Mechanisms of antibiotic resistance

Preparation of Activated Carbon-Reinforced Composite Beads Based on MnO2/MCM-41@Fe3O4 and Calcium Alginate for Efficient Removal of Tetracycline in Aqueous Solutions

Tetracycline (TC) is a common antibiotic; when untreated TC enters the environment, it will cause a negative impact on the human body through the food chain. In the present study, MnO2/MCM-41@Fe3O4 (FeMnMCM) prepared using a hydrothermal and redox method and Camellia oleifera shell-activated carbon (COFAC) prepared through alkali activation were encapsulated using alginate (ALG) and calcium chloride as a cross-linking matrix to give the composite beads COFAC-FeMnMCM-ALG. The resultant COFAC-FeMnMCM-ALG composite beads were then carefully characterized, showing a high immobilization of MnO2/MCM-41@Fe3O4, with porous COFAC as an effective bioadsorbent for enriching the pollutants in the treated samples. These bead catalysts were subsequently applied to the oxidative degradation of TC in a Fenton oxidation system. Several parameters affecting the degradation were investigated, including the H2O2 concentration, catalyst dosage, initial TC concentration, and temperature. A very high catalytic activity towards the degradation of TC was demonstrated. The electron paramagnetic resonance (EPR) and quenching results showed that ·OH and ·O2- were generated in the system, with ·OH as the main radical species. In addition, the COFAC-FeMnMCM-ALG catalyst exhibited excellent recyclability/reusability. We conclude that the as-prepared COFAC-FeMnMCM-ALG composite beads, which integrate MnO2 and Fe3O4 with bioadsorbents, provide a new idea for the design of catalysts for advanced oxidation processes (AOPs) and have great potential in the Fenton oxidation system to degrade toxic pollutants.

Concerns about the use of antimicrobials in swine herds and alternative trends

Pig productivity in Brazil has advanced a lot in recent decades. Specialized breeds are more vulnerable to pathogens, which has boosted the use of antimicrobials by farmers. The selective pressure generated favors the emergence of resistant bacteria, which compromises the effectiveness of this treatment and limits therapeutic options. In addition to increasing costs and mortality rates in the production system, public awareness of this issue has increased. The authorities have imposed restrictive measures to control the use of antimicrobials and have banned their use as growth promoters. This literature review highlights biosecurity and animal welfare to prevent pig diseases. Hence, we describe alternatives to the use of antimicrobials in pig production for the selection of effective non-antibiotic feed additives that help maintain good health and help the pig resist disease when infection occurs.

2D/2D Bi2MoO6/CoAl LDH S-scheme heterojunction for enhanced removal of tetracycline: Performance, toxicity, and mechanism

In this paper, the two-dimensional (2D) layered CoAl LDH (CoAl) was coupled with Bi2MoO6 (BMO) nanoplate and used for tetracycline (TC) degradation. Based on the results of UV-visible diffuse reflectance spectrum (UV-vis DRS), Motty-Schottky curves, and in situ X-ray photoelectron spectroscopy (XPS), a novel 2D/2D Bi2MoO6/CoAl LDH S-scheme heterojunction photocatalyst was built. The photodegradation rate constant of TC by the optimized sample BMO/CoAl30 was 3.637 × 10-2 min-1, which was 1.26 times and 4.01 times higher than that of Bi2MoO6 and CoAl LDH, respectively. The favorable photocatalytic performance of the heterojunction was attributed to the increased interfacial contact area of the 2D/2D structure. Besides, the transfer of photogenerated electrons from Bi2MoO6 to CoAl LDH under the effect of the built-in electric field (BIEF) reduced the recombination of photogenerated carriers and further improved the photocatalytic performance. The reactive species of h+, ·O2-, and 1O2 exhibited critical roles to degrade TC molecules by reactive radicals capture experiments and electron spin resonance (ESR) tests. The intermediate products of TC degradation and toxicity of intermediates were analyzed by liquid chromatography-mass spectrometer (LC-MS) and Toxicity Estimation Software Tool (T.E.S.T). Additionally, the BMO/CoAl composite photocatalysts showed high stability and environmental tolerance during the testing of cycles and environmental impacts with various water sources, organic contaminants, initial pH, and inorganic ions. This work provides a new protocol for designing and constructing novel 2D/2D S-scheme heterojunction photocatalysts for wastewater treatment.

High-throughput computational screening for identification of potential hits against bacterial Acriflavine resistance protein B (AcrB) efflux pump

Antibiotic resistance is a pressing global health challenge, driven in part by the remarkable efflux capabilities of efflux pump in AcrB (Acriflavine Resistance Protein B) protein in Gram-negative bacteria. In this study, a multi-approached computational screening strategy encompassing molecular docking, In silico absorption, distribution, metabolism, excretion and toxicity (ADMET) analysis, druglikeness assessment, molecular dynamics simulations and density functional theory studies was employed to identify novel hits capable of acting against AcrB-mediated antibiotic resistance. Ligand library was acquired from the COCONUT database. Performed computational analyses unveiled four promising hit molecules (CNP0298667, CNP0399927, CNP0321542 and CNP0269513). Notably, CNP0298667 exhibited the highest negative binding affinity of -11.5 kcal/mol, indicating a possibility of strong potential to disrupt AcrB function. Importantly, all four hits met stringent druglikeness criteria and demonstrated favorable in silico ADMET profiles, underscoring their potential for further development. MD simulations over 100 ns revealed that the CNP0321542-4DX5 and CNP0269513-4DX5 complexes formed robust and stable interactions with the AcrB efflux pump. The identified hits represent a promising starting point for the design and optimization of novel therapeutics aimed at combating AcrB-mediated antibiotic resistance in Gram-negative bacteria.Communicated by Ramaswamy H. Sarma.

Prevalence of antibiotic resistance in lactic acid bacteria isolated from traditional fermented Indian food products

The emergence of antimicrobial resistance (AMR) in lactic acid bacteria (LAB) raises questions on qualified presumptive safety status and poses challenge of AMR transmission in food milieu. This study focuses on isolation, identification and characterization of AMR in LAB prevalent in traditional fermented Indian food products. The analysis of 16SrRNA based phylogenetic tree showed placements of isolates among four different genera Lactobacillus, Enterococcus, Weissella and Leuconostoc. In E-strip gradient test of susceptibility to 14 different antibiotics, over 50% of isolates showed resistance to ampicillin, chloramphenicol, ciprofloxacin, erythromycin, kanamycin, linezolid, streptomycin, trimethoprim and vancomycin. A multivariate principal component analysis, an antibiogram and multiple antibiotic resistance index-values (> 0.2) indicated presence of multidrug-resistance among the isolates. This study reports prevalence of an alarmingly high rate of AMR LAB strains in traditional fermented foods and is important to regulators and public health authorities for developing strategies to control transmission in food systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01305-1.

Strategies for the Discovery of Oxazolidinone Antibacterial Agents: Development and Future Perspectives

Oxazolidinones represent a significant class of synthetic bacterial protein synthesis inhibitors that are primarily effective against Gram-positive bacteria. The commercial success of linezolid, the first FDA-approved oxazolidinone antibiotic, has motivated researchers to develop more potent oxazolidinones by employing various drug development strategies to fight against antimicrobial resistance, some of which have shown promising results. Thus, this Perspective aims to discuss the strategies employed in constructing oxazolidinone-based antibacterial agents and summarize recent advances in discovering oxazolidinone antibiotics to provide valuable insights for potentially developing next-generation oxazolidinone antibacterial agents or other pharmaceuticals.

