Mechanisms of Antibiotic Resistance. Microbiol Spectr. 2016;4. [PMID: 27227291 DOI: 10.1128/microbiolspec.vmbf-0016-2015]

Mechanistic Understanding of the Interactions of Cationic Conjugated Oligo- and Polyelectrolytes with Wild-type and Ampicillin-resistant Escherichia coli

An in-depth understanding of cell-drug binding modes and action mechanisms can potentially guide the future design of novel drugs and antimicrobial materials and help to combat antibiotic resistance. Light-harvesting π-conjugated molecules have been demonstrated for their antimicrobial effects, but their impact on bacterial outer cell envelope needs to be studied in detail. Here, we synthesized poly(phenylene) based model cationic conjugated oligo- (2QA-CCOE, 4QA-CCOE) and polyelectrolytes (CCPE), and systematically explored their interactions with the outer cell membrane of wild-type and ampicillin (amp)-resistant Gram-negative bacteria, Escherichia coli (E. coli). Incubation of the E. coli cells in CCOE/CCPE solution inhibited the subsequent bacterial growth in LB media. About 99% growth inhibition was achieved if amp-resistant E. coli was treated for ~3-5 min, 1 h and 6 h with 100 μM of CCPE, 4QA-CCOE, and 2QA-CCOE solutions, respectively. Interestingly, these CCPE and CCOEs inhibited the growth of both wild-type and amp-resistant E. coli to a similar extent. A large surface charge reversal of bacteria upon treatment with CCPE suggested the formation of a coating of CCPE on the outer surface of bacteria; while a low reversal of bacterial surface charge suggested intercalation of CCOEs within the lipid bilayer of bacteria.

A novel mechanism of inhibition by phenylthiourea on PvdP, a tyrosinase synthesizing pyoverdine of Pseudomonas aeruginosa

The biosynthesis of pyoverdine, the major siderophore of Pseudomonas aeruginosa, is a well-organized process involving a discrete number of enzyme-catalyzed steps. The final step of this process involves the PvdP tyrosinase, which converts ferribactin into pyoverdine. Thus, inhibition of the PvdP tyrosinase activity provides an attractive strategy to interfere with siderophore synthesis to manage P. aeruginosa infections. Here, we report phenylthiourea as a non-competitive inhibitor of PvdP for which we solved a crystal structure in complex with PvdP. The crystal structure indicates that phenylthiourea binds to an allosteric binding site and thereby interferes with its tyrosinase activity. We further provide proofs that PvdP tyrosinase inhibition by phenylthiourea requires the C-terminal lid region. This provides opportunities to develop inhibitors that target the allosteric site, which seems to be confined to fluorescent pseudomonads, and not the tyrosinase active site. Furthermore, increases the chances to identify PvdP inhibitors that selectively interfere with siderophore synthesis.

Prevalence and antibiotic sensitivity of bacteria isolated from imported ornamental fish in Italy: A translocation of resistant strains?

The rapid expansion of the ornamental aquaculture industry over the past decades has resulted in a concomitant increase in the use of antibiotics to combat infectious diseases. The aim of this study was to assess the possible role of ornamental fish in the translocation of antibiotic resistant bacteria, with possible consequences for aquarium and public health. We assessed the prevalence of bacterial infections and the antibiotic resistance profile of bacteria isolated from 134 ornamental fish imported into northwest Italy during two years of monitoring. Ornamental fish analyzed were imported mainly from Singapore (40%) and Israel (20%), followed by Thailand (13%), Sri Lanka (12%), Czech Republic (7%), Vietnam (5%) and Indonesia (3%). The most commonly imported fish were freshwater species, particularly those belonging to the Poeciliidae family. Bacteriological exam was positive in 68% of the fish examined. The most frequently isolated bacterium was Aeromonas sobria (37%). Bacteria showed resistance against lincomycin, ampicillin, oxytetracycline and tetracycline. Sensitivity was found for florfenicol, chloramphenicol, gentamicin, and trimethoprim/sulfamethoxazole. Odds ratio (OR) values were calculated as a measure of the association between antibiotic resistance of A. sobria and selected factors (country of origin, fish family and fish species), considering Thailand, Poeciliidae and Poecilia reticulata as control cases. Higher values were found for Vietnam (OR 5.6) and Xiphophorus helleri and X. maculatus (OR 3.0 and 3.7 respectively). Our findings underline the need to improve targeted surveillance of antimicrobial resistance and prevent the translocation of resistant or multi-resistant bacterial strains in ornamental fish, especially in fish imported from countries where surveillance is limited or lacking.

Quantification of Airborne Resistant Organisms With Temporal and Spatial Diversity in Bangladesh: Protocol for a Cross-Sectional Study

BACKGROUND

Antimicrobial resistance is a widespread, alarming issue in global health and a significant contributor to human death and illness, especially in low and middle-income countries like Bangladesh. Despite extensive work conducted in environmental settings, there is a scarcity of knowledge about the presence of resistant organisms in the air.

OBJECTIVE

The objective of this protocol is to quantify and characterize the airborne resistomes in Bangladesh, which will be a guide to identify high-risk environments for multidrug-resistant pathogens with their spatiotemporal diversity.

METHODS

This is a cross-sectional study with an environmental, systematic, and grid sampling strategy focused on collecting air samples from different outdoor environments during the dry and wet seasons. The four environmental compartments are the frequent human exposure sites in both urban and rural settings: urban residential areas (n=20), live bird markets (n=20), rural households (n=20), and poultry farms (n=20). We obtained air samples from 80 locations in two seasons by using an active microbial air sampler. From each location, five air samples were collected in different media to yield the total bacterial count of 3rd generation cephalosporin (3GC) resistant Enterobacteriaceae, carbapenem-resistant Enterobacteriaceae, vancomycin-resistant Enterococci and methicillin-resistant Staphylococcus aureus.

RESULTS

The study started in January 2018, and the collection of air samples was completed in November 2018. We have received 800 air samples from 80 study locations in both dry and wet seasons. Currently, the laboratory analysis is ongoing, and we expect to receive the preliminary results by October 2019. We will publish the complete result as soon as we clean and analyze the data and draft the manuscript.

CONCLUSIONS

The existence of resistant bacteria in the air like those producing extended-spectrum beta-lactamases, carbapenem-resistant Enterobacteriaceae, vancomycin-resistant Enterococci, and methicillin-resistant Staphylococcus aureus will justify our hypothesis that the outdoor environment (air) in Bangladesh acts as a reservoir for bacteria that carry genes conferring resistance to antibiotics. To our knowledge, this is the first study to explore the presence of superbugs in the air in commonly exposed areas in Bangladesh.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/14574.

Synthesis and antimicrobial evaluation of new halogenated 1,3-Thiazolidin-4-ones

The ongoing prevalence of multidrug-resistant bacterial pathogens requires the development of new effective antibacterial agents. In this study, two series of halogenated 1,3-thiazolidin-4-ones were synthesized and characterized. All the synthesized thiazolidinone derivatives were evaluated for their antimicrobial activity. Biological screening of the tested compounds revealed the antibacterial activity of the chlorinated thiazolidinones 4a, 4b and 4c against Escherichia coli TolC-mutant, with MIC values of 16 µg/mL. A combination of a sub-inhibitory concentration of colistin (0.25 × MIC) with compounds 4a, 4b or 4c showed antibacterial activity against different Gram-negative bacteria (MICs = 4-16 µg/mL). Interestingly, compounds 4a, 4b and 4c were not cytotoxic to murine fibroblasts and Caco-2 cells. The chlorinated thiazolidinone derivative 16d demonstrated a bacteriostatic activity against a panel of pathogenic Gram-positive bacteria, including clinical isolates of methicillin and vancomycin-resistant Staphylococcus aureus, Listeria monocytogenes and multidrug-resistant Staphylococcus epidermidis (MICs = 8 - 64 µg/mL), with no cytotoxicity against both Caco-2 and L929 cells. Compound 16d was superior to vancomycin in disruption of the pre-formed MRSA biofilm. Furthermore, the three fluorinated thiazolidinone derivatives 26c, 30c and 33c showed a hindrance to hemolysin activity, without cytotoxicity against L929 cells.

