High prevalence of Escherichia coli clinical isolates in India harbouring four amino acid inserts in PBP3 adversely impacting activity of aztreonam/avibactam
Hariharan Periasamy, Prashant Joshi, Snehal Palwe, Rahul Shrivastava, Sachin Bhagwat, Mahesh Patel
Abstract
Clinical resistance to b-lactams is mediated by several enzymatic and non-enzymatic mechanisms such as b-lactamases, PBP alterations and efflux/impermeability.Unlike in Gram-positive bacteria such as methicillin-resistant staphylococci and penicillin-resistant pneumococci, b-lactam resistance in Gram-negative bacteria is largely mediated through b-lactamases and rarely due to PBP modifications.Previously, Alm et al. 1 described four novel amino acid inserts in PBP3 of NDM-as well as ESBL-producing Escherichia coli isolated from India, China, Thailand, Turkey, Kuwait and Lebanon.These isolates showed elevated aztreonam/avibactam MICs of 4-16 mg/L (aztreonam EUCAST susceptible breakpoint 1 mg/L 2 ) despite aztreonam being stable to NDM and avibactam inhibiting associated serine b-lactamases.The genomic analysis of ftsI encoding PBP3 (primary target of aztreonam) revealed four amino acid insertions (12 bp duplications), YRIN or YRIK, after residue 333.Moreover, these novel inserts were exclusively found in E. coli and not in the large number of Klebsiella pneumoniae and Enterobacter cloacae studied.Previously, Zhang et al., 3 Sader et al. 4 and Kazmierczak et al. 5 also reported PBP3 insertions in E. coli.To assess the prevalence of this resistance mechanism in India, we undertook comprehensive screening of 459 E. coli isolates collected during a 2016-18 surveillance study involving 16 Indian tertiary care hospitals. 6These isolates were from clinical sources such as pus, wound swabs, sputum, tracheal secretions, blood and urine.We determined aztreonam/avibactam MICs (CLSI broth microdilution method) and observed raised aztreonam/avibactam MICs (2-32 mg/L) in 106/459 (23%) isolates.From these isolates, 76 were randomly selected for PBP3 gene analysis using primers designed to amplify the full-length ftsI.We discovered a very high proportion of isolates (72/76) carrying PBP3 insertions of