Reduced bacterial resistance antibiotics with improved microbiota tolerance in human intestinal: Molecular design and mechanism analysis

Antibiotic selectivity and bacterial resistance are critical global public health issues. We constructed a multi-class machine learning model to study antibiotic effects on human intestinal microbiota abundance and identified key features. Binding energies of β-lactam antibiotics with Escherichia coli PBP3 mutant protein were calculated, and a 2D-QSAR model for bacterial resistance was established. Sensitivity analysis identified key features affecting bacterial resistance. By coupling key features from the machine learning model and 2D-QSAR model, we designed ten flucloxacillin (FLU) substitutes that improved intestinal microbiota tolerance and reduced antibiotic bacterial resistance. Concurrently, the substitutes exhibited superior degradability in soil, aquatic environments, and under photolytic conditions, coupled with a reduced environmental toxicity compared to the FLU. Evaluations under combined medication revealed significant improvements in functionality and bacterial resistance for 80% of FLU substitutes, with 50% showing more than a twofold increase. Mechanistic analysis demonstrated enhanced binding to target proteins and increased biodegradability for FLU substitutes due to more concentrated surface charges. Reduced solvent hindrance and increased cell membrane permeability of FLU substitutes, mainly due to enhanced interactions with phospholipid bilayers, contributed to their functional selectivity. This study aims to address poor antibiotic selectivity and strong bacterial resistance, providing guidance for designing antibiotic substitutes.

1-deoxy-D-xylulose-5-phosphate synthase from Pseudomonas aeruginosa and Klebsiella pneumoniae reveals conformational changes upon cofactor binding

The ESKAPE bacteria are the six highly virulent and antibiotic-resistant pathogens that require the most urgent attention for the development of novel antibiotics. Detailed knowledge of target proteins specific to bacteria is essential to develop novel treatment options. The methylerythritol-phosphate (MEP) pathway, which is absent in humans, represents a potentially valuable target for the development of novel antibiotics. Within the MEP pathway, the enzyme 1-deoxy-D-xylulose-5-phosphate synthase (DXPS) catalyzes a crucial, rate-limiting first step and a branch point in the biosynthesis of the vitamins B1 and B6. We report the high-resolution crystal structures of DXPS from the important ESKAPE pathogens Pseudomonas aeruginosa and Klebsiella pneumoniae in both the co-factor-bound and the apo forms. We demonstrate that the absence of the cofactor thiamine diphosphate results in conformational changes that lead to disordered loops close to the active site that might be important for the design of potent DXPS inhibitors. Collectively, our results provide important structural details that aid in the assessment of DXPS as a potential target in the ongoing efforts to combat antibiotic resistance.

On the use of antibiotics to control plant pathogenic bacteria: a genetic and genomic perspective

Despite growing attention, antibiotics (such as streptomycin, oxytetracycline or kasugamycin) are still used worldwide for the control of major bacterial plant diseases. This raises concerns on their potential, yet unknown impact on antibiotic and multidrug resistances and the spread of their genetic determinants among bacterial pathogens. Antibiotic resistance genes (ARGs) have been identified in plant pathogenic bacteria (PPB), with streptomycin resistance genes being the most commonly reported. Therefore, the contribution of mobile genetic elements (MGEs) to their spread among PPB, as well as their ability to transfer to other bacteria, need to be further explored. The only well-documented example of ARGs vector in PPB, Tn5393 and its highly similar variants (carrying streptomycin resistance genes), is concerning because of its presence outside PPB, in Salmonella enterica and Klebsiella pneumoniae, two major human pathogens. Although its structure among PPB is still relatively simple, in human- and animal-associated bacteria, Tn5393 has evolved into complex associations with other MGEs and ARGs. This review sheds light on ARGs and MGEs associated with PPB, but also investigates the potential role of antibiotic use in resistance selection in plant-associated bacteria.

Different rapid startups for high-solid anaerobic digestion treating pig manure: Metagenomic insights into antibiotic resistance genes fate and microbial metabolic pathway

High-solid anaerobic digestion (HSAD), as an emerging disposal technology for swine manure, was commonly hampered by the long lag phase and slow startup, resulting in poor performance. Rapid startups by different leachate reflux forms can solve the problem, but related study was scarcely reported. Therefore, metagenomic analysis was used to exploit the effects of different rapid startups on the biogas performance, antibiotic resistance genes (ARGs) removal and microbial metabolic pathway during HSAD. Compared anaerobic digestion with natural start (T1), three different rapid startups were set, including with autologous leachate reflux (T2), with water reflux (T3) and with exogenous leachate reflux (T4). The results showed that rapid startups (T2-T4) enhanced biogas yield and the cumulative methane yield was increased by 3.7-7.3 times compared with the control. Totally, 922 ARGs were found, most of which belonged to multidrug and MLS ARGs. About 56% of these ARGs could be reduced in T4, while just 32% of ARGs were reduced in T1. Antibiotic efflux pump is the main mechanism of microbial action, which could be decreased largely by these treatments. Moreover, all the rapid startups (T2-T4) made Methanosarcina content (9.59%-75.91%) higher than that in the natural startup of T1 (4.54%-40.27%). This is why these fast-startups helped methane production fast. Network analysis showed that microbial community and environmental factors (pH and VFAs) both contributed to the spread of ARGs. The reconstructed methane metabolic pathway by different identified genes showed that all methanogenesis pathways existed but acetate metabolic pathway was dominant. And the rapid startups made the abundance of acetate metabolic (M00357) higher than the natural startup.

Novel Biocompatible Green Silver Nanoparticles Efficiently Eliminates Multidrug Resistant Nosocomial Pathogens and Mycobacterium Species

Bacterial infection is a major crisis of 21st era and the emergence of multidrug resistant (MDR) pathogens cause significant health problems. We developed, green chemistry-based silver nanoparticles (G-Ag NPs) using Citrus pseudolimon fruit peel extract. G-Ag NPs has a spherical shape in the range of ~ 40 nm with a surface charge of - 31 Mv. This nano-bioagent is an eco-friendly tool to combat menace of MDR. Biochemical tests prove that G-Ag NPs are compatible with human red blood cells and peripheral blood mononuclear cells. There have been many reports on the synthesis of silver nanoparticles, but this study suggests a green technique for making non-cytotoxic, non-hemolytic organometallic silver nanoparticles with a high therapeutic index for possible use in the medical field. On the same line, G-Ag NPs are very effective against Mycobacterium sp. and MDR strains including Escherichia coli, Klebsiella species, Pseudomonas aeruginosa, and Acinetobacter baumannii isolated from patient samples. Based on it, we filed a patent to Indian Patent Office (reference no. 202111048797) which can revolutionize the prevention of biomedical device borne infections in hospital pre/post-operated cases. This work could be further explored in future by in vivo experimentation with mice model to direct its possible clinical utility.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-023-01061-0.

The Impact of Tetracycline Pollution on the Aquatic Environment and Removal Strategies

Antibacterial drugs are among the most commonly used medications in the world. Tetracycline is a widely used antibiotic for human and animal therapy due to its broad-spectrum activity, high effectiveness, and reasonable cost. The indications for treatment with tetracycline include pneumonia, bone and joint infections, infectious disorders of the skin, sexually transmitted and gastrointestinal infections. However, tetracycline has become a serious threat to the environment because of its overuse by humans and veterinarians and weak ability to degrade. Tetracycline is capable of accumulating along the food chain, causing toxicity to the microbial community, encouraging the development and spread of antibiotic resistance, creating threats to drinking and irrigation water, and disrupting microbial flora in the human intestine. It is essential to address the negative impact of tetracycline on the environment, as it causes ecological imbalance. Ineffective wastewater systems are among the main reasons for the increased antibiotic concentrations in aquatic sources. It is possible to degrade tetracycline by breaking it down into small molecules with less harmful or nonhazardous effects. A range of methods for physical, chemical, and biological degradation exists. The review will discuss the negative effects of tetracycline consumption on the aquatic environment and describe available removal methods.