Biofilm formation and antibiotic resistance of Klebsiella pneumoniae isolated from clinical samples in a tertiary care hospital, Klaten, Indonesia

Background

Klebsiella pneumoniae (K. pneumoniae) is a common cause of health-care associated infections (HAIs) and has high levels of antibiotic resistance. These bacteria are well-known for their ability to produce biofilm. The purpose of this study was to identify the antibiotic resistance pattern and biofilm-producing capacity of K. pneumoniae isolated from clinical samples in a tertiary care hospital in Klaten, Indonesia.

Methods

K. pneumoniae was isolated from inpatients in Soeradji Tirtonegoro Hospital Klaten from June 2017 to May 2018. Identification of K. pneumoniae isolate was done by analyzing colony morphology, microscopic examination, and by performing biochemical testing. Testing of antibiotics susceptibility and biofilm-producing capacity used the Kirby-Bauer disk diffusion method and adherence quantitative assays, respectively.

Results

A total of 167 (17.36%) K. pneumoniae isolates were isolated from 962 total clinical bacterial isolates during the study. Most of them were collected from patients aged more than 60 years old and were mainly obtained from respiratory specimens (51.50%). Most of K. pneumoniae isolates were extensively resistant to antibiotics. A more favorable profile was found only towards meropenem, amikacin, and piperacillin-tazobactam, showing 1.20%; 4.79% and 10.53% of resistance, respectively. The overall proportion of multidrug-resistant K. pneumoniae isolates was 54.49%. In addition, 148 (85.63%) isolates were biofilm producers, with 45 (26.95%) isolates as strong, 48 (28.74%) isolates as moderate, and 50 (29.94%) isolates as weak biofilm producers.

Conclusion

Most of the K. pneumoniae isolates demonstrated resistance to a wide range of antibiotics and are biofilm producers.

Effects of treatment with enrofloxacin or tulathromycin on fecal microbiota composition and genetic function of dairy calves

The increasing concerns with antimicrobial resistance highlights the need for studies evaluating the impacts of antimicrobial use in livestock on antimicrobial resistance using new sequencing technologies. Through shotgun sequencing, we investigated the changes in the fecal microbiome composition and function, with a focus on functions related to antimicrobial resistance, of dairy calves. Heifers 2 to 3 weeks old, which were not treated with antibiotics by the farm before enrollment, were randomly allocated to one of three study groups: control (no treatment), a single treatment of enrofloxacin, or a single treatment of tulathromycin. Fecal samples were collected at days 4, 14, 56 and 112 days after enrollment, and DNA extraction and sequencing was conducted. The effect of antibiotic treatment on each taxon and genetic functional level by time (including Day 0 as a covariate) revealed few changes in the microbiota. At the genus level, enrofloxacin group had higher relative abundance of Blautia, Coprococcus and Desulfovibrio and lower abundance of Bacteroides when compared to other study groups. The SEED database was used for genetic functional analyses, which showed that calves in the enrofloxacin group started with a higher relative abundance of "Resistance to antibiotics and toxic compounds" function on Day 0, however an increase in antibiotic resistance genes after treatment with enrofloxacin was not observed. "Resistance to Fluoroquinolones" and "Erythromycin resistance", of relevance given the study groups, were not statistically different in relative abundance between study groups. "Resistance to fluoroquinolones" increased during the study period regardless of study group. Despite small differences over the first weeks between study groups, at Day 112 the microbiota composition and genetic functional profile was similar among all study groups. In our study, enrofloxacin or tulathromycin had minimal impacts on the microbial composition and genetic functional microbiota of calves over the study period.

Efficacy and Mechanism of Traditional Medicinal Plants and Bioactive Compounds against Clinically Important Pathogens

Traditional medicinal plants have been cultivated to treat various human illnesses and avert numerous infectious diseases. They display an extensive range of beneficial pharmacological and health effects for humans. These plants generally synthesize a diverse range of bioactive compounds which have been established to be potent antimicrobial agents against a wide range of pathogenic organisms. Various research studies have demonstrated the antimicrobial activity of traditional plants scientifically or experimentally measured with reports on pathogenic microorganisms resistant to antimicrobials. The antimicrobial activity of medicinal plants or their bioactive compounds arising from several functional activities may be capable of inhibiting virulence factors as well as targeting microbial cells. Some bioactive compounds derived from traditional plants manifest the ability to reverse antibiotic resistance and improve synergetic action with current antibiotic agents. Therefore, the advancement of bioactive-based pharmacological agents can be an auspicious method for treating antibiotic-resistant infections. This review considers the functional and molecular roles of medicinal plants and their bioactive compounds, focusing typically on their antimicrobial activities against clinically important pathogens.

Impacts of florfenicol on the microbiota landscape and resistome as revealed by metagenomic analysis

BACKGROUND

Drug-resistant fish pathogens can cause significant economic loss to fish farmers. Since 2012, florfenicol has become an approved drug for treating both septicemia and columnaris diseases in freshwater fish. Due to the limited drug options available for aquaculture, the impact of the therapeutical florfenicol treatment on the microbiota landscape as well as the resistome present in the aquaculture farm environment needs to be evaluated.

RESULTS

Time-series metagenomic analyses were conducted to the aquatic microbiota present in the tank-based catfish production systems, in which catfish received standard therapeutic 10-day florfenicol treatment following the federal veterinary regulations. Results showed that the florfenicol treatment shifted the structure of the microbiota and reduced the biodiversity of it by acting as a strong stressor. Planctomycetes, Chloroflexi, and 13 other phyla were susceptible to the florfenicol treatment and their abundance was inhibited by the treatment. In contrast, the abundance of several bacteria belonging to the Proteobacteria, Bacteroidetes, Actinobacteria, and Verrucomicrobia phyla increased. These bacteria with increased abundance either harbor florfenicol-resistant genes (FRGs) or had beneficial mutations. The florfenicol treatment promoted the proliferation of florfenicol-resistant genes. The copy number of phenicol-specific resistance genes as well as multiple classes of antibiotic-resistant genes (ARGs) exhibited strong correlations across different genetic exchange communities (p < 0.05), indicating the horizontal transfer of florfenicol-resistant genes among these bacterial species or genera. Florfenicol treatment also induced mutation-driven resistance. Significant changes in single-nucleotide polymorphism (SNP) allele frequencies were observed in membrane transporters, genes involved in recombination, and in genes with primary functions of a resistance phenotype.

CONCLUSIONS

The therapeutical level of florfenicol treatment significantly altered the microbiome and resistome present in catfish tanks. Both intra-population and inter-population horizontal ARG transfer was observed, with the intra-population transfer being more common. The oxazolidinone/phenicol-resistant gene optrA was the most prevalent transferred ARG. In addition to horizontal gene transfer, bacteria could also acquire florfenicol resistance by regulating the innate efflux systems via mutations. The observations made by this study are of great importance for guiding the strategic use of florfenicol, thus preventing the formation, persistence, and spreading of florfenicol-resistant bacteria and resistance genes in aquaculture.

Antimicrobial resistance, virulence & plasmid profiles among clinical isolates of Shigella serogroups

Background & objectives:

Bacillary dysentery caused by Shigella spp. remains an important cause of the crisis in low-income countries. It has been observed that Shigella species have become increasingly resistant to most widely used antimicrobials. In this study, the antimicrobial resistance, virulence and plasmid profile of clinical isolates of Shigella species were determined.

Methods:

Sixty clinical Shigella isolates were subjected to whole-genome sequencing using Ion Torrent platform and the genome sequences were analyzed for the presence of acquired resistance genes, virulence genes and plasmids using web-based software tools.

Results:

Genome analysis revealed more resistance genes in Shigella flexneri than in other serogroups. Among β-lactamases, bla_OXA-1 was predominantly seen followed by the bla_TEM-1B and bla_EC genes. For quinolone resistance, the qnrS gene was widely seen. Novel mutations in gyrB, parC and parE genes were observed. Cephalosporins resistance gene, bla_CTX-M-15 was identified and plasmid-mediated AmpC β-lactamases genes were found among the isolates. Further, a co-trimoxazole resistance gene was identified in most of the isolates studied. Virulence genes such as ipaD, ipaH, virF, senB, iha, capU, lpfA, sigA, pic, sepA, celb and gad were identified. Plasmid analysis revealed that the IncFII was the most commonly seen plasmid type in the isolates.

