomiragia subsp. philomiragia subsp. nov.

Dissemination of community-acquired methicillin-resistant Staphylococcus aureus clones in northern Norway: sequence types 8 and 80 predominate

Increasing frequencies of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) strain isolation have been reported from many countries. The overall prevalence of MRSA in Norway is still very low. MRSA isolates (n = 67) detected between 1995 and 2003 in northern Norway were analyzed by pulsed-field gel electrophoresis, multilocus sequence typing, and staphylococcal cassette chromosome mec (SCCmec) typing. Sixty-seven isolates were associated with 13 different sequence types. Two successful MRSA clones predominated. Sequence type 8 (ST8) (40%) and ST80 (19%) containing SCCmec type IV were detected in hospitals and communities in different geographic regions during a 7-year period. In general, there was a low level of antimicrobial resistance. Only 26% of the isolates were multiresistant. International epidemic clones were detected. The frequent findings of SCCmec type IV (91%) along with heterogeneous genetic backgrounds suggest a horizontal spread of SCCmec type IV among staphylococcal strains in parallel with the clonal spread of successful MRSA strains.

Phenotypic and genotypic aminoglycoside resistance in blood culture isolates of coagulase-negative staphylococci from a single neonatal intensive care unit, 1989–2000

OBJECTIVES

To investigate the prevalence of aminoglycoside resistance and genes encoding aminoglycoside-modifying enzymes (AME) in blood culture isolates of coagulase-negative staphylococci (CoNS) from neonates.

MATERIALS AND METHODS

A total of 180 isolates from 148 patients collected in a single neonatal unit over a 12 year period were examined for susceptibility to gentamicin, tobramycin, netilmicin, amikacin and arbekacin by Etest and/or disc diffusion. AME genes were detected by PCR.

RESULTS

The overall non-susceptibility rates to gentamicin, tobramycin, netilmicin, amikacin and arbekacin were 66%, 68%, 52%, 38% and 1%, respectively. Gentamicin non-susceptibility rates were 4% and 91% in methicillin-susceptible and -resistant isolates, respectively. aac(6')-Ie-aph(2'')-Ia, aph(3')-IIIa and/or ant(4')-Ia were encountered in 125 (69%), 1 (0.5%) and 30 (16.6%) isolates, respectively. Forty-six (26%) isolates negative for AME genes were susceptible to all aminoglycosides. In contrast, 115 (92%), 91 (73%) and 66 (53%) of aac(6')-Ie-aph(2'')-Ia positive isolates were non-susceptible to gentamicin, netilmicin and amikacin, respectively. Only one isolate showed arbekacin resistance. However, aac(6')-Ie-aph(2'')-Ia positive isolates and isolates with gentamicin MIC > or =128 mg/L displayed a significant reduction in arbekacin inhibition zones.

CONCLUSIONS

A high prevalence of aminoglycoside resistance was detected and associated with methicillin resistance. Discrepancies between phenotypic and genetic detection of aminoglycoside resistance were discerned. Gentamicin was the preferred substrate for phenotypic detection of aac(6')-Ie-aph(2'')-Ia. Arbekacin showed favourable antibacterial activity even in aac(6')-Ie-aph(2'')-Ia-positive isolates. We suggest including arbekacin in future clinical trials of empirical treatment of late onset neonatal sepsis.