Novel Mobilizable Genomic Island GEI-D18A Mediates Conjugational Transfer of Antibiotic Resistance Genes in the Multidrug-Resistant Strain Rheinheimera sp. D18

An efflux pump in genomic island GI-M202a mediates the transfer of polymyxin B resistance in Pandoraea pnomenusa M202

BACKGROUND

Polymyxin B is considered a last-line therapeutic option against multidrug-resistant gram-negative bacteria, especially in COVID-19 coinfections or other serious infections. However, the risk of antimicrobial resistance and its spread to the environment should be brought to the forefront.

METHODS

Pandoraea pnomenusa M202 was isolated under selection with 8 mg/L polymyxin B from hospital sewage and then was sequenced by the PacBio RS II and Illumina HiSeq 4000 platforms. Mating experiments were performed to evaluate the transfer of the major facilitator superfamily (MFS) transporter in genomic islands (GIs) to Escherichia coli 25DN. The recombinant E. coli strain Mrc-3 harboring MFS transporter encoding gene FKQ53_RS21695 was also constructed. The influence of efflux pump inhibitors (EPIs) on MICs was determined. The mechanism of polymyxin B excretion mediated by FKQ53_RS21695 was investigated by Discovery Studio 2.0 based on homology modeling.

RESULTS

The MIC of polymyxin B for the multidrug-resistant bacterial strain P. pnomenusa M202, isolated from hospital sewage, was 96 mg/L. GI-M202a, harboring an MFS transporter-encoding gene and conjugative transfer protein-encoding genes of the type IV secretion system, was identified in P. pnomenusa M202. The mating experiment between M202 and E. coli 25DN reflected the transferability of polymyxin B resistance via GI-M202a. EPI and heterogeneous expression assays also suggested that the MFS transporter gene FKQ53_RS21695 in GI-M202a was responsible for polymyxin B resistance. Molecular docking revealed that the polymyxin B fatty acyl group inserts into the hydrophobic region of the transmembrane core with Pi-alkyl and unfavorable bump interactions, and then polymyxin B rotates around Tyr43 to externally display the peptide group during the efflux process, accompanied by an inward-to-outward conformational change in the MFS transporter. Additionally, verapamil and CCCP exhibited significant inhibition via competition for binding sites.

CONCLUSIONS

These findings demonstrated that GI-M202a along with the MFS transporter FKQ53_RS21695 in P. pnomenusa M202 could mediate the transmission of polymyxin B resistance.

Glabridin inhibited the spread of polymyxin-resistant Enterobacterium carrying ICEMmoMP63

Introduction

The role of integrative and conjugative elements (ICEs) in antibiotic resistance in Morganella morganii is unknown. This study aimed to determine whether an ICE identified in the M. morganii genome contributed to the polymyxin resistance.

Methods

Whole-genome sequencing was performed followed by bioinformatics analyses to identify ICEs and antibiotic resistance genes. Conjugation assays were performed to analyze the transferability of a discovered ICE. A drug transporter encoded on the ICE was heterogeneously expressed in Escherichia coli, minimum inhibitory concentrations of antibiotics were determined, and a traditional Chinese medicine library was screened for potential efflux pump inhibitors.

Results

An antibiotic resistance-conferring ICE, named ICEMmoMP63, was identified. ICEMmoMP63 was verified to be horizontally transferred among Enterobacteriaceae bacteria. G3577_03020 in ICEMmoMP63 was found to mediate multiple antibiotic resistances, especially polymyxin resistance. However, natural compound glabridin was demonstrated to inhibit polymyxin resistance.

Discussion

Our findings support the need for monitoring dissemination of ICEMmoMP63 in Enterobacteriaceae bacteria. Combined glabridin and polymyxin may have therapeutic potential for treating infections from multi-drug resistant bacteria carrying ICEMmoMP63.

Rheinheimera faecalis sp. nov., isolated from Ceratotherium simum feces

A novel strain YR1^T, Gram-stain-negative, rod-shaped, catalase- and oxidase-positive, and aerobic bacterium, was isolated from the feces of Ceratotherium simum. The strain grew at 9-42 °C (optimal temperature, 30 °C), at pH 6.0-10.0 (optimal pH, 7.0), and in the presence of 0-3% (w/v) NaCl (optimal salinity, 0%). Phylogenetic analyses based on 16S rRNA gene sequencing indicated that strain YR1^T was most closely related to Rheinheimera soli BD-d46^T (98.6%), R. riviphila KYPC3^T (98.6%), and R. mangrovi LHK 132^T (98.1%). Moreover, the average nucleotide identity, average amino acid identity, and digital DNA-DNA hybridization values between strain YR1^T and R. mangrovi LHK 132 ^T were 88.3%, 92.1%, and 35.3%, respectively, indicating that strain YR1^T is a novel species in the genus Rheinheimera. The genome size and genomic DNA G + C content of strain YR1^T were 4.5 Mbp and 46.37%, respectively. The major polar lipids were phosphatidylethanolamine and phosphatidylglycerol, while the predominant respiratory quinone was Q-8. Summed feature 3 (C_16:1 ω7c and/or C_16:1 ω6c), C_{16: 0}, and summed feature 8 (C_18:1 ω7c) were the primary cellular fatty acids (> 16%). Based on these genotypic and phenotypic characteristics, strain YR1^T was identified as a novel species in the genus Rheinheimera, for which the name Rheinheimera faecalis sp. nov. is proposed, with the type strain is YR1^T (= KACC 22402^T = JCM 34823^T).