Interpretation & conclusions:

The presence of quinolone and cephalosporin resistance genes in Shigella serogroups has serious implications for the further spread of this resistance to other enteric pathogens or commensal organisms. This suggests the need for continuous surveillance to understand the epidemiology of the resistance.

Phenazine Antibiotic-Inspired Discovery of Bacterial Biofilm-Eradicating Agents

Bacterial biofilms are surface-attached communities of slow-growing and non-replicating persister cells that demonstrate high levels of antibiotic tolerance. Biofilms occur in nearly 80 % of infections and present unique challenges to our current arsenal of antibiotic therapies, all of which were initially discovered for their abilities to target rapidly dividing, free-floating planktonic bacteria. Bacterial biofilms are credited as the underlying cause of chronic and recurring bacterial infections. Innovative approaches are required to identify new small molecules that operate through bacterial growth-independent mechanisms to effectively eradicate biofilms. One source of inspiration comes from within the lungs of young cystic fibrosis (CF) patients, who often endure persistent Staphylococcus aureus infections. As these CF patients age, Pseudomonas aeruginosa co-infects the lungs and utilizes phenazine antibiotics to eradicate the established S. aureus infection. Our group has taken a special interest in this microbial competition strategy and we are investigating the potential of phenazine antibiotic-inspired compounds and synthetic analogues thereof to eradicate persistent bacterial biofilms. To discover new biofilm-eradicating agents, we have established an interdisciplinary research program involving synthetic medicinal chemistry, microbiology and molecular biology. From these efforts, we have identified a series of halogenated phenazines (HPs) that potently eradicate bacterial biofilms, and future work aims to translate these preliminary findings into ground-breaking clinical advances for the treatment of persistent biofilm infections.

Community-acquired serious bacterial infections in the first 90 days of life: a revisit in the era of multi-drug-resistant organisms

BACKGROUND

Infants in the first 90 days of life are more prone to develop serious bacterial infections (SBIs). Multi-drug-resistant organisms (MDROs) are emerging as important pathogens causing SBIs. We reviewed the epidemiology of SBIs in infants 0-90 days old and compared the clinical features, laboratory values and final outcome for SBIs due to MDROs vs. non-MDROs.

METHODS

Episodes of culture-proven SBIs (bacteremia, urinary tract infections, or meningitis) with age at onset of 0-90 days during a 7-year period were retrospectively reviewed. Health care-associated infections were excluded. We collected demographics, clinical features, and laboratory and microbiology data. We compared clinical characteristics, laboratory data, microbiologic results and final outcome for SBIs due to MDROs vs. non-MDROs.

RESULTS

Ninety-four episodes (88 patients) including bacteremia (42.6%), urinary tract infections (54.3%) and meningitis (3.1%) were caused by Gram-negative bacteria (67%), and Gram-positive bacteria (33%). Escherichia coli, Klebsiella pneumoniae and GBS were the most common causes. MDROs caused SBIs in 39 patients (44.3%). SBIs due to MDROs were associated with more delay in providing targeted antimicrobial therapy compared to non-MDROs (74.4% vs. 0%, P ≤ 0.001), but no difference in case-fatality rate (12.8% vs. 12.2%, P = 1.0). Clinical features or basic laboratory values were not statistically different between the two groups.

CONCLUSIONS

The bacteriology of SBIs in the first 90 days of life is changing to include more MDROs, which causes more delay in providing targeted antimicrobial therapy. Awareness of the local epidemiology is crucial to ensure appropriate antibiotics are provided in a timely manner.

Dual and selective inhibitors of pteridine reductase 1 (PTR1) and dihydrofolate reductase-thymidylate synthase (DHFR-TS) from Leishmania chagasi

Leishmaniasis is a tropical disease found in more than 90 countries. The drugs available to treat this disease have nonspecific action and high toxicity. In order to develop novel therapeutic alternatives to fight this ailment, pteridine reductase 1 (PTR1) and dihydrofolate reductase-thymidylate synthase (DHF-TS) have been targeted, once Leishmania is auxotrophic for folates. Although PTR1 and DHFR-TS from other protozoan parasites have been studied, their homologs in Leishmania chagasi have been poorly characterized. Hence, this work describes the optimal conditions to express the recombinant LcPTR1 and LcDHFR-TS enzymes, as well as balanced assay conditions for screening. Last but not the least, we show that 2,4 diaminopyrimidine derivatives are low-micromolar competitive inhibitors of both enzymes (LcPTR1 Ki = 1.50-2.30 µM and LcDHFR Ki = 0.28-3.00 µM) with poor selectivity index. On the other hand, compound 5 (2,4-diaminoquinazoline derivative) is a selective LcPTR1 inhibitor (Ki = 0.47 µM, selectivity index = 20).

Nanoluciferase-Based Method for Detecting Gene Expression in Caenorhabditis elegans

Genetic reporters such as the green fluorescent protein (GFP) can facilitate measurement of promoter activity and gene expression. However, animal autofluorescence limits the sensitivity of GFP and other fluorescent reporters in whole-animal settings like in the nematode Caenorhabditis elegans Here, we present a highly sensitive Nanoluciferase (NanoLuc)-based method in a multiwell format to detect constitutive and inducible gene expression in C. elegans We optimize detection of bioluminescent signals from NanoLuc in C. elegans and show that it can be detected at 400,000-fold over background in a population of 100 animals expressing intestinal NanoLuc driven by the vha-6 promoter. We can reliably detect signal in single vha-6p::Nanoluc-expressing worms from all developmental stages. Furthermore, we can detect signal from a 1/100 dilution of lysate from a single vha-6p::Nanoluc-expressing adult and from a single vha-6p::Nanoluc-expressing adult "hidden" in a pool of 5000 N2 wild-type animals. We also optimize various steps of this protocol, which involves a lysis step that can be performed in minutes. As a proof-of-concept, we used NanoLuc to monitor the promoter activity of the pals-5 stress/immune reporter and were able to measure 300- and 50-fold increased NanoLuc activity after proteasome blockade and infection with microsporidia, respectively. Altogether, these results indicate that NanoLuc provides a highly sensitive genetic reporter for rapidly monitoring whole-animal gene expression in C. elegans.

Topical (local) antibiotics for respiratory infections with sore throat: An antibiotic stewardship perspective

WHAT IS KNOWN AND OBJECTIVE

The overuse and misuse of antibiotics, especially for viral, and self-limiting, respiratory tract infections such as sore throat, increases the risk of the development and spread of antimicrobial resistance within communities. Up to 80% of sore throat cases have a viral aetiology, and even when the infection is bacterial, most cases resolve without antibiotics. However, antibiotics are still frequently and often inappropriately prescribed for the treatment of sore throat. Furthermore, topical (local) antibiotics for treatment of sore throat are widely available over the counter. The objective of this systematic review was to establish the evidence for the benefits, risk of harm and antimicrobial resistance associated with topical (local) antibiotics used for patients with sore throat.

METHODS

Eligible studies included those in patients with sore throat of any aetiology receiving the topical (local) antibiotics tyrothricin, bacitracin, gramicidin or neomycin where the antibiotic was topically/locally applied via the nasal cavity or throat. Nasal applications were included as these are occasionally used to treat upper respiratory tract infections that may involve sore throat. There was no restriction or requirement regarding comparator. The outcomes of interest included efficacy, safety, and in vitro culture and antimicrobial resistance data.

RESULTS AND DISCUSSION

This systematic review found sparse and mainly poor-quality evidence relating to the use of topical (local) antibiotics for sore throat, and it was not possible to establish the benefits, risk of harm or impact of use on antimicrobial resistance.

