Quality of MALDI-TOF mass spectra in routine diagnostics: results from an international external quality assessment including 36 laboratories from 12 countries using 47 challenging bacterial strains

OBJECTIVES

Matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) is a widely used method for bacterial species identification. Incomplete databases and mass spectral quality (MSQ) still represent major challenges. Important proxies for MSQ are the number of detected marker masses, reproducibility, and measurement precision. We aimed to assess MSQs across diagnostic laboratories and the potential of simple workflow adaptations to improve it.

METHODS

For baseline MSQ assessment, 47 diverse bacterial strains, which are challenging to identify by MALDI-TOF MS, were routinely measured in 36 laboratories from 12 countries, and well-defined MSQ features were used. After an intervention consisting of detailed reported feedback and instructions on how to acquire MALDI-TOF mass spectra, measurements were repeated and MSQs were compared.

RESULTS

At baseline, we observed heterogeneous MSQ between the devices, considering the median number of marker masses detected (range = [2-25]), reproducibility between technical replicates (range = [55%-86%]), and measurement error (range = [147 parts per million (ppm)-588 ppm]). As a general trend, the spectral quality was improved after the intervention for devices, which yielded low MSQs in the baseline assessment as follows: for four out of five devices with a high measurement error, the measurement precision was improved (p-values <0.001, paired Wilcoxon test); for six out of ten devices, which detected a low number of marker masses, the number of detected marker masses increased (p-values <0.001, paired Wilcoxon test).

DISCUSSION

We have identified simple workflow adaptations, which, to some extent, improve MSQ of poorly performing devices and should be considered by laboratories yielding a low MSQ. Improving MALDI-TOF MSQ in routine diagnostics is essential for increasing the resolution of bacterial identification by MALDI-TOF MS, which is dependent on the reproducible detection of marker masses. The heterogeneity identified in this external quality assessment (EQA) requires further study.

Whole-genome sequence-informed MALDI-TOF MS diagnostics reveal importance of Klebsiella oxytoca group in invasive infections: a retrospective clinical study

BACKGROUND

Klebsiella spp. are opportunistic pathogens which can cause severe infections, are often multi-drug resistant and are a common cause of hospital-acquired infections. Multiple new Klebsiella species have recently been described, yet their clinical impact and antibiotic resistance profiles are largely unknown. We aimed to explore Klebsiella group- and species-specific clinical impact, antimicrobial resistance (AMR) and virulence.

METHODS

We analysed whole-genome sequence data of a diverse selection of Klebsiella spp. isolates and identified resistance and virulence factors. Using the genomes of 3594 Klebsiella isolates, we predicted the masses of 56 ribosomal subunit proteins and identified species-specific marker masses. We then re-analysed over 22,000 Matrix-Assisted Laser Desorption Ionization - Time Of Flight (MALDI-TOF) mass spectra routinely acquired at eight healthcare institutions in four countries looking for these species-specific markers. Analyses of clinical and microbiological endpoints from a subset of 957 patients with infections from Klebsiella species were performed using generalized linear mixed-effects models.

RESULTS

Our comparative genomic analysis shows group- and species-specific trends in accessory genome composition. With the identified species-specific marker masses, eight Klebsiella species can be distinguished using MALDI-TOF MS. We identified K. pneumoniae (71.2%; n = 12,523), K. quasipneumoniae (3.3%; n = 575), K. variicola (9.8%; n = 1717), "K. quasivariicola" (0.3%; n = 52), K. oxytoca (8.2%; n = 1445), K. michiganensis (4.8%; n = 836), K. grimontii (2.4%; n = 425) and K. huaxensis (0.1%; n = 12). Isolates belonging to the K. oxytoca group, which includes the species K. oxytoca, K. michiganensis and K. grimontii, were less often resistant to 4th-generation cephalosporins than isolates of the K. pneumoniae group, which includes the species K. pneumoniae, K. quasipneumoniae, K. variicola and "K. quasivariicola" (odds ratio = 0.17, p < 0.001, 95% confidence interval [0.09,0.28]). Within the K. pneumoniae group, isolates identified as K. pneumoniae were more often resistant to 4th-generation cephalosporins than K. variicola isolates (odds ratio = 2.61, p = 0.003, 95% confidence interval [1.38,5.06]). K. oxytoca group isolates were found to be more likely associated with invasive infection to primary sterile sites than K. pneumoniae group isolates (odds ratio = 2.39, p = 0.0044, 95% confidence interval [1.05,5.53]).

