Silver nanoparticles possess unique properties which find myriad applications such as antimicrobial, anticancer, larvicidal, catalytic, and wound healing activities. Biogenic syntheses of silver nanoparticles using plants and their pharmacological and other potential applications are gaining momentum owing to its assured rewards. This critical review is aimed at providing an insight into the phytomediated synthesis of silver nanoparticles, its significant applications in various fields, and characterization techniques involved.

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Biosynthesis of Silver Nanoparticles and Its Applications

Understanding the fate and biological effects of Ag- and TiO2-nanoparticles in the environment: The quest for advanced analytics and interdisciplinary concepts

Soil biota, antimicrobial resistance and planetary health

ABSTRACT To determine the prevalence and genotypes of extended-spectrum beta-lactamases (ESBLs) among clinical isolates of Klebsiella pneumoniae and Escherichia coli, we performed antibiotic susceptibility testing, pI determination, induction testing, transconjugation, and DNA sequencing analysis. Among the 509 isolates collected from 13 university hospitals in Korea, 39.2% produced ESBLs. ESBL-producing isolates were detected in every region in Korea. A total of 44.6% of the isolates produced both TEM- and SHV-type ESBLs, and 52% of ESBL-producing isolates transferred resistance to ceftazidime by transconjugation. The ESBLs were TEM-19, TEM-20, TEM-52, SHV-2a, SHV-12, and one new variant identified for the first time in Korea, namely, TEM-116. TEM-1 and SHV-12 were by far the most common variants. TEM-1, TEM-116, and SHV-12 showed a high prevalence in K. pneumoniae. Two isolates (E. coli SH16 and K. pneumoniae SV3) produced CMY-1-like beta-lactamases, which play a decisive role in resistance to cefoxitin and cefotetan, as well as TEM-type enzymes (TEM-20 and TEM-52, respectively). Using MIC patterns and DNA sequencing analysis, we postulated a possible evolution scheme among TEM-type beta-lactamases in Korea: from TEM-1 to TEM-19, from TEM-19 to TEM-20, and from TEM-20 to TEM-52.

https://ir.ymlib.yonsei.ac.kr/bitstream/22282913/112996/1/T200404806.pdf

Molecular Characterization of Extended-Spectrum Beta-Lactamases Produced by Clinical Isolates of Klebsiella pneumoniae and Escherichia coli from a Korean Nationwide Survey

Antimicrobial resistance (AMR) represents one of the most important human- and animal health-threatening issues worldwide. Bacterial capability to face antimicrobial compounds is an ancient feature, enabling bacterial survival over time and the dynamic surrounding. Moreover, bacteria make use of their evolutionary machinery to adapt to the selective pressure exerted by antibiotic treatments, resulting in reduced efficacy of the therapeutic intervention against human and animal infections. The mechanisms responsible for both innate and acquired AMR are thoroughly investigated. Commonly, AMR traits are included in mobilizable genetic elements enabling the homogeneous diffusion of the AMR traits pool between the ecosystems of diverse sectors, such as human medicine, veterinary medicine, and the environment. Thus, a coordinated multisectoral approach, such as One-Health, provides a detailed comprehensive picture of the AMR onset and diffusion. Following a general revision of the molecular mechanisms responsible for both innate and acquired AMR, the present manuscript focuses on reviewing the contribution of veterinary medicine to the overall issue of AMR. The main sources of AMR amenable to veterinary medicine are described, driving the attention towards the indissoluble cross-talk existing between the diverse ecosystems and sectors and their cumulative cooperation to this warning phenomenon.

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Antimicrobial Resistance in Veterinary Medicine: An Overview.

History of mankind is regarded as struggle against infectious diseases Rather than observing the withering away of bacterial diseases, antibiotic resistance has emerged as a serious global health concern Medium of antibiotic resistance in bacteria varies greatly and comprises of target protection, target substitution, antibiotic detoxification and block of intracellular antibiotic accumulation Further aggravation to prevailing situation arose on observing bacteria gradually becoming resistant to different classes of antibiotics through acquisition of resistance genes from same and different genera of bacteria Attributing bacteria with feature of better adaptability, dispersal of antibiotic resistance genes to minimize effects of antibiotics by various means including horizontal gene transfer (conjugation, transformation, and transduction), Mobile genetic elements (plasmids, transposons, insertion sequences, integrons, and integrative-conjugative elements) and bacterial toxin-antitoxin system led to speedy bloom of antibiotic resistance amongst bacteria Proficiency of bacteria to obtain resistance genes generated an unpleasant situation; a grave, but a lot unacknowledged, feature of resistance gene transfer

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Antibiotics, Resistome and Resistance Mechanisms: A Bacterial Perspective.