WHAT IS NEW AND CONCLUSIONS

Further research is necessary to ascertain the risks and benefits of topical (local) antibiotics, their contribution to antimicrobial resistance and the risk of harm. We do, however, question whether it is appropriate and rational to use topical (local) antibiotics for the treatment of sore throat caused by respiratory tract infections in the absence of robust evidence.

Bacterial Biofilm Eradication Agents: A Current Review

Most free-living bacteria can attach to surfaces and aggregate to grow into multicellular communities encased in extracellular polymeric substances called biofilms. Biofilms are recalcitrant to antibiotic therapy and a major cause of persistent and recurrent infections by clinically important pathogens worldwide (e.g., Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus). Currently, most biofilm remediation strategies involve the development of biofilm-inhibition agents, aimed at preventing the early stages of biofilm formation, or biofilm-dispersal agents, aimed at disrupting the biofilm cell community. While both strategies offer some clinical promise, neither represents a direct treatment and eradication strategy for established biofilms. Consequently, the discovery and development of biofilm eradication agents as comprehensive, stand-alone biofilm treatment options has become a fundamental area of research. Here we review our current understanding of biofilm antibiotic tolerance mechanisms and provide an overview of biofilm remediation strategies, focusing primarily on the most promising biofilm eradication agents and approaches. Many of these offer exciting prospects for the future of biofilm therapeutics for a large number of infections that are currently refractory to conventional antibiotics.

Antimicrobial Activity of Silver Containing Crosslinked Poly(Acrylic Acid) Fibers

Bacterial and fungal pathogens have caused serious problems to the human health. This is particularly true for untreatable infectious diseases and clinical situations where there is no reliable treatment for infected patients. To increase the antimicrobial activity of materials, we introduce silver nanoparticle (NP) patches in which the NPs are incorporated to the surface of smooth and uniform poly(acrylic acid) (PAA) nanofibers. The PAA nanofibers were thermally crosslinked with ethylene glycol via heat treatment through a mild method. The characterization of the resulting PAA-silver NP patches was done using scanning electron microscopy (SEM), UV spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). To demonstrate the antimicrobial activity of PAA, we incorporated the patches containing the silver NPs into strains of fungi such as Candida albicans (C. albican) and bacteria such as Methicillin-resistant Staphylococcus aureus (MRSA). The PAA-silver fibers achieved zones of inhibition against C. albicans and MRSA indicating their antimicrobial activity against both fungi and bacteria. We conclude that silver NP patches exhibited multiple inhibitory actions for the interruption and blockage of activity fungal and bacterial strains, which has the potential as an antimicrobial agent in infectious diseases. Moreover, the proposed material has the potential to be used in antimicrobial textile fabrics, food packaging films, and wound dressings.

Animal Models of Type III Secretion System-Mediated Pathogenesis

The type III secretion system (T3SS) is a conserved virulence factor used by many Gram-negative pathogenic bacteria and has become an important target for anti-virulence drugs. Most T3SS inhibitors to date have been discovered using in vitro screening assays. Pharmacokinetics and other important characteristics of pharmaceuticals cannot be determined with in vitro assays alone. In vivo assays are required to study pathogens in their natural environment and are an important step in the development of new drugs and vaccines. Animal models are also required to understand whether T3SS inhibition will enable the host to clear the infection. This review covers selected animal models (mouse, rat, guinea pig, rabbit, cat, dog, pig, cattle, primates, chicken, zebrafish, nematode, wax moth, flea, fly, and amoeba), where T3SS activity and infectivity have been studied in relation to specific pathogens (Escherichia coli, Salmonella spp., Pseudomonas spp., Shigella spp., Bordetella spp., Vibrio spp., Chlamydia spp., and Yersinia spp.). These assays may be appropriate for those researching T3SS inhibition.

Antimicrobial Resistance and Resistance Determinant Insights into Multi-Drug Resistant Gram-Negative Bacteria Isolates from Paediatric Patients in China

Introduction

The emergence of multi-drug-resistant Gram-negative bacteria (GNB) is a concern in China and globally. This study investigated antimicrobial resistance traits and resistance determinant detection in GNB isolates from paediatric patients in China.

Methods

In the present study, a total of 170 isolates of GNB including the most prevalent Escherichia coli, Klebsiella pneumoniae and Acinetobacter baumannii were collected from Shenzhen Children’s Hospital, China. ESBLs production was confirmed by using the combination disc diffusion method, and carbapenemase production was confirmed by using a carbapenem inactivation method followed by antimicrobial susceptibility. In addition, β-lactamase-encoding genes and co-existence of plasmid-borne colistin resistance mcr-1 gene were determined by PCR and sequencing.

Results

Overall, 170 etiological agents (GNB) were recovered from 158 paediatric patients. The most prevalent species was E. coli 40% (n=68), followed by K. pneumoniae 17.64% (n=30), and Enterobacter cloacae 14.11% (n=24). Of 170 GNB, 71.76% (n=122) were multi-drug-resistant, 12.35% (n=21) extreme-drug resistant, and 7.64% (n=13) single-drug-resistant, while 8.23% (n=14) were sensitive to all of the studied antibiotics. The prevalence of ESBLs and carbapenemase producers were 60% and 17%, respectively. bla_CTX-M was the most prevalent resistance gene (59.42%), followed by bla_TEM (41.17%), bla_SHV (34.270%), bla_KPC (34.11%), bla_OXA-48 (18.82%) and bla_NDM-1 (17.64%).

Conclusion

The present study provides insights into the linkage between the resistance patterns of GNB to commonly used antibiotics and their uses in China. The findings are useful for understanding the genetics of resistance traits and difficulty in tackling of GNB in paediatric patients.

Effectiveness of Efflux Pump Inhibitors as Biofilm Disruptors and Resistance Breakers in Gram-Negative (ESKAPEE) Bacteria

Antibiotic resistance represents a significant threat to the modern healthcare provision. The ESKAPEE pathogens (Enterococcus faecium., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp. and Escherichia coli), in particular, have proven to be especially challenging to treat, due to their intrinsic and acquired ability to rapidly develop resistance mechanisms in response to environmental threats. The development of biofilm has been characterised as an essential contributing factor towards antimicrobial-resistance and tolerance. Several studies have implicated the involvement of efflux pumps in antibiotic resistance, both directly, via drug extrusion and indirectly, through the formation of biofilm. As a result, the underlying mechanism of these pumps has attracted considerable interest due to the potential of targeting these protein structures and developing novel adjunct therapies. Subsequent investigations have revealed the ability of efflux pump-inhibitors (EPIs) to block drug-extrusion and disrupt biofilm formation, thereby, potentiating antibiotics and reversing resistance of pathogen towards them. This review will discuss the potential of EPIs as a possible solution to antimicrobial resistance, examining different challenges to the design of these compounds, with an emphasis on Gram-negative ESKAPEE pathogens.

Antimicrobial pharmaceuticals in the aquatic environment - occurrence and environmental implications

The environmental occurrence of antimicrobial pharmaceuticals and antibiotic resistant bacteria and antibiotic resistant genes has become a global phenomenon and a multifaceted threat. Integrated actions of many parties are needed to prevent further aggravation of the problem. Well-directed actions require clear understanding of the problem, which can be ensured by frequent revaluation of the existing knowledge and disseminating it among relevant audiences. The goal of this review paper is to discuss the occurrence and abundance of antimicrobial pharmaceuticals in the aquatic environment in context of adverse effects caused directly by these substances and the threat associated with the antibiotics resistance phenomenon. Several classes of antimicrobial pharmaceuticals (aminoglycosides, β-lactams, glycopeptides, macrolides, fluoroquinolones, sulfonamides and trimethoprim, tetracyclines) have been selected to illustrate their sources, environmental abundance, degradation routes (transformation products) and environmental implications including their ecotoxic effect and the spread of antibiotic resistance within the compartments of the aquatic environment and wastewater treatment plants. Wastewater treatment plants are indeed the main source responsible for the prevalence of these factors in the aquatic environment, since predominantly the plants have not been designed to retain antimicrobial pharmaceuticals. In order to limit the prevalence of these impurities into the environment, better source control is recommended as well as the establishment of stricter environmental quality standards. Counteracting all the above-mentioned threats requires to undertake integrated activities based on cooperation of professionals and scientists from various fields of science or industry, such as environmental sciences, medicine, veterinary, pharmacology, chemical engineering and others.

