Identification of Tet45, a tetracycline efflux pump, from a poultry-litter-exposed soil isolate and persistence of tet(45) in the soil

Deciphering the genomic character of the multidrug-resistant Staphylococcus aureus from Dhaka, Bangladesh

Staphylococcus aureus is one of the leading agents of nosocomial and community-acquired infections. In this study, we explored the genomic characterization of eight methicillin-resistant clinical isolates of S. aureus from Dhaka, Bangladesh. Notably, all strains were resistant to penicillin, cephalosporins, and monobactams, with partial susceptibility to meropenem and complete susceptibility to amikacin, vancomycin, and tigecycline antibiotics. The strains were found to have an average genome size of 2.73 Mbp and an average of 32.64% GC content. Multi-locus sequence typing analysis characterized the most predominant sequence type as ST361, which belongs to the clonal complex CC361. All isolates harbored the mecA gene, often linked to SCCmec_type IV variants. Multidrug resistance was attributed to efflux pumps NorA, NorC, SdrM, and LmrS alongside genes encoding beta-lactamase BlaZ and factors like ErmC and MepA. Additionally, virulence factors including adsA, sdrC, cap8D, harA, esaA, essC, isdB, geh, and lip were commonly identified. Furthermore, genes associated with heme uptake and clumping were present, highlighting their roles in S. aureus colonization and pathogenesis. Nine secondary metabolite biosynthetic gene clusters were found, of which six were common in all the strains. Numerous toxin-antitoxin systems were predicted, with ParE and ParB-like nuclease domains found to be the most prevalent toxin and antitoxin, respectively. Pan-genome analysis revealed 2007 core genes and 229 unique genes in the studied strains. Finally, the phylogenomic analysis showed that most Bangladeshi strains were grouped into two unique clades. This study provides a genomic and comparative insight into the multidrug resistance and pathogenicity of S. aureus strains, which will play a crucial role in the future antibiotic stewardship of Bangladesh.

Identification, phylogenetic analysis, and genome mining of the tetracycline-resistant Bacillus thuringiensis strain m401 reveal its potential for biotechnological and biocontrol applications

Bacillus thuringiensis is an entomopathogen belonging to the Bacillus cereus clade. We isolated a tetracycline-resistant strain called m401, recovered it from honey, and identified it as Bacillus thuringiensis sv. kumamotoensis based on the average nucleotide identity calculations (ANIb) comparison and the analysis of the gyrB gene sequences of different B. thuringiensis serovars. Sequences with homology to virulence factors [cytK, nheA, nheB, nheC, hblA, hblB, hblC, hblD, entFM, and inhA] and tetracycline resistance genes [tet(45), tet(V), and tet(M)/tet(W)/tet(O)/tet(S) family] were identified in the bacterial chromosome. The prediction of plasmid-coding regions revealed homolog sequences to the MarR and TetR/AcrR family of transcriptional regulators, toxins, and lantipeptides. The genome mining analysis revealed 12 regions of biosynthetic gene clusters responsible for synthesizing secondary metabolites. We identified biosynthetic gene clusters coding for bacteriocins, siderophores, ribosomally synthesized post-translationally modified peptide products, and non-ribosomal peptide synthetase clusters that provide evidence for the possible use of Bt m401 as a biocontrol agent. Furthermore, Bt m401 showed high inhibition against all Paenibacillus larvae genotypes tested in vitro. In conclusion, Bt m401 owns various genes involved in different biological processes, such as transductional regulators associated with antibiotic resistance, toxins, and antimicrobial peptides with potential biotechnological and biocontrol applications.

Whole genome sequence analysis enabled affirmation of the probiotic potential of marine sporulater Bacillus amyloliquefaciens BTSS3 isolated from Centroscyllium fabricii