CONCLUSIONS

Currently misdiagnosed Klebsiella spp. can be distinguished using a ribosomal marker-based approach for MALDI-TOF MS. Klebsiella groups and species differed in AMR profiles, and in their association with invasive infection, highlighting the importance for species identification to enable effective treatment options.

[Proximal interphalangeal (PIP) finger prosthesis - what have we learnt? Experiences over 10 years]

PURPOSE

In the following article we evaluate the clinical and radiological results after PIP joint replacement to answer the question if the outcome improved over the last years.

PATIENTS AND METHODS

In a retrospective clinical study 53 patients with 66 PIP joint implants (SBI-Avanta, Small Bone Innovations, Inc.) were assessed on the basis of clinical and radiological parameters. We examined the patients' range of motion, their grip strength, the rate of radiological loosening, the development of pain and the patients' satisfaction. 2 groups were included in the study. Patients operated from 2001 to 2007 (group A) were compared with patients operated from 2008 to 2011 (group B). To facilitate a standardized examination, we developed a score providing a comprehensive representation of the outcome after PIP joint replacement.

RESULTS

Group B showed significant improvement in the rate of loosening of the prosthesis (44-4%) in the last follow-up examination. Further improvement was demonstrated in pain reduction, range of motion (77°/67°), the patients' satisfaction and development of swan neck deformity (11%/18%). There was no significant improvement in the patients' grip strength and the rate of revision surgery.

CONCLUSION

Overall, the results after PIP joint replacement are very good. All patients reported a marked improvement in pain reduction. In group B a significant reduction in the rate of loosening of the prosthesis was shown. Moreover, the rate of swan neck deformity, the range of motion, the reduction of pain and the patient's satisfaction improved over the last years. The application of a new PIP-joint-score for a standardized evaluation of the outcome indicated a good correlation with patient satisfaction over time. The experience of the past years enabled improvements in PIP joint replacement. We consider cementing the prosthesis, a large contact area between the prosthesis and the bone and an emphasis on easy intraoperative flexion/extension as factors which can improve the results after PIP joint replacement. However, some problems could not been solved to date. In this respect, prospective clinical and biomechanical studies are necessary.

[Experience with the SRTM-PIP prosthesis as joint replacement: a retrospective overview with a follow-up of 2.4 years]

PURPOSE

In the following article we present our results with a cemented titanium/polyethylene prosthesis.

PATIENTS AND METHODS

The SR (TM)-PIP-prosthesis from the firm SBI (©) (formally Avanta (©)) was implanted in 39 patients in our clinic from 2001-2007. In all, we were able to follow-up in a retrospect clinical study 32 patients with 39 proximal interphalangeal joint prostheses. We examined the range of motion, the strength and looked for deformities. The patients had to fill in a questionnaire before examination about their pain and limitation in daily life. We also performed X-rays of the operated fingers.

RESULTS

The postoperative range of motion was about 67°. The strength mean value was 24.7 kg. 4 patients needed surgical revisions, in one case due to loosening of the proximal part of the prosthesis. 2 patients also received a tenoarthrolysis because of extension deficits and one patient because of a swan-neck deformity. We noted 7 swan-neck deformities and in 7 cases we found implant loosening of the proximal part of the prothesis. The postoperative Quick-DASH score was about 32.2 and showed a good result. All participants reported a marked improvement in pain reduction.

CONCLUSION

These positive results, the reduction of pain and the satisfaction of the patients advocate the use of this prosthesis for the proximal interphalangeal joint. The postoperative ROM is comparable to those of other prostheses. Concerning implant loosening and swan-neck deformity, these results still offer room for improvement. Critical judgement and further development of the prosthesis design, the operation technique and the instrumentation are required to further optimise the results.