Loop-mediated isothermal amplification of vanA gene enables a rapid and naked-eye detection of vancomycin-resistant enterococci infection

Nucleic acid amplification-based microfluidic approaches for antimicrobial susceptibility testing

Because of the global spread of antimicrobials, there is an urgent need to develop rapid and effective tools for antimicrobial susceptibility testing to help clinicians prescribe accurate and appropriate antibiotic doses sooner. The conventional methods for antimicrobial susceptibility testing are usually based on bacterial culture methods, which are time-consuming, complicated, and labor-intensive. Therefore, other approaches are needed to address these issues. Recently, microfluidic technology has gained significant attention in infection management due to its advantages including rapid detection, high sensitivity and specificity, highly automated assay, simplicity, low cost, and potential for point-of-care testing in low-resource areas. Microfluidic advances for antimicrobial susceptibility testing can be classified into phenotypic (usually culture-based) and genotypic tests. Genotypic antimicrobial susceptibility testing is the detection of resistant genes in a microorganism using methods such as nucleic acid amplification. This review (with 107 references) surveys the different forms of nucleic acid amplification-based microdevices used for genotypic antimicrobial susceptibility testing. The first section reviews the serious threat of antimicrobial-resistant microorganisms and the urgent need for fast check-ups. Next, several conventional antimicrobial susceptibility testing methods are discussed, and microfluidic technology as a promising candidate for rapid detection of antimicrobial-resistant microorganisms is briefly introduced. The next section highlights several advancements of microdevices, with an emphasis on their working principles and performance. The review concludes with the importance of fully integrated microdevices and a discussion on future perspectives.

Rapid and sensitive detection of the vanA resistance gene from clinical Enterococcus faecium and Enterococcus faecalis isolates by loop-mediated isothermal amplification

OBJECTIVES

Vancomycin resistance in Enterococcus spp., mediated mainly by the vanA resistance gene, has become a major health concern as it has spread worldwide. Therefore, a rapid method is urgently required to detect the vanA gene for timely and appropriate antimicrobial control of resistant Enterococcus infections.

METHODS

The loop-mediated isothermal amplification (LAMP) assay was optimised for vanA detection in Enterococcus spp. isolates.

RESULTS

The LAMP primer set designed in this study could reliably recognise seven distinct regions of the vanA gene and amplify the gene within 25min at an isothermal temperature of 65°C with high specificity. The sensitivity of the optimised assay was high, with a detection limit for vanA as low as 100pg/μL, which is 100-fold more sensitive than the PCR assay. A special advantage of this optimised LAMP method is that the vanA gene could be detected directly from clinical specimens.

CONCLUSION

This optimised LAMP assay has great application potential for efficient detection of vanA in clinical diagnosis and epidemiological studies.

Development of Visual Detection of α-Thalassemia-1 (the - -SEA Deletion) Using pH-Sensitive Loop-Mediated Isothermal Amplification

Detection of α-thalassemia-1 (α-thal-1) carriers provides valuable insight for genetic consulting in prevention and control programs for couples who are at risk of conceiving a fetus with severe thalassemia, both Hb Bart's hydrops fetalis and hemolytic Hb H disease. The traditional method is complicated, time-consuming and requires high instrument cost and expertise. Loop-mediated isothermal amplification (LAMP) based on pH-sensitive dye technology, shows all the characteristics required of a real-time analysis with simple operation for potential use in the clinical diagnosis of high incidence α-thal-1 [Southeast Asian (SEA) or - -^SEA deletion]. Four primers specific for six distinct regions of the α-globin gene deletion were designed and analyzed by LAMP using the pH-indicator dye, phenol red. The amplification of the - -^SEA deletion changed the color of phenol red from pink to orange. The diagnostic ability of detection of the - -^SEA deletion by pH-sensitive LAMP was validated using both known and unknown blood samples and compared to the conventional polymerase chain reaction (PCR) method. Color inspection of pH-sensitive LAMP products could clearly identify the - -^SEA deletion. There was no cross reaction with a normal α-globin gene, α-thal-1 Thai (- -^THAI deletion), α-thal-2 [-α^3.7 (rightward) and -α^4.2 (leftward) deletion] and β-thalassemia (β-thal). Detection of the SEA deletion by pH-sensitive LAMP was consistent as compared to conventional PCR. The pH-sensitive LAMP method developed for this deletion carrier diagnosis has high sensitivity, specificity, simplicity, and requires simple instrumentation that makes it applicable for resource-limited laboratories in rural areas of developing countries.

Vancomycin-resistant gene identification from live bacteria on an integrated microfluidic system by using low temperature lysis and loop-mediated isothermal amplification

Vancomycin-resistant Enterococcus (VRE) is a kind of enterococci, which shows resistance toward antibiotics. It may last for a long period of time and meanwhile transmit the vancomycin-resistant gene (vanA) to other bacteria. In the United States alone, the resistant rate of Enterococcus to vancomycin increased from a mere 0.3% to a whopping 40% in the past two decades. Therefore, timely diagnosis and control of VRE is of great need so that clinicians can prevent patients from becoming infected. Nowadays, VRE is diagnosed by antibiotic susceptibility test or molecular diagnosis assays such as matrix-assisted laser desorption ionization/time-of-flight mass spectrometry and polymerase chain reaction. However, the existing diagnostic methods have some drawbacks, for example, time-consumption, no genetic information, or high false-positive rate. This study reports an integrated microfluidic system, which can automatically identify the vancomycin resistant gene (vanA) from live bacteria in clinical samples. A new approach using ethidium monoazide, nucleic acid specific probes, low temperature chemical lysis, and loop-mediated isothermal amplification (LAMP) has been presented. The experimental results showed that the developed system can detect the vanA gene from live Enterococcus in joint fluid samples with detection limit as low as 10 colony formation units/reaction within 1 h. This is the first time that an integrated microfluidic system has been demonstrated to detect vanA gene from live bacteria by using the LAMP approach. With its high sensitivity and accuracy, the proposed system may be useful to monitor antibiotic resistance genes from live bacteria in clinical samples in the near future.

Rapid detection of Pseudomonas aeruginosa and Acinetobacter baumannii Harboring bla(VIM-2), bla(IMP-1) and bla(OXA-23) genes by using loop-mediated isothermal amplification methods

Background

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) and Acinetobacter baumannii (CRAB) are the leading causes of nosocomial infections. A rapid and sensitive test to detect CRPA and CRAB is required for appropriate antibiotic treatment. We optimized a loop-mediated isothermal amplification (LAMP) assay to detect the presence of bla_VIM-2, bla_IMP-1, and bla_OXA-23, which are critical components for carbapenem resistance.

Methods

Two sets of primers, inner and outer primers, were manually designed as previously described. The LAMP buffer was optimized (at 2mM MgSO₄) by testing different concentrations of MgSO₄. The optimal reaction temperature and incubation time were determined by using a gradient thermocycler. Then, the optimized bla_VIM-2, bla_IMP-1, and bla_OXA-23 LAMP reactions were evaluated by using 120 P. aeruginosa and 99 A. baumannii clinical isolates.

Results

Only one strain of the 100 CRPA isolates harbored bla_IMP-1, whereas none of them harbored bla_VIM-2. These results indicate that the acquisition of bla_VIM-2 or bla_IMP-1 may not play a major role in carbapenem resistance in Korea. Fifty two strains of the 75 CRAB isolates contained bla_OXA-23, but none contained bla_VIM-2 and bla_IMP-1 alleles.

Conclusions

Our results demonstrate the usefulness of LAMP for the diagnosis of CRPA and CRAB.