High-resolution melting-curve analysis of ligation-mediated real-time PCR for rapid evaluation of an epidemiological outbreak of extended-spectrum-beta-lactamase-producing Escherichia coli

Rapid high-resolution melting genotyping scheme for Escherichia coli based on MLST derived single nucleotide polymorphisms

Routinely used typing methods including MLST, rep-PCR and whole genome sequencing (WGS) are time-consuming, costly, and often low throughput. Here, we describe a novel mini-MLST scheme for Eschericha coli as an alternative method for rapid genotyping. Using the proposed mini-MLST scheme, 10,946 existing STs were converted into 1,038 Melting Types (MelTs). To validate the new mini-MLST scheme, in silico analysis was performed on 73,704 strains retrieved from EnteroBase resulting in discriminatory power D = 0.9465 (CI 95% 0.9726-0.9736) for mini-MLST and D = 0.9731 (CI 95% 0.9726-0.9736) for MLST. Moreover, validation on clinical isolates was conducted with a significant concordance between MLST, rep-PCR and WGS. To conclude, the great portability, efficient processing, cost-effectiveness, and high throughput of mini-MLST represents immense benefits, even when accompanied with a slightly lower discriminatory power than other typing methods. This study proved mini-MLST is an ideal method to screen and subgroup large sets of isolates and/or quick strain typing during outbreaks. In addition, our results clearly showed its suitability for prospective surveillance monitoring of emergent and high-risk E. coli clones'.

Rapid Methods for Antimicrobial Resistance Diagnostics

Antimicrobial resistance (AMR) is one of the most challenging threats in public health; thus, there is a growing demand for methods and technologies that enable rapid antimicrobial susceptibility testing (AST). The conventional methods and technologies addressing AMR diagnostics and AST employed in clinical microbiology are tedious, with high turnaround times (TAT), and are usually expensive. As a result, empirical antimicrobial therapies are prescribed leading to AMR spread, which in turn causes higher mortality rates and increased healthcare costs. This review describes the developments in current cutting-edge methods and technologies, organized by key enabling research domains, towards fighting the looming AMR menace by employing recent advances in AMR diagnostic tools. First, we summarize the conventional methods addressing AMR detection, surveillance, and AST. Thereafter, we examine more recent non-conventional methods and the advancements in each field, including whole genome sequencing (WGS), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectrometry, Fourier transform infrared (FTIR) spectroscopy, and microfluidics technology. Following, we provide examples of commercially available diagnostic platforms for AST. Finally, perspectives on the implementation of emerging concepts towards developing paradigm-changing technologies and methodologies for AMR diagnostics are discussed.

A novel high-resolution melting analysis approach for rapid detection of vancomycin-resistant enterococci

BACKGROUND

Vancomycin-resistant enterococci (VRE) are resistant to most classes of antibiotics. Diagnosis of VRE using standard methods takes 2 to 5 days. Development of a rapid PCR-assay that detects and identifies resistant genes in bacteria would provide time-critical information on the presence of VRE in clinical samples allowing early treatment and management of infected patients.

OBJECTIVES

Investigate the use of high resolution melting analysis (HRMA) and 16S-rRNA-PCR approach for rapid and cost-effective identification of VRE.

DESIGN

Descriptive antibiotic susceptibility studies.

SETTING

Manchester Academic Health Sciences Centre and School of Translational Medicine, University of Manchester, UK, and Department of Clinical Laboratory Sciences, Taibah University, Saudi Arabia.

MATERIALS AND METHODS

PCR-HRMA using 16S-rRNA V1-primers was used to detect and identify VRE. DNA from different strains of vancomycin-resistant and -sensitive Enterococcus faecalis (VSE) and Enterococcus faecium were amplified using V1-primer followed by HRMA in a single run. Differentiation of VRE from VSE was based on curve shapes generated against reference organisms (Bacteroides fragilis).

MAIN OUTCOMES MEASURES

Amplification curves and difference plots for VRE and VSE.

RESULTS

Difference plots were generated for all vancomycin-resistant and -sensitive E faecalis and E faecium strains by subtracting their fluo.rescence melting profile from that of a reference-species B fragilis. A characteristic curve shape was produced by vancomycin-sensitive E faecalis and E faecium. However, vancomycin-resistant strains of these bacteria were associated with a markedly different curve shape facilitating a clear differentiation.

CONCLUSION

The 16S-PCR-HRMA approach has the potential for detecting vancomycin-resistant E faecium and E faecalis. Data with VRE provide the basis for combining VRE identification with pathogens speciation in a rapid, cheap assay able to identify a pathogen as an Enterococcus and whether it is vancomycin-sensitive or -resistant E faecium or E faecalis in a single PCR and HRMA run.

LIMITATIONS

Tested on specific, but not all, reference Enterococcus species and clinical isolates.

CONFLICT OF INTEREST

None.