Antimicrobial peptides: new hope in the war against multidrug resistance

The discovery of antibiotics marked a golden age in the revolution of human medicine. However, decades later, bacterial infections remain a global healthcare threat, and a return to the pre-antibiotic era seems inevitable if stringent measures are not adopted to curb the rapid emergence and spread of multidrug resistance and the indiscriminate use of antibiotics. In hospital settings, multidrug resistant (MDR) pathogens, including carbapenem-resistant Pseudomonas aeruginosa, vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and extended-spectrum β-lactamases (ESBL) bearing Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae are amongst the most problematic due to the paucity of treatment options, increased hospital stay, and exorbitant medical costs. Antimicrobial peptides (AMPs) provide an excellent potential strategy for combating these threats. Compared to empirical antibiotics, they show low tendency to select for resistance, rapid killing action, broad-spectrum activity, and extraordinary clinical efficacy against several MDR strains. Therefore, this review highlights multidrug resistance among nosocomial bacterial pathogens and its implications and reiterates the importance of AMPs as next-generation antibiotics for combating MDR superbugs.

Development of novel nanoantibiotics using an outer membrane vesicle-based drug efflux mechanism

Conventionally used antibiotics are present in low concentrations at the infection site and require multiple administrations to sustain a continuous bactericidal effect, which not only increases their systemic toxicity but also results in bacterial drug resistance. In this study, we first identified an interesting drug resistance mechanism mediated by bacterial outer membrane vesicles (OMVs) and then designed novel antibiotic-loaded OMVs using this mechanism. We show that these antibiotic-loaded OMVs can effectively enter and kill pathogenic bacteria in vitro. In a mouse model of intestinal bacterial infection, one low-dose oral administration of antibiotic-loaded OMVs showed that the drug was retained in the intestine for 36 h, and no systemic spread was detected 12 h after drug administration. The antibiotic-loaded OMVs significantly reduced the bacterial load in the small intestine and feces of infected mice. Safety experiments confirmed that the antibiotic-loaded OMVs had excellent biocompatibility. This study extends the application range of OMVs and provides new ideas for the development of antibacterial drugs.

PA. Review of Antibiotic Resistance, Ecology, Dissemination, and Mitigation in U.S. Broiler Poultry Systems

Since the onset of land application of poultry litter, transportation of microorganisms, antibiotics, and disinfectants to new locations has occurred. While some studies provide evidence that antimicrobial resistance (AMR), an evolutionary phenomenon, could be influenced by animal production systems, other research suggests AMR originates in the environment from non-anthropogenic sources. In addition, AMR impacts the effective prevention and treatment of poultry illnesses and is increasingly a threat to global public health. Therefore, there is a need to understand the dissemination of AMR genes to the environment, particularly those directly relevant to animal health using the One Health Approach. This review focuses on the potential movement of resistance genes to the soil via land application of poultry litter. Additionally, we highlight impacts of AMR on microbial ecology and explore hypotheses explaining gene movement pathways from U.S. broiler operations to the environment. Current approaches for decreasing antibiotic use in U.S. poultry operations are also described in this review.

Betaproteobacteria are predominant in drinking water: are there reasons for concern?

Betaproteobacteria include some of the most abundant and ubiquitous bacterial genera that can be found in drinking water, including mineral water. The combination of physiology and ecology traits place some Betaproteobacteria in the list of potential, yet sometimes neglected, opportunistic pathogens that can be transmitted by water or aqueous solutions. Indeed, some drinking water Betaproteobacteria with intrinsic and sometimes acquired antibiotic resistance, harbouring virulence factors and often found in biofilm structures, can persist after water disinfection and reach the consumer. This literature review summarises and discusses the current knowledge about the occurrence and implications of Betaproteobacteria in drinking water. Although the sparse knowledge on the ecology and physiology of Betaproteobacteria thriving in tap or bottled natural mineral/spring drinking water (DW) is an evidence of this review, it is demonstrated that DW holds a high diversity of Betaproteobacteria, whose presence may not be innocuous. Frequently belonging to genera also found in humans, DW Betaproteobacteria are ubiquitous in different habitats, have the potential to resist antibiotics either due to intrinsic or acquired mechanisms, and hold different virulence factors. The combination of these factors places DW Betaproteobacteria in the list of candidates of emerging opportunistic pathogens. Improved bacterial identification of clinical isolates associated with opportunistic infections and additional genomic and physiological studies may contribute to elucidate the potential impact of these bacteria.

Antibiotic resistance in Vibrio cholerae El Tor strains isolated during cholera complications in Siberia and the Far East of Russia

Currently, the spread of antimicrobial resistance (AMR) is a global trend and poses a severe threat to public health. The causative agent of cholera, a severe infectious disease with pandemic expansion, becomes more and more resistant to a wider range of drugs with every coming year. The Vibrio cholerae genome is highly flexible and adaptive; the acquisition of the SXT mobile element with a cluster of antibiotic resistance genes on it has marked a new stage in the adaptive evolution of the pathogen. The territory of Siberia and the Russian Far East is free of cholera; however, in the 1970s and 1990s a number of infection importation cases and acute outbreaks associated with the cholera importation were reported. The aim of this study was to describe the phenotypic characteristics and genetic determinants of AMR in V. cholerae strains isolated during epidemic complications in Siberia and the Far East of Russia, as well as to clarify the origin of the strains. The present research comprises analysis of nine V. cholerae El Tor strains isolated from patients and water sources during epidemic complications in Siberia and the Russian Far East in the 1990s. Here, we compared the phenotypic manifestations of antibiotic resistance among strains, harbored the resistance patterns in genomes; we also determined the structure, the type of SXT elements, and the mobilome profile based on the accepted classification. We identified that strains that caused outbreaks in Vladivostok and Yuzhno-Sakhalinsk in 1999 had ICEVchCHN4210 type SXT element with deletion of some loci. The research shows that the integration of the genome, SNP and the mobilome, associated with antibiotic resistance, analyses is necessary to understand the cholera epidemiology, it also helps to establish the origin of strains. The study of resistance determinants features allowed to make a conclusion about the heterogeneity of V. cholerae strains that were isolated during outbreaks in Vladivostok and Yuzhno-Sakhalinsk in 1999.

Peptide Mix from Olivancillaria hiatula Interferes with Cell-to-Cell Communication in Pseudomonas aeruginosa

Bacteria in biofilms are encased in an extracellular polymeric matrix that limits exposure of microbial cells to lethal doses of antimicrobial agents, leading to resistance. In Pseudomonas aeruginosa, biofilm formation is regulated by cell-to-cell communication, called quorum sensing. Quorum sensing facilitates a variety of bacterial physiological functions such as swarming motility and protease, pyoverdine, and pyocyanin productions. Peptide mix from the marine mollusc, Olivancillaria hiatula, has been studied for its antibiofilm activity against Pseudomonas aeruginosa. Microscopy and microtiter plate-based assays were used to evaluate biofilm inhibitory activities. Effect of the peptide mix on quorum sensing-mediated processes was also evaluated. Peptide mix proved to be a good antibiofilm agent, requiring less than 39 μg/mL to inhibit 50% biofilm formation. Micrographs obtained confirmed biofilm inhibition at 1/2 MIC whereas 2.5 mg/mL was required to degrade preformed biofilm. There was a marked attenuation in quorum sensing-mediated phenotypes as well. At 1/2 MIC of peptide, the expression of pyocyanin, pyoverdine, and protease was inhibited by 60%, 72%, and 54%, respectively. Additionally, swarming motility was repressed by peptide in a dose-dependent manner. These results suggest that the peptide mix from Olivancillaria hiatula probably inhibits biofilm formation by interfering with cell-to-cell communication in Pseudomonas aeruginosa.

