The molecular epidemiology of antimicrobial resistance genes and the characterisation of their genetic support

One of the growing public health concerns in the 21st century is the increasing prevalence of bacteria that are resistant to antibiotics. This has been due to the overuse and misuse of antibiotics in healthcare and agriculture. Increased levels of antibiotic resistant bacteria have been observed and new antibiotic-resistant strains of bacteria will continue to arise. Bacterial resistance to antimicrobials is typically gained through the acquisition of genes that confer antibiotic resistance. Such genes are often associated with mobile genetic elements (MGEs) such as plasmids and transposons and are capable of moving between different bacteria both within a species and in between different species. In order to attempt to curb the spread of antimicrobial resistance a greater understanding of the effect of antibiotics on both commensal and pathogenic strains of bacteria is required, including the investigation into the genetic basis of antibiotic resistance. The presence of mobile genetic elements was investigated in bacteria that were obtained from swabs from infected wounds and saliva from healthy volunteers. These isolates were predominantly members of the Streptococcus and Staphylococcus genus. Two isolates from wound sites confirmed to be Corynebacterium striatum demonstrated resistance to tetracycline (MIC >512ug/ml). Further investigation has revealed that the resistance gene present is tetW. A ribosomal protection protein that has only been observed once before in this species of bacteria in China. To date there have been no such observations in the EU or US. This suggests that the Corynebacterium striatum isolates acquired the tetW gene via a plasmid obtained by horizontal gene transfer. Sequence analysis of the DNA regions flanking this gene indicate that it may be located upon a transposon that belongs to the Tn5253 family. The presence of novel plasmids in metagenomic DNA from saliva was investigated using transposon aided capture (TRACA), the plasmids that were discovered mostly belonged to the pTRACA42 family, plasmids were found that carried antibiotic resistance genes that confer resistance to chloramphenicol, ampicillin and kanamycin, clonal resistance was confirmed via minimum inhibitory concentration (MIC) testing. In order to detect the transposon Tn916, a screening method based upon the characterisation of the digestion profile of two polymerase chain reaction (PCR) amplicons with the restriction enzyme HincII. This method was used to successfully detect Tn916 in the control strain Bacillus subtilus 34A. Overall, the data generated throughout this study adds to the body of evidence supporting that there is a large reservoir of antibiotic resistance genes that are located upon mobile elements, in particular those that belong to the Tn916 family play a significant role in the maintenance of tetracycline and erythromycin resistance genes.