Extinction of Antimicrobial Resistant Pathogens Using Silver Embedded Silica Nanoparticles and an Efflux Pump Blocker.

Control measures against antimicrobial resistant bacterial pathogens are important challenges in our daily life. In this study, we discuss the sensitivity and resistance of four bacterial pathogens, Vibrio alginolyticus, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis, to silver-silica hybrid nanoparticles. Successively, by combining with an efflux pump blocking agent Verapamil, we find that these hybrid nanoparticles induce complete mortality to even the most resistive S. aureus. The above pathogens are selected from a pool of 100 bacterial strains resistant to silver nitrate. While S. aureus shows increased resistance to the nanoparticles, the cell wall integrity and genetic stability of V. alginolyticus and E. coli are compromised in the presence of the hybrid nanoparticles. These studies suggest that the antimicrobial properties of the nanoparticles against Gram-negative pathogens originate from increased oxidative stress, which is confirmed by the blocking of reactive oxygen species (ROS) using scavengers such as ascorbic acid and observing DNA damage. The antimicrobial property of the nanoparticle when combined with its nontoxic nature to mammalian cells makes it a promising agent for controlling drug-resistant Gram-negative pathogens.

Diversity and seasonal distribution of ammonia-oxidizing archaea in the water column of a tropical estuary along the southeast Arabian Sea.

Diversity and distribution pattern of ammonia-oxidizing archaea (AOA) were studied across a salinity gradient in the water column of Cochin Estuary (CE), a tropical monsoonal estuary along the southeast Arabian Sea. The water column of CE was found to be nutrient rich with high bacterial (3.7-6.7 × 108 cells L-1) and archaeal abundance (1.9-4.5 × 108 cells L-1). Diversity and seasonal variation in the distribution pattern of AOA were studied using clone library analysis and Denaturing gradient gel electrophoresis (DGGE). Clone library analysis of both the amoA and 16S rRNA gene sequences showed similar diversity pattern, however the diversity was more clear when the 16S rRNA gene sequences were analyzed. More than 70% of the sequences retrieved were clustered under uncultured Thaumarchaeota group 1 lineage and the major fractions of the remaining sequences were grouped into the Nitrosopumilus lineage and Nitrosopelagicus lineage. The AOA community in the CE was less adaptable to changing environmental conditions and its distribution showed seasonal variations within the DGGE banding pattern with higher diversity during the pre-monsoon period. The distribution of AOA also showed its preference to intermediate salinity for their higher diversity. Summer monsoon associated runoff and flushing played a critical role in regulating the seasonality of AOA distribution.

Diversity of sediment-associated Planctomycetes in the Arabian Sea oxygen minimum zone.

We examined the diversity of Planctomycetes in the sediment sample collected from an oxygen minimum zone (OMZ) in the southeast Arabian Sea. A 16SrRNA gene library was constructed using the forward primer specific for Planctomycetes and a universal reverse primer. The 237 sequences obtained were grouped into 130 operational taxonomic units, and the majority of them were clustered with phylum Planctomycetes (45.0%) and unclassified bacteria (27.0%). There were sequences that clustered with distantly separated monophyletic groups such as Latescibacteria (9%), Actinobacteria (6%), Proteobacteria (5%), and others (8%). Among Planctomycetes, 55.7% belonged to family Planctomycetaceae, followed by unclassified Planctomycetes (25.0%) and family candidatus Brocadiaceae (19.2%). The family Planctomycetaceae included the genera Blastopirellula (11.5%), Rhodopirellula (3.8%), and a large number unclassified Planctomycetaceae sequences (40.4%). The members of family candidatus Brocadiaceae included the genera candidatus Scalindua (11.5%), candidatus Brocadia (1.9%) and unclassified genera (5.8). Our study indicates the relatively large diversity of Planctomycetes in sediments underlying the oxygen minimum zone of Arabian Sea. Also, the sequence data generated in the present study may support the efforts on isolation and purification of Planctomycetes from marine environment for understanding their biogeochemical significance.

Sponge-Associated Bacteria Produce Non-cytotoxic Melanin Which Protects Animal Cells from Photo-Toxicity.

Melanin is a photo-protective polymer found in many organisms. Our research shows that the bacteria associated with darkly pigmented sponges (Haliclona pigmentifera, Sigmadocia pumila, Fasciospongia cavernosa, Spongia officinalis, and Callyspongia diffusa) secrete non-cytotoxic melanin, with antioxidant activity that protects animal cells from photo-toxicity. Out of 156 bacterial strains screened, 22 produced melanin and these melanin-producing bacteria (MPB) were identified as Vibrio spp., Providencia sp., Bacillus sp., Shewanella sp., Staphylococcus sp., Planococcus sp., Salinococcus sp., and Glutamicibacter sp. Maximum melanin production was exhibited by Vibrio alginolyticus Marine Microbial Reference Facility (MMRF) 534 (50 mg ml-1), followed by two isolates of Vibrio harveyi MMRF 535 (40 mg ml-1) and MMRF 546 (30 mg ml-1). Using pathway inhibition assay and FT-IR spectral analysis, we identified the melanin secreted into the culture medium of MPB as 1,8-dihydroxynaphthalene-melanin. The bacterial melanin was non-cytotoxic to mouse fibroblast L929 cells and brine shrimps up to a concentration of 200 and 500 ppm, respectively. Bacterial melanin showed antioxidant activity at very low concentration (IC50-9.0 ppm) and at 50 ppm, melanin protected L929 cells from UV-induced intracellular reactive oxygen stress. Our study proposes sponge-associated bacteria as a potential source of non-cytotoxic melanin with antioxidant potentials.