Inhibition of Enzymatic Acetylation-Mediated Resistance to Plazomicin by Silver Ions

Plazomicin is a recent U.S. Food and Drug Administration (FDA)-approved semisynthetic aminoglycoside. Its structure consists of a sisomicin scaffold modified by adding a 2(S)-hydroxy aminobutyryl group at the N1 position and a hydroxyethyl substituent at the 6' position. These substitutions produced a molecule refractory to most aminoglycoside-modifying enzymes. The main enzyme within this group that recognizes plazomicin as substrate is the aminoglycoside 2'-N-acetyltransferase type Ia [AAC(2')-Ia], which reduces the antibiotic's potency. Designing formulations that combine an antimicrobial with an inhibitor of resistance is a recognized strategy to extend the useful life of existing antibiotics. We have recently found that several metal ions inhibit the enzymatic inactivation of numerous aminoglycosides mediated by the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib]. In particular, Ag+, which also enhances the effect of aminoglycosides by other mechanisms, is very effective in interfering with AAC(6')-Ib-mediated resistance to amikacin. Here we report that silver acetate is a potent inhibitor of AAC(2')-Ia-mediated acetylation of plazomicin in vitro, and it reduces resistance levels of Escherichia coli carrying aac(2')-Ia. The resistance reversion assays produced equivalent results when the structural gene was expressed under the control of the natural or the blaTEM-1 promoters. The antibiotic effect of plazomicin in combination with silver was bactericidal, and the mix did not show significant toxicity to human embryonic kidney 293 (HEK293) cells.

An Inventory of Anthelmintic Plants across the Globe

A wide range of novelties and significant developments in the field of veterinary science to treat helminth parasites by using natural plant products have been assessed in recent years. To the best of our knowledge, to date, there has not been such a comprehensive review of 19 years of articles on the anthelmintic potential of plants against various types of helminths in different parts of the world. Therefore, the present study reviews the available information on a large number of medicinal plants and their pharmacological effects, which may facilitate the development of an effective management strategy against helminth parasites. An electronic search in four major databases (PubMed, Scopus, Web of Science, and Google Scholar) was performed for articles published between January 2003 and April 2022. Information about plant species, local name, family, distribution, plant tissue used, and target parasite species was tabulated. All relevant studies meeting the inclusion criteria were assessed, and 118 research articles were included. In total, 259 plant species were reviewed as a potential source of anthelmintic drugs. These plants can be used as a source of natural drugs to treat helminth infections in animals, and their use would potentially reduce economic losses and improve livestock production.

Impact of the COVID-19 pandemic on dispensing medicines in the community pharmacy

BACKGROUND

The world has faced an unprecedented challenge since COVID-19 emerged as a pandemic, which has led to quarantine and disruptions in drug services. During the pandemic, drug use habits and availability changed, causing a shift in behaviors and, in turn, medicine misuse. In Iraq, this is a major problem because many medicines can be easily obtained.

OBJECTIVE

The study aims to describe the pattern of dispensing medications during the pandemic and to evaluate the biochemical and pathological consequences.

METHOD

The analytical, observational, cross-sectional study was performed via a compiled questionnaire for 400 random pharmacists, and the analysis and interpretation of the biochemical changes and medical reports.

RESULTS

Results revealed that dispensing of medications since the COVID-19 outbreak has increased by 74%, and the demand for medicines seems higher than required in comparison to the periods before the pandemic, while 60% of the dispensed medicines were taken just in case needed. In addition, the availability of medicines decreased by 61%, and the dispensing of common medicines increased due to the belief in their prophylactic action. Several biochemical abnormalities and pathological consequences were recorded due to the irrational use of medicines, and the highest percentage (12%) was seen in hepatic and liver enzymatic dysfunction and 8% for the endocrine and hormonal abnormalities.

CONCLUSION

It can be concluded that most of the dispensed medicines were not used on a therapeutic or scientific basis during the pandemic.

Effects of captive and primate-focused tourism on the gut microbiome of Tibetan macaques

Documenting the effects of anthropogenic activities on the gut microbiome of wild animals is important to their conservation practices. Captivity and ecotourism are generally considered two common anthropogenic disturbances on the health of nonhuman primates. Here, we examined the divergences of gut microbiome in different environments of Tibetan macaques. Our results showed that there were no significant differences in the alpha diversity, predominant families and genera of gut microbiomes between wild and tourist groups. However, these indexes decreased significantly in the captive individuals. In addition, the significant differences of beta diversity and community compositions between wild and tourism groups also were detected. In particular, higher potential pathogenic and predicted KEGG pathway of drug resistance (antimicrobial) were detected in the gut microbiome of individuals in captive environment. Our results indicated that living in the wild are beneficial to maintaining gut microbial diversity of Tibetan macaques, while captivity environment is harmful to the health of this macaque. Exploring ways to restore the native gut microbiome and its diversity of captive individual should pay more attention to in the future studies.

Antibiotic Abuse and Antimicrobial Resistance in Hospital Environment: A Retrospective Observational Comparative Study

Background and Objectives: Antimicrobial resistance represents a serious problem, and it may be life-threatening in the case of severe hospital-acquired infections (HAI). Antibiotic abuse and multidrug resistance (MDR) have significantly increased this burden in the last decades. The aim of this study was to investigate the distribution and susceptibility rates of five selected bacterial species (E. coli, K. pneumoniae, P. aeruginosa, S. aureus and E. faecium) in two healthcare settings located in the Apulia region (Italy). Materials and Methods: Setting n.1 was a university hospital and setting n.2 was a research institute working on oncological patients. All the enrolled patients were diagnosed for bacterial HAI. The observation period was between August and September 2021. Clinical samples were obtained from several biological sources, in different hospital wards. Bacterial identification and susceptibility were tested by using the software VITEC 2 Single system. Results: In this study, a higher incidence of multi-drug-resistant K. pneumoniae was reported (42,2% in setting n.1 and 50% in setting n.2), with respect to the Italian 2019 statistics report (30.3%). All the isolates of E. faecium and S. aureus were susceptible to linezolid. All the bacterial isolates of P. aeruginosa and most of K. pneumoniae were susceptible to ceftazidime–avibactam. Amikacin and nitrofurantoin represented a good option for treating E. coli infections. Multidrug-resistant (MDR) P. aeruginosa, methicillin-resistant S. aureus (MRSA) and vancomycin-resistantE. faecium (VRE) had a lower incidence in the clinical setting, with respect to E. coli and K. pneumoniae. Conclusions: The data obtained in this study can support clinicians towards a rational and safe use of antibiotics for treating the infections caused by these resistant strains, to enhance the overall efficacy of the current antibiotic protocols used in the main healthcare environments.

Antibiotics and antibiotic resistant bacteria/genes in urban wastewater: A comparison of their fate in conventional treatment systems and constructed wetlands

There is a growing concern that the use and misuse of antibiotics can increase the detection of antibiotic resistant genes (ARGs) in wastewater. Conventional wastewater treatment plants provide a pathway for ARGs and antibiotic resistant bacteria (ARB) to be released into natural water bodies. Research has indicated that conventional primary and secondary treatment systems can reduce ARGs/ARB to varying degrees. However, in developing/low-income countries, only 8-28% of wastewater is treated via conventional treatment processes, resulting in the environment being exposed to high levels of ARGs, ARB and pharmaceuticals in raw sewage. The use of constructed wetlands (CWs) has the potential to provide a low-cost solution for wastewater treatment, with respect to removal of nutrients, pathogens, ARB/ARGs either as a standalone treatment process or when integrated with conventional treatment systems. Recently, CWs have also been employed for the reduction of antibiotic residues, pharmaceuticals, and emerging contaminants. Given the benefits of ARG removal, low cost of construction, maintenance, energy requirement, and performance efficiencies, CWs offer a promising solution for developing/low-income countries. This review promotes a better understanding of the performance efficiency of treatment technologies (both conventional systems and CWs) for the reduction of antibiotics and ARGs/ARB from wastewater and explores workable alternatives.