Probiotics are microorganisms when administered in adequate amounts, confer health benefits on the host. Many probiotics find application in various industries however, probiotic bacteria linked to marine environments are less explored.Although Bifidobacteria, Lactobacilli, and Streptococcus thermophilus are the most frequently used probiotics, Bacillus spp. have acquired much acceptance in human functional foods due to their increased tolerance and enduring competence in harsh environments like the gastrointestinal (GI) tract. In this study, the 4 Mbp genome sequence of Bacillus amyloliquefaciens strain BTSS3, a marine spore former isolated from deep-sea shark Centroscyllium fabricii, with antimicrobial and probiotic properties was sequenced, assembled, and annotated. Analysis revealed the presence of numerous genes presenting probiotic traits like production of vitamins, secondary metabolites, amino acids, secretory proteins, enzymes and other proteins that allow survival in GI tract as well as adhesion to intestinal mucosa. Adhesion by colonization in the gut was studied in vivo in zebrafish (Danio rerio) using FITC labelled B.amyloliquefaciens BTSS3. Preliminary study revealed the ability of the marine Bacillus to attach to the intestinal mucosa of the fish gut. The genomic data and the in vivo experiment affirms that this marine spore former is a promising probiotic candidate with potential biotechnological applications.

Antimicrobial Susceptibility Profile and Whole-Genome Analysis of a Strong Biofilm-Forming Bacillus Sp. B87 Strain Isolated from Food

Members of the Bacillus cereus group are considered to be foodborne pathogens commonly associated with diarrheal and emetic gastrointestinal syndromes. Biofilm formation is a major virulence determinant of various pathogenic bacteria, including the B. cereus strains, since it can protect the bacteria against antimicrobial agents and the host immune response. Moreover, a biofilm allows the exchange of genetic material, such as antimicrobial resistance genes, among the different bacterial strains inside the matrix. The aim of the current study was to genotypically and phenotypically characterize Bacillus sp. B87, a strain that was isolated from food and which exhibited strong biofilm-forming capacity. Based on the analysis of the phylogenetic relationship, the isolate was phylogenetically mapped close to Bacillus pacificus. Antimicrobial susceptibility testing revealed that the isolate was resistant to tetracycline and β-lactam antimicrobial agents, which corresponded with the genotypic characterization using the whole-genome analysis. The genome of Bacillus sp. B87 carried the three-component non-hemolytic enterotoxin (NHE), which is a type of enterotoxin that causes diarrheal symptoms. In addition, the genome also contained several genes that participate in biofilm formation, including the pelDEA_DAFG operon. These findings expand our understanding of antimicrobial resistance and virulence in Bacillus species based on the link between genotypic and phenotypic characterization.

Identification of a novel tetracycline resistance gene, tet(63), located on a multiresistance plasmid from Staphylococcus aureus

OBJECTIVES

To identify and characterize a novel tetracycline resistance gene on a multiresistance plasmid from Staphylococcus aureus SA01 of chicken origin.

METHODS

MICs were determined by broth microdilution according to CLSI recommendations. The whole genome sequence of S. aureus SA01 was determined via Illumina HiSeq and Oxford Nanopore platforms followed by a hybrid assembly. The new tet gene was cloned and expressed in S. aureus. The functionality of the corresponding protein as an efflux pump was tested by efflux pump inhibition assays.

RESULTS

A novel tetracycline resistance gene, tet(63), was identified on a plasmid in S. aureus SA01. The cloned tet(63) gene was functionally expressed in S. aureus and shown to confer resistance to tetracycline and doxycycline, and a slightly elevated MIC of minocycline. The tet(63) gene encodes a 459 amino acid efflux protein of the major facilitator superfamily that consists of 14 predicted transmembrane helices. The results of efflux pump inhibitor assays confirmed the function of Tet(63) as an efflux protein. The deduced amino acid sequence of the Tet(63) protein exhibited 73.0% identity to the tetracycline efflux protein Tet(K). The plasmid pSA01-tet, on which tet(63) was located, had a size of 25664 bp and also carried the resistance genes aadD, aacA-aphD and erm(C).

CONCLUSIONS

A novel tetracycline resistance gene, tet(63), was identified in S. aureus. Its location on a multiresistance plasmid might support the co-selection of tet(63) under the selective pressure imposed by the use of macrolides, lincosamides and aminoglycosides.