Epidemiological characterization of a nosocomial outbreak of extended spectrum β-lactamase Escherichia coli ST-131 confirms the clinical value of core genome multilocus sequence typing

Enhanced precision of epidemiological typing in clinically suspected nosocomial outbreaks is crucial. Our aim was to investigate whether single nucleotide polymorphism (SNP) analysis and core genome (cg) multilocus sequence typing (MLST) of whole genome sequencing (WGS) data would more reliably identify a nosocomial outbreak, compared to earlier molecular typing methods. Sixteen isolates from a nosocomial outbreak of ESBL E. coli ST-131 in southeastern Sweden and three control strains were subjected to WGS. Sequences were explored by SNP analysis and cgMLST. cgMLST clearly differentiated between the outbreak isolates and the control isolates (>1400 differences). All clinically identified outbreak isolates showed close clustering (≥2 allele differences), except for two isolates (>50 allele differences). These data confirmed that the isolates with >50 differing genes did not belong to the nosocomial outbreak. The number of SNPs within the outbreak was ≤7, whereas the two discrepant isolates had >700 SNPs. Two of the ESBL E. coli ST-131 isolates did not belong to the clinically identified outbreak. Our results illustrate the power of WGS in terms of resolution, which may avoid overestimation of patients belonging to outbreaks as judged from epidemiological data and previously employed molecular methods with lower discriminatory ability.

A high-throughput assay for the comprehensive profiling of DNA ligase fidelity

DNA ligases have broad application in molecular biology, from traditional cloning methods to modern synthetic biology and molecular diagnostics protocols. Ligation-based detection of polynucleotide sequences can be achieved by the ligation of probe oligonucleotides when annealed to a complementary target sequence. In order to achieve a high sensitivity and low background, the ligase must efficiently join correctly base-paired substrates, while discriminating against the ligation of substrates containing even one mismatched base pair. In the current study, we report the use of capillary electrophoresis to rapidly generate mismatch fidelity profiles that interrogate all 256 possible base-pair combinations at a ligation junction in a single experiment. Rapid screening of ligase fidelity in a 96-well plate format has allowed the study of ligase fidelity in unprecedented depth. As an example of this new method, herein we report the ligation fidelity of Thermus thermophilus DNA ligase at a range of temperatures, buffer pH and monovalent cation strength. This screen allows the selection of reaction conditions that maximize fidelity without sacrificing activity, while generating a profile of specific mismatches that ligate detectably under each set of conditions.

Escherichia coli ST131, an intriguing clonal group

In 2008, a previously unknown Escherichia coli clonal group, sequence type 131 (ST131), was identified on three continents. Today, ST131 is the predominant E. coli lineage among extraintestinal pathogenic E. coli (ExPEC) isolates worldwide. Retrospective studies have suggested that it may originally have risen to prominence as early as 2003. Unlike other classical group B2 ExPEC isolates, ST131 isolates are commonly reported to produce extended-spectrum β-lactamases, such as CTX-M-15, and almost all are resistant to fluoroquinolones. Moreover, ST131 E. coli isolates are considered to be truly pathogenic, due to the spectrum of infections they cause in both community and hospital settings and the large number of virulence-associated genes they contain. ST131 isolates therefore seem to contradict the widely held view that high levels of antimicrobial resistance are necessarily associated with a fitness cost leading to a decrease in pathogenesis. Six years after the first description of E. coli ST131, this review outlines the principal traits of ST131 clonal group isolates, based on the growing body of published data, and highlights what is currently known and what we need to find out to provide public health authorities with better information to help combat ST131.

Evaluation of high-resolution melting curve analysis of ligation-mediated real-time PCR, a rapid method for epidemiological typing of ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter Species) pathogens

A single-tube method, ligation-mediated real-time PCR high-resolution melt analysis (LMqPCR HRMA), was modified for the rapid typing of Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. (ESKAPE) pathogens. A 97% agreement (60/62 isolates) was achieved in comparison to pulsed-field gel electrophoresis (PFGE) results, which indicates that LMqPCR HRMA is a rapid and accurate screening tool for monitoring nosocomial outbreaks.

[Impact of enterobacteriaceae-producing extended-spectrum beta-lactamases (ESBLE) incidence increasing on barrier precautions implementation in a university hospital]

AIM OF THE STUDY

The French national surveillance program of multidrug-resistant bacteria (MDR) shows an increase of enterobacteriaceae-producing extended-spectrum beta-lactamases (ESBLE) incidence. The objectives of this study were to assess: the incidence of EBLSE in a large French university hospital between 2005 and 2010, and the difference of barrier precautions implementation between ESBL and other MDR.

METHODS

The ESBLE incidence measure used data from the laboratory of bacteriology. The application of isolation and barrier precautions was analyzed from the MRB national surveillance data over a 3-year period from 2006 to 2008. Data were entered and analyzed using Epi Info software. The Chi(2) test was used for the comparison of proportions.

RESULTS

The overall incidence of ESBLE was significantly higher in 2010 than in 2005 (0.20/1000 patients-days vs 0.03/1000 patients-days, respectively) (P<0.001). The same was observed for Escherichia coli incidence with rates ranging from 0.02/1000 patients-days in 2005 to 0.15/1000 patients-days in 2010. Isolation precautions for patients with EBLSE were applied in relation for most patients with MRB (ESBLE vs others), without significant difference.

CONCLUSION

The surveillance programme of MRB showed a significant increase of ESBLE, especially for E. coli. Isolation and barrier precautions were used for most patients with MRB, including ESBLE.