Klebsiella pneumoniae is an opportunistic pathogen that frequently causes nosocomial and community-acquired (CA) infections. Until now, a limited number of studies has been focused on the analyses of changes affecting the virulence attributes. Genotypic and phenotypic methods were used to characterise the 39 clinical K. pneumoniae isolates; all belonged to the pan-drug resistant, widespread clone ST 15 and expressed the K24 capsule. PFGE has revealed that the isolates could be divided into three distinct genomic clusters. All isolates possessed allS and uge genes, known to contribute to the virulence of K. pneumoniae and 10.25% of the isolates showed hypermucoviscosity, 94.87% produced type 1 fimbriae, 92.3% produced type 3 fimbriae, and 92.3% were able to produce biofilm. In vivo persistence could be supported by serum resistance 46.15%, enterobactin (94.87%) and aerobactin (5.12%) production and invasion of the INT407 and T24 cell lines. Sequence analysis of the whole genomes of the four representative strains 11/3, 50/1, 53/2 and 53/3 has revealed high sequence homology to the reference K. pneumoniae strain HS11286. Our results represent the divergence of virulence attributes among the isolates derived from a common ancestor clone ST 15, in an evolutionary process that occurred both in the hospital and in the community.

Background: Due to their antibacterial activities, essential oils can be potential alternatives to antibiotics in certain cases. West Indian lemongrass (Cymbopogon citratus) essential oil (LEO) is effective against a broad range of bacteria by inhibiting spore formation, and is considered safe. In this study, we demonstrated its therapeutical potential in the treatment of pitted keratolysis (PK), a superficial skin infection affecting the pressure-bearing areas of plantar surfaces. Methods: For in vitro antibacterial efficacy testing, LEO was mixed into different ointment bases, including Hydrogelum methylcellulose FoNo VIII., Ungentum oleosum FoNo VIII. (Ung. oleoso), Unguentum stearini FoNo VIII. (Ung. stearin), and Vaselinum cholesterinatum FoNo VIII. (Vasel. cholest.), at different concentrations of 1, 3, and 5%. These formulations were tested on representatives of three bacterial species associated with PK: Kytococcus sedentarius, Dermatophilus congolensis, and Bacillus thuringiensis. Results: In the in vitro tests, Hydrogelum methylcellulose (HM) gel best supported the antibacterial effects of LEO, reducing the number of living bacteria on agar plates by 4–5 orders of magnitude in a concentration-dependent manner during the 30 min exposure times. This was also confirmed by the Franz diffusion cell drug release test; after 30 min, several active compounds could be detected in the HM samples, in contrast to the other bases. Shelf-life experiments showed that the HM base supported the antibacterial features of 3% LEO for at least 2 years without significant loss of efficacy. Conclusions: Our study highlights that ointments containing essential oils potentially have a place in the treatment of PK. Therefore, antibiotics may potentially be replaced for the treatment of PK, thereby reducing environmental antibiotic pressure, which is one of the driving forces behind the spread of antibiotic resistance.

Background/Objectives: The treatment of multidrug-resistant and hypervirulent Klebsiella pneumoniae is one of today’s biggest healthcare challenges. The depletion of therapeutic options necessities the application of new methods. One promising approach is to use phage-derived enzymes that target the capsule and make the causative more visible to the immune system. As proteins, these enzymes must be optimised by reducing their size and antigenicity to make them suitable for repeated use. Methods: In this study, the recently isolated and cloned K2B1orf61 K2 capsule-specific depolymerase was analysed structurally, and certain amino acid residues were deleted by cloning. The following amino acid residues were removed from the 80th (D2_N80), 115th (D3_N115), and 200th (D4_N200) N-terminal, and 250 (D5_C250) and 20 (D6_C20) from the C-terminal positions of the wild-type molecule (D1_wt). The resulting derivative molecules were compared with in vitro and in vivo tests. Results: In the presence of wild-type depolymerase, human serum was able to eliminate the target bacterium and save the lives of mice challenged with the bacterium in an originally lethal intraperitoneal model. However, the D5_C250 derivative lost all activity, meaning that the bacteria with the K2 capsule in the serum survived and all the mice died. Derivatives D2_N80, D3_N115, and D6_C20 exhibited prolonged activity in the serum killing assay, effectively eliminating bacteria within 5 h. Similar activity differences were revealed in the intraperitoneal experiment: D5_C250 had no rescue effect; however, D1_wt, D2_N80, D3_N115, D4_200, and D6_20 resulted in survival rates of 100%, 60%, 80%, 100%, and 20%, respectively. Conclusions: Our results demonstrate that molecular trimming is a promising procedure for developing ideal therapeutic depolymerases.