Isolation and Genome Sequence Characterization of Bacteriophage vB_SalM_PM10, a Cba120virus, Concurrently Infecting Salmonella enterica Serovars Typhimurium, Typhi, and Enteritidis.

The prevalence of multidrug-resistant Salmonella is ever increasing and calls for alternatives to antibiotics. The use of phages has been anticipated to reduce the multidrug-resistant human pathogens in food environment. Salmonella phage vB_SalM_PM10 (PM10) was isolated from sewage-polluted river in India. It shows an icosahedral head (94 ± 4 nm) along with a long contractile tail (106 ± 7 × 18 ± 2 nm), a morphotype of family Ackermannviridae. Additionally, the phage displayed the features resembling to existing Cba120viruses. Phage PM10 could infect S. enterica serovars Typhimurium, Typhi, and Enteritidis. The genome sequencing analysis of phage PM10 revealed circular 158.08 kb double-stranded DNA, with the GC content of 44.6%. Two hundred and nine ORFs, 171 putative promoters, 122 rho-independent terminators, and 5 transfer RNA encoding genes were found in the genome. The genome-wide comparisons and phylogenetic analyses showed that phage PM10 is closely related to Salmonella phage PhiSH19. Comparison of the tail-spike protein sequences encoded in PM10 and PhiSH19 genome showed the variation, which might have facilitated PM10's simultaneous infectivity to aforementioned S. enterica serovars. This is a varied host range than that of PhiSH19 or any other Cba120viruses.

Development and evaluation of taxon-specific primers for the selected Caudovirales taxa.

The phage taxonomy is primarily based on the morphology derived from Transmission Electron Microscopic (TEM) studies. TEM based characterization is authentic and accepted by scientific community. However, TEM based identification is expensive and time consuming. After the phage isolation, before analysis TEM, a DNA based rapid method could be introduced. The DNA based method could dramatically reduce the number of samples analyzed by TEM and thereby increase the speed and reduce the cost of identification. In the present work, four environmental phage isolates were identified based on TEM studies and genome size. The identification of these four phages was validated using DNA based method. The taxon-specific DNA markers were identified through multiple sequence alignments. The primers were designed at conserved genes (DNA polymerase or integrase) of 4 different phage taxa viz. family Ackermannviridae, genus Jerseyvirus, genus T4virus, and genus P22virus. These primers were evaluated using both in vitro and in silico approach for the amplification of the target taxons. Majority of the primer sets were found to amplify member species of the targeted taxa in vitro. In In silico analysis, six primer sets intended for identification of family Ackermannviridae showed positive amplification of ≥86.7% classified species. Further, the primers targeting the genus Jerseyvirus and T4virus showed the amplification of 53.8% and ≥84.6% species, respectively. The present work is a case study performed to explore the possibility of use of taxon-specific primers for identification and taxonomic studies of newly isolated phages to supplement the TEM.

Preparation of silver nanoparticles in the presence of polyoxometalates.

The mechanisms of reduction of silver ions and subsequently oxidation of silver atoms in the presence of polyoxometalates (POMs) are discussed. A step-by-step room temperature electron reduction of silver ions and its subsequent reactions has been used in this work to monitor oxidation of silver atoms and its clusters. The silver atoms can transfer electron to POMs is revealed by decrease in the yield of silver clusters and increase in their decay rates. The results of continuous γ-irradiation are compared using UV-visible (UV-Vis) absorption spectra, underlying the effect of silver atoms accumulation in the absence of POMs. Silver nanoparticles (Ag NPs) prepared by reduced silicotungstic acid (STA) were used as Raman substrate and also for antibacterial studies against panel of human pathogenic bacteria. The Ag NPs exhibited antibacterial activity against both Gram-positive and Gram-negative bacterial pathogens evaluated by well diffusion assay. The inhibition zones were within the range of 10 to 14 mm. We have also explored the surface enhanced Raman scattering (SERS) activity of the Ag NPs substrates using 1.0 × 10-7 M solution of crystal violet (CV) as Raman probe molecule. It was possible to detect SERS spectral pattern of CV on Ag NPs substrate with a high signal-to-noise ratio. Both SERS and antibacterial studies show that this simple, low cost, and greener method for synthesizing Ag NPs may be valuable in future studies about SERS sensor development and bio-applications.