Detection of Escherichia coli sequence type 131 by matrix-assisted laser desorption ionization time-of-flight mass spectrometry: implications for infection control policies?

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.

Direct antimicrobial resistance prediction from clinical MALDI-TOF mass spectra using machine learning

Early use of effective antimicrobial treatments is critical for the outcome of infections and the prevention of treatment resistance. Antimicrobial resistance testing enables the selection of optimal antibiotic treatments, but current culture-based techniques can take up to 72 hours to generate results. We have developed a novel machine learning approach to predict antimicrobial resistance directly from matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectra profiles of clinical isolates. We trained calibrated classifiers on a newly created publicly available database of mass spectra profiles from the clinically most relevant isolates with linked antimicrobial susceptibility phenotypes. This dataset combines more than 300,000 mass spectra with more than 750,000 antimicrobial resistance phenotypes from four medical institutions. Validation on a panel of clinically important pathogens, including Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae, resulting in areas under the receiver operating characteristic curve of 0.80, 0.74 and 0.74, respectively, demonstrated the potential of using machine learning to substantially accelerate antimicrobial resistance determination and change of clinical management. Furthermore, a retrospective clinical case study of 63 patients found that implementing this approach would have changed the clinical treatment in nine cases, which would have been beneficial in eight cases (89%). MALDI-TOF mass spectra-based machine learning may thus be an important new tool for treatment optimization and antibiotic stewardship.

Investigation of High-Risk ST131 Clone in Extended Spectrum β-Lactamase–Producing Escherichia coli Isolates in Children

Objective Antimicrobial resistance poses a serious threat to children's health. In recent years, high-risk Escherichia coli ST131 has become an important target for global surveillance studies. The E.coli ST131 clone is associated with extended spectrum β-lactamase (ESBL) production, as well as multidrug resistance and treatment failure. Studies on this clone in the pediatric age group are limited. We aim to investigate the rate of high-risk E. coli ST131 clone in ESBL-positive E. coli isolates obtained from pediatric patients.

Methods A total of 292 ESBL-positive E. coli isolates from clinical samples of pediatric patients was included in the study. MALDI-TOF MS system was used for bacterial identification. Susceptibility tests were performed using BD Phoenix automated system. ST131 detection was done by MALDI-TOF-MS. Fisher's exact test was used to compare the groups (significance <0.05).

Results A total of 292 isolates was analyzed. The high-risk ST131 clone was detected in 117 (40%) of the 292 ESBL-positive isolates. ST131 rates were found to be significantly higher in children under the age of 5 years compared with children over the age of 5 years (49.3 vs. 31.1%, p = 0.0019). Ciprofloxacin resistance was higher in ST131 isolates (45.6 vs. 31.7%; p < 0.05).

Conclusion The rate of the ST131 clone was found to be high in the pediatric population. The significantly high rate of resistance to ciprofloxacin, which is not commonly used in the pediatric population, in ST131 isolates reveals the importance of the spread of high-risk clones for the development of resistance.

Factors Associated With MALDI-TOF Mass Spectral Quality of Species Identification in Clinical Routine Diagnostics

Background

An accurate and timely identification of bacterial species is critical in clinical diagnostics. Species identification allows a potential first adaptation of empiric antibiotic treatments before the resistance profile is available. Matrix assisted Laser Desorption Ionization Time of Flight mass spectrometry (MALDI-TOF MS) is a widely used method for bacterial species identification. However, important challenges in species identification remain. These arise from (i) incomplete databases, (ii) close relatedness of species of interest, and (iii) spectral quality, which is currently vaguely defined.

Methods

We selected 47 clinically relevant bacterial isolates from 39 species, which can be challenging to identify by MALDI-TOF MS. We measured these isolates under various analytical conditions on two MALDI-TOF MS systems. First, we identified spectral features, which were associated with correct species identification in three different databases. Considering these features, we then systematically compared spectra produced with three different sample preparation protocols. In addition, we varied quantities of bacterial colony material applied and bacterial colony age.

Results

We identified (i) the number of ribosomal marker peaks detected, (ii) the median relative intensity of ribosomal marker peaks, (iii) the sum of the intensity of all detected peaks, (iv) a high measurement precision, and (v) reproducibility of peaks to act as good proxies of spectral quality. We found that using formic acid, measuring bacterial colonies at a young age, and frequently calibrating the MALDI-TOF MS device increase mass spectral quality. We further observed significant differences in spectral quality between different bacterial taxa and optimal measurement conditions vary per taxon.

Conclusion

We identified and applied quality measures for MALDI-TOF MS and optimized spectral quality in routine settings. Phylogenetic marker peaks can be reproducibly detected and provide an increased resolution and the ability to distinguish between challenging species such as those within the Enterobacter cloacae complex, Burkholderia cepacia complex, or viridans streptococci.

