Molecular epidemiology of 16S rRNA methyltransferase in Brazil: RmtG in Klebsiella aerogenes ST93 (CC4)

In-depth analysis of Klebsiella aerogenes resistome, virulome and plasmidome worldwide

Klebsiella aerogenes is an emergent pathogen associated with outbreaks of carbapenem-resistant strains. To date, studies focusing on K. aerogenes have been small-scale and/or geographically restricted. Here, we analyzed the epidemiology, resistome, virulome, and plasmidome of this species based on 561 genomes, spanning all continents. Furthermore, we sequenced four new strains from Brazil (mostly from the Amazon region). Dozens of STs occur worldwide, but the pandemic clones ST93 and ST4 have prevailed in several countries. Almost all genomes were clinical, however, most of them did not carry ESBL or carbapenemases, instead, they carried chromosomal alterations (omp36, ampD, ampG, ampR) associated with resistance to β-lactams. Integrons were also identified, presenting gene cassettes not yet reported in this species (blaIMP, blaVIM, blaGES). Considering the virulence loci, the yersiniabactin and colibactin operons were found in the ICEKp10 element, which is disseminated in genomes of several STs, as well as an incomplete salmochelin cluster. In contrast, the aerobactin hypervirulence trait was observed only in one ST432 genome. Plasmids were common, mainly from the ColRNAI replicon, with some carrying resistance genes (mcr, blaTEM, blaNDM, blaIMP, blaKPC, blaVIM) and virulence genes (EAST1, senB). Interestingly, 172 genomes of different STs presented putative plasmids containing the colicin gene.

Microbial diversity in camel milk from Xinjiang, China as revealed by metataxonomic analysis

The quality of raw camel milk is affected by its bacterial composition and diversity. However, few studies have investigated the bacterial composition and diversity of raw camel milk. In this study, we obtained 20 samples of camel milk during spring and summer in Urumqi and Hami, Xinjiang, China. Single-molecule real-time sequencing technology was used to analyze the bacterial community composition. The results revealed that there were significant seasonal differences in the bacterial composition and diversity of camel milk. Overall, Epilithonimonas was the most abundant bacterial genus in our samples. Through the annotated genes inferred by PICRUSt2 were mapped against KEGG database. Non-parametric analysis of the bacterial community prediction function revealed a strong bacterial interdependence with metabolic pathways (81.83%). There were clear regional and seasonal differences in level 3 metabolic pathways such as fat, vitamins, and amino acids in camel milk. In addition, we identified lactic acid bacteria in camel milk with antibacterial and anti-tumor activities. Our findings revealed that camel milk from Xinjiang had serious risk of contamination by psychrophilic and pathogenic bacteria. Our research established a crucial theoretical foundation for ensuring the quality and safety of camel milk, thereby contributing significantly to the robust growth of China's camel milk industry.

Research Updates of Plasmid-Mediated Aminoglycoside Resistance 16S rRNA Methyltransferase

With the wide spread of multidrug-resistant bacteria, a variety of aminoglycosides have been used in clinical practice as one of the effective options for antimicrobial combinations. However, in recent years, the emergence of high-level resistance against pan-aminoglycosides has worsened the status of antimicrobial resistance, so the production of 16S rRNA methyltransferase (16S-RMTase) should not be ignored as one of the most important resistance mechanisms. What is more, on account of transferable plasmids, the horizontal transfer of resistance genes between pathogens becomes easier and more widespread, which brings challenges to the treatment of infectious diseases and infection control of drug-resistant bacteria. In this review, we will make a presentation on the prevalence and genetic environment of 16S-RMTase encoding genes that lead to high-level resistance to aminoglycosides.

Development of a Candidate Multi-Epitope Subunit Vaccine against Klebsiella aerogenes: Subtractive Proteomics and Immuno-Informatics Approach

Klebsiella aerogenes is a Gram-negative bacterium which has gained considerable importance in recent years. It is involved in 10% of nosocomial and community-acquired urinary tract infections and 12% of hospital-acquired pneumonia. This organism has an intrinsic ability to produce inducible chromosomal AmpC beta-lactamases, which confer high resistance. The drug resistance in K. aerogenes has been reported in China, Israel, Poland, Italy and the United States, with a high mortality rate (~50%). This study aims to combine immunological approaches with molecular docking approaches for three highly antigenic proteins to design vaccines against K. aerogenes. The synthesis of the B-cell, T-cell (CTL and HTL) and IFN-γ epitopes of the targeted proteins was performed and most conserved epitopes were chosen for future research studies. The vaccine was predicted by connecting the respective epitopes, i.e., B cells, CTL and HTL with KK, AAY and GPGPG linkers and all these were connected with N-terminal adjuvants with EAAAK linker. The humoral response of the constructed vaccine was measured through IFN-γ and B-cell epitopes. Before being used as vaccine candidate, all identified B-cell, HTL and CTL epitopes were tested for antigenicity, allergenicity and toxicity to check the safety profiles of our vaccine. To find out the compatibility of constructed vaccine with receptors, MHC-I, followed by MHC-II and TLR4 receptors, was docked with the vaccine. Lastly, in order to precisely certify the proper expression and integrity of our construct, in silico cloning was carried out. Further studies are needed to confirm the safety features and immunogenicity of the vaccine.