The emergence of novel macrolide resistance island in Macrococcus caseolyticus and Staphylococcus aureus of food origin

Food-derived Staphylococcaceae species with severe antimicrobial resistance, especially Staphylococcus aureus, is a major threat to public health. Macrococcus caseolyticus (M. caseolyticus) is a member of the Staphylococcaceae family which plays a vital role in fermented products and disease causation in animals. In our previous study, several Staphylococcus aureus antibiotic-resistant island msr (SaRI_msr) were found in multidrug-resistant S. aureus. In this study, novel SaRI_msr, SaRI_msr-III emerged from S. aureus. Another novel SaRI_msr-like further emerged in M. caseolyticus from food. These isolates' prevalence and genetic environment were investigated and characterized to understand the distribution and transmission of these novel SaRI_msr strains. All SaRI_msr-positive S. aureus isolates exhibited a multidrug resistance (MDR) phenotype, within which a series of antimicrobial resistance genes (ARGs) and virulence factor genes (VFs) were identified. In addition, three SaRI_msr types, SaRI_msr-I (15.1 kb), SaRI_msr-II (16-17 kb), and SaRI_msr-III (18 kb) carrying mef(D)-msr(F), were identified in these isolates' chromosomes. SaRI_msr-(I-III) contains a site-specific integrase gene int and operon mef(D)-msr(F). SaRI_msr-III has an additional orf3-orf4-IS30 arrangement downstream of mef(D) and msr(F). Moreover, the SaRI_msr-like and macrolide-resistant transposon Tn6776 forming a novel mosaic structure coexisted in one M. caseolyticus isolate. Within this mosaic structure, the macrolide-resistant genes mef(D)-msr(F) were absent in SaRI_msr-like, whereas an operon, mef(F)-msr(G), was identified in Tn6776. The SaRI_msr-(I-III) and SaRI_msr-like structure were inserted into the rpsI gene encoding the 30S ribosomal protein S9 in the chromosome. Excision and cyclisation of SaRI_msr-III, SaRI_msr-like, operon mef(D)-msr(F), and orf3-orf4-IS30 arrangements were confirmed using two-step PCR. This study is the first to report MDR S. aureus harbouring novel SaRI_msr-III and M. caseolyticus containing novel mosaic structures isolated from retail foods. Similar SaRI_msr-type resistant islands' occurrence and propagation in Staphylococcaceae species require continuous monitoring and investigation.

The Integrative and Conjugative Element ICECspPOL2 Contributes to the Outbreak of Multi-Antibiotic-Resistant Bacteria for Chryseobacterium Spp. and Elizabethkingia Spp

Antibiotic resistance genes (ARGs) and horizontal transfer of ARGs among bacterial species in the environment can have serious clinical implications as such transfers can lead to disease outbreaks from multidrug-resistant (MDR) bacteria. Infections due to antibiotic-resistant Chryseobacterium and Elizabethkingia in intensive care units have been increasing in recent years. In this study, the multi-antibiotic-resistant strain Chryseobacterium sp. POL2 was isolated from the wastewater of a livestock farm. Whole-genome sequencing and annotation revealed that the POL2 genome encodes dozens of ARGs. The integrative and conjugative element (ICE) ICECspPOL2, which encodes ARGs associated with four types of antibiotics, including carbapenem, was identified in the POL2 genome, and phylogenetic affiliation analysis suggested that ICECspPOL2 evolved from related ICEEas of Elizabethkingia spp. Conjugation assays verified that ICECspPOL2 can horizontally transfer to Elizabethkingia species, suggesting that ICECspPOL2 contributes to the dissemination of multiple ARGs among Chryseobacterium spp. and Elizabethkingia spp. Because Elizabethkingia spp. is associated with clinically significant infections and high mortality, there would be challenges to clinical treatment if these bacteria acquire ICECspPOL2 with its multiple ARGs, especially the carbapenem resistance gene. Therefore, the results of this study support the need for monitoring the dissemination of this type of ICE in Chryseobacterium and Elizabethkingia strains to prevent further outbreaks of MDR bacteria. IMPORTANCE Infections with multiple antibiotic-resistant Chryseobacterium and Elizabethkingia in intensive care units have been increasing in recent years. In this study, the mobile integrative and conjugative element ICECspPOL2, which was associated with the transmission of a carbapenem resistance gene, was identified in the genome of the multi-antibiotic-resistant strain Chryseobacterium sp. POL2. ICECspPOL2 is closely related to the ICEEas from Elizabethkingia species, and ICECspPOL2 can horizontally transfer to Elizabethkingia species with the tRNA-Glu-TTC gene as the insertion site. Because Elizabethkingia species are associated with clinically significant infections and high mortality, the ability of ICECspPOL2 to transfer carbapenem resistance from environmental strains of Chryseobacterium to Elizabethkingia is of clinical concern.