Antibiotics Resistance Pattern of Food-Borne Bacteria Isolated from Ice Cream in Bangladesh: A Multidisciplinary Study

Ice cream is one of the most popular food items consumed during the summer season in Bangladesh by all ages but mostly school-going students. Due to the ingredients and handling process of ice cream, it acts as a good shelter for pathogenic and nonpathogenic microorganisms. Therefore, we aimed to investigate the microbial count, prevalence, isolate and characterize multidrug-resistant bacteria in ice cream samples collected from nearby shops of schools in Tangail district, Bangladesh. Ice-cream consumer and nonconsumer students were selected by providing questionnaires. Total viable count (TVC) and total coliform count (TCC) were determined by pour plate methods, where conventional methods were performed for bacterial identification. The Kirby-Bauer disk diffusion method was used to determine the antimicrobial susceptibility of bacterial isolates. Kado and Liu method, with some modifications, was used to extract plasmid from the isolated bacteria and visualized through gel electrophoresis. The demographic characteristics showed that the degree of symptoms regarding microorganisms mediated disorders and rate of antibiotics intake in ice cream consumers were significantly higher than the nonconsumers. The range of TVC and TCC in the ice cream samples was found 0–9.9 × 109 CFU/ml and 0–900 CFU/ml, respectively. Interestingly, 93.75% of the total ice cream samples also showed fungal positive. A total of 12 different bacterial species were identified, including Proteus spp, E. coli, V.cholera, Pseudomonas spp, Shigella spp, Klebsiella spp, Aeromonas spp, V. Parahemolyticus. Salmonella paratyphi, Citrobacterspp, Plesiomonasspp, and Staphylococcus aureus. The antimicrobial susceptibility assay showed the multiple resistance frequency of these isolates to different antimicrobial drugs. All individual isolates were screened for plasmid DNA, and we found that seven strains harbored a single or more than two plasmids sized approximately between 1.9 and 140 MDa, indicating a possible connection between resistance phenotype pattern and genotype.

Multidrug-Resistant Bacterial Pathogens and Public Health: The Antimicrobial Effect of Cyanobacterial-Biosynthesized Silver Nanoparticles

Background: Cyanobacteria are considered as green nano-factories. Manipulation of the size of biogenic silver nanoparticles is needed to produce particles that suit the different applications such as the use as antibacterial agents. The present study attempts to manipulate the size of biosynthesized silver nanoparticles produced by cyanobacteria and to test the different-sized nanoparticles against pathogenic clinical bacteria. Methods: Cyanothece-like. coccoid unicellular cyanobacterium was tested for its ability to biosynthesize nanosilver particles of different sizes. A stock solution of silver nitrate was prepared from which three different concentrations were added to cyanobacterial culture. UV-visible spectroscopy and FTIR were conducted to characterize the silver nanoparticles produced in the cell free filtrate. Dynamic Light Scattering (DLS) was performed to determine the size of the nanoparticles produced at each concentration. The antimicrobial bioassays were conducted on broad host methicillin-resistant Staphylococcus aureus (MRSA), and Streptococcus sp., was conducted to detect the nanoparticle size that was most efficient as an antimicrobial agent. Results. The UV-Visible spectra showed excellent congruence of the plasmon peak characteristic of nanosilver at 450 nm for all three different concentrations, varying peak heights were recorded according to the concentration used. The FTIR of the three solutions revealed the absence of characteristic functional groups in the solution. All three concentrations showed spectra at 1636 and 2050–2290 nm indicating uniformity of composition. Moreover, DLS analysis revealed that the silver nanoparticles produced with lowest concentration of precursor AgNO₃ had smallest size followed by those resulting from the higher precursor concentration. The nanoparticles resulting from highest concentration of precursor AgNO₃ were the biggest in size and tending to agglomerate when their size was above 100 nm. The three types of differently-sized silver nanoparticles were used against two bacterial pathogenic strains with broad host range; MRSA-(Methicillin-resistant Staphylococcus aureus) and Streptococcus sp. The three types of nanoparticles showed antimicrobial effects with the smallest nanoparticles being the most efficient in inhibiting bacterial growth. Discussion: Nanosilver particles biosynthesized by Cyanothece-like cyanobacterium can serve as antibacterial agent against pathogens including multi-drug resistant strains. The most appropriate nanoparticle size for efficient antimicrobial activity had to be identified. Hence, size-manipulation experiment was conducted to find the most effective size of nanosilver particles. This size manipulation was achieved by controlling the amount of starting precursor. Excessive precursor material resulted in the agglomeration of the silver nanoparticles to a size greater than 100 nm. Thereby decreasing their ability to penetrate into the inner vicinity of microbial cells and consequently decreasing their antibacterial potency. Conclusion: Antibacterial nanosilver particles can be biosynthesized and their size manipulated by green synthesis. The use of biogenic nanosilver particles as small as possible is recommended to obtain effective antibacterial agents.

Effect of Resin Acid and Zinc Oxide on Immune Status of Weaned Piglets Challenged With E. coli Lipopolysaccharide

With the ban of zinc oxide (ZnO) at high dosages in piglet diets in Europe by 2022, alternative nutritional solutions are being tested to support piglet immune defence during their weaning, the most critical and stressful moment of pig production. The present study evaluated the effect of zinc oxide (ZnO; 2,500 mg/kg diet) and resin acid concentrate (RAC; 200 mg/kg diet) on the immune defence of weaned piglets challenged with lipopolysaccharide (LPS). Piglets were challenged at days 7 and 21 post-weaning, and blood was sampled 1.5 and 3.0 h after each challenge to determine serum levels of pro- and anti-inflammatory cytokines. The levels of serum tumour necrosis factor alpha (TNF-α) and interleukin 8 (IL-8) increased at days 7 and 21, and those of IL-6 at day 21 when challenged piglets were fed a diet supplemented with ZnO. In challenged piglets fed with RAC, the serum levels of IL-1β, IL-6, IL-8, IL-10 and TNF-α were increased at days 7 and 21, except for that of IL-1β, which was not affected at day 21. The increased levels of these cytokines indicate the successful immune-modulatory effect of ZnO and RAC, which appears as a candidate to replace ZnO in weaned piglets' diets.

Enhancement of the Bactericidal Effect of Antibiotics by Inhibition of Enzymes Involved in Production of Hydrogen Sulfide in Bacteria

Counteraction of the origin and distribution of multidrug-resistant pathogens responsible for intra-hospital infections is a worldwide issue in medicine. In this brief review, we discuss the results of our recent investigations, which argue that many antibiotics, along with inactivation of their traditional biochemical targets, can induce oxidative stress (ROS production), thus resulting in increased bactericidal efficiency. As we previously showed, hydrogen sulfide, which is produced in the cells of different pathogens protects them not only against oxidative stress but also against bactericidal antibiotics. Next, we clarified the interplay of oxidative stress, cysteine metabolism, and hydrogen sulfide production. Finally, demonstrated that small molecules, which inhibit a bacterial enzyme involved in hydrogen sulfide production, potentiate bactericidal antibiotics including quinolones, beta-lactams, and aminoglycosides against bacterial pathogens in in vitro and in mouse models of infection. These inhibitors also suppress bacterial tolerance to antibiotics by disrupting the biofilm formation and substantially reducing the number of persister bacteria, which survive the antibiotic treatment. We hypothesise that agents which limit hydrogen sulfide biosynthesis are effective tools to counteract the origin and distribution of multidrug-resistant pathogens.