Tracking Antimicrobial Resistance Determinants in Diarrheal Pathogens: A Cross-Institutional Pilot Study

Infectious diarrhea affects over four billion individuals annually and causes over a million deaths each year. Though not typically prescribed for treatment of uncomplicated diarrheal disease, antimicrobials serve as a critical part of the armamentarium used to treat severe or persistent cases. Due to widespread over- and misuse of antimicrobials, there has been an alarming increase in global resistance, for which a standardized methodology for geographic surveillance would be highly beneficial. To demonstrate that a standardized methodology could be used to provide molecular surveillance of antimicrobial resistance (AMR) genes, we initiated a pilot study to test 130 diarrheal pathogens (Campylobacter spp., Escherichia coli, Salmonella, and Shigella spp.) from the USA, Peru, Egypt, Cambodia, and Kenya for the presence/absence of over 200 AMR determinants. We detected a total of 55 different determinants conferring resistance to ten different categories of antimicrobials: genes detected in ≥ 25 samples included bla_TEM, tet(A), tet(B), mac(A), mac(B), aadA1/A2, strA, strB, sul1, sul2, qacEΔ1, cmr, and dfrA1. The number of determinants per strain ranged from none (several Campylobacter spp. strains) to sixteen, with isolates from Egypt harboring a wider variety and greater number of genes per isolate than other sites. Two samples harbored carbapenemase genes, bla_OXA-48 or bla_NDM. Genes conferring resistance to azithromycin (ere(A), mph(A)/mph(K), erm(B)), a first-line therapeutic for severe diarrhea, were detected in over 10% of all Enterobacteriaceae tested: these included >25% of the Enterobacteriaceae from Egypt and Kenya. Forty-six percent of the Egyptian Enterobacteriaceae harbored genes encoding CTX-M-1 or CTX-M-9 families of extended-spectrum β-lactamases. Overall, the data provide cross-comparable resistome information to establish regional trends in support of international surveillance activities and potentially guide geospatially informed medical care.

High diversity and abundance of cultivable tetracycline-resistant bacteria in soil following pig manure application

By performing a microcosm experiment mimicking fertilization, we assessed the dynamic distribution of tetracycline-resistant bacteria (TRB) and corresponding tetracycline resistance genes (TRGs) from pig manure (PM) to the fertilized soil, by culture-dependent methods and PCR detection. Cultivable TRB were most abundant in PM, followed by fertilized soil and unfertilized soil. By restriction fragment length polymorphism (RFLP) analysis, TRB were assigned to 29, 20, and 153 operational taxonomic units (OTUs) in PM, unfertilized soil, and fertilized soil, respectively. After identification, they were further grouped into 19, 12, and 62 species, showing an enhanced diversity of cultivable TRB in the soil following PM application. The proportions of potentially pathogenic TRB in fertilized soil decreased by 69.35% and 41.92% compared with PM and unfertilized soil. Bacillus cereus was likely widely distributed TRB under various environments, and Rhodococcus erythropolis and Acinetobacter sp. probably spread from PM to the soil via fertilization. Meanwhile, tetL was the most common efflux pump gene in both unfertilized and fertilized soils relative to PM; tetB(P) and tet36 were common in PM, whereas tetO was predominant in unfertilized and fertilized soil samples. Sequencing indicated that over 65% of randomly selected TRB in fertilized soil with acquired resistance derived from PM.

Review of Eravacycline, a Novel Fluorocycline Antibacterial Agent

Eravacycline is an investigational, synthetic fluorocycline antibacterial agent that is structurally similar to tigecycline with two modifications to the D-ring of its tetracycline core: a fluorine atom replaces the dimethylamine moiety at C-7 and a pyrrolidinoacetamido group replaces the 2-tertiary-butyl glycylamido at C-9. Like other tetracyclines, eravacycline inhibits bacterial protein synthesis through binding to the 30S ribosomal subunit. Eravacycline demonstrates broad-spectrum antimicrobial activity against Gram-positive, Gram-negative, and anaerobic bacteria with the exception of Pseudomonas aeruginosa. Eravacycline is two- to fourfold more potent than tigecycline versus Gram-positive cocci and two- to eightfold more potent than tigecycline versus Gram-negative bacilli. Intravenous eravacycline demonstrates linear pharmacokinetics that have been described by a four-compartment model. Oral bioavailability of eravacycline is estimated at 28 % (range 26-32 %) and a single oral dose of 200 mg achieves a maximum plasma concentration (C max) and area under the plasma concentration-time curve from 0 to infinity (AUC0-∞) of 0.23 ± 0.04 mg/L and 3.34 ± 1.11 mg·h/L, respectively. A population pharmacokinetic study of intravenous (IV) eravacycline demonstrated a mean steady-state volume of distribution (V ss) of 320 L or 4.2 L/kg, a mean terminal elimination half-life (t ½) of 48 h, and a mean total clearance (CL) of 13.5 L/h. In a neutropenic murine thigh infection model, the pharmacodynamic parameter that demonstrated the best correlation with antibacterial response was the ratio of area under the plasma concentration-time curve over 24 h to the minimum inhibitory concentration (AUC0-24h/MIC). Several animal model studies including mouse systemic infection, thigh infection, lung infection, and pyelonephritis models have been published and demonstrated the in vivo efficacy of eravacycline. A phase II clinical trial evaluating the efficacy and safety of eravacycline in the treatment of community-acquired complicated intra-abdominal infection (cIAI) has been published as well, and phase III clinical trials in cIAI and complicated urinary tract infection (cUTI) have been completed. The eravacycline phase III program, known as IGNITE (Investigating Gram-Negative Infections Treated with Eravacycline), investigated its safety and efficacy in cIAI (IGNITE 1) and cUTI (IGNITE 2). Eravacycline met the primary endpoint in IGNITE 1, while data analysis for IGNITE 2 is currently ongoing. Common adverse events reported in phase I-III studies included gastrointestinal effects such as nausea and vomiting. Eravacycline is a promising intravenous and oral fluorocycline that may offer an alternative treatment option for patients with serious infections, particularly those caused by multidrug-resistant Gram-negative pathogens.