Improved Resistance Prediction in Mycobacterium tuberculosis by Better Handling of Insertions and Deletions, Premature Stop Codons, and Filtering of Non-informative Sites

Resistance in Mycobacterium tuberculosis is a major obstacle for effective treatment of tuberculosis. Multiple studies have shown promising results for predicting drug resistance in M. tuberculosis based on whole genome sequencing (WGS) data, however, these tools are often limited to this single species. We have previously developed a common platform for resistance prediction in multiple species. This platform detects acquired resistance genes (ResFinder) and species-specific chromosomal mutations (PointFinder) associated with resistance, all based on WGS data. In this study, we present a new version of PointFinder together with an updated M. tuberculosis database. PointFinder now includes predictions based on insertions and deletions, and it explicitly reports frameshift mutations and premature stop codons. We found that premature stop codons in four resistance-associated genes (katG, ethA, pncA, and gidB) were over-represented in resistant strains, and we saw an increased prediction performance when including premature stop codons in these genes as resistance markers. Different M. tuberculosis resistance prediction tools vary in performance mostly due to the mutation library used. We found that a well-established mutation library included non-predictive linage markers, and through forward feature selection we eliminated those from the mutation library. Compared to other similar web-based tools, PointFinder performs equally good. The advantages of PointFinder is that together with ResFinder it serves as a common web-based and downloadable platform for resistance detection in multiple species. It is easy to use for clinicians and already widely used in the research community.

Structure of Pseudomonas aeruginosa ribosomes from an aminoglycoside-resistant clinical isolate

Resistance to antibiotics has become a major threat to modern medicine. The ribosome plays a fundamental role in cell vitality by the translation of the genetic code into proteins; hence, it is a major target for clinically useful antibiotics. We report here the cryo-electron microscopy structures of the ribosome of a pathogenic aminoglycoside (AG)-resistant Pseudomonas aeruginosa strain, as well as of a nonresistance strain isolated from a cystic fibrosis patient. The structural studies disclosed defective ribosome complex formation due to a conformational change of rRNA helix H69, an essential intersubunit bridge, and a secondary binding site of the AGs. In addition, a stable conformation of nucleotides A1486 and A1487, pointing into helix h44, is created compared to a non-AG-bound ribosome. We suggest that altering the conformations of ribosomal protein uL6 and rRNA helix H69, which interact with initiation-factor IF2, interferes with proper protein synthesis initiation.

Recent updates on drug resistance in Mycobacterium tuberculosis

Tuberculosis (TB) along with acquired immune deficiency syndrome and malaria rank among the top three fatal infectious diseases which pose threat to global public health, especially in middle and low income countries. TB caused by Mycobacterium tuberculosis (Mtb) is an airborne infectious disease and one-third of the world's population gets infected with TB leading to nearly 1·6 million deaths annually. TB drugs are administered in different combinations of four first-line drugs (rifampicin, isoniazid, pyrazinamide and ethambutol) which form the core of treatment regimens in the initial treatment phase of 6-9 months. Several reasons account for the failure of TB therapy such as (i) late diagnosis, (ii) lack of timely and proper administration of effective drugs, (iii) lower availability of less toxic, inexpensive and effective drugs, (iv) long treatment duration, (v) nonadherence to drug regimen and (vi) evolution of drug-resistant TB strains. Drug-resistant TB poses a significant challenge to TB therapy and control programs. In the background of worldwide emergence of 558 000 new TB cases with resistance to rifampicin in the year 2017 and of them, 82% becoming multidrug-resistant TB (MDR-TB), it is essential to continuously update the knowledge on the mechanisms and molecular basis for evolution of Mtb drug resistance. This narrative and traditional review summarizes the progress on the anti-tubercular agents, their mode of action and drug resistance mechanisms in Mtb. The aim of this review is to provide recent updates on drug resistance mechanisms, newly developed/repurposed anti-TB agents in pipeline and international recommendations to manage MDR-TB. It is based on recent literature and WHO guidelines and aims to facilitate better understanding of drug resistance for effective TB therapy and clinical management.

Detection of Pan drug resistance OXA-48 producing Providencia in an ICU patient for the first time in Nepal

Background

Resistance to antimicrobial agents of pathogenic bacteria has become a major problem in routine medical practices. Carbapenem resistance has long been increasing. The production of carbapenem- hydrolysing β-lactamases (carbapenamases), which include NDM, KPC, OXA-48, IMP-1 and VIM is the most common mechanism.

Case presentation

A 56 years old male presented with fever and mental changes with progressively decreasing sensorium for the last 3 days. He was admitted to Intensive care unit (ICU) with a diagnosis of meningoencephalitis. On day seven, he developed ventilator associated pneumonia due Klebsiella pnemoniae and Acinetobacter baumannii. He was on meropenem, but the isolates were susceptible to colistin, tigecyclin and amikacin solely. Hence, amikacin was started with addition of intravenous and nebulized colistin. Subsequently, vital signs improved with resolution of fever. However, on day 18, he developed fever once again with a drop in blood pressure. Inotropic support was maintained, and echinocandins and tigecycline were added to the regimen.

Repeat blood and urine culture grew Providencia species, which were resistant to most of the drugs on phenotypic Kirby-Bauer disk diffusion method and are intrinsically resistant to colistin and tigecycline. Phenotypic detection of ESBL (combined disk method), MBL, KPCs, AmpC and co-producer were tested according to updated CLSI guideline and all were negative. But the Modified Hodges test was found to be positive. Consequenty, OXA-48 drug resistance pattern was brought into action by blank disc method according to A Tsakris et al., which revealed indentation of growth toward both EDTA and EDTA/PBA disk indicating production of OXA-48 carbapenamase. To confirm the resistance pattern we processed the isolated colonies for Xpert Carba-R (Cepheid) assay, which detected blaOXA-48 gene and confirmed the OXA-48 drug resistance pattern. Hence, the infecting organism was not susceptible to any of the antibiotics. The patient was kept under isolation and on 31th day of admission, he died of septic shock.

Conclusions

Carbapenamase production along with intrinsic colistin resistance in infecting bacterial pathogens can cause fatal outcomes in the resource limited countries like Nepal where new antibiotic combinations ceftazidime+ Avibactam, or aztreonam +avibactam are not available. Drug resistance patterns including OXA 48 producer should be characterized in all cases by standard phenotypic methods or by Xpert Carba-R assay and larger studies are required to know the exact burden of OXA 48 producer in Nepal.

Comparative genomic analyses reveal diverse virulence factors and antimicrobial resistance mechanisms in clinical Elizabethkingia meningoseptica strains

Three human clinical isolates of bacteria (designated strains Em1, Em2 and Em3) had high average nucleotide identity (ANI) to Elizabethkingia meningoseptica. Their genome sizes (3.89, 4.04 and 4.04 Mb) were comparable to those of other Elizabethkingia species and strains, and exhibited open pan-genome characteristics, with two strains being nearly identical and the third divergent. These strains were susceptible only to trimethoprim/sulfamethoxazole and ciprofloxacin amongst 16 antibiotics in minimum inhibitory tests. The resistome exhibited a high diversity of resistance genes, including 5 different lactamase- and 18 efflux protein- encoding genes. Forty-four genes encoding virulence factors were conserved among the strains. Sialic acid transporters and curli synthesis genes were well conserved in E. meningoseptica but absent in E. anophelis and E. miricola. E. meningoseptica carried several genes contributing to biofilm formation. 58 glycoside hydrolases (GH) and 25 putative polysaccharide utilization loci (PULs) were found. The strains carried numerous genes encoding two-component system proteins (56), transcription factor proteins (187~191), and DNA-binding proteins (6~7). Several prophages and CRISPR/Cas elements were uniquely present in the genomes.

