Declining Trend in Antimicrobial Sensitivity in Respiratory Tract Bacterial Pathogens against Commonly Used Drugs at a Tertiary Care Hospital.

OBJECTIVES: Antimicrobial resistance (AMR) is a major health issue. To determine trends in bacterial organisms in respiratory tract infections (RTIs) and their antibiotic sensitivity at a tertiary care center in India, we performed this study. METHODS: Successive samples received from January 2017 to December 2021 from the respiratory tract (sputum, endotracheal secretion, and bronchoalveolar lavage) from intensive care units and medical inpatients were processed for bacterial growth. The identification of isolates and antibiotic sensitivity patterns was performed using an automated VITEK-2 system. Descriptive statistics are reported. RESULTS: We received 7,204 respiratory samples. Significant bacterial growth was in 3,000 (41.6%), and 2,992 (41.5%) were gram-negative. Klebsiella pneumoniae was the most prevalent, followed by Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli, and Enterobacter aerogenes. Increasing secular trends were observed for Klebsiella and Pseudomonas and declining trends for Acinetobacter and Escherichia (p < 0.05). Antimicrobial sensitivity patterns showed that Klebsiella, Pseudomonas, Acinetobacter, E. coli, and Enterobacter had a high sensitivity with colistin and polymyxin (99-100%). Moderate sensitivity was observed with carbapenems (Acinetobacter: 47.5%, Enterobacter: 62.0%, Escherichia: 76.5%, Klebsiella: 72.3%, Pseudomonas: 66.7%) and tigecycline (Acinetobacter: 50.4%, Enterobacter: 68.0%, Escherichia: 81.1%, Klebsiella: 66.6%, Pseudomonas: 0%). Aminoglycosides had <50% sensitivity for various organisms, and <25% sensitivity was observed with third-generation cephalosporins and quinolones. Trend analysis showed persistent sensitivity of various pathogenic bacteria to colistin and polymyxin and declining pharmacological sensitivity in Acinetobacter (carbapenems and tigecycline), Escherichia (carbapenems, quinolones, and tigecycline), Klebsiella (carbapenems, quinolones, aminoglycosides, and tigecycline), and Pseudomonas (carbapenems and aminoglycosides) species (p < 0.05). CONCLUSION: Common respiratory tract gram-negative bacterial pathogens at a tertiary care hospital are K. pneumoniae, P. aeruginosa, A. baumannii, and E. coli. All these bacteria demonstrate high sensitivity only with colistin and polymyxin. Significant AMR is observed to carbapenems, tigecycline, aminoglycosides, and third-generation cephalosporins. Secular trends show declining antimicrobial sensitivity among various bacterial pathogens.

Bark thickness and related parameters of tree species along an elevation transect leading to treeline in Central Himalaya.

Since treelines are generally fire-free, the trees growing there are expected to have thin bark, unless adaptation to other factors than fire results in the selection of a thick bark. Related to this is also higher proportional investment in inner bark in such an environment of infrequent fire. This study has considered stem bark thickness both in absolute and relative terms and also in the frame of the composition of outer and inner bark components of 20 tree species along an elevation transect (2100-3300 m) in high ranges of the Central Himalaya leading to treelines. The study species varied from 2.1 to 16.2 mm for total bark thickness and from 1.2 to 18.85% for relative bark thickness. The average absolute total bark thickness across the tree species decreased with elevation from forest to treeline, both when trees of all diameters (10.2 ± 0.84 mm for forest and 6.9 ± 1.79 mm for treeline) and those of the same stem diameter range (18-20 m) were compared (9.10 ± 1.30 mm for forest species and 6.38 ± 1.31 mm for treeline species). Nevertheless, the treeline bark thickness was similar to those of several forest communities considered to have comparatively thick bark. Like many other biological structures, bark carries out multiple functions; therefore, its thickness could be affected by more than one environmental factor. We suggest that the requirement of mechanical resistance to the snowfall, rainstorms, wind and adaptation to a high sunlight and UV radiations or storage of water, and non-structural carbohydrates could affect total, outer and inner bark thickness. Studies on these aspects in similar ecosystems may help understand the multi-functional attributes of the bark. For trees of comparable sizes (trees with 18-20 cm diameter at breast height) treeline species also had lower relative bark thickness (< 6%) than trees of forest below it (> 7%). The median proportion of inner bark of the total bark (70.5%) for our 20 species was more than that for savannas (~ 50%), exposed to frequent fire regime and similar to those of in cool sclerophyllous forests and temperate rain forests where fire return time is > 100 years. However, it was lower than the inner bark proportion reported for tropical rain forests. To conclude, in spite of a fire-free environment, the Himalayan treeline and adjoining forest species show mixed bark characters.

