General Medicine

New LAMP Assay a Suitable Alternative Molecular Test for Characterizing E coli Culture Isolates

Sweta Gupta
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Although sensitivity is an important consideration when deciding among HIV tests, there are other factors to consider, such as test invasiveness, available resources, need for additional studies, and patient adherence.6 Serum- and plasma-based HIV testing is the most invasive and requires the most resources, such as access to a skilled clinician or phlebotomist and access to special equipment (eg, needles, biohazard containers, laboratory). Whole blood testing can be performed by venipuncture or finger-stick. When blood-based tests yield a sufficient specimen sample using venipuncture, additional studies can be undertaken, such as HIV subtyping and assessment for coinfections, including hepatitis or syphilis. In contrast, oral fluid tests do not require special equipment and can be performed in any setting, including at home, providing results in minutes. These tests also eliminate safety and biohazard concerns, such as needlestick injuries and sharps disposal.

Although sensitivity is an important consideration when deciding among HIV tests, there are other factors to consider, such as test invasiveness, available resources, need for additional studies, and patient adherence.6


Serum- and plasma-based HIV testing is the most invasive and requires the most resources, such as access to a skilled clinician or phlebotomist and access to special equipment (eg, needles, biohazard containers, laboratory).


Whole blood testing can be performed by venipuncture or finger-stick. When blood-based tests yield a sufficient specimen sample using venipuncture, additional studies can be undertaken, such as HIV subtyping and assessment for coinfections, including hepatitis or syphilis. In contrast, oral fluid tests do not require special equipment and can be performed in any setting, including at home, providing results in minutes. These tests also eliminate safety and biohazard concerns, such as needlestick injuries and sharps disposal.

Eazyplex EHEC assay, a molecular assay based on loop-mediated isothermal amplification (LAMP), is fast, easy to perform, and provides reliable results.

Eazyplex® EHEC assay (Amplex Diagnostics, Gars-Bahnhof, Germany), a molecular assay based on loop-mediated isothermal amplification (LAMP), is fast, easy to perform, and provides reliable results as a culture confirmation assay for the diagnosis of infection with Shiga toxin-producing Escherichia coli (STEC), Shigella spp, or enteroinvasive E coli, according to study results published in the European Journal of Clinical Microbiology & Infectious Diseases.

To evaluate the performance of the newly introduced eazyplex enterohemorrhagic E coli (EHEC) completeLAMP assay, researchers used 18 retrospective samples (12 strains of Shiga toxin-producing E coli possessing different Shiga toxin (stx) subtypes and 6 strains of Shigella spp) and 31 prospective samples (16 isolates and 15 enrichment broths cultured from diarrheal stool specimens). Results were compared with real-time polymerase chain reaction (PCR) as a reference standard. Microarray analysis was performed to identify the serovar (O:H), the stx subtype, and additional virulence factors.

In the retrospective evaluation, all strains were correctly identified regarding stx types 1 and 2, adhesion intimin (eae), and enterohemolysin A (ehlyA), which is a characteristic virulence factor especially for classical EHEC strains. The gene was correctly identified in all cases.

In the prospective evaluation, LAMP eazyplex EHEC assay identified and characterized culture isolates in accordance with the PCR and microarray with only 1 exception of a false-positive eazyplex result for eae [isolate O91:H14 (2)]. All 16 isolates harbored additional virulence factors such as adhesins and toxins. From 15 specimens, Shiga toxin-producing E coli infection was confirmed by positive results from a Gram negative enrichment broth, but no isolate could be recovered from single colonies.

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Combining data from the retrospective analysis and prospective testing, the sensitivities and specificities of the eazyplex EHEC assay were as follows: 94.7% and 100% for stx1, 100% and 100% for stx2, 93.3% and 97.1% for eae, 100% and 100% for ehlyA, and 100% and 100% for invasion-associated plasmid antigen H as Shigella spp/enteroinvasive E coli target, respectively. The time to result of the assay ranged from 8.5 to 13 minutes.

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Because the cost for a complete test strip covering 7 specific targets are relatively high, researchers “suggested to implement the eazyplex® EHEC assay as a culture confirmation test and to use a sensitive stx PCR as an initial screening test.”

Reference

Penzel A, Schützler K, Dröge J, et al. Rapid culture-based identification of Shiga toxin-producing Escherichia coli and Shigella spp./Enteroinvasive E. coli using the eazyplex® EHEC complete assay [published online September 16, 2019]. Eur J Clin Microbiol Infect Dis. doi:10.1007/s10096-019-03704-x

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