Evaluation of the EasyScreen™ ESBL/CPO Detection Kit for the Detection of ß-Lactam Resistance Genes

Early detection of multidrug resistant bacteria is of paramount importance for implementing appropriate infection control strategies and proper antibacterial therapies. We have evaluated a novel real-time PCR assay using fluorescent probes and 3base^® technology, the EasyScreen^TM ESBL/CPO Detection Kit (Genetic Signatures, Newtown, Australia), for the detection of 15 β-lactamase genes (bla_VIM, bla_NDM, bla_IMP, bla_OXA-48, bla_KPC, bla_OXA-23, bla_OXA-51, bla_SME,bla_IMI, bla_GES,bla_TEM,bla_SHV, bla_CTX-M,bla_CMY, bla) and colistin resistance mcr-1 gene from 341 bacterial isolates (219 Enterobacterales, 66 P. aeruginosa and 56 A. baumannii) that were grown on Mueller-Hinton (MH) agar plates. One colony was suspended in provided extraction buffer, which lyses and converts the nucleic acids into a 3base^®-DNA form (cytosines are converted into uracil, and subsequently thymine during PCR). The converted bacterial DNA is then added to the 6 PCR mixes, with primers for three targets plus one internal control. The EasyScreen^TM ESBL/CPO Detection Kit was able to detect the 5-major (NDM, VIM, IMP, KPC, OXA-48) and 2-minor (IMI, Sme) carbapenemases and their variants irrespective of the species expressing them with nearly 100% sensitivity and specificity. With cephalosporinases CMY (82% of sensitivity) and DHA (87% of sensitivity) detection of chromosomally encoded variants was less efficient. Similarly, the chromosomally encoded OXA-51 variants were not consistently detected in A. baumannii. Despite being capable of efficiently detecting bla_CTX-M-, bla_TEM-, bla_SHV- and bla_GES-like genes, the EasyScreen™ ESBL/CPO Detection Kit was not able to distinguish between penicillinases and ESBL-variants of TEM and SHV and between GES-ESBLs and GES-carbapenemases. As GES enzymes are still rare, their detection as an ESBL or a carbapenemase remains important. Detection of mcr-1 was efficient, but none of the other mcr-alleles were detected in the 341 bacterial isolates tested. The EasyScreen^TM ESBL/CPO Detection Kit is adapted for the detection of the most prevalent carbapenemases encountered in Gram-negatives isolated worldwide.