Identification of specific protein amino acid substitutions of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli ST131: a proteomics approach using mass spectrometry

The global pandemic of ESBL-producing Escherichia coli is associated with sequence type 131 (ST131). However, mechanisms of ST131 spread remain unclear. This study searched for proteins with amino acid substitutions specific for ST131 and used proteomics analysis to clarify ST131 characteristics. Five proteins had ST131-specific amino acid substitutions: uncharacterized protein YahO with E34A (m/z 7655); UPF0337 protein YjbJ with V59D, D60S and T63K (m/z 8351); uncharacterized protein YnfD with S106T (m/z 8448); and acid stress chaperone HdeA with Q92K and N94S (m/z 9714). Soluble cytochrome b562 (m/z 11783) showed seven amino acid substitutions, and the sequence differed between clade C of the pandemic clade and non-C. In silico analysis showed YahO protein-protein interaction with YjbJ, possibly related to biofilm formation. Although the function of soluble cytochrome b562 is electron transport of unknown function, its involvement in biofilm formation was predicted. HdeA was a gastric acid resistance-related protein. The function of YnfD was completely unclear. In conclusion, ST131-specific protein amino acid substitutions consisted mainly of a gastric acid resistance protein and proteins of unknown function (possibly involved in biofilm formation), which might be mechanisms for long-term colonization in the human intestinal tract.

The Changing Role of the Clinical Microbiology Laboratory in Defining Resistance in Gram-negatives

The evolution of resistance in Gram-negatives has challenged the clinical microbiology laboratory to implement new methods for their detection. Multidrug-resistant strains present major challenges to conventional and new detection methods. More rapid pathogen identification and antimicrobial susceptibility testing have been developed for use directly on specimens, including fluorescence in situ hybridization tests, automated polymerase chain reaction systems, microarrays, mass spectroscopy, next-generation sequencing, and microfluidics. Review of these methods shows the advances that have been made in rapid detection of resistance in cultures, but limited progress in direct detection from specimens.

Can MALDI-TOF Mass Spectrometry Reasonably Type Bacteria?

Bacterial typing is crucial to tackle the spread of bacterial pathogens but current methods are time-consuming and costly. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been recently integrated into the microbiology laboratory workflow for a quick and low-cost microbial species identification. Independent research groups have successfully redirected the original function of this technology from their primary purpose to discriminate subgroups within pathogen species. However, identical bacterial subgroups could be identified by unrelated peaks by independent methods, thus limiting their robustness and exportability. We propose several guidelines that could improve the performance of MALDI-TOF MS-based typing methods for use as a first-line epidemiological tool.

Trends of extended-spectrum β-lactamase-producing Escherichia coli sequence type 131 and its H30 subclone in a French hospital over a 15-year period

Sequence type 131 (ST131) is a predominant lineage among extraintestinal pathogenic Escherichia coli. It plays a major role in the worldwide dissemination of E. coli producing extended-spectrum β-lactamases (ESBLs). Here we describe the long-term epidemiology of this clonal group in a French university hospital, where the incidence of ESBL-producing E. coli has increased from 0.018 case per 1000 patient-days in the year 2000 to 0.50 case per 1000 patient-days in 2014. The first of the 141 ST131 isolates was recovered in 2006, and the ST131 clonal group accounted for 18.1% of total ESBL-producing E. coli over the whole period (2000-2014). Subclonal typing showed that 75.9% (107/141) of ST131 isolates were H30, of which 81.3% (87/107) were H30-Rx. The large majority (137/141) of ESBLs produced were of the CTX-M group, with 94 CTX-M-15, 19 CTX-M-1, 10 CTX-M-27, 8 CTX-M-14 and four other CTX-M types (n = 6). Pulsed-field gel electrophoresis (PFGE) analysis showed high diversity, which increased during the course of the study. The 141 ST131 isolates clustered in 53 pulsotypes (PTs), with 2 dominant PTs (PT14 and PT13) with 36 and 17 isolates, respectively. These findings showed that ST131 was a predominant clone among ESBL-producing E. coli in our hospital, even though it only accounted for <20%. Moreover, ST131 should be regarded not as a unified entity but as a cluster of distinct clonal subsets even if the increase in resistance within ST131 has a strong clonal basis, being attributable mainly to the spread of C1/H30-R and C2/H30-Rx clades.

Community carriage of ESBL-producing Escherichia coli is associated with strains of low pathogenicity: a Swedish nationwide study

OBJECTIVES

Community carriage of ESBL-producing Escherichia coli (EPE) is common worldwide and there is a need to understand the connection between carriage and infection. We compared the molecular characteristics of EPE among Swedish community carriers with those of EPE causing invasive infections.

METHODS

We collected 2134 faecal samples from randomly selected Swedish inhabitants and examined them for the presence of EPE. All participating volunteers answered a questionnaire about putative risk factors for EPE carriage. Suspected EPE isolates (n = 418) from patients with bloodstream infection (BSI) were collected from Swedish laboratories. Isolates were genotypically and phenotypically characterized.

RESULTS

Our results show that the EPE population found in carriers generally had lower pathogenicity compared with the isolates from BSIs, since carriers had a lower proportion of E. coli belonging to phylogroup B2, ST131 and ST131 subclone H30-Rx. Isolates from carriers also had lower levels of multiresistance. The Swedish carriage rate of EPE was 4.7% (101/2134) among healthy volunteers. Risk factors associated with carriage were travel to countries in Asia (OR = 3.6, 95% CI = 1.4-9.2) and Africa (OR = 3.6, 95% CI = 1.7-7.7) and a diet without pork (OR = 0.5, 95% CI = 0.3-0.8 for pork eaters).

CONCLUSIONS

E. coli host factors previously associated with higher pathogenicity were all more common in BSIs compared with carriers. This indicates that the risk of invasive infection with EPE may be relatively modest in many community carriers and that EPE carriage of high-risk strains should be the focus of attention for prevention.