Machine learning for identifying resistance features of Klebsiella pneumoniae using whole-genome sequence single nucleotide polymorphisms

Introduction. Klebsiella pneumoniae, a gram-negative bacterium, is a common pathogen causing nosocomial infection. The drug-resistance rate of K. pneumoniae is increasing year by year, posing a severe threat to public health worldwide. K. pneumoniae has been listed as one of the pathogens causing the global crisis of antimicrobial resistance in nosocomial infections. We need to explore the drug resistance of K. pneumoniae for clinical diagnosis. Single nucleotide polymorphisms (SNPs) are of high density and have rich genetic information in whole-genome sequencing (WGS), which can affect the structure or expression of proteins. SNPs can be used to explore mutation sites associated with bacterial resistance.Hypothesis/Gap Statement. Machine learning methods can detect genetic features associated with the drug resistance of K. pneumoniae from whole-genome SNP data.Aims. This work used Fast Feature Selection (FFS) and Codon Mutation Detection (CMD) machine learning methods to detect genetic features related to drug resistance of K. pneumoniae from whole-genome SNP data.Methods. WGS data on resistance of K. pneumoniae strains to four antibiotics (tetracycline, gentamicin, imipenem, amikacin) were downloaded from the European Nucleotide Archive (ENA). Sequence alignments were performed with MUMmer 3 to complete SNP calling using K. pneumoniae HS11286 chromosome as the reference genome. The FFS algorithm was applied to feature selection of the SNP dataset. The training set was constructed based on mutation sites with mutation frequency >0.995. Based on the original SNP training set, 70% of SNPs were randomly selected from each dataset as the test set to verify the accuracy of the training results. Finally, the resistance genes were obtained by the CMD algorithm and Venny.Results. The number of strains resistant to tetracycline, gentamicin, imipenem and amikacin was 931, 1048, 789 and 203, respectively. Machine learning algorithms were applied to the SNP training set and test set, and 28 and 23 resistance genes were predicted, respectively. The 28 resistance genes in the training set included 22 genes in the test set, which verified the accuracy of gene prediction. Among them, some genes (KPHS_35310, KPHS_18220, KPHS_35880, etc.) corresponded to known resistance genes (Eef2, lpxK, MdtC, etc). Logistic regression classifiers were established based on the identified SNPs in the training set. The area under the curves (AUCs) of the four antibiotics was 0.939, 0.950, 0.912 and 0.935, showing a strong ability to predict bacterial resistance.Conclusion. Machine learning methods can effectively be used to predict resistance genes and associated SNPs. The FFS and CMD algorithms have wide applicability. They can be used for the drug-resistance analysis of any microorganism with genomic variation and phenotypic data. This work lays a foundation for resistance research in clinical applications.

Antibiotic resistance in microbes: History, mechanisms, therapeutic strategies and future prospects

Antibiotics have been used to cure bacterial infections for more than 70 years, and these low-molecular-weight bioactive agents have also been used for a variety of other medicinal applications. In the battle against microbes, antibiotics have certainly been a blessing to human civilization by saving millions of lives. Globally, infections caused by multidrug-resistant (MDR) bacteria are on the rise. Antibiotics are being used to combat diversified bacterial infections. Synthetic biology techniques, in combination with molecular, functional genomic, and metagenomic studies of bacteria, plants, and even marine invertebrates are aimed at unlocking the world's natural products faster than previous methods of antibiotic discovery. There are currently only few viable remedies, potential preventive techniques, and a limited number of antibiotics, thereby necessitating the discovery of innovative medicinal approaches and antimicrobial therapies. MDR is also facilitated by biofilms, which makes infection control more complex. In this review, we have spotlighted comprehensively various aspects of antibiotics viz. overview of antibiotics era, mode of actions of antibiotics, development and mechanisms of antibiotic resistance in bacteria, and future strategies to fight the emerging antimicrobial resistant threat.

Antibiotic resistance genes in bacteria: Occurrence, spread, and control

The production and use of antibiotics are becoming increasingly common worldwide, and the problem of antibiotic resistance is increasing alarmingly. Drug-resistant infections threaten human life and health and impose a heavy burden on the global economy. The origin and molecular basis of bacterial resistance is the presence of antibiotic resistance genes (ARGs). Investigations on ARGs mostly focus on the environments in which antibiotics are frequently used, such as hospitals and farms. This literature review summarizes the current knowledge of the occurrence of antibiotic-resistant bacteria in nonclinical environments, such as air, aircraft wastewater, migratory bird feces, and sea areas in-depth, which have rarely been involved in previous studies. Furthermore, the mechanism of action of plasmid and phage during horizontal gene transfer was analyzed, and the transmission mechanism of ARGs was summarized. This review highlights the new mechanisms that enhance antibiotic resistance and the evolutionary background of multidrug resistance; in addition, some promising points for controlling or reducing the occurrence and spread of antimicrobial resistance are also proposed.

Emergence of mcr-1-Harboring Salmonella enterica Serovar Sinstorf Type ST155 Isolated From Patients With Diarrhea in Jiangsu, China

Background: This study analyzed the antimicrobial resistance phenotypes and mechanisms of quinolone, cephalosporins, and colistin resistance in nontyphoidal Salmonella from patients with diarrhea in Jiangsu, China. Methods: A total of 741 nontyphoidal Salmonella isolates were collected from hospitals in major cities of Jiangsu Province, China between 2016 and 2017. Their susceptibility to commonly used antibiotics was evaluated by broth micro-dilution and sequencing analysis of resistance genes screened by a PCR method. For mcr-1 positive isolates, genetic relationship study was carried out by pulsed-field gel electrophoresis and multiloci sequence typing analysis. The transferability of these plasmids was measured with conjugation experiments and the genetic locations of mcr-1 were analyzed by pulsed-field gel electrophoresis profiles of S1-digested genomic DNA and subsequent Southern blot hybridization. Results: Among 741 nontyphoidal Salmonella isolates, the most common serotypes identified were S. Typhimurium (n=257, 34.7%) and S. Enteritidis (n=127, 17.1%), and the isolates showed 21.7, 20.6, and 5.0% resistance to cephalosporins, ciprofloxacin, and colistin, respectively. Among the 335 nalidixic acid-resistant Salmonella, 213 (63.6%) and 45 (13.4%) had at least one mutation in gyrA and parC. Among the plasmid-borne resistance, qnrS1 (85; 41.9%) and aac(6')-Ib-cr4 (75; 36.9%) were the most common quinolone resistance (PMQR) genes, while bla _CTX-M-14 (n=35) and bla _CTX-M-55 (n=46) were found to be dominant extended-spectrum beta-lactamase (ESBL) genes in nontyphoidal Salmonella. In addition, eight mcr-1-harboring strains were detected since 2016 and they were predominate in children under the age of 7years. Conjugation assays showed the donor Salmonella strain has functional and transferable colistin resistance and Southern blot hybridization revealed that mcr-1 was located in a high molecular weight plasmid. Conclusion: In nontyphoidal Salmonella, there is a rapidly increasing trend of colistin resistance and this is the first report of patients harboring mcr-1-positive Salmonella with a new ST type ST155 and new serotype S. Sinstorf. These findings demonstrate the necessity for cautious use and the continuous monitoring of colistin in clinical applications.

Antibiotic Resistance Genes in Lemur Gut and Soil Microbiota Along a Gradient of Anthropogenic Disturbance

The overuse of man-made antibiotics has facilitated the global propagation of antibiotic resistance genes in animals, across natural and anthropogenically disturbed environments. Although antibiotic treatment is the most well-studied route by which resistance genes can develop and spread within host-associated microbiota, resistomes also can be acquired or enriched via more indirect routes, such as via transmission between hosts or via contact with antibiotic-contaminated matter within the environment. Relatively little is known about the impacts of anthropogenic disturbance on reservoirs of resistance genes in wildlife and their environments. We therefore tested for (a) antibiotic resistance genes in primate hosts experiencing different severities and types of anthropogenic disturbance (i.e., non-wildlife animal presence, human presence, direct human contact, and antibiotic treatment), and (b) covariation between host-associated and environmental resistomes. We used shotgun metagenomic sequencing of ring-tailed lemur (Lemur catta) gut resistomes and associated soil resistomes sampled from up to 10 sites: seven in the wilderness of Madagascar and three in captivity in Madagascar or the United States. We found that, compared to wild lemurs, captive lemurs harbored greater abundances of resistance genes, but not necessarily more diverse resistomes. Abundances of resistance genes were positively correlated with our assessments of anthropogenic disturbance, a pattern that was robust across all ten lemur populations. The composition of lemur resistomes was site-specific and the types of resistance genes reflected antibiotic usage in the country of origin, such as vancomycin use in Madagascar. We found support for multiple routes of ARG enrichment (e.g., via human contact, antibiotic treatment, and environmental acquisition) that differed across lemur populations, but could result in similar degrees of enrichment. Soil resistomes varied across natural habitats in Madagascar and, at sites with greater anthropogenic disturbance, lemurs and soil resistomes covaried. As one of the broadest, single-species investigations of wildlife resistomes to date, we show that the transmission and enrichment of antibiotic resistance genes varies across environments, thereby adding to the mounting evidence that the resistance crisis extends outside of traditional clinical settings.