Temporal dynamics of urban air pollutants and their correlation with associated meteorological parameters: an investigation in northern Indian cities.

This study delves into the intricate dynamics of air pollution in the rapidly expanding northern regions of India, examining the intertwined influences of agricultural burning, industrialization, and meteorological conditions. Through comprehensive analysis of key pollutants (PM2.5, PM10, NO2, SO2, CO, O3) across ten monitoring stations in Uttar Pradesh, Haryana, Delhi, and Punjab, a consistent pattern of high pollution levels emerges, particularly notable in Delhi. Varanasi leads in SO2 and O3 concentrations, while Moradabad stands out for CO levels, and Jalandhar for SO2 concentrations. The study further elucidates the regional distribution of pollutants, with Punjab receiving significant contributions from SW, SE, and NE directions, while Haryana and Delhi predominantly face air masses from SE and NE directions. Uttar Pradesh's pollution sources are primarily local, with additional inputs from various directions. Moreover, significant negative correlations (p < 0.05) between PM10, NO2, SO2, O3, and relative humidity (RH) underscore the pivotal role of meteorological factors in shaping pollutant levels. Strong positive correlations between PM2.5 and NO2 (0.71 to 0.93) suggest shared emission sources or similar atmospheric conditions in several cities. This comprehensive understanding highlights the urgent need for targeted mitigation strategies to address the multifaceted drivers of air pollution, ensuring the protection of public health and environmental sustainability across the region.

Peroxynitrite is essential for aerenchyma formation in rice roots under waterlogging conditions.

MAIN CONCLUSION: In this study, we report that peroxynitrite is necessary for ethylene-mediated aerenchyma formation in rice roots under waterlogging conditions. Plants under waterlogging stress face anoxygenic conditions which reduce their metabolism and induce several adaptations. The formation of aerenchyma is of paramount importance for the survival of plants under waterlogging conditions. Though some studies have shown the involvement of ethylene in aerenchyma formation under waterlogging conditions, the implication of peroxynitrite (ONOO-) in such a developmental process remains elusive. Here, we report an increase in aerenchyma formation in rice roots exposed to waterlogging conditions under which the number of aerenchyma cells and their size was further enhanced in response to exogenous ethephon (a donor of ethylene) or SNP (a donor of nitric oxide) treatment. Application of epicatechin (a peroxynitrite scavenger) to waterlogged plants inhibited the aerenchyma formation, signifying that ONOO- might have a role in aerenchyma formation. Interestingly, epicatechin and ethephon co-treated waterlogged plants were unable to form aerenchyma, indicating the necessity of ONOO- in ethylene-mediated aerenchyma formation under waterlogging conditions. Taken together, our results highlight the role of ONOO- in ethylene-mediated aerenchyma formation in rice and could be used in the future to develop waterlogging stress-tolerant varieties of rice.

Synergetic anaerobic digestion of food waste for enhanced production of biogas and value-added products: strategies, challenges, and techno-economic analysis.

The generation of food waste (FW) is increasing at an alarming rate, contributing to a total of 32% of all the waste produced globally. Anaerobic digestion (AD) is an effective method for dealing with organic wastes of various compositions, like FW. Waste valorization into value-added products has increased due to the conversion of FW into biogas using AD technology. A variety of pathways are adopted by microbes to avoid unfavorable conditions in AD, including competition between sulfate-reducing bacteria and methane (CH4)-forming bacteria. Anaerobic bacteria decompose organic matter to produce biogas, a digester gas. The composition depends on the type of raw material and the method by which the digestion process is conducted. Studies have shown that the biogas produced by AD contains 65-75% CH4 and 35-45% carbon dioxide (CO2). Methanothrix soehngenii and Methanosaeta concilii are examples of species that convert acetate to CH4 and CO2. Methanobacterium bryantii, Methanobacterium thermoautotrophicum, and Methanobrevibacter arboriphilus are examples of species that produce CH4 from hydrogen and CO2. Methanobacterium formicicum, Methanobrevibacter smithii, and Methanococcus voltae are examples of species that consume formate, hydrogen, and CO2 and produce CH4. The popularity of AD has increased for the development of biorefinery because it is seen as a more environmentally acceptable alternative in comparison to physico-chemical techniques for resource and energy recovery. The review examines the possibility of using accessible FW to produce important value-added products such as organic acids (acetate/butyrate), biopolymers, and other essential value-added products.

