High distribution of 16S rRNA methylase genes rmtB and armA among Enterobacter cloacae strains isolated from an Ahvaz teaching hospital, Iran

Within-Host Resistance and Virulence Evolution of a Hypervirulent Carbapenem-Resistant Klebsiella pneumoniae ST11 Under Antibiotic Pressure

Background

Hypervirulent carbapenem-resistant Klebsiella pneumoniae (hv-CRKP) has recently aroused an extremely severe health challenge and public concern. However, the underlying mechanisms of fitness costs that accompany antibiotic resistance acquisition remain largely unexplored. Here, we report a hv-CRKP-associated fatal infection and reveal a reduction in virulence due to the acquisition of aminoglycoside resistance.

Methods

The bacterial identification, antimicrobial susceptibility, hypermucoviscosity, virulence factors, MLST and serotypes were profiled.The clonal homology and plasmid acquisition among hv-CRKP strains were detected by XbaI and S1-PFGE. The virulence potential of the strains was evaluated using Galleria mellonella larvae infection model, serum resistance assay, capsular polysaccharide quantification, and biofilm formation assay. Genomic variations were identified using whole-genome sequencing (WGS).

Results

Four K. pneumoniae carbapenemase (KPC)-producing CRKP strains were consecutively isolated from an 86-year-old patient with severe pneumonia. Whole-genome sequencing (WGS) showed that all four hv-CRKP strains belonged to the ST11-KL64 clone. PFGE analysis revealed that the four ST11-KL64 hv-CRKP strains could be grouped into the same PFGE type. Under the pressure of antibiotics, the antimicrobial resistance of the strains increased and the virulence potential decreased. Further sequencing, using the Nanopore platform, was performed on three representative isolates (WYKP586, WYKP589, and WYKP594). Genomic analysis showed that the plasmids of these three strains underwent a large number of breaks and recombination events under antibiotic pressure. We found that as aminoglycoside resistance emerged via acquisition of the rmtB gene, the hypermucoviscosity and virulence of the strains decreased because of internal mutations in the rmpA and rmpA2 genes.

Conclusion

This study shows that ST11-KL64 hv-CRKP can further evolve to acquire aminoglycoside resistance accompanied by decreased virulence to adapt to antibiotic pressure in the host.

Molecular epidemiology and transmission of rmtB-positive Escherichia coli among ducks and environment

This study aimed to investigate the transmission and molecular epidemiological characteristics of the rmtB gene in Escherichia coli (E. coli) strains isolated from duck farms in Guangdong Province of China from 2018 to 2021. A total of 164 (19.4%, 164/844) rmtB-positive E. coli strains were recovered from feces, viscera, and environment. We performed antibiotic susceptibility tests, pulsed-field gel electrophoresis (PFGE), and conjugation experiments. We obtained the genetic context of 46 rmtB-carrying E. coli isolates and constructed a phylogenetic tree via whole genome sequencing (WGS) and bioinformatic analysis. The isolation rate of rmtB-carrying E. coli isolates in duck farms increased yearly from 2018 to 2020 but decreased in 2021. All rmtB-harboring E. coli strains were multidrug resistant (MDR), and 99.4% of the strains were resistant to more than 10 drugs. Surprisingly, duck- and environment-associated strains similarly showed high MDR. Conjugation experiments revealed that the rmtB gene horizontally cocarried bla_CTX-M and bla_TEM gene dissemination via IncFII plasmids. Insertion sequences IS26, ISCR1, and ISCR3 were closely associated with the spread of rmtB-harboring E. coli isolates. WGS analysis indicated that ST48 was the most prevalent sequence type. The results of single nucleotide polymorphism (SNP) differences revealed potential clonal transmission between ducks and the environment. Based on One Health principles, we need to strictly use veterinary antibiotics, monitor the distribution of MDR strains, and evaluate the impact of plasmid-mediated rmtB gene on human, animal, and environmental health.

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.

Coexistence of genes encoding aminoglycoside modifying enzymes among clinical Acinetobacter baumannii isolates in Ahvaz, Southwest Iran

Aminoglycosides are widely recommended for treatment of Acinetobacter baumannii infections in combination with β-lactams or quinolones. This cross-sectional study was aimed to investigate the coexistence of aminoglycoside modifying enzyme (AME) genes among A. baumannii isolates from clinical samples in Ahvaz, Iran. A total of 85 clinical A. baumannii isolates typed by ERIC-PCR were investigated for the presence of AME genes, including ant(3″)-Ia, aac(6')-Ib, aac(3')-Ia, ant(2″)-Ia, and aph(3')-VIa by PCR. The resistance rates to aminoglycoside agents were evaluated by disk diffusion. In this study, 84 out of 85 A. baumannii isolates were resistant to at least one of the aminoglycosides and harbored at least one AME gene. The most common gene encoding AMEs was aph (3')VIa, followed by aac(3')-Ia, ant(3″)-Ia, ant (2″)-Ia, and aac(6')-Ib. The aminoglycoside-resistant genotypes were completely matched to resistant phenotypes to each one of the aminoglycoside agents. There was a clear association between AME gene types and the phenotype of resistance to aminoglycosides with their ERIC-PCR types. Our findings highlight the coexistence of AME genes and clonal dissemination of multiresistant A. baumannii in hospital setting.

Enterobacter spp.: Update on Taxonomy, Clinical Aspects, and Emerging Antimicrobial Resistance

The genus Enterobacter is a member of the ESKAPE group, which contains the major resistant bacterial pathogens. First described in 1960, this group member has proven to be more complex as a result of the exponential evolution of phenotypic and genotypic methods. Today, 22 species belong to the Enterobacter genus. These species are described in the environment and have been reported as opportunistic pathogens in plants, animals, and humans. The pathogenicity/virulence of this bacterium remains rather unclear due to the limited amount of work performed to date in this field. In contrast, its resistance against antibacterial agents has been extensively studied. In the face of antibiotic treatment, it is able to manage different mechanisms of resistance via various local and global regulator genes and the modulation of the expression of different proteins, including enzymes (β-lactamases, etc.) or membrane transporters, such as porins and efflux pumps. During various hospital outbreaks, the Enterobacter aerogenes and E. cloacae complex exhibited a multidrug-resistant phenotype, which has stimulated questions about the role of cascade regulation in the emergence of these well-adapted clones.