High prevalence of Escherichia coli clinical isolates in India harbouring four amino acid inserts in PBP3 adversely impacting activity of aztreonam/avibactam

Genetic Features Leading to Reduced Susceptibility to Aztreonam-Avibactam among Metallo-β-Lactamase-Producing Escherichia coli Isolates

“…Previous studies focusing on the mechanisms of decreased susceptibility of MBLproducing Enterobacterales to ATM-AVI highlight the role a four-amino-acid insertion in the PBP3 protein (1,10). In our study, we identified a significant proportion of isolates possessing a four-amino-acid insertion of PBP3 protein, which is consistent with previously published studies (1,10). All the MBL-producing isolates identified with an elevated MIC of ATM-AVI possessed a four-amino-acid insertion in the PBP3 protein, either YRIN or YRIK.…”

“…More specifically, there are extremely limited therapeutic options against enterobacterial isolates producing metallo-␤-lactamases (MBL), being sources of nosocomial but also community-acquired infections worldwide. Among the most common MBL circulating, there are the New Delhi metallo-␤-lactamase (NDM), the Verona-integronmediated (VIM) enzyme, and imipenemase (IMP) that are all found in Escherichia coli, the most common human pathogen (1)(2)(3)(4). MBLs hydrolyze penicillins, broad-spectrum cephalosporins, and carbapenems and are not inhibited by the ␤-lactamase inhibitors clavulanate and tazobactam.…”

“…Considering that most MBL-producing Enterobacterales (including E. coli), and particularly those producing the NDM-type enzymes, are highly resistant to other non-␤-lactam antibiotics (aminoglycosides, trimethoprim-sulfamethoxazole, tetracycline, and fluoroquinolones), this ATM-AVI combination therapy is among the last-resort options against MBL-producing E. coli. However, MBL-producing E. coli isolates showing high MIC values for ATM-AVI were recently reported (1,10). To date, breakpoints for determining susceptibility or resistance to ATM-AVI have still not been defined.…”

“…Due to its involvement in the peptidoglycan biosynthesis and cell division and its high conservation among Gram-negative bacteria, PBP3 is among the most widely used drug targets for developing novel antibiotics since the discovery of penicillin (12,13). In E. coli, it was recently shown that the insertion of four specific amino acids in the PBP3 protein sequence (YRIN or YRIK) was a source of reduced susceptibility to ATM-AVI among NDM producers and, particularly, among isolates originating from India (1,10).…”

Resistance to aztreonam in combination with non-β-lactam β-lactamase inhibitors due to the layering of mechanisms in Escherichia coli identified following mixed culture selection

“…Further WGS analysis revealed a 12 nt tandem duplication in ftsI in N16, predicted to cause the insertion of the amino acid sequence YRIN after proline 333 in PBP3. This aztreonam target site mutation has previously been seen in clinical isolates, and associated with elevated MICs of aztreonam, with and without avibactam (13–15). Accordingly, the collective effects of CTX-M-15 and CMY production, loss of OmpF and a target site mutation in PBP3 explain why N16 is resistant to aztreonam in the presence of all three serine β-lactamase inhibitors tested.…”