HighlightsPopulation growth globally increases the generation of FW.FW generation, recycling, and reuse have been discussed.Biogas and bio-fertilizers can be recovered from FW through AD.

Heterogeneous Chiral Covalent Organic Framework for the Enantioselective Epoxidation of Styrenes and Chromenes.

Herein, we report the synthesis of two-dimensional chiral ZnII Salen covalent organic frameworks (COFs) (2) via rapid microwave-promoted condensation of C3-symmetric 1,3,5-tris[(5-tert-butyl-3-formyl-4-hydroxyphenyl)ethynyl]benzene 1 with (1R,2R)-1,2-diaminocyclohexane in excellent yields. The synthesized chiral ZnII Salen COF (2) showed a 454 m2 g-1 BET surface area with excellent crystallinity and thermal stability. Further, the post-synthetic metal exchange reaction was performed for chiral ZnII Salen COFs (2) with Mn(OAc)2·4H2O to synthesize chiral MnIII Salen COFs (3) and utilized as an effective heterogeneous catalyst for the enantioselective epoxidation of styrenes and chromenes to afford chiral epoxides up to 72% ee. Chiral MnIII Salen COF (3) could easily be separated by centrifugation and reused up to four recycles with an observable loss in activity without impairing enantioselectivity.

Chir pine and banj oak responses to pre-monsoon drought across slope aspects and positions in Central Himalaya.

The difference in maintaining a safety margin with regard to hydraulic conductance between pine and oak species influences their distribution in a region. Chir pine (Pinus roxburghii) and banj oak (Quercus leucotrichophora) are the principal species of Central Himalayan forests between 1000 and 2000 m elevations. Nearly 80% of annual precipitation of ~ 1400 mm in the region occurs during monsoon, from mid-June to September, whereafter droughts of varying length and intensity are common. The main objective of the study is to find out the responses of these two evergreen tree species to pre-monsoon (March to mid-June) water stress and topographical heterogeneity that occur in Central Himalaya. We measured soil and tree water potential and osmotic adjustment across five seasons on three slope positions, namely, hill base, mid-slope, and hill top, on north and south slope aspects. Chir pine showed an early response to pre-monsoon drought by restraining daily change in Ψ to 0.89 MPa, while predawn Ψ (ΨPD) was still moderate (isohydric tendency). In contrast, the daily reduction in Ψ of banj oak kept on increasing up to 1.49 MPa, despite severely low ΨPD (anisohydric tendency). In both tree species, Ψ was invariably lower on south aspect than north aspect and declined from hill base to hill top. Such responses to slope aspect and position, however, were relatively less apparent in chir pine, which tended to maintain a wide safety margin when under stress. As for soil Ψ, banj oak site retained monsoon rainwater more effectively than chir pine.

Gall Bladder Duplication with Choledochal Cyst: A Rare Entity.

A 4-year-old male child presented with complaints of abdominal pain and vomiting along with yellowish discoloration of the eyes. Investigations were suggestive of acute pancreatitis and double gall bladder (GB) with dilated common bile duct (CBD) with intraluminal calculi and Type II choledochal cyst. He underwent surgical resection of double GB with dilated CBD with hepatico-docho-jejunostomy. On follow-up, the patient was asymptomatic. Our case highlights the importance of preoperative diagnosis to deal with increased operative difficulty and complications.

A Rare Case of True Pancreatic Cyst.

Pancreatic cysts can be true or pseudocysts. True pancreatic cysts in children are rare clinical entities. We present a 23-month-old boy with a cystic lesion in the distal body and tail of the pancreas which on histopathology was found to be a rare true congenital simple cyst of the pancreas.

Type VI Choledochal Cyst - An Emerging Rare Entity (11th Pediatric Case of Type VI) with a Review of Literature.