Synthesis and biological screening of new thiadiazolopyrimidine-based polycyclic compounds

Novel tri-and tetra-cyclic compounds based on the thiadiazolopyrimidine ring system were synthesized, and their antimicrobial activity was estimated. The obtained results evidenced the substantial efficiencies of pyrano-thiadiazolopyrimidine compounds 8a-b and 9a-b toward the two strains of gram-positive bacteria (S. aureus and B. cereus). Besides, tetracyclic pyrazolopyrimido-thiadiazolopyrimidine derivatives 16a-b and 17a-b displayed prominent efficiencies toward the two strains of gram-negative bacteria (E. coli and P. aeruginosa). In addition, compounds 8a-b and 9a-b displayed good efficacy toward C. albicans. The activity of antiquorum sensing (anti-QS) inhibition of the newly synthesized thiadiazolopyrimidine-based compounds toward C. violaceum was tested, suggesting satisfactory activity for derivatives 16a-b, 17a-b, 8b, and 9a. The cytotoxic activity of these derivatives was screened toward various cancer cell lines (MCF-7, PC3, Hep-2, and HepG2) and standard normal fibroblast cells (WI38) by utilizing the MTT assay. The pyrazolopyrimido-thiadiazolopyrimidine derivatives 16a, 16b17a, and 17b showed potent cytotoxic efficacy against the MCF-7 cells with the IC50 values ranging from 5.69 to 9.36 µM. Also, the endorsed structural activity relationship (SAR) of the inspected thiadiazolopyrimidine derivatives provided a correlation between the chemical structure and anticancer efficiency. The in silico docking studies were implemented for silencing the hormonal signaling in the breast (PDB Code-5NQR). The results were found to be consistent with the cytotoxic activity.

Fluoroquinolone-Transition Metal Complexes: A Strategy to Overcome Bacterial Resistance

Fluoroquinolones (FQs) are antibiotics widely used in the clinical practice due to their large spectrum of action against Gram-negative and some Gram-positive bacteria. Nevertheless, the misuse and overuse of these antibiotics has triggered the development of bacterial resistance mechanisms. One of the strategies to circumvent this problem is the complexation of FQs with transition metal ions, known as metalloantibiotics, which can promote different activity and enhanced pharmacological behaviour. Here, we discuss the stability of FQ metalloantibiotics and their possible translocation pathways. The main goal of the present review is to frame the present knowledge on the conjunction of biophysical and biological tools that can help to unravel the antibacterial action of FQ metalloantibiotics. An additional goal is to shed light on the studies that must be accomplished to ensure stability and viability of such metalloantibiotics. Potentiometric, spectroscopic, microscopic, microbiological, and computational techniques are surveyed. Stability and partition constants, interaction with membrane porins and elucidation of their role in the influx, determination of the antimicrobial activity against multidrug-resistant (MDR) clinical isolates, elucidation of the mechanism of action, and toxicity assays are described for FQ metalloantibiotics.

Effects of acid, alkaline, cold, and heat environmental stresses on the antibiotic resistance of the Salmonella enterica serovar Typhimurium

Antibiotic resistance in Salmonella enterica serovar Typhimurium (S. ser. Typhimurium) has become a critical safety hazard in food. Sublethal environmental stresses can influence resistance in Salmonella during food processing. This study simulated environmental stresses in food processing. The antibiotic resistance of three strains of S. ser. Typhimurium (the ATCC 14028 strain and two wild-type isolates from chicken and pork product processing) was evaluated under different pH levels (5.0, 5.5, 6.0, 8.0, and 9.0). Also, dynamic changes in resistance with treatment duration under cold (4 °C, -20 °C) and heat (55 °C) treatment were studied. The results showed that acid and alkaline stresses reduced the resistance of S. ser. Typhimurium to eight antibiotics; meanwhile, the resistance of meropenem (MERO) increased. The minimal inhibitory concentration (MIC) of MERO was increased 16- to 64-fold. With acid or alkaline stress, the extracellular ATP content increased, and the scanning electron microscopy (SEM) result clearly revealed the appearance of wrinkles and holes on the outer membrane of Salmonella. These observations imply changes in membrane permeability, which may decrease the antibiotic resistance of Salmonella. Cold or heat stress increased the resistance of S. ser. Typhimurium to tetracycline, cefotaxime, ceftazidime, nalidixic acid, azithromycin, and ampicillin; the MIC increased 2- to 4-fold. The antibiotic resistance only changed when cold and heat stresses occurred over a certain period of time and remained unchanged when the stress persisted. This study reports on the ability of S. ser. Typhimurium to develop antibiotic resistance after environmental stresses. It can provide valuable information for meat processing to improve interventions and risk management.

Bacterial Biofilm Growth on 3D-Printed Materials

Recent advances in 3D printing have led to a rise in the use of 3D printed materials in prosthetics and external medical devices. These devices, while inexpensive, have not been adequately studied for their ability to resist biofouling and biofilm buildup. Bacterial biofilms are a major cause of biofouling in the medical field and, therefore, hospital-acquired, and medical device infections. These surface-attached bacteria are highly recalcitrant to conventional antimicrobial agents and result in chronic infections. During the COVID-19 pandemic, the U.S. Food and Drug Administration and medical officials have considered 3D printed medical devices as alternatives to conventional devices, due to manufacturing shortages. This abundant use of 3D printed devices in the medical fields warrants studies to assess the ability of different microorganisms to attach and colonize to such surfaces. In this study, we describe methods to determine bacterial biofouling and biofilm formation on 3D printed materials. We explored the biofilm-forming ability of multiple opportunistic pathogens commonly found on the human body including Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus to colonize eight commonly used polylactic acid (PLA) polymers. Biofilm quantification, surface topography, digital optical microscopy, and 3D projections were employed to better understand the bacterial attachment to 3D printed surfaces. We found that biofilm formation depends on surface structure, hydrophobicity, and that there was a wide range of antimicrobial properties among the tested polymers. We compared our tested materials with commercially available antimicrobial PLA polymers.

Antibiotic-Resistant Bacteria in Aquaculture and Climate Change: A Challenge for Health in the Mediterranean Area

Aquaculture is the productive activity that will play a crucial role in the challenges of the millennium, such as the need for proteins that support humans and the respect for the environment. Aquaculture is an important economic activity in the Mediterranean basin. A great impact is presented, however, by aquaculture practices as they involve the use of antibiotics for treatment and prophylaxis. As a consequence of the use of antibiotics in aquaculture, antibiotic resistance is induced in the surrounding bacteria in the column water, sediment, and fish-associated bacterial strains. Through horizontal gene transfer, bacteria can diffuse antibiotic-resistance genes and mobile resistance genes further spreading genetic determinants. Once triggered, antibiotic resistance easily spreads among aquatic microbial communities and, from there, can reach human pathogenic bacteria, making vain the use of antibiotics for human health. Climate change claims a significant role in this context, as rising temperatures can affect cell physiology in bacteria in the same way as antibiotics, causing antibiotic resistance to begin with. The Mediterranean Sea represents a 'hot spot' in terms of climate change and aspects of antibiotic resistance in aquaculture in this area can be significantly amplified, thus increasing threats to human health. Practices must be adopted to counteract negative impacts on human health, with a reduction in the use of antibiotics as a pivotal point. In the meantime, it is necessary to act against climate change by reducing anthropogenic impacts, for example by reducing CO2 emissions into the atmosphere. The One Health type approach, which involves the intervention of different skills, such as veterinary, ecology, and medicine in compliance with the principles of sustainability, is necessary and strongly recommended to face these important challenges for human and animal health, and for environmental safety in the Mediterranean area.

