Mobile colistin resistance (mcr) genes and recent developments in colistin resistance detection.

The peptide antibiotic colistin has been reserved as a last resort antibiotic treatment option for cases where other antibiotics including carbapenems have failed. Recent emergence of colistin resistance and discovery of mobile colistin resistance (mcr) genes, which encode the cell wall modifying phosphoethanolamine transferase enzyme, complicates the issue. The mcr genes have been associated with conjugative plasmids and can be horizontally transferred between different bacterial species. The global spread of mcr genes has been extensively documented and this warrants surveillance of the resistance genes in the community. However, susceptibility testing of colistin is fraught with practical challenges owing to the chemical nature of the drug and multiple mechanisms of resistance. Although broth microdilution is the current gold standard for colistin susceptibility testing, the method poses technical challenges. Hence, alternative detection methods for screening colistin resistance are the need of the hour. Several methods have been studied in the recent times to address this issue. In this review, we discuss some of the recent developments in the detection of colistin resistance.

Targeting Staphylococcus aureus and its biofilms with novel antibacterial compounds produced by Lactiplantibacillus plantarum SJ33.

The emergence of microbial resistance to conventional antibiotics, partially attributed to biofilm formation, has urged for new antimicrobial compounds. Here, we reported two novel low molecular weight (LMW) compounds from Lactiplantibacillus plantarum SJ33 and evaluated their biofilm inhibitory effects on Staphylococcus aureus. The compounds C1 and C2 were purified by RP-HPLC and structurally identified as 3-amino-5-hydroxy-6-(hydroxymethyl)-4-(1-hydroxyprop-2-yn-1-yl)-3,3a,4,5,6,7a-hexahydro-7H-indazol-7-one and 1-(dimethylamino)-3-hydroxy-3-((2-hydroxypropan-2-yl)oxy)-1-(methylamino)-butan-2-one by spectroscopic techniques. High ESI-MS data confirmed the molecular weight of C1 and C2 as 254.1141 and 234.1658 Da, respectively. Time-kill assay demonstrated bactericidal action of compounds, whereas scanning electron microscopy revealed morphological changes in treated S. aureus MTCC96 and methicillin-resistant S. aureus (MRSA) cells. The antibacterial compounds reduced biofilm formation in S. aureus MTCC96 and MRSA by crystal violet assay. Further, fluorescence and scanning electron microscopic images exhibited biofilm formation by pathogens and biofilm inhibition by compounds treatment. The Quantitative RT PCR revealed the down-regulation of icaC and icaD genes involved in intercellular adhesion of biofilms. The results confirmed the anti-biofilm activity of novel LMW compounds by eliminating preformed biofilms formed by S. aureus MTCC96 and MRSA.

SCR7, an inhibitor of NHEJ can sensitize tumor cells to ionization radiation.

Nonhomologous end joining (NHEJ), one of the major DNA double-strand break repair pathways, plays a significant role in cancer cell proliferation and resistance to radio and chemotherapeutic agents. Previously, we had described a small molecule inhibitor, SCR7, which inhibited NHEJ in a DNA Ligase IV dependent manner. Here, we report that SCR7 potentiates the effect of γ-radiation (IR) that induces DNA breaks as intermediates to eradicate cancer cells. Dose fractionation studies revealed that coadministration of SCR7 and IR (0.5 Gy) in mice Dalton's lymphoma (DLA) model led to a significant reduction in mice tumor cell proliferation, which was equivalent to that observed for 2 Gy dose when both solid and liquid tumor models were used. Besides, co-treatment with SCR7 and 1 Gy of IR further improved the efficacy. Notably, there was no significant change in blood parameters, kidney and liver functions upon combinatorial treatment of SCR7 and IR. Further, the co-treatment of SCR7 and IR resulted in a significant increase in unrepaired DSBs within cancer cells compared to either of the agent alone. Anatomy, histology, and other studies in tumor models confirmed the cumulative effects of both agents in activating apoptotic pathways to induce cytotoxicity by modulating DNA damage response and repair pathways. Thus, we report that SCR7 has the potential to reduce the side effects of radiotherapy by lowering its effective dose ex vivo and in mice tumor models, with implications in cancer therapy.

Swarming Inhibitory Potential of Cinnamtannin B1 from Cinnamomum tamala T. Nees and Eberm on Pseudomonas aeruginosa.

In a preliminary screening, the methanol extract of Cinnamomum tamala leaves was found to inhibit the swarming motility of Pseudomonas aeruginosa. Bioassay-guided fractionation by silica gel column chromatography led to the identification of cinnamtannin B1 (1) as one of the active components of the extract. It inhibited the swarming motility (at 12.5 µg/mL) and biofilm formation (at 25 µg/mL) ofP. aeruginosa. Comparative gene expression analysis revealed downregulation of rhlA and fliC genes upon treatment with the tannin. The tannin may be affecting rhamnolipid and flagellin production. Thus, cinnamtannin B1 is an active component of C. tamala responsible for inhibiting the swarming motility of P. aeruginosa.

Inhibition of Swarming motility of Pseudomonas aeruginosa by Methanol extracts of Alpinia officinarum Hance. and Cinnamomum tamala T. Nees and Eberm.

Bacterial drug resistance is a challenge in clinical settings, especially in countries like India. Hence, discovery of novel alternative therapeutics has become a necessity in the fight against drug resistance. Compounds that inhibit bacterial virulence properties form new therapeutic alternatives. Pseudomonas aeruginosa is an opportunistic, nosocomial pathogen that infects immune-compromised patients. Swarming motility is an important virulence property of Pseudomonas which aids it in reaching host cells under nutrient limiting conditions. Here, we report the screening of five plant extracts against swarming motility of P. aeruginosa and show that methanol extracts of Alpinia officinarum and Cinnamomum tamala inhibit swarming motility at 5 µg mL-1 without inhibiting its growth. These extracts did not inhibit swimming and twitching motilities indicating a mode of action specific to swarming pathway. Preliminary experiments indicated that rhamnolipid production was not affected. This study reveals the potential of the two plants in anti-virulence drug discovery.

Ethyl p-methoxycinnamate isolated from a traditional anti-tuberculosis medicinal herb inhibits drug resistant strains of Mycobacterium tuberculosis in vitro.

Many plants are used in Ayurveda for the treatment of tuberculosis. Our aim was to examine if these plants possess any specific molecule that inhibits Mycobacterium tuberculosis. One of them, Kaempferia galanga, yielded an anti-TB molecule, ethyl p-methoxycinnamate (EPMC). By resazurin microtitre assay (REMA), EPMC was shown to inhibit M. tuberculosis H37Ra, H37Rv, drug susceptible and multidrug resistant (MDR) clinical isolates (MIC 0.242-0.485mM). No cross resistance was observed to any standard anti-TB drugs in the MDR strains. The compound did not inhibit any prototype bacteria tested. EPMC seems to be a potential anti-TB lead molecule.