Choledochal cysts (CCs) are abnormal dilatations of the biliary system. Usually, CCs are classified into five types. The sixth type (Type VI) is an emerging and rare type, reported the first case in 1991. We report this rare CC, Type VI seen in our experience for the first time. We have also reviewed the literature; only 26 cases of Type VI were found, including adults and children, ever since the first case has been reported in 1991. To the best of our knowledge, this is the 11th pediatric case report of a Type VI choledochal cyst.

Different stages of microbial community during the anaerobic digestion of food waste.

Large-scale food waste (FW) disposal has resulted in severe environmental degradation and financial losses around the world. Although FW has a high biomass energy contents and a growing large number of national projects to recover energy from FW by anaerobic digestion (AD) are being developed. AD is a promising solution for FW management and energy generation when compared to typical disposal options including landfill disposal, incineration, and composting. AD of FW can be combined with an existing AD operation or linked to the manufacture of value-added products to reduce costs and increase income. AD is a metabolic process that requires four different types of microbes: hydrolyzers, acidogens, acetogens, and methanogens. Microbes use a variety of strategies to avoid difficult situations in the AD, such as competition for the same substrate between sulfate-reducing bacteria and methane-forming bacteria. An improved comprehension of the microbiology involved in the anaerobic digestion of FW will provide new insight into the circumstances needed to maximize this procedure, including its possibilities for use in co-digestion mechanisms. This paper reviewed the present scientific knowledge of microbial community during the AD and the connection between microbial diversity during the AD of FW.

Chir pine forest and pre-monsoon drought determine spatial, and temporal patterns of forest fires in Uttarakhand Himalaya.

Associated with farming practices (between 300 and 2000 m elevations), human-ignited small, and patchy surface forest fires occur almost every year in Uttarakhand (between 28°43`- 31°27` N and 77°34`- 81°02`E; area 51,125 km2), a Himalayan state of India. Using fire incidence data of 19 years (2002-2020) generated by MODIS, we analysed the factors which drive temporal and spatial patterns of fire in the region. The fire incidence data were organized by 24 forest divisions, the unit of state forest management and administration. The standardized regression model showed that pre-monsoon temperature (March to May or mid-June), proportional area of the forest division under chir pine (Pinus roxburghii) forest (positive effect), and pre-monsoon and winter precipitation (negative effect) accounted for 56% of the variance in fire incidence density (FID). The pre-monsoon temperature (warmer) and precipitation (lower) were significantly different in 2009, 2012, 2016 and 2019, the years with high FID (average 54.9 fire/100 km2) than the rest of years with low FID (average 20.9 fire/100 km2). During the two decades of warming, high FID (> 30 incidence per year /100 km2) occurred after every three to four years, and fire peaks tended to increase with time. The study suggests that effective fire management can be attained by improving pre-monsoon precipitation forecasting and targeting forest compartments with a higher occurrence of chir pine and fire-vulnerable oaks. Furthermore, since fires are human-ignited, periodical analysis of changes in population distribution and communities' dependence on forests would need to be conducted. Supplementary Information: The online version contains supplementary material available at 10.1007/s42965-023-00306-9.

When do cover crops reduce nitrate leaching? A global meta-analysis.

The global increases in the surface and groundwater nitrate (NO3 - ) concentrations due to synthetic fertilizer input have emerged as major sustainability threats to terrestrial and aquatic ecosystems. Cover crops can reportedly reduce nitrate leaching from croplands. However, the underlying mechanisms and the effectiveness of cover crops in reducing nitrate leaching across species, soil types, agronomic management, and climates remain elusive. We conducted a global meta-analysis to evaluate the effects of cover crops on nitrate leaching and water drainage. A random-effects analysis was established to investigate seven moderating variables in 41 articles. Results showed that globally, cover crops reduced nitrate leaching by 69% compared with fallow while demonstrating no effect on water drainage. Overall, cover crops from Brassicaceae and Poaceae families showed the greatest effect with 75% and 52% reduction in nitrate leaching, respectively. Cover cropping on Ultisols, Histosols, and Inceptisols resulted in the greatest reduction in nitrate leaching (77%, 78%, and 77%, respectively). Greater efficacy of cover crops at reducing nitrate leaching was evident with increasing soil sand content. In general, cover crops appeared to perform better to reduce nitrate leaching in vegetable systems compared to field crops. Cover cropping on conventional tillage resulted in a 63% reduction in nitrate leaching compared with no-tillage (50%) and reduced tillage (38%) systems. The impact of cover crops on water drainage was nonsignificant which implies that nitrate leaching control by cover crops is unlikely exerted through reducing water drainage. This study brings further insight into the intrinsic factors affecting cover crop efficacy and management practices that enhance cover crop potential in reducing nitrate leaching from agricultural systems.