A small-molecule inhibitor of BamA impervious to efflux and the outer membrane permeability barrier

The development of new antimicrobial drugs is a priority to combat the increasing spread of multidrug-resistant bacteria. This development is especially problematic in gram-negative bacteria due to the outer membrane (OM) permeability barrier and multidrug efflux pumps. Therefore, we screened for compounds that target essential, nonredundant, surface-exposed processes in gram-negative bacteria. We identified a compound, MRL-494, that inhibits assembly of OM proteins (OMPs) by the β-barrel assembly machine (BAM complex). The BAM complex contains one essential surface-exposed protein, BamA. We constructed a bamA mutagenesis library, screened for resistance to MRL-494, and identified the mutation bamA _E470K BamA^E470K restores OMP biogenesis in the presence of MRL-494. The mutant protein has both altered conformation and activity, suggesting it could either inhibit MRL-494 binding or allow BamA to function in the presence of MRL-494. By cellular thermal shift assay (CETSA), we determined that MRL-494 stabilizes BamA and BamA^E470K from thermally induced aggregation, indicating direct or proximal binding to both BamA and BamA^E470K Thus, it is the altered activity of BamA^E470K responsible for resistance to MRL-494. Strikingly, MRL-494 possesses a second mechanism of action that kills gram-positive organisms. In microbes lacking an OM, MRL-494 lethally disrupts the cytoplasmic membrane. We suggest that the compound cannot disrupt the cytoplasmic membrane of gram-negative bacteria because it cannot penetrate the OM. Instead, MRL-494 inhibits OMP biogenesis from outside the OM by targeting BamA. The identification of a small molecule that inhibits OMP biogenesis at the cell surface represents a distinct class of antibacterial agents.

Improved Intestinal Mucus Permeation of Vancomycin via Incorporation Into Nanocarrier Containing Papain-Palmitate

The aim of this study was to improve intestinal mucus permeation of a peptide antibiotic via incorporation into papain-palmitate-modified self-emulsifying drug delivery systems (SEDDS) as nanocarrier. Vancomycin as a peptide antibiotic was lipidized by hydrophobic ion pair formation using sodium bis-2-ethylhexyl-sulphosuccinate before incorporation in SEDDS comprising Capmul MCM, propylenglycol, and Kolliphor EL (2:1:2). As mucolytic agent, 0.5% papain-palmitate was introduced in SEDDS formulation containing the vancomycin-sodium bis-2-ethylhexyl-sulphosuccinate ion pair. The formulation was evaluated regarding droplet size, zeta potential, and cytotoxicity using Caco-2 cells previous to intestinal mucus permeation studies using Transwell diffusion and rotating tube method. The hydrophobic ion pair product yielded from surfactant to drug ratio of 3:1 provided a 25-fold increase in lipophilicity, drug payload in SEDDS of 5%, and log D_{SEDDS/release medium} of 2.2. The formulation exhibited a droplet size and zeta potential of 221.5 ± 14.8 nm and -4.2 ± 0.8 mV, respectively. Cytotoxicity study showed that SEDDS formulations were not toxic. Introducing 0.5% papain-palmitate increased the mucus permeability of SEDDS 2.8-fold and 3.3-fold in Transwell diffusion and rotating tube studies, respectively. According to these results, papain decorated SEDDS might be a potential strategy to improve the mucus permeating properties of peptide antibiotics.

Biosynthesis of Fe3O4@Ag Nanocomposite and Evaluation of Its Performance on Expression of norA and norB Efflux Pump Genes in Ciprofloxacin-Resistant Staphylococcus aureus

At present, the universal health problem with Staphylococcus aureus is the emergence of multidrug-resistant strains due to the overuse of antibiotics. Drug extrusion through efflux pumps is one of the bacterial mechanisms to neutralize the bactericidal effect of antibiotics. The antibacterial activity of silver nanoparticle as well as Fe₃O₄ nanoparticle had been previously studied and widely described. Today, the development of green methods for nanomaterial synthesis is an important aspect of research in the field of nanotechnology. Here, we report the biosynthesis and characterization of Fe₃O₄@Ag nanocomposite by Spirulina platensis cyanobacterium and it impacts on the expression of efflux pump genes in ciprofloxacin-resistant S. aureus (CRSA). The physical properties of biosynthesized nanocomposite measured and confirmed by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning and transmission electron microscopy. The minimum inhibitory concentration (MIC) of ciprofloxacin in CRSA strains was determined in the presence of Fe₃O₄@Ag nanoparticles by broth microdilution method. The effect of Fe₃O₄@Ag nanocomposite on the expression of norA and norB genes was evaluated by real-time PCR. The physical analysis confirmed well-dispersed, highly stable, and mostly spherical Fe₃O₄/Ag NPs with the average size of 30-68 nm. The results of antibacterial tests showed the synergistic effects of nanocomposite and antibiotics in MIC reduction. Additionally, in the presence of Fe₃O₄@Ag nanocomposite, the expression of norA and norB genes was decreased more than twofold compared to control. In conclusion, the Fe₃O₄/Ag nanocomposite can use as an effective inhibitor of antibiotic resistance in medicine.

Genetic Variability of the AcrAB-TolC Multidrug Efflux Pump Underlies SkQ1 Resistance in Gram-Negative Bacteria

SkQ1, a novel antibiotic targeting bacterial bioenergetics, is highly effective against both gram-positive and gram-negative bacteria. However, some gram-negative bacteria, such as Escherichia coli and Klebsiella pneumoniae, are highly resistant to it. In different gram-negative bacteria, this resistance is associated with the identity of their AcrB transporter protein sequence with the sequence of the AcrB protein from E. coli. SkQ1 is expelled from E. coli cells by the AcrAB-TolC multidrug efflux pump. In this study, we demonstrate that SkQ1 resistance in E. coli, in contrast to chloramphenicol resistance, does not depend on the presence of the multidrug efflux pump accessory protein AcrZ.

Genome Mining and Comparative Pathogenomic Analysis of An Endemic Methicillin-Resistant Staphylococcus Aureus (MRSA) Clone, ST612-CC8-t1257-SCCmec_IVd(2B), Isolated in South Africa

This study undertook genome mining and comparative genomics to gain genetic insights into the dominance of the methicillin-resistant Staphylococcus aureus (MRSA) endemic clone ST612-CC8-t1257-SCCmec_IVd(2B), obtained from the poultry food chain in South Africa. Functional annotation of the genome revealed a vast array of similar central metabolic, cellular and biochemical networks within the endemic clone crucial for its survival in the microbial community. In-silico analysis of the clone revealed the possession of uniform defense systems, restriction-modification system (type I and IV), accessory gene regulator (type I), arginine catabolic mobile element (type II), and type 1 clustered, regularly interspaced, short palindromic repeat (CRISPR)Cas array (N = 7 ± 1), which offer protection against exogenous attacks. The estimated pathogenic potential predicted a higher probability (average Pscore ≈ 0.927) of the clone being pathogenic to its host. The clone carried a battery of putative virulence determinants whose expression are critical for establishing infection. However, there was a slight difference in their possession of adherence factors (biofilm operon system) and toxins (hemolysins and enterotoxins). Further analysis revealed a conserved environmental tolerance and persistence mechanisms related to stress (oxidative and osmotic), heat shock, sporulation, bacteriocins, and detoxification, which enable it to withstand lethal threats and contribute to its success in diverse ecological niches. Phylogenomic analysis with close sister lineages revealed that the clone was closely related to the MRSA isolate SHV713 from Australia. The results of this bioinformatic analysis provide valuable insights into the biology of this endemic clone.

Watching DNA Replication Inhibitors in Action: Exploiting Time-Lapse Microfluidic Microscopy as a Tool for Target-Drug Interaction Studies in Mycobacterium

Spreading resistance to antibiotics and the emergence of multidrug-resistant strains have become frequent in many bacterial species, including mycobacteria, which are the causative agents of severe diseases and which have profound impacts on global health. Here, we used a system of microfluidics, fluorescence microscopy, and target-tagged fluorescent reporter strains of Mycobacterium smegmatis to perform real-time monitoring of replisome and chromosome dynamics following the addition of replication-altering drugs (novobiocin, nalidixic acid, and griselimycin) at the single-cell level. We found that novobiocin stalled replication forks and caused relaxation of the nucleoid and that nalidixic acid triggered rapid replisome collapse and compaction of the nucleoid, while griselimycin caused replisome instability, with the subsequent overinitiation of chromosome replication and overrelaxation of the nucleoid. In addition to study target-drug interactions, our system also enabled us to observe how the tested antibiotics affected the physiology of mycobacterial cells (i.e., growth, chromosome segregation, etc.).