Colistin regained global interest as a consequence of the rising prevalence of multidrug-resistant Gram-negative Enterobacteriaceae. In parallel, colistin-resistant bacteria emerged in response to the unregulated use of this antibiotic. However, some Gram-negative species are intrinsically resistant to colistin activity, such as Neisseria meningitides, Burkholderia species, and Proteus mirabilis. Most identified colistin resistance usually involves modulation of lipid A that decreases or removes early charge-based interaction with colistin through up-regulation of multistep capsular polysaccharide expression. The membrane modifications occur by the addition of cationic phosphoethanolamine (pEtN) or 4-amino-l-arabinose on lipid A that results in decrease in the negative charge on the bacterial surface. Therefore, electrostatic interaction between polycationic colistin and lipopolysaccharide (LPS) is halted. It has been reported that these modifications on the bacterial surface occur due to overexpression of chromosomally mediated two-component system genes (PmrAB and PhoPQ) and mutation in lipid A biosynthesis genes that result in loss of the ability to produce lipid A and consequently LPS chain, thereafter recently identified variants of plasmid-borne genes (mcr-1 to mcr-10). It was hypothesized that mcr genes derived from intrinsically resistant environmental bacteria that carried chromosomal pmrC gene, a part of the pmrCAB operon, code three proteins viz. pEtN response regulator PmrA, sensor kinase protein PmrAB, and phosphotransferase PmrC. These plasmid-borne mcr genes become a serious concern as they assist in the dissemination of colistin resistance to other pathogenic bacteria. This review presents the progress of multiple strategies of colistin resistance mechanisms in bacteria, mainly focusing on surface changes of the outer membrane LPS structure and other resistance genetic determinants. New handier and versatile methods have been discussed for rapid detection of colistin resistance determinants and the latest approaches to revert colistin resistance that include the use of new drugs, drug combinations and inhibitors. Indeed, more investigations are required to identify the exact role of different colistin resistance determinants that will aid in developing new less toxic and potent drugs to treat bacterial infections. Therefore, colistin resistance should be considered a severe medical issue requiring multisectoral research with proper surveillance and suitable monitoring systems to report the dissemination rate of these resistant genes.

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Current Update on Intrinsic and Acquired Colistin Resistance Mechanisms in Bacteria.

Increased use of colistin, a last resort drug due to failure of carbapenems, has possibly contributed in development and spread of resistance to colistin among Enterobacteriaceae. The colistin belongs to the family of polymyxins, cationic polypeptides, with broad-spectrum activity against Gram-negative bacteria. In this study, we obtained 253 non-duplicate bacterial isolates from sewage water in Delhi and phenotypically screened for colistin resistance. Of the 47 positive isolates, the colistin resistance gene mcr-1 was detected among 5 isolates. Based on 16S ribosomal RNA–based identification, bacterial isolates were found to be Escherichia coli, Aeromonas veronii, and Aeromonas dhakensis. Extended spectrum β-lactamases (ESBL)–resistant determinants CTX-M and TEM were detected in all five mcr-1 positive isolates. On the basis of literature survey, this is the first report of mcr-1 gene from Aeromonas veronii and Aeromonas dhakensis worldwide. Furthermore, mcr-1 gene has not been reported earlier from sewage water in India. Antibiotic susceptibility test of all five isolates against 9 different classes of drugs revealed multidrug-resistant phenotype with high minimum inhibitory concentration values. In vitro transconjugation studies showed successful transfer of mcr-1 and other ESBL-resistant determinants. The occurrence of colistin resistance phenotype conferred by plasmid-based mcr-1 gene in the environment and an ever-increasing list of bacterial isolates is a cause of concern. A comprehensive survey of different water bodies and epidemiological studies are required to assess the risk of dissemination of resistance determinants.

Emergence of mcr-1 conferred colistin resistance among bacterial isolates from urban sewage water in India.

Synthesis and characterization of surface-active antimicrobial hyperbranched polyurethane coatings based on oleo-ethers of boric acid

In the present study, we have investigated prevalence and diversity of ESBL genes among Klebsiella isolates obtained from highly polluted stretch of river Yamuna, India Phenotypic screenings of 116 Klebsiella isolates revealed ~30% were positive for ESBL production Antibiotic profiling showed multidrug resistance phenotype among 90% isolates Prevalence of blaTEM, blaSHV and blaCTX-M genes were found to be 57, 54 and 48% respectively Furthermore, we identified eight variants of blaSHV (SHV-1, SHV-11, SHV-27, SHV-28, SHV-38, SHV-61, SHV-144, SHV-148), three each of blaTEM (TEM-1, TEM-116, TEM-206) and blaCTX-M (CTX-M-15, CTX-M-55, CTX-M-188) among Klebsiella spp Co-occurrence of blaTEM, blaSHV and blaCTX-M (any two or all three) was observed among 45% Klebsiella isolates Occurrence of blaCTX-M-188 and blaTEM-206 in environmental isolates of K pneumoniae has not been reported earlier Identification of blaTEM-206, blaSHV-27 and blaSHV-144 from Klebsiella spp and blaTEM-116 from K quasipneumoniae and K variicola is the first report from India

Prevalence and diversity of blaTEM, blaSHV and blaCTX-M variants among multidrug resistant Klebsiella spp. from an urban riverine environment in India.

Mohammad Tahir Siddiqui

Papers

Antibiotics, Resistome and Resistance Mechanisms: A Bacterial Perspective.

Current Update on Intrinsic and Acquired Colistin Resistance Mechanisms in Bacteria.

Emergence of mcr-1 conferred colistin resistance among bacterial isolates from urban sewage water in India.

Synthesis and characterization of surface-active antimicrobial hyperbranched polyurethane coatings based on oleo-ethers of boric acid

Prevalence and diversity of blaTEM, blaSHV and blaCTX-M variants among multidrug resistant Klebsiella spp. from an urban riverine environment in India.