Probiotic Bacillus cereus Strains, a Potential Risk for Public Health in China

Bacillus cereus is an important cause of foodborne infectious disease and food poisoning. However, B. cereus has also been used as a probiotic in human medicine and livestock production, with low standards of safety assessment. In this study, we evaluated the safety of 15 commercial probiotic B. cereus preparations from China in terms of mislabeling, toxin production, and transferable antimicrobial resistance. Most preparations were incorrectly labeled, as they contained additional bacterial species; one product did not contain viable B. cereus at all. In total, 18 B. cereus group strains-specifically B. cereus and Bacillus thuringiensis-were isolated. Enterotoxin genes nhe, hbl, and cytK1, as well as the ces-gene were assessed by PCR. Enterotoxin production and cytotoxicity were confirmed by ELISA and cell culture assays, respectively. All isolated B. cereus group strains produced the enterotoxin Nhe; 15 strains additionally produced Hbl. Antimicrobial resistance was assessed by microdilution; resistance genes were detected by PCR and further characterized by sequencing, transformation and conjugation assays. Nearly half of the strains harbored the antimicrobial resistance gene tet(45). In one strain, tet(45) was situated on a mobile genetic element-encoding a site-specific recombination mechanism-and was transferable to Staphylococcus aureus and Bacillus subtilis by electro-transformation. In view of the wide and uncontrolled use of these products, stricter regulations for safety assessment, including determination of virulence factors and transferable antimicrobial resistance genes, are urgently needed.

Impact of bioaccessible pyrene on the abundance of antibiotic resistance genes during Sphingobium sp.- and sophorolipid-enhanced bioremediation in soil

Soils are exposed to various types of chemical contaminants due to anthropogenic activities; however, research on persistent organic pollutants and the existence of antibiotic resistance genes (ARGs) is limited. To our knowledge, the present work for the first time focused on the bioremediation of soil co-contaminated with pyrene and tetracycline/sulfonamide-resistance genes. After 90 days of incubation, the pyrene concentration and the abundance of the four ARGs (tetW, tetM, sulI, and sulII) significantly decreased in different treatment conditions (p<0.05). The greatest pyrene removal (47.8%) and greatest decrease in ARG abundance (from 10(-7) to 10(-8) ARG copies per 16S rRNA copy) were observed in microcosms with a combination of bacterial and sophorolipid treatment. Throughout the incubation, pyrene bioaccessibility constantly declined in the microcosm inoculated with bacteria. However, an increased pyrene bioaccessibility and ARG abundance at day 40 were observed in soil treated with sophorolipid alone. Tenax extraction methods and linear correlation analysis indicated a strong positive relationship between the rapidly desorbing fraction (Fr) of pyrene and ARG abundance. Therefore, we conclude that bioaccessible pyrene rather than total pyrene plays a major role in the maintenance and fluctuation of ARG abundance in the soil.

