Klebsiella pneumoniae is a multidrug-resistant opportunistic human pathogen related to various infections. As such, synthetic peptides have emerged as potential alternative molecules. Mo-CBP3-PepI has presented great activity against K. pneumoniae by presenting an MIC50 at a very low concentration (31.25 µg mL-1). Here, fluorescence microscopy and proteomic analysis revealed the alteration in cell membrane permeability, ROS overproduction, and protein profile of K. pneumoniae cells treated with Mo-CBP3-PepI. Mo-CBP3-PepI led to ROS overaccumulation and membrane pore formation in K. pneumoniae cells. Furthermore, the proteomic analysis highlighted changes in essential metabolic pathways. For example, after treatment of K. pneumoniae cells with Mo-CBP3-PepI, it was seen a reduction in the abundance of protein related to DNA and protein metabolism, cytoskeleton and cell wall organization, redox metabolism, regulation factors, ribosomal proteins, and resistance to antibiotics. These reductions lead to the inhibition of DNA repair, inhibition of cell wall turnover, protein turnover, and ROS accumulation leading to cell death. Our findings indicated that Mo-CBP3-PepI might have mechanisms of action against K. pneumoniae cells, mitigating the development of resistance and thus being a potent molecule to be employed in producing new drugs against K. pneumoniae infections.

Angiotensin-converting enzyme 2 (ACE2) and the transmembrane serine protease 2 (TMPRSS2) are recognized as entry proteins of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and recently their Single Nucleotide Polymorphisms (SNP) have been studied in different populations to elucidate the impact on disease. The aim of this study was to evaluate the genetic SNP of ACE2 (rs35803318) and TMPRSS2 (rs2070788) genes in COVID-19 patients from Northeast Brazil compared with global populations, as well as the expression quantitative trait locus (eQTL). For ACE2 (rs35803318), we found 92.6% CC, 3.4% CT, and 4.0% TT genotype carriers in SARS-CoV-2-positive patients. Surprisingly, only the genotype frequencies of ACE2 SNP were not in Hardy-Weinberg equilibrium. For TMPRSS2 rs2070788, we found 22.3% GG, 50.7% AG, and 27% AA genotype carriers in SARS-CoV-2-positive patients. The expression quantitative trait loci (eQTLs) revealed that rs35803318 was associated with an altered PIR gene expression, and rs2070788 was found eQTLs association only with lung tissue. No significant association was identified between the genotype distribution of SNPs and the 'patient's outcome. In conclusion, our results suggest that ACE2 and TMPRSS2 may not be protective factors for global populations, including the Brazilian population, since the presence of SNPs does not affect the 'patient's outcome as described by other studies.