Identification and profiling of microbial community from industrial sludge.

The purpose of this study is to identify microbial communities in pulp and paper industry sludge and their metagenomic profiling on the basis of; phylum, class, order, family, genus and species level. Results revealed that the dominant phyla in 16S rRNA Illumina Miseq analysis inside sludge were Anaerolinea, Pseudomonas, Clostridia, Bacteriodia, Gammaproteobacteria, Spirochetia, Deltaproteobacteria, Spirochaetaceae, Prolixibacteraceae and some unknown microbial strains are also dominant. Metagenomics is a molecular biology-based technology that uses bioinformatics to evaluate huge gene sequences extracted from environmental samples to assess the composition and function of microbiota. The results of metabarcoding of the V3-V4 16S rRNA regions acquired from paired-end Illumina MiSeq sequencing were used to analyze bacterial communities and structure. The present work demonstrates the potential approach to sludge treatment in the open environment via the naturally adapted microorganism, which could be an essential addition to the disposal site. In summary, these investigations indicate that the indigenous microbial community is an acceptable bioresource for remediation or detoxification following secondary treatment. This research aims at understanding the structure of microbial communities and their diversity (%) in highly contaminated sludge to perform in situ bioremediation.

Crosstalk and gene expression in microorganisms under metals stress.

Contamination of the environment with heavy metals (HMs) has led to huge global environmental issues. Industrialization activities such as mining, manufacturing, and construction generate massive amounts of toxic waste, posing environmental risks. HMs soil pollution causes a variety of environmental issues and has a detrimental effect on both animals and plants. To remove HMs from the soil, traditional physico-chemical techniques such as immobilization, electro-remediation, stabilization, and chemical reduction are used. Moreover, the high energy, trained manpower, and hazardous chemicals required by these methods make them expensive and non-environmentally friendly. Bioremediation process, which involves microorganism-based and microorganism-associated-plant-based approaches, is an ecologically sound and cost-effective strategy for restoring HMs polluted soil. Microbes adjust their physiology to these conditions to live, which can involve significant variations in the expression of the genes. A set of genes are activated in response to toxic metals in microbes. They can also adapt by modifying their shape, fruiting bodies creating biofilms, filaments, or chemotactically migrating away from stress chemicals. Microbes including Bacillus sp., Pseudomonas sp., and Aspergillus sp. has been found to have high metals remediation and tolerance capacity of up to 98% whether isolated or in combination with plants like Helianthus annuus, Trifolium repens, and Vallisneria denseserrulata. Several of the regulatory systems that have been discovered are unique, but there is also a lot of "cross-talk" among networks. This review discusses the current state of knowledge regarding the microbial signaling responses, and the function of microbes in HMs stress resistance.

Interface morphology driven exchange interaction and magnetization reversal in a Gd/Co multilayer.

Rare-earth (RE)/transition metal (TM) ferromagnetic heterostructures with competing interfacial coupling and Zeeman energy provide a rich ground to study different phase states as a function of magnetic field and temperature. The interface morphology as a knob in these RE/TM heterostructures provides an excellent opportunity to engineer the macroscopic magnetic response by tuning the interface dependent microscopic interactions between the layers. We have investigated the interface morphology driven structure and magnetic properties of a Gd/Co multilayer. The interface morphology of the multilayer was controlled by annealing the multilayer at a relatively low temperature of 573 K under vacuum conditions. Combining the different experimental techniques and a simple one-dimensional spin-based model calculation, we studied the detailed magnetic structure and magnetization reversal mechanism in this system across compensation temperature (Tcomp), which suggested a strong interface dependent coupling in the system. We showed that changes in the interface morphology of the Gd/Co multilayer strongly influence the macroscopic magnetic properties of the system. The calculation also confirms the formation of a helical magnetic structure with a 2π domain wall in this system below Tcomp. The experimental finding and the simulation of this technologically important system will help to understand the physics of all-optical switching and related applications.

Omics approaches in bioremediation of environmental contaminants: An integrated approach for environmental safety and sustainability.