Digital Counting of Biomolecules Using Engineered Functional DNA Superstructures

There is currently a great need for developing a simple and effective biosensing platform for the detection of single biomolecules (e.g., DNAs, RNAs, or proteins) in the biological, medical, and environmental fields. Here, we show a versatile and sensitive fluorescence counting strategy for quantifying proteins and microRNAs by employing functional DNA superstructures (denoted as 3D DNA). A 3D DNA biolabel was first engineered to become highly fluorescent and carry recognition elements for the target of interest. The presence of a target cross-links the resultant of the 3D DNA biolabel and a surface-bound capturing antibody or DNA oligonucleotide, thus forming a sandwich complex that can be easily resolved using traditional fluorescence microscopy. The broad utility of this platform is illustrated by engineering two different 3D DNA biolabels that enable the quantification of β-lactamase (one secreted bacterial hydrolase) and miR-21 (one overexpressed microRNA in cancer cells) with detection limits of 100 aM and 1 fM, respectively. We envision that the approach described herein will find useful applications in chemical biology, medical diagnostics, and biosensing.

Prevalence and hazardous impact of pharmaceutical and personal care products and antibiotics in environment: A review on emerging contaminants

Antibiotic resistance is a global health emergency linked to unrestrained use of pharmaceutical and personal care products (PPCPs) as prophylactic agent and therapeutic purposes across various industries. Occurrence of pharmaceuticals are identified in ground water, surface water, soils, and wastewater treatment plants (WWTPs) in ng/L to μg/L concentration range. The prevalence of organic compounds including antimicrobial agents, hormones, antibiotics, preservatives, disinfectants, synthetic musks etc. in environment have posed serious health concerns. The aim of this review is to elucidate the major sources accountable for emergence of antibiotic resistance. For this purpose, variety of introductory sources and fate of PPCPs in aquatic environment including human and veterinary wastes, aquaculture and agriculture related wastes, and other anthropogenic activities have been discussed. Furthermore, genetic and enzymatic factors responsible for transfer and appearance of antibiotic resistance genes are presented. Ecotoxicity of PPCPs has been studied in environment in order to present risk imposed to human and ecological health. As per published literature reports, the removal of antibiotics and related traces being difficult, couples the possibility of emergence of antibiotic resistance and hence sustainability in global water resources. Therefore, research on environmental behavior and control strategies should be conducted along with assessing their chronic toxicity to identify potential human and ecological risks.

Occurrence of antibiotic-resistant bacteria on hydroponically grown butterhead lettuce (Lactuca sativa var. capitata)

Antibiotics used during production of food crops to control plant diseases may result in selection of antibiotic-resistant bacteria and occurrence of antibiotic residues. The aim of this research was to evaluate the effect of antibiotics used in butterhead lettuce production on persistence of commensal microbiota. Butterhead lettuce were treated with antibiotics (oxytetracycline, gentamicin, and streptomycin) at different concentrations (100, 200, 300, 400 and 500 ppm) starting at 5 weeks' growth by spraying once daily for 4 weeks and harvesting 7 days after the final spray application. The population of total aerobic bacteria and antibiotic-resistant bacteria were determined. The results showed antibiotic usage significantly decreased bacterial populations on lettuce. Moreover, increased concentration of antibiotics resulted in significantly greater decrease in bacterial populations. At a concentration of 500 ppm, all antibiotics achieved an approximate 2 log CFU/g decrease in bacterial populations. A stable population (4 log CFU/g) of potentially antibiotic-resistant commensal microbiota were maintained throughout production. Screening for level of susceptibility indicated that bacteria exhibited greater resistance to oxytetracycline than gentamicin. In conclusion, application of antibiotics failed to eliminate commensal microbiota, demonstrating large populations of antibiotic-resistant bacteria reside on lettuce grown under conditions used in the present study. This is the first study focused on antibiotic usage on hydroponic systems. Results of this study suggest regulations directed at antibiotic use on food crops must be developed and implemented to control the selection and spread of antibiotic-resistant bacteria that present a global health concern.

Structural and Cellular Insights into the l,d-Transpeptidase YcbB as a Therapeutic Target in Citrobacter rodentium, Salmonella Typhimurium, and Salmonella Typhi Infections

The bacterial cell wall plays a key role in viability and is an important drug target. The cell wall is made of elongated polymers that are cross-linked to one another to form a load-bearing mesh. An alternative cell wall cross-linking mechanism used by the l,d-transpeptidase YcbB has been implicated in the stress-regulated roles of β-lactam resistance, outer membrane defect rescue, and typhoid toxin release. The role for this stress-linked cross-linking in the context of a host infection was unclear. Here, we resolve the crystallographic structures of both Salmonella Typhi YcbB and Citrobacter rodentium YcbB acylated with ertapenem that delineate the conserved structural characteristics of YcbB. In parallel, we show that the general involvement of YcbB in peptidoglycan reinforcement under conditions of bacterial outer envelope stress does not play a significant role in acute infections of mice by C. rodentium and S Typhimurium. Cumulatively, in this work we provide a foundation for the development of novel YcbB-specific antibacterial therapeutics to assist in treatment of increasingly drug-resistant S Typhi infections.

The relationship between culturable doxycycline-resistant bacterial communities and antibiotic resistance gene hosts in pig farm wastewater treatment plants

Pig farm wastewater treatment plants (WWTPs) are an important repository for resistant bacterial communities (RBCs) and antibiotic resistance genes (ARGs). However, the relationship between RBCs and ARG hosts has not been well characterized. In this study, water samples from influent and effluent from five pig farm WWTPs were collected. Gradient concentrations of doxycycline (DOX) were used to screen the culturable RBCs. The abundance of 21 subtypes of ARGs and the bacterial community were investigated. This study detected a large number of culturable DOX-RBCs and ARGs in the influent and effluent of pig farm WWTPs. The abundances of ARGs and RBCs in all effluent samples was significantly lower than that in the influent samples (P < 0.05), which indicated that the WWTPs can effectively remove most ARGs and RBCs in pig farm wastewater. The main potential culturable RBCs in pig farm wastewater were the dominant bacteria Proteobacteria, Actinobacteria, Pseudomonas, and Rheinheimera. However, most of the ARGs were mainly present in Bacteroidetes, Actinobacteria, Corynebacteriaceae, Macellibacteroides, Acinetobacter, and Enterobacteriaceae, which are considered potential ARG hosts. The results presented here showed that there were obvious differences between the species of culturable DOX-RBCs and ARG hosts in the pig farm WWTPs, which may be due to various environmental factors. This highlights the urgent need for further research on the relationship between RBCs and ARG hosts.

Current Trends in Experimental and Computational Approaches to Combat Antimicrobial Resistance

A multitude of factors, such as drug misuse, lack of strong regulatory measures, improper sewage disposal, and low-quality medicine and medications, have been attributed to the emergence of drug resistant microbes. The emergence and outbreaks of multidrug resistance to last-line antibiotics has become quite common. This is further fueled by the slow rate of drug development and the lack of effective resistome surveillance systems. In this review, we provide insights into the recent advances made in computational approaches for the surveillance of antibiotic resistomes, as well as experimental formulation of combinatorial drugs. We explore the multiple roles of antibiotics in nature and the current status of combinatorial and adjuvant-based antibiotic treatments with nanoparticles, phytochemical, and other non-antibiotics based on synergetic effects. Furthermore, advancements in machine learning algorithms could also be applied to combat the spread of antibiotic resistance. Development of resistance to new antibiotics is quite rapid. Hence, we review the recent literature on discoveries of novel antibiotic resistant genes though shotgun and expression-based metagenomics. To decelerate the spread of antibiotic resistant genes, surveillance of the resistome is of utmost importance. Therefore, we discuss integrative applications of whole-genome sequencing and metagenomics together with machine learning models as a means for state-of-the-art surveillance of the antibiotic resistome. We further explore the interactions and negative effects between antibiotics and microbiomes upon drug administration.