Positive relationship detected between soil bioaccessible organic pollutants and antibiotic resistance genes at dairy farms in Nanjing, Eastern China

Co-contaminated soils by organic pollutants (OPs), antibiotics and antibiotic resistance genes (ARGs) have been becoming an emerging problem. However, it is unclear if an interaction exists between mixed pollutants and ARG abundance. Therefore, the potential relationship between OP contents and ARG and class 1 integron-integrase gene (intI1) abundance was investigated from seven dairy farms in Nanjing, Eastern China. Phenanthrene, pentachlorophenol, sulfadiazine, roxithromycin, associated ARG genes, and intI1 had the highest detection frequencies. Correlation analysis suggested a stronger positive relationship between the ARG abundance and the bioaccessible OP content than the total OP content. Additionally, the significant correlation between the bioaccessible mixed pollutant contents and ARG/intI1 abundance suggested a direct/indirect impact of the bioaccessible mixed pollutants on soil ARG dissemination. This study provided a preliminary understanding of the interaction between mixed pollutants and ARGs in co-contaminated soils.

Learning from agriculture: understanding low-dose antimicrobials as drivers of resistome expansion

Antimicrobial resistance is a growing public health challenge worldwide, with agricultural use of antimicrobials being one major contributor to the emergence and dissemination of antimicrobial resistance (AMR). Globally, most antimicrobials are used in industrial food animal production, a major context for microbiomes encountering low-doses or subtherapeutic-levels of antimicrobial agents from all mechanistic classes. This modern practice exerts broad eco-evolutionary effects on the gut microbiome of food animals, which is subsequently transferred to animal waste. This waste contains complex constituents that are challenging to treat, including AMR determinants and low-dose antimicrobials. Unconfined storage or land deposition of a large volume of animal waste causes its wide contact with the environment and drives the expansion of the environmental resistome through mobilome facilitated horizontal genet transfer. The expanded environmental resistome, which encompasses both natural constituents and anthropogenic inputs, can persist under multiple stressors from agriculture and may re-enter humans, thus posing a public health risk to humans. For these reasons, this review focuses on agricultural antimicrobial use as a laboratory for understanding low-dose antimicrobials as drivers of resistome expansion, briefly summarizes current knowledge on this topic, highlights the importance of research specifically on environmental microbial ecosystems considering AMR as environmental pollution, and calls attention to the needs for longitudinal studies at the systems level.

Previously undescribed plasmids recovered from activated sludge confer tetracycline resistance and phenotypic changes to Acinetobacter oleivorans DR1

We used culture-dependent and culture-independent methods to extract previously undescribed plasmids harboring tetracycline (TC) resistance genes from activated sludge. The extracted plasmids were transformed into naturally competent Acinetobacter oleivorans DR1 to recover a non-Escherichia coli-based plasmid. The transformed cells showed 80-100-fold higher TC resistance than the wild-type strain. Restriction length polymorphism performed using 30 transformed cells showed four different types of plasmids. Illumina-based whole sequencing of the four plasmids identified three previously unreported plasmids and one previously reported plasmid. All plasmids carried TC resistance-related genes (tetL, tetH), tetracycline transcriptional regulators (tetR), and mobilization-related genes. As per expression analysis, TC resistance genes were functional in the presence of TC. The recovered plasmids showed mosaic gene acquisition through horizontal gene transfer. Membrane fluidity, hydrophobicity, biofilm formation, motility, growth rate, sensitivity to stresses, and quorum sensing signals of the transformed cells were different from those of the wild-type cells. Plasmid-bearing cells seemed to have an energy burden for maintaining and expressing plasmid genes. Our data showed that acquisition of TC resistance through plasmid uptake is related to loss of biological fitness. Thus, cells acquiring antibiotic resistance plasmids can survive in the presence of antibiotics, but must pay ecological costs.

Intestinal microbiome of poultry and its interaction with host and diet

The gastrointestinal (GI) tract of poultry is densely populated with microorganisms which closely and intensively interact with the host and ingested feed. The gut microbiome benefits the host by providing nutrients from otherwise poorly utilized dietary substrates and modulating the development and function of the digestive and immune system. In return, the host provides a permissive habitat and nutrients for bacterial colonization and growth. Gut microbiome can be affected by diet, and different dietary interventions are used by poultry producers to enhance bird growth and reduce risk of enteric infection by pathogens. There also exist extensive interactions among members of the gut microbiome. A comprehensive understanding of these interactions will help develop new dietary or managerial interventions that can enhance bird growth, maximize host feed utilization, and protect birds from enteric diseases caused by pathogenic bacteria.