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Nosocomial infections caused by antibiotic-resistant Gram-negative pathogens are of grave concern today. Polymyxins are considered as the last resorts of therapy to treat these multi-drug resistant (MDR) bacteria. But their associated nephrotoxicity and neurotoxicity calls for the development of safer polymyxin therapy until novel and less toxic antibiotics are discovered. No other polymyxin molecule except polymyxin B and E (colistin) is explored thoroughly in literature to demonstrate its clinical relevance. In the present study, we have isolated two antimicrobial compounds named P1 and P2 from the soil isolate Paenibacillus dendritiformis strain PV3-16, which we later identified as polymyxin A 2 and A 1 respectively. We tested their minimum inhibitory concentrations (MICs) against MDR clinical isolates, performed membrane permeabilization assays and determined their interaction with lipopolysaccharide (LPS). Finally, we studied their toxicity against human Leukemic monocyte cell line (THP-1) and embryonic kidney cell line (HEK 293). Both compounds displayed equal efficacy when compared with standard polymyxins. P1 was 2-4 fold more active in most of the clinical strains tested. Moreover, P1 showed higher affinity toward LPS. In cytotoxicity studies, P1 had IC 50 value (>1000 μg/ml) similar to colistin against HEK cells but immune cells, i.e., THP-1 cell lines were more sensitive to polymyxins. P1 showed less toxicity in THP-1 cell line than all other polymyxins checked. To sum up, P1 (polymyxin A 2 ) possessed better efficacy than polymyxin B and E and had least toxicity to immune cells. Since polymyxin A was not investigated thoroughly, we performed the comprehensive in vitro assessment of this molecule. Moreover, this is the first report of isolation and characterization of polymyxin A from P. dendritiformis . This compound should be further investigated for its in vivo efficacy and toxicity to develop it as a drug candidate.

Burkholderia cenocepacia is a clinically dominant form among the other virulent species of Burkholderia cepacia complex (Bcc). In the present study, we sequenced and analyzed the genomes of seven nosocomial Bcc isolates, five of which were isolated from the bloodstream infections and two isolates were recovered from the hospital setting during the surveillance. Genome-based species identification of the Bcc isolates using a type strain explicitly identified the species as B. cenocepacia. Moreover, single nucleotide polymorphism analysis revealed that the six isolates were clonal and phylogenetically distinct from the other B. cenocepacia . Comparative genomics distinctly revealed the larger genome size of six clonal isolates as well as the presence of a novel 107 kb genomic island named as BcenGI15, which encodes putative pathogenicity-associated genes. We have shown that the BcenGI15 has an ability to actively excise from the genome and forming an extrachromosomal circular form suggesting its mobile nature. Surprisingly, a homolog of BcenGI15 was also present in the genome of a clinical isolate named Burkholderia pseudomallei strain EY1. This novel genetic element is present only in the variants of B. cenocepacia and B. pseudomallei isolates suggesting its interspecies existence in the main pathogenic species of the genus Burkholderia . In conclusion, the whole genome analysis of the genomically distinct B. cenocepacia clinical isolates has advanced our understanding of the epidemiology and evolution of this important nosocomial pathogen as well as its relatives.

Genomic resource of type strains and historically important strains of genus Stenotrophomonas allowed us to reveal the existence of 18 distinct species by applying modern phylogenomic criterions. Apart from Stenotrophomonas maltophilia, S. africana represents another species of clinical importance. Interestingly, Pseudomonas hibsicola, P. beteli, and S. pavani that are of plant origin are closer to S. maltophilia than the majority of the environmental isolates. The genus has an open pan-genome. By providing the case study on genes encoding metallo-β-lactamase and Clustered Regularly Interspaced Short Palindrome Repeats (CRISPR) regions, we have tried to show the importance of this genomic dataset in understanding its ecology.