Tackling Multidrug Resistance in Streptococci - From Novel Biotherapeutic Strategies to Nanomedicines

The pyogenic streptococci group includes pathogenic species for humans and other animals and has been associated with enduring morbidity and high mortality. The main reason for the treatment failure of streptococcal infections is the increased resistance to antibiotics. In recent years, infectious diseases caused by pyogenic streptococci resistant to multiple antibiotics have been raising with a significant impact to public health and veterinary industry. The rise of antibiotic-resistant streptococci has been associated to diverse mechanisms, such as efflux pumps and modifications of the antimicrobial target. Among streptococci, antibiotic resistance emerges from previously sensitive populations as result of horizontal gene transfer or chromosomal point mutations due to excessive use of antimicrobials. Streptococci strains are also recognized as biofilm producers. The increased resistance of biofilms to antibiotics among streptococci promote persistent infection, which comprise circa 80% of microbial infections in humans. Therefore, to overcome drug resistance, new strategies, including new antibacterial and antibiofilm agents, have been studied. Interestingly, the use of systems based on nanoparticles have been applied to tackle infection and reduce the emergence of drug resistance. Herein, we present a synopsis of mechanisms associated to drug resistance in (pyogenic) streptococci and discuss some innovative strategies as alternative to conventional antibiotics, such as bacteriocins, bacteriophage, and phage lysins, and metal nanoparticles. We shall provide focused discussion on the advantages and limitations of agents considering application, efficacy and safety in the context of impact to the host and evolution of bacterial resistance.

Predominance of positive epistasis among drug resistance-associated mutations in HIV-1 protease

Drug-resistant mutations often have deleterious impacts on replication fitness, posing a fitness cost that can only be overcome by compensatory mutations. However, the role of fitness cost in the evolution of drug resistance has often been overlooked in clinical studies or in vitro selection experiments, as these observations only capture the outcome of drug selection. In this study, we systematically profile the fitness landscape of resistance-associated sites in HIV-1 protease using deep mutational scanning. We construct a mutant library covering combinations of mutations at 11 sites in HIV-1 protease, all of which are associated with resistance to protease inhibitors in clinic. Using deep sequencing, we quantify the fitness of thousands of HIV-1 protease mutants after multiple cycles of replication in human T cells. Although the majority of resistance-associated mutations have deleterious effects on viral replication, we find that epistasis among resistance-associated mutations is predominantly positive. Furthermore, our fitness data are consistent with genetic interactions inferred directly from HIV sequence data of patients. Fitness valleys formed by strong positive epistasis reduce the likelihood of reversal of drug resistance mutations. Overall, our results support the view that strong compensatory effects are involved in the emergence of clinically observed resistance mutations and provide insights to understanding fitness barriers in the evolution and reversion of drug resistance.

Antimicrobial activity of polypyrrole nanoparticles and aqueous extract of Moringa oleifera against Staphylococcus spp. carriers of multi-drug efflux system genes isolated from dairy farms

Our objectives were to identify genes of the multi-drug efflux system and to evaluate the antimicrobial activities of polypyrrole nanoparticles (PPy-NPs) and aqueous extract of Moringa oleifera against Staphylococcus spp. isolated from dairy farms in Northeast Brazil. Initially, 162 Staphylococcus spp. isolates were subjected to in vitro antimicrobial sensitivity tests. Of these, 35 presented antimicrobial multi-drug resistance phenotypes. These 35 isolates were then referred for the detection of norA, norB, norC, msrA, mgrA, tet-38, and lmrS genes, all of which feature in multi-drug efflux systems. In the isolates carrying the genes, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of PPy-NPs and Moringa oleifera aqueous extract were determined. In the molecular analysis of the 35 isolates norA, norC, tet-38, and msrA genes were detected and for the other genes norB, lmrS and mgrA there was no amplification. Antimicrobial activity was verified of PPy-NPs and aqueous extract of Moringa oleifera in Staphylococcus spp. carrying multi-drug efflux system genes. We concluded that there are multi-drug efflux system genes present in the Staphylococcus spp. from the agricultural environment in Northeast Brazil, and that aqueous extract of Moringa oleifera and PPy-NPs show bactericidal activity against these isolates.

Teixobactin: A Paving Stone toward a New Class of Antibiotics?

Antimicrobial resistance is a serious threat to human health worldwide, prompting research efforts on a massive scale in search of novel antibiotics to fill an urgent need for a remedy. Teixobactin, a macrocyclic depsipeptide natural product, isolated from uncultured bacteria (Eleftheria terrae), displayed potent activity against several Gram-positive pathogenic bacteria. The distinct pharmacological profile and interesting structural features of teixobactin with nonstandard amino acid (three d-amino acids and l-allo-enduracididine) residues attracted several research groups to work on this target molecule in search of novel antibiotics with new mechanism. Herein, we present a comprehensive and critical perspective on immense possibilities offered by teixobactin in the domain of drug discovery. Efforts made by various research groups since its isolation are discussed, highlighting the molecule's considerable potential with special emphasis on replacement of amino acids. Critical analysis of synthetic efforts, SAR studies, and the way forward are provided hereunder.

Insight into Structure-Function Relationships of β-Lactamase and BLIPs Interface Plasticity using Protein-Protein Interactions

BACKGROUND

Mostly BLIPs are identified in soil bacteria Streptomyces and originally isolated from Streptomyces clavuligerus and can be utilized as a model system for biophysical, structural, mutagenic and computational studies. BLIP possess homology with two proteins viz., BLIP-I (Streptomyces exofoliatus) and BLP (beta-lactamase inhibitory protein like protein from S. clavuligerus). BLIP consists of 165 amino acid, possessing two homologues domains comprising helix-loop-helix motif packed against four stranded beta-sheet resulting into solvent exposed concave surface with extended four stranded beta-sheet. BLIP-I is a 157 amino acid long protein obtained from S. exofoliatus having 37% sequence identity to BLIP and inhibits beta-lactamase.

METHODS

This review is intended to briefly illustrate the beta-lactamase inhibitory activity of BLIP via proteinprotein interaction and aims to open up a new avenue to combat antimicrobial resistance using peptide based inhibition.

RESULTS

D49A mutation in BLIP-I results in a decrease in affinity for TEM-1 from 0.5 nM to 10 nM (Ki). It is capable of inhibiting TEM-1 and bactopenemase and differs from BLIP only in modulating cell wall synthesis enzyme. Whereas, BLP is a 154 amino acid long protein isolated from S. clavuligerus via DNA sequencing analysis of Cephamycin-Clavulanate gene bunch. It shares 32% sequence similarity with BLIP and 42% with BLIP-I. Its biological function is unclear and lacks beta-lactamase inhibitory activity.

CONCLUSION

Protein-protein interactions mediate a significant role in regulation and modulation of cellular developments and processes. Specific biological markers and geometric characteristics are manifested by active site binding clefts of protein surfaces which determines the specificity and affinity for their targets. TEM1.BLIP is a classical model to study protein-protein interaction. β-Lactamase inhibitory proteins (BLIPs) interacts and inhibits various β-lactamases with extensive range of affinities.

Fraudulent antibiotic products on the market for aquaculture use

Antibiotics in aquaculture are used to treat bacterial infections. In order for these products to work effectively fish need to be properly dosed. One of the emerging issues in aquaculture is under-dosing large populations of fish with antibiotics. This happens inadvertently for a number of reasons including the use of fraudulent medications. In this study we evaluated 17 antibiotic products (8 florfenicol and 9 oxytetracycline brands purchased in Asia) by HPLC to determine if the product labels accurately reflected the active pharmaceutical ingredient (API) in the package. We determined authenticity scores for different batches of products at two separate laboratories by comparing the observed API to the label API concentration. We found that 48 % of the antibiotic batches had authenticity scores below 80 % (i.e. observed API in package was at least 20 % less than the label API concentration). Further, there were 9 or the 31 batches of drugs tested had no measureable API. Some products had variation in their authenticity scores between batches making it difficult to rely on a brand. The price of florfenicol products may help identify products with low authenticity scores, but in the case of oxytetracycline, the price of all the products tested was relatively similar. The findings in this study suggest that not all florfenicol and oxytetracycline antibiotic products on the market in Asia have API concentrations indicated on their labels. This could be problematic for medicating fish on aquaculture farms.