Biology subjects

Srikumar, S.

Publications and source records attributed to Srikumar, S..

3 recordsLinked to original sources

bioRxiv2020

Silver nanoparticles induce a triclosan like antibacterial action mechanism in multi-drug resistant Klebsiella pneumoniae

Infections associated with antimicrobial-resistant bacteria now represent a significant threat to human health using conventional therapy, necessitating the development of alternate and more effective antibacterial compounds. Silver nanoparticles (Ag NPs) have been proposed as potential antimicrobial agents to combat infections. A complete understanding of their antimicrobial activity is required before these molecules can be used in therapy. Lysozyme coated Ag NPs were synthesized and characterized by TEM-EDS, XRD, UV-vis, FTIR spectroscopy, zeta potential and oxidative potential assay. Biochemical assays and deep level transcriptional analysis using RNA sequencing were used to decipher how Ag NPs exert their antibacterial action against multi-drug resistant Klebsiella pneumoniae MGH78578. RNAseq data revealed that Ag NPs induced a triclosan-like bactericidal mechanism responsible for the inhibition of the type II fatty acid biosynthesis. Additionally, released Ag+ generated oxidative stress both extra- and intracellularly in K. pneumoniae. The data showed that triclosan-like activity and oxidative stress cumulatively underpinned the antibacterial activity of Ag NPs. This result was confirmed by the analysis of the bactericidal effect of Ag NPs against the isogenic K. pneumoniae MGH78578{Delta} soxS mutant, which exhibits a compromised oxidative stress response compared to the wild type. Silver nanoparticles induce a triclosan-like antibacterial action mechanism in multi-drug resistant K. pneumoniae. This study extends our understanding of anti-Klebsiella mechanisms associated with exposure to Ag NPs. This allowed us to model how bacteria might develop resistance against silver nanoparticles, should the latter be used in therapy.

microbiology↗

bioRxiv2020

Analysis of the oxidative stress regulon identifies soxS as a genetic target for resistance reversal in multi-drug resistant Klebsiella pneumoniae

In bacteria, the defense system deployd to counter oxidative stress is orchestrated by three transcriptional factors - SoxS, SoxR, and OxyR. Although the regulon that these factors control is known in many bacteria, similar data is not available for Klebsiella pneumoniae. To address this data gap, oxidative stress was artificially induced in K. pneumoniae MGH 78578 using paraquat and the corresponding oxidative stress regulon recorded using RNA-seq. The soxS gene was significantly induced during oxidative stress and a knock-out mutant was constructed, to explore its functionality. The wild-type and mutant were grown in the presence of paraquat and subjected to RNA-seq to elucidate the soxS regulon in K. pneumoniae MGH78578. Genes that are commonly regulated both in the oxidative stress regulon and soxS regulon were identified and denoted as the oxidative SoxS regulon - these included a stringent group of genes specifically regulated by SoxS. Efflux pump encoding genes such as acrAB-tolC, acrE, and global regulators such as marRAB were identified as part of this regulon. Consequently, the isogenic soxS mutant was found to exhibit a reduction in the minimum bactericidal concentration against tetracycline compared to that of the wild type. Impaired efflux activity, allowing tetracycline to be accumulated in the cytoplasm to bactericidal levels, was further evaluated using a tetraphenylphosphonium (TPP+) accumulation assay. The soxS mutant was also susceptible to tetracycline in vivo, in a zebrafish embryo model. We conclude that the soxS gene could be considered as a genetic target against which an inhibitor could be developed in the future and used in combinatorial therapy with tetracycline to combat infections associated with multi-drug resistant K. pneumoniae.

microbiology↗

bioRxiv2020

Chemical composition and larvicidal activity against Aedes mosquitoes of flower extracts from Clitoria Ternatea

BackgroundMosquito is a human health tread nowadays, the major health problems caused by them are malaria, dengue fever, yellow fever, zika as well as several other outbreaks. The major problem in controlling dengue vectors are the resistant problems. Different classes of insecticides used for public have raised the concern of resistant problem with mosquitoes and environmental pollution. Thus, alternative chemical compounds search is necessary to be searched for overcoming the resistance problem of using pesticides in vectors and the chemical free environment respectively. Thus, to solve these problems, purpose of this study is to identify the larvicidal mechanism, metabolite, antioxidant, chemical compounds and its structure from C. ternatea flower and to test its efficacies against early 4th instar larvae of Ae. aegypti and Ae albopictus. MethodsClitoria ternatea flowers were collected from the Garden of the Faculty of Medicine in International Quest University, Ipoh, Perak and used for crude extraction. Then, the metabolite test, antioxidant test, chromatography techniques were conducted to identify chemical composition of extracts and their chemical structures were identified using GCMS-QP2010 Ultra (Shimadzu). Next, following WHO procedures for larval bioassays, the extracts were used to evaluate against early 4th instar larvae of Aedes mosquito vectors. ResultsThe larvicidal activity of Clitoria ternatea flowers extracts evidently affected the early 4th instar larvae of Aedes mosquito vectors. The highest larvicidal activity was observed against early 4th instar larvae of Ae. aegypti with the LC50 and LC95 values of 1056 and 2491 mg/L, respectively. Meanwhile larvae bioassay test for Ae.albopictus recorded with the LC50 and LC95 values of 1425 and 2753 mg/L. Moreover, the results for non target organism test on Guppy fish, Poecilia reticulate showed no mortalities with flower extracts at 2500 mg/L and posses no toxic effects on fish. In this study, total of 16 chemical compounds and 6 chemical compounds have been reported to posses direct effects on insecticidal, larvicidal and pupicidal effects. Namely 6 chemicals used for insecticidal properties were Glycerin, 2-Hydroxy-gamma-butyrolactone, Neophytadiene, n-Hexadecanoic acid, cis-Vaccenic acid, and Octadecanoic acid with total of 28.7%. Clitoria ternatea flower extracts also showed different types of phenols such as anthocyanin, flavonoid and tannin. ConclusionsOur findings showed that crude extract of Clitoria ternatea flower bioactive molecules to be effective and may be developed as biolarvicides for Aedes mosquito vector control. Furthermore, this study also provided a baseline understanding for future research work on the field applications of Clitoria ternatea flower extracts which could be tested for its long term effects on other non target organisms, including human health.

biochemistry↗