The survival and removal mechanism of Sphingobacterium changzhouense TC931 under tetracycline stress and its' ecological safety after application

Sphingobacterium changzhouense TC931 was isolated as a novel TC (tetracycline) removal bacterium through adsorption on extracellular polymerase substances (EPS) and cellular surface and biodegradation. TC biodegradation efficiency by strain TC931 was affected by solution initial pH and carbon source. Polysaccharides and hydrocarbons in EPS and cellular surface were responsible for TC biosorption. Eight possible biodegradation products were identified and the biodegradation pathway was proposed. Strain TC931 was rich in antibiotic resistance genes, and tetX_-TC931 and antibiotics resistance genome island (GI) may be acquired via horizontal gene transfer in early evolutionary history. The GI was incomplete and may stable in strain TC931, but it could develop into an intact and transferability GI with help of other mobile genetic elements. This work offers a theoretical basis for understanding the survival and biodegradation mechanisms of S. changzhouense TC931 under TC stress, and offers an ecological safety assessment for its application in environmental bioremediation.

dfrA trimethoprim resistance genes found in Gram-negative bacteria: compilation and unambiguous numbering

To track the spread of antibiotic resistance genes, accurate identification of individual genes is essential. Acquired trimethoprim resistance genes encoding trimethoprim-insensitive homologues of the sensitive dihydrofolate reductases encoded by the folA genes of bacteria are increasingly found in genome sequences. However, naming and numbering in publicly available records (journal publications or entries in the GenBank non-redundant DNA database) has not always been unambiguous. In addition, the nomenclature has evolved over time. Here, the changes in nomenclature and the most commonly encountered problems and pitfalls affecting dfrA gene identification arising from historically incorrect or inaccurate numbering are explained. The complete set of dfrA genes/DfrA proteins found in Gram-negative bacteria for which readily searchable sequence information is currently available has been compiled using less than 98% identity for both the gene and the derived protein sequence as the criteria for assignment of a new number. In most cases, trimethoprim resistance has been demonstrated. The gene context, predominantly in a gene cassette or near the ori end of CR1 or CR2, is also covered. The RefSeq database that underpins the programs used to automatically identify resistance genes in genome data sets has been curated to assign all sequences listed to the correct number. This led to the assignment of corrected or new gene numbers to several mis-assigned sequences. The unique numbers assigned for the dfrA/DfrA set are now listed in the RefSeq database, which we propose provides a way forward that should end future duplication of numbers and the confusion that causes.

A Novel Mobile Element ICERspD18B in Rheinheimera sp. D18 Contributes to Antibiotic and Arsenic Resistance

Antibiotics and organoarsenical compounds are frequently used as feed additives in many countries. However, these compounds can cause serious antibiotic and arsenic (As) pollution in the environment, and the spread of antibiotic and As resistance genes from the environment. In this report, we characterized the 28.5 kb genomic island (GI), named as ICERspD18B, as a novel chromosomal integrative and conjugative element (ICE) in multidrug-resistant Rheinheimera sp. D18. Notably, ICERspD18B contains six antibiotic resistance genes (ARGs) and an arsenic tolerance operon, as well as genes encoding conjugative transfer proteins of a type IV secretion system, relaxase, site-specific integrase, and DNA replication or partitioning proteins. The transconjugant strain 25D18-B4 was generated using Escherichia coli 25DN as the recipient strain. ICERspD18B was inserted into 3'-end of the guaA gene in 25D18-B4. In addition, 25D18-B4 had markedly higher minimum inhibitory concentrations for arsenic compounds and antibiotics when compared to the parental E. coli strain. These findings demonstrated that the integrative and conjugative element ICERspD18B could mediate both antibiotic and arsenic resistance in Rheinheimera sp. D18 and the transconjugant 25D18-B4.