Investigating the presence of hypervirulent carbapenemase-producing Klebsiella pneumoniae, through three phenotypic tests, in the Maltese islands

Hypervirulence and multi-drug resistance are two separate qualities of Klebsiella pneumoniae that have posed a public health threat in separate strains for decades now. The convergence of these two phenotypes into singular strains of Klebsiella pneumoniae have created a super bug, causing both severe infections in the young and healthy and having limited antibiotic treatment available against them. These strains were first discovered in Asia in 2013 but are now emerging all around the globe. In this study, hypervirulence was assessed in 493 known carabapenemase-producing Klebsiella pneumoniae strains isolated and cryopreserved between 2019 and 2021 from various specimen types from health institutions around the Maltese islands. Three phenotypic tests were used, namely, the string test for hypermucoviscosity, lateral flow assays for the identification of K1 and K2 capsular serotypes, and quantification of siderophore production. Since the latter test was the one that was known to be the most significant for the detection of hypervirulence, and none of the strains surpassed the set limit of a concentration of 30µg/ml, none of the 493 assayed strains were deemed hypervirulent. Hypermucoviscous, K1 and K2 capsular serotype belonging strains were found, though, so much so that a statistically significant relationship was found between hypermucoviscosity and capsular serotype. Other statistical tests carried out exploring the relationship between hypermucoviscosity and siderophore concentration and hypermucoviscosity and type of carabapenemase gene were not found to be statistically significant. According to this research, hypervirulent carabapenemase-producing Klebsiella pneumoniae strains have not yet arrived in the Maltese archipelago.