Comparison of Antibiotic Resistance Mechanisms in Antibiotic-Producing and Pathogenic Bacteria

Antibiotic resistance poses a tremendous threat to human health. To overcome this problem, it is essential to know the mechanism of antibiotic resistance in antibiotic-producing and pathogenic bacteria. This paper deals with this problem from four points of view. First, the antibiotic resistance genes in producers are discussed related to their biosynthesis. Most resistance genes are present within the biosynthetic gene clusters, but some genes such as paromomycin acetyltransferases are located far outside the gene cluster. Second, when the antibiotic resistance genes in pathogens are compared with those in the producers, resistance mechanisms have dependency on antibiotic classes, and, in addition, new types of resistance mechanisms such as Eis aminoglycoside acetyltransferase and self-sacrifice proteins in enediyne antibiotics emerge in pathogens. Third, the relationships of the resistance genes between producers and pathogens are reevaluated at their amino acid sequence as well as nucleotide sequence levels. Pathogenic bacteria possess other resistance mechanisms than those in antibiotic producers. In addition, resistance mechanisms are little different between early stage of antibiotic use and the present time, e.g., β-lactam resistance in Staphylococcus aureus. Lastly, guanine + cytosine (GC) barrier in gene transfer to pathogenic bacteria is considered. Now, the resistance genes constitute resistome composed of complicated mixture from divergent environments.

Evaluation of synergistic effect of tazobactam with meropenem and ciprofloxacin against multi-drug resistant Acinetobacter baumannii isolated from burn patients in Tehran

Background:Acinetobacter baumannii is an increasingly important cause of nosocomial infections worldwide. In addition to the intrinsic resistance of Acinetobacter baumannii to many antibiotics, available treatment approaches with older antibiotics are significantly associated with an increase in multiresistant strains. The aim of this study was to evaluate the synergistic effect of tazobactam with meropenem and ciprofloxacin against carbapenems and drug resistant Acinetobacter baumannii isolated from burn patients in a tertiary burn center in Tehran.

Materials and methods: In this study, a total of 47 clinical isolates of A. baumannii were included from burn patients admitted to the Shahid Motahari Burns Hospital, Tehran, from June 2018 to August 2018. The disk diffusion method was used to determine resistance patterns. The synergistic effect of tazobactam with meropenem and ciprofloxacin was evaluated by determining the MIC. A PCR assay was performed to determine bla_OXA-40-like, bla_OXA-58-like and bla_OXA-24-like.

Results: Antibiotic susceptibility testing revealed that all of the isolates were resistant to meropenem and ciprofloxacin. The MIC values decreased in the cases of combined use of ciprofloxacin and meropenem with tazobactam. The bla_OXA-24-like gene was the predominant carbapenemase gene (93.6%), followed by bla_OXA-40-like, which was detected in 48.9% of isolates. None of the A. baumannii isolates harbored the bla_OXA-58-like gene.

Conclusions: Based on in-vitro antimicrobial susceptibility in the current study, the MIC of tazobactam combined with meropenem or ciprofloxacin have been shown to be variable. Furthermore, the data acquired from such in vitro conditions should be confirmed by reliable results from sufficiently controlled clinical trials.

Antibiotic Use: A Cross-Sectional Study Evaluating the Understanding, Usage and Perspectives of Medical Students and Pathfinders of a Public Defence University in Malaysia

Background: Antimicrobial prescribing behaviors are often influenced by the local culture and prescribing appropriateness of medical doctors and other health care professionals. Globally, antimicrobial utilization practices have a profound impact on antimicrobial resistance and are a tremendous public health concern. The aim of this survey was to explore the knowledge and attitudes of medical students from the National Defence University of Malaysia regarding antimicrobial usage and antimicrobial resistance. Research design and methods: This was a cross-sectional study. The study population consisted of undergraduate medical students in each year group from the National Defence University of Malaysia. Students receive limited formal training on the use of antibiotics in their curriculum, and most of this learning is opportunistic whilst on clinical placement. Universal sampling was used as the study population was small. Data were collected utilizing a previously validated instrument regarding antibiotic use. Simple descriptive statistics were used to generate frequencies and percentages with SPSS V21. This research was approved by the Centre for Research and Innovation Management, National Defence University of Malaysia. Results: 206 questionnaires were distributed with a response rate of 99.03%, 54% (110) male, and 46% (94) female. Out of the respondents, 65% (132) had used antibiotics in the last year. Respondents displayed a moderate level of knowledge about antibiotics. Conclusions: This study revealed that the older the student was, or when the year of study and total knowledge score was higher, the students were less likely to stop antimicrobials when they felt better or use leftover antibiotics without consulting a doctor. Therefore, the nearer the students were to graduation, the better their knowledge and skills were, and this translated into their own behaviors regarding use of antimicrobials. This finding has clear implications for curriculum design and the inclusion of formal teaching throughout the medical program on antimicrobial use and antimicrobial resistance (AMR). However, more research is needed on this topic, including the prescribing habits and antibiotic use of practicing doctors.

Microbe-Derived Indole Metabolite Demonstrates Potent Multidrug Efflux Pump Inhibition in Staphylococcus aureus

Efflux pumps are always at the forefront of bacterial multidrug resistance and account for the failure of antibiotics. The present study explored the potential of 2-(2-Aminophenyl) indole (RP2), an efflux pump inhibitor (EPI) isolated from the soil bacterium, to overcome the efflux-mediated resistance in Staphylococcus aureus. The RP2/antibiotic combination was tested against efflux pump over-expressed S. aureus strains. The compound was further examined for the ethidium bromide (EtBr) uptake and efflux inhibition assay (a hallmark of EPI functionality) and cytoplasmic membrane depolarization. The safety profile of RP2 was investigated using in vitro cytotoxicity assay and Ca²⁺ channel inhibitory effect. The in vivo efficacy of RP2 was studied in an animal model in combination with ciprofloxacin. RP2 exhibited the synergistic activity with several antibiotics in efflux pump over-expressed strains of S. aureus. In the mechanistic experiments, RP2 increased the accumulation of EtBr, and demonstrated the inhibition of its efflux. The antibiotic-EPI combinations resulted in extended post antibiotic effects as well as a decrease in mutation prevention concentration of antibiotics. Additionally, the in silico docking studies suggested the binding of RP2 to the active site of modeled structure of NorA efflux pump. The compound displayed low mammalian cytotoxicity and had no Ca²⁺ channel inhibitory effect. In ex vivo experiments, RP2 reduced the intracellular invasion of S. aureus in macrophages. Furthermore, the RP2/ciprofloxacin combination demonstrated remarkable efficacy in a murine thigh infection model. In conclusion, RP2 represents a promising candidate as bacterial EPI, which can be used in the form of a novel therapeutic regimen along with existing and upcoming antibiotics, for the eradication of S. aureus infections.

Bicyclic Boronate VNRX-5133 Inhibits Metallo- and Serine-β-Lactamases

The bicyclic boronate VNRX-5133 (taniborbactam) is a new type of β-lactamase inhibitor in clinical development. We report that VNRX-5133 inhibits serine-β-lactamases (SBLs) and some clinically important metallo-β-lactamases (MBLs), including NDM-1 and VIM-1/2. VNRX-5133 activity against IMP-1 and tested B2/B3 MBLs was lower/not observed. Crystallography reveals how VNRX-5133 binds to the class D SBL OXA-10 and MBL NDM-1. The crystallographic results highlight the ability of bicyclic boronates to inhibit SBLs and MBLs via binding of a tetrahedral (sp³) boron species. The structures imply conserved binding of the bicyclic core with SBLs/MBLs. With NDM-1, by crystallography, we observed an unanticipated VNRX-5133 binding mode involving cyclization of its acylamino oxygen onto the boron of the bicyclic core. Different side-chain binding modes for bicyclic boronates for SBLs and MBLs imply scope for side-chain optimization. The results further support the “high-energy-intermediate” analogue approach for broad-spectrum β-lactamase inhibitor development and highlight the ability of boron inhibitors to interchange between different hybridization states/binding modes.