Non-degradable pollutants have emerged as a result of industrialization, population growth, and lifestyle changes, endangering human health and the environment. Bioremediation is the process of clearing hazardous contaminants with the help of microorganisms, and cost-effective approach. The low-cost and environmentally acceptable approach to removing environmental pollutants from ecosystems is microbial bioremediation. However, to execute these different bioremediation approaches successfully, this is imperative to have a complete understanding of the variables impacting the development, metabolism, dynamics, and native microbial communities' activity in polluted areas. The emergence of new technologies like next-generation sequencing, protein and metabolic profiling, and advanced bioinformatic tools have provided critical insights into microbial communities and underlying mechanisms in environmental contaminant bioremediation. These omics approaches are meta-genomics, meta-transcriptomics, meta-proteomics, and metabolomics. Moreover, the advancements in these technologies have greatly aided in determining the effectiveness and implementing microbiological bioremediation approaches. At Environmental Protection Agency (EPA)-The government placed special emphasis on exploring how molecular and "omic" technologies may be used to determine the nature, behavior, and functions of the intrinsic microbial communities present at pollution containment systems. Several omics techniques are unquestionably more informative and valuable in elucidating the mechanism of the process and identifying the essential player's involved enzymes and their regulatory elements. This review provides an overview and description of the omics platforms that have been described in recent reports on omics approaches in bioremediation and that demonstrate the effectiveness of integrated omics approaches and their novel future use.

Engineering D-glucose utilization in Azospirillum brasilense Sp7 promotes rice root colonization.

Bacteria of the genus Azospirillum include several plant associated bacteria which often promote the growth of their host plants. Although the host range of Azospirillum brasilense Sp7 is much wider than its close relative Azospirillum lipoferum 4B, it lacks the ability to efficiently utilize D-glucose for its growth. By comparing the genomes of both the species, the genes of A. lipoferum 4B responsible for conferring D-glucose utilization ability in A. brasilese Sp7 were identified by cloning individual or a combination of genes in a broad host range expression vector, mobilizing them in A. brasilense Sp7 and examining the ability of exconjugants to use D-glucose as sole carbon source for growth. These genes also included the homologs of genes involved in N-acetyl glucosamine utilization in Pseudomonas aeruginosa PAO1. A transcriptional fusion of the 5 genes encoding glucose-6-phosphate dehydrogenase and 4 components of glucose phosphotransferase system were able to improve D-glucose utilization ability in A. brasilense Sp7. The A. brasilense Sp7 strain engineered with D-glucose utilization ability showed significantly improved root colonization of rice seedling. The improvement in the ability of A. brasilense Sp7 to colonize rice roots is expected to bring benefits to rice by promoting its growth. KEY POINTS: • Genes required for glucose utilization in Azospirillum lipoferum were identified. • A gene cassette encoding glucose utilization was constructed. • Transfer of gene cassette in A. brasilense improves glucose utilization and rice root colonization..

DABCO-based chiral ionic liquids as recoverable and reusable organocatalyst for asymmetric Diels-Alder reaction.

New DABCO-based chiral ionic liquids were synthesized and evaluated in asymmetric Diels-Alder reaction of cyclopentadiene with α,ß-unsaturated aldehydes or 4-phenyl-3-buten-2-one. Chiral ionic liquid of modified MacMillan catalyst having a DABCO cation and hexafluorophosphate anion acts as organocatalyst (5 mol%) for the Diels-Alder reaction of crotonaldehyde and cyclopentadiene producing 98% of the product and 87% ee (endo) in CH3 CN/H2 O (95/5) at 25°C in 2 h. The scope and limitations of the catalysis were also studied by using cyclopentadiene and α,ß-unsaturated aldehydes, and the Diels-Alder products were obtained in 18%-92% yields with 68%-93% ee. The catalyst was recycled and reused up to 6 cycles with a slight drop in ee and conversion of the product.

Ring shaped fs supercontinuum with a thermally induced self-diffraction effect.

A broadband femtosecond supercontinuum (SC) light with a dark core has been generated in a pump-probe type geometry. It has been achieved by introducing a small thermal perturbation in a highly absorbing medium with a continuous wave pump laser. The SC was generated with the help of a photonic crystal fiber and a nJ femtosecond oscillator. Numerical simulations for the system were done by employing the Fresnel-Kirchhoff formula. The power dependence of the dark core diameter was also studied experimentally, and the results agree well with numerical simulations. The dark core size can be controlled by varying the input power of the pump beam.