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Plasmid-mediated resistance is the transfer of antimicrobial-resistant coding genes which are carried on plasmids. The plasmids can be transferred between prokaryotes through horizontal gene transfer. The spread of multiple antimicrobial resistance has been enhanced by selective pressure from human and veterinary medicine.
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ESBL Enterbacteriaceae
Plasmid encoded beta-lactamase is responsible for the emergence of resistant strains of Enterobacteriaceae. These enzymes are collectively termed as extended spectrum beta lactamases (ESBL).
They are especially problematic because strains that produce them may appear to be susceptible to the third generation cephalosporins but are in fact resistant to these antibiotics.These beta-lactamases degrade all the beta-lactam antibiotics except carbapenems and sometimes beta-lactam/beta-lactamase inhibitor combinations (e.g.-Piperacillin/Tazobactam.)
In addition, since the plasmids that carry ESBL genes also commonly encode resistance determinants for many other antibiotics, ESBL strains are often resistant to many non-beta-lactam antibiotics as well
NDM-1
The enzyme which conferred resistance to beta-lactam as well as non beta-lactam antibiotics in the enterbacteriaceae bacteria among the UK patients was named as New Delhi metallo-beta-lactamase 1 (NDM-1) based on the assumption that the genetically encoded plasmids that conferred resistance to these bacteria originated in India and Pakistan. However, various types of beta lactamases that conferred resistance to carbapenems and beta-lactam antibiotics like cephalosporins had already been reported in Canada, USA, Australia, Sweden and in the UK.,