Overview of Salmonella Genomic Island 1-Related Elements Among Gamma-Proteobacteria Reveals Their Wide Distribution Among Environmental Species

Novel multidrug resistance genomic islands and transposon carrying blaVEB-1 identified in mcr-positive Aeromonas strains from raw meat in China

OBJECTIVES

To characterize the genetic environments of ESBL gene blaVEB-1 in mcr-positive Aeromonas strains from raw meat in China.

METHODS

Whole genomes of Aeromonas strains were sequenced using the Illumina or Nanopore platforms. Genetic environments of blaVEB-1 were analysed using the BLAST program.

RESULTS

The blaVEB-1 gene was detected in five Aeromonas strains carrying the mcr-7-like gene. WGS revealed that all blaVEB-1 genes were located on Aeromonas chromosome, and were carried by two novel different genomic islands named Aeromonas veronii genomic islands AveGI1 and AveGI2, as well as one transposon named Tn7690. AveGI1 is a new member of the Salmonella genomic island 1 family, incorporated into the 3'-end of mnmE (trmE). AveGI2 is a novel genomic island that has a size of 23 180 bp and is incorporated into the 3'-end of syd. The MDR regions of AveGI1 and AveGI2 are two different class 1 integrons containing 10 and five resistance genes, respectively. Tn7690 is a Tn1722 derivative containing In4-type integron and Tn5393, which harbours 10 resistance genes and integrates into different positions on the chromosomes of three strains with the capacity for mobility.

CONCLUSIONS

We report chromosomally located novel MDR genomic islands and transposon that carry blaVEB-1 in mcr-positive Aeromonas strains. These genetic elements may mediate the spread of blaVEB-1 in Aeromonas, and may also evolve by capturing new antimicrobial resistance genes or other mobile genetic elements.

Deciphering the genetic network and programmed regulation of antimicrobial resistance in bacterial pathogens

Antimicrobial resistance (AMR) in bacteria is an important global health problem affecting humans, animals, and the environment. AMR is considered as one of the major components in the "global one health". Misuse/overuse of antibiotics in any one of the segments can impact the integrity of the others. In the presence of antibiotic selective pressure, bacteria tend to develop several defense mechanisms, which include structural changes of the bacterial outer membrane, enzymatic processes, gene upregulation, mutations, adaptive resistance, and biofilm formation. Several components of mobile genetic elements (MGEs) play an important role in the dissemination of AMR. Each one of these components has a specific function that lasts long, irrespective of any antibiotic pressure. Integrative and conjugative elements (ICEs), insertion sequence elements (ISs), and transposons carry the antimicrobial resistance genes (ARGs) on different genetic backbones. Successful transfer of ARGs depends on the class of plasmids, regulons, ISs proximity, and type of recombination systems. Additionally, phage-bacterial networks play a major role in the transmission of ARGs, especially in bacteria from the environment and foods of animal origin. Several other functional attributes of bacteria also get successfully modified to acquire ARGs. These include efflux pumps, toxin-antitoxin systems, regulatory small RNAs, guanosine pentaphosphate signaling, quorum sensing, two-component system, and clustered regularly interspaced short palindromic repeats (CRISPR) systems. The metabolic and virulence state of bacteria is also associated with a range of genetic and phenotypic resistance mechanisms. In spite of the availability of a considerable information on AMR, the network associations between selection pressures and several of the components mentioned above are poorly understood. Understanding how a pathogen resists and regulates the ARGs in response to antimicrobials can help in controlling the development of resistance. Here, we provide an overview of the importance of genetic network and regulation of AMR in bacterial pathogens.