Comparative Genomic Analysis and Phenotypic Characterization of Bronchoscope-Associated Klebsiella aerogenes

Bronchoscopes have been linked to outbreaks of nosocomial infections. The phenotypic and genomic profiles of bronchoscope-associated Klebsiella aerogenes isolates are largely unknown. In this work, a total of 358 isolates and 13 isolates were recovered from samples after clinical procedures and samples after decontamination procedures, respectively, over the five months. Antimicrobial susceptibility testing found seven K. aerogenes isolates exhibiting a low-level resistance to antimicrobial agents. Among seven K. aerogenes isolates, we found five sequence types (STs) clustered into three main clades. Collectively, this study described for the first time the phenotypic and genomic characteristics of bronchoscope-associated K. aerogenes.

Aminoglycoside Resistance: Updates with a Focus on Acquired 16S Ribosomal RNA Methyltransferases

The clinical usefulness of aminoglycosides has been revisited as an effective choice against β-lactam-resistant and fluoroquinolone-resistant gram-negative bacterial infections. Plazomicin, a next-generation aminoglycoside, was introduced for the treatment of complicated urinary tract infections and acute pyelonephritis. In contrast, bacteria have resisted aminoglycosides, including plazomicin, by producing 16S ribosomal RNA (rRNA) methyltransferases (MTases) that confer high-level and broad-range aminoglycoside resistance. Aminoglycoside-resistant 16S rRNA MTase-producing gram-negative pathogens are widespread in various settings and are becoming a grave concern. This article provides up-to-date information with a focus on aminoglycoside-resistant 16S rRNA MTases.

Tracking resistomes, virulence genes, and bacterial pathogens in long-term manure-amended greenhouse soils

Organic manure has been implicated as an important source of antibiotic resistance genes (ARGs) in agricultural soils. However, the profiles of biocide resistance genes (BRGs), metal resistance genes (MRGs) and virulence genes (VGs) and their bacterial hosts in manure-amended soils remain largely unknown. Herein, a systematic metagenome-based survey was conducted to comprehensively explore the changes in resistomes, VGs and their bacterial hosts, mobile genetic elements (MGEs), and pathogenic bacteria in manure-amended greenhouse soils. Many manure-borne ARGs, BRGs, MRGs, VGs, and bacterial pathogens could be transferred into soils by applying manures, and their abundance and diversity were markedly positively correlated with greenhouse planting years (manure amendment years). The main ARGs transferred from manures to soils conferred resistance to tetracycline, aminoglycoside, and macrolide-lincosamide-streptogramin. Both statistical analysis and gene arrangements showed a good positive co-occurrence pattern of ARGs/BRGs/MRGs/VGs and MGEs. Furthermore, bacterial hosts of resistomes and VGs were significantly changed in the greenhouse soils in comparison with the field soils. Our findings confirmed the migration and dissemination of resistomes, VGs, and bacterial pathogens, and their accumulation and persistence were correlated with the continuous application of manures.

Genomic analysis unveils important aspects of population structure, virulence, and antimicrobial resistance in Klebsiella aerogenes

Klebsiella aerogenes is an important pathogen in healthcare-associated infections. Nevertheless, in comparison to other clinically important pathogens, K. aerogenes population structure, genetic diversity, and pathogenicity remain poorly understood. Here, we elucidate K. aerogenes clonal complexes (CCs) and genomic features associated with resistance and virulence. We present a detailed description of the population structure of K. aerogenes based on 97 publicly available genomes by using both multilocus sequence typing and single-nucleotide polymorphisms extracted from the core genome. We also assessed virulence and resistance profiles using Virulence Finder Database and Comprehensive Antibiotic Resistance Database, respectively. We show that K. aerogenes has an open pangenome and a large effective population size, which account for its high genomic diversity and support that negative selection prevents fixation of most deleterious alleles. The population is structured in at least 10 CCs, including two novel ones identified here, CC9 and CC10. The repertoires of resistance genes comprise a high number of antibiotic efflux proteins as well as narrow- and extended-spectrum β-lactamases. Regarding the population structure, we identified two clusters based on virulence profiles because of the presence of the toxin-encoding clb operon and the siderophore production genes, irp and ybt. Notably, CC3 comprises the majority of K. aerogenes isolates associated with hospital outbreaks, emphasizing the importance of constant monitoring of this pathogen. Collectively, our results may provide a foundation for the development of new therapeutic